Patent Application
20100004323
The present invention relates to novel promoter constructs which may be used in the treatment of ocular diseases. More particularly, the invention relates to polynucleotides and vectors containing photoreceptor specific promoters operably linked to one or more enhancer elements and uses thereof in ocular cell gene expression.
The neural retina is an exquisitely sensitive light detector comprised of photoreceptor cells. These cells are responsible for phototransduction, a process which encompasses a series of signal amplification steps, and enhances the sensitivity of the visual system such that a single photon of light may be detected.
The eye is susceptible to a number of hereditary and/or age related degenerative disorders. Degenerative ocular diseases, such as, but not limited to, retinitis pigmentosa, Stargardt's disease, diabetic retinopathies, retinal vascularization, retinal dystrophy disease and others have a genetic basis, with genes expressed in photoreceptor cells implicated in these diseases. For example, visual impairments in retinitis pigmentosa, which is considered to be the leading cause of inherited blindness affecting approximately 1 in 3,500 people (Pagon R A (1988) “Retinitis Pigmentosa” Surv Ophthalmol 33:137-77), are caused by the progressive degeneration of retinal photoreceptor retinitis pigmentosa cells, which is triggered by a mutation of certain genes. The majority of these genes cause photoreceptor defects when mutated (Rivolta et al. (2002) Hum Mol Genet 11:1219-27). Specific examples of genes implicated in retinitis pigmentosa are the gene encoding rhodopsin, the light absorbing molecule found within the outer segment, and the gene encoding peripherin which helps maintain the normal structure of the outer segment.
Stargardt's disease, also known as fundus flavimaculatus and Stargardt's macular dystrophy, is the most common form of inherited juvenile macular dystrophy. Inherited as an autosomal recessive trait, it is a severe form of macular dystrophy that begins in late childhood, leading to legal blindness. Stargardt's disease is caused by mutations in the ABCR/ABCA4 gene which encodes an ATP-binding cassette transporter expressed in photoreceptor cells. Mutations in the ABCR/ABCA4 gene produce a dysfunctional protein which permits the accumulation of yellow fatty material in the retina causing flecks and, ultimately, loss of vision.
A great deal of research is now focused on preventing blindness by developing therapies that have potential for reversing or slowing the loss of photoreceptor cells as a result of disease. Retinal gene therapy has been considered a possible therapeutic option and offers particular promise with well over one hundred different genes being implicated as the cause of retinal disorders (The University of Texas Health Science Center, Houston, Tex. “Retinal Information Network”, http://www.sph.uth.tmc.edu./Retnet/). Gene-based therapy of several types already has been attempted in animal models with retinal degenerations, including the replacement of missing enzymes in recessive disorders (Bennett et al. (1996) Nat. Med. 2:649-654; Takahashi et al. (1999) J. Virol. 73:7812-7816), gene-based delivery of protective neurotrophic factors (Cayouette et al. (1997) Human Gene Ther. 8:423-430; Utezaet al. (1999) Proc. Natl. Acad. Sci. USA 96:3126-3131), and the introduction of antiapoptosis genes such as bcl-2 (Bennett et al. (1998) Gene Ther. 5:1156-1164).
WO 02/082904 describes a method for treating an ocular disorder characterized by the defect or absence of a normal gene in the ocular cells comprising administering by subretinal injection a recombinant adeno-associated virus carrying a nucleic acid sequence encoding the normal gene under the control of a promoter sequence which expresses the product of the gene in the ocular cells.
Di Polo et al. (1995) Proc Natl Acad Sci USA 92:4016-4020 demonstrated that a reporter gene driven by the cGMP phosphodiesterase (PDE) promoter is transcribed in a restinobasltoma cell line, thereby indicating that it is suitable for transcriptional regulation studies of rod-specific genes.
Ying et al. (1998) Curr Eye Res 17(8):777-82 and Fong et al. (2005) Exp Eye Res 81(4):376-88 report the use of a GNAT2 promoter and the interphotoreceptor retinoid-binding protein (IRBP) enhancer in gene expression, while May et al. (2003) Clin Experiment Ophthalmol 31(5):445-50 teaches the use of the IRBP enhancer element in combination with the rhodopsin promoter element.
There remains a need in the art for improved methods for effectively treating blindness. In particular there is a need for novel gene delivery systems and methods of improving gene expression in photoreceptors cells following gene transfer. The present invention addresses these needs.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.
According to a first aspect of the present invention there is provided a polynucleotide comprising a promoter of the β subunit of cGMP-phosphodiesterase operably linked to one or more enhancer elements wherein said enhancer elements are not naturally operably linked to the promoter.
According to another aspect of the present invention there is provided a polynucleotide comprising a promoter of the β subunit of cGMP-phosphodiesterase operably linked to one or more retinoid-binding protein (IRBP) enhancer elements.
Preferably, the polynucleotide further comprises a nucleotide of interest (NOI) operably linked to the promoter of the β subunit of cGMP-phosphodiesterase.
Preferably, the promoter of the β subunit of cGMP-phosphodiesterase is the promoter of the β subunit of type 6 cGMP-phosphodiesterase (PDE6B).
In one embodiment, the polynucleotide comprises one IRBP enhancer element.
In another embodiment, the polynucleotide comprises two IRBP enhancer elements.
In another embodiment, the polynucleotide comprises three IRBP enhancer elements.
Preferably the promoter is operably linked downstream of the one or more enhancer elements.
According to second aspect of the present invention there is provided a polynucleotide comprising a photoreceptor cell specific promoter operably linked to two or more IRBP enhancer elements.
Preferably the polynucleotide of the second aspect of the present invention further comprises a nucleotide of interest (NOI) operably linked to the promoter.
Preferably the polynucleotide of the second aspect of the present invention is selected from the rhodopsin promoter, the promoter of the β subunit of cGMP-phosphodiesterase or the retinitis pigmentosa 1 promoter.
Preferably, the promoter of the β subunit of cGMP-phosphodiesterase is the promoter of the β subunit of type 6 cGMP-phosphodiesterase (PDE6B).
Preferably the polynucleotide of the second aspect of the present invention comprises two IRBP enhancer elements.
Preferably the polynucleotide of the second aspect of the present invention comprises three IRBP enhancer elements.
Preferably the polynucleotide of the second aspect of the present invention is operably linked downstream of the two or more enhancer elements.
In one embodiment, the NOI of the present invention is a therapeutic protein.
In another embodiment the NOI encodes a protein selected from the group comprising brain derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), neurotrophin-3 (NT-3), acidic fibroblast growth factor (aFGF), basic fibroblast growth factor (bFGF), interleukin 1beta (IL-1β), tumour necrosis factor-alpha (TNF-α) insulin-like growth factor-2, VEGF-C/VEGF-2
In another embodiment, the NOI encodes a protein normally expressed in an ocular cell.
In another embodiment, the NOI encodes a protein normally expressed in a photoreceptor cell.
In another embodiment, the NOI encodes a protein selected from the group comprising arylhydrocarbon-interacting receptor protein like 1 (AIPL1), CRB1, lecithin retinal acetyltransferase (LRAT), photoreceptor-specific homeo box (CRX), retinal guanylate cyclase (GUCY2D), RPGR Interacting Protein 1 (RPGRIP1), LCA2, LCA3, LCA5, dystrophin, PRPH2, CNTF, ABCR/ABCA4, EMP1, TIMP3, MERTCK and ELOVL4.
In one embodiment, the NOI encodes a microRNA, a siRNA or an antisense RNA.
Preferably the polynucleotide of the present invention is an isolated polynucleotide. The term “isolated” polynucleotide, as used herein, is a polynucleotide that is separated from other nucleic acid molecules which are present in the natural source of the nucleic acid.
According to another aspect of the present invention there is provided a vector comprising the polynucleotide of the present invention.
Preferably the vector is a viral vector, more preferably a retroviral vector, even more preferably a lentiviral vector.
Preferably the lentiviral vector is derived from HIV or EIAV.
More preferably, the lentivirus is derived from EIAV.
The viral vector of the present invention may be pseudotyped.
According to another aspect of the present invention there is provided a polynucleotide comprising the sequence shown in
According to another aspect of the present invention there is provided a vector comprising the sequence shown in
According to another aspect of the present invention there is provided a vector of the invention in the form of an integrated provirus.
According to another aspect of the present invention there is provided a viral vector particle obtainable from a viral vector of the present invention.
According to another aspect of the present invention there is provided a cell transfected or transduced with a polynucleotide of the invention, a vector of the present invention or a viral vector particle of the present invention.
Preferably the cell is an ocular cell, more preferably a photoreceptor cell.
According to another aspect of the present invention there is provided a viral vector particle production system for producing the viral vector particle of the present invention which system comprises a set of nucleic acid sequences encoding the viral genome, gag and env proteins or a functional substitute thereof.
According to another aspect of the present invention there is provided a polynucleotide, a vector particle, a viral vector particle or a cell of the present invention for use in medicine.
According to another aspect of the present invention there is provided a method of delivering a NOI to an ocular cell comprising transfecting or transducing the ocular cell with a polynucleotide, a vector or a viral vector particle of the present invention.
According to another aspect of the present invention there is provided use of a polynucleotide, a vector or a viral vector particle of the present invention for the preparation of a medicament to deliver one or more NOIs to an ocular cell.
According to another aspect of the present invention there is provided use of a polynucleotide, a vector, a viral vector particle or a cell of the present invention for the preparation of a medicament for treating or preventing an ocular disorder.
According to another aspect of the present invention there is provided a method for treating an ocular disorder characterized by the defect or absence of a normal gene in the ocular cells of a subject, said method comprising the step of: administering to said subject an effective amount of a polynucleotide, a vector or a viral vector particle of the present invention wherein said NOI encodes said normal gene.
Preferably the method comprises intraocular delivery, more preferably subretinal injection.
Preferably the ocular disorder is a retinal degenerative disease or retinopathy.
More preferably the ocular disorder is selected from retinitis pigmentosa, Stargardt's disease, diabetic retinopathies, retinal vacsularization, retinoblastoma and retinal dystrophy disease.
It is noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as “comprises”, “comprised”, “comprising” and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean “includes”, “included”, “including”, and the like; and that terms such as “consisting essentially of” and “consists essentially of” have the meaning ascribed to them in U.S. Patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.
These and other embodiments are disclosed or are obvious from and encompassed by, the following Detailed Description.
The following detailed description, given by way of example, but not intended to limit the invention solely to the specific embodiments described, may best be understood in conjunction with the accompanying drawings, in which:
Various preferred features and embodiment of the present invention will now be described by way of non-limiting examples.
The practice of the present invention will employ, unless otherwise indicated, conventional techniques of chemistry, molecular biology, microbiology, recombinant DNA and immunology, which are within the capabilities of a person of ordinary skill in the art. Such techniques are explained in the literature. See, for example, J. Sambrook, E. F. Fritsch, and T. Maniatis (1989) Molecular Cloning: A Laboratory Manual, Second Edition, Books 1-3, Cold Spring Harbor Laboratory Press; Ausubel, F. M. et al. (1995 and periodic supplements) Current Protocols in Molecular Biology, Ch. 9, 13, and 16, John Wiley & Sons, New York, N.Y.; B. Roe, J. Crabtree, and A. Kahn (1996) DNA Isolation and Sequencing: Essential Techniques, John Wiley & Sons; J. M. Polak and James O'D. McGee (1990) In Situ Hybridization: Principles and Practice; Oxford University Press; M. J. Gait (ed.) (1984) Oligonucleotide Synthesis: A Practical Approach, IRL Press; and, D. M. J. Lilley and J. E. Dahlberg (1992) Methods of Enzymology: DNA Structure Part A: Synthesis and Physical Analysis of DNA Methods in Enzymology, Academic Press. Each of these general texts is herein incorporated by reference.
Polynucleotides
Polynucleotides of the invention may comprise DNA or RNA. They may be single-stranded or double-stranded. It will be understood by a skilled person that numerous different polynucleotides can encode the same polypeptide as a result of the degeneracy of the genetic code. In addition, it is to be understood that skilled persons may, using routine techniques, make nucleotide substitutions that do not affect the polypeptide sequence encoded by the polynucleotides used in the invention to reflect the codon usage of any particular host organism in which the polypeptides are to be expressed. The polynucleotides may be modified by any method available in the art.
Such modifications may be carried out in order to enhance the in vivo activity or life span of polynucleotides of the invention.
Polynucleotides such as DNA polynucleotides may be produced recombinantly, synthetically, or by any means available to those of skill in the art. They may also be cloned by standard techniques.
Longer polynucleotides will generally be produced using recombinant means, for example using PCR (polymerase chain reaction) cloning techniques. This will involve making a pair of primers (e.g. of about 15 to 30 nucleotides) flanking a target sequence which it is desired to clone, bringing the primers into contact with mRNA or cDNA obtained from an animal or human cell, performing a polymerase chain reaction under conditions which bring about amplification of the desired region, isolating the amplified fragment (e.g. by purifying the reaction mixture on an agarose gel) and recovering the amplified DNA. The primers may be designed to contain suitable restriction enzyme recognition sites so that the amplified DNA can be cloned into a suitable cloning vector.
Protein
As used herein, the term “protein” includes single-chain polypeptide molecules as well as multiple-polypeptide complexes where individual constituent polypeptides are linked by covalent or non-covalent means. As used herein, the terms “polypeptide” and “peptide” refer to a polymer in which the monomers are amino acids and are joined together through peptide or disulfide bonds. The terms subunit and domain may also refer to polypeptides and peptides having biological function.
Operably Linked
A first nucleic acid sequence is operably linked with a second nucleic acid sequence when the sequences are placed in a functional relationship. For example, a coding sequence is operably linked to a promoter if the promoter activates the transcription of the coding sequence. Similarly, a photoreceptor cell specific promoter and an enhancer are operably linked when the enhancer modifies the photoreceptor cell specific transcription of operably linked sequences. Enhancers may function when separated from promoters and as such, an enhancer may be operably linked to a photoreceptor cell specific promoter but may not be contiguous. Generally, however, operably linked sequences are contiguous.
Promoters
The photoreceptor cell specific promoter may be any nucleotide sequence which functions to activate photoreceptor cell specific transcription, meaning that the sequence activates transcription of operably linked sequences in a photoreceptor cell and substantially not in other cell types. A promoter does not substantially activate transcription if the levels of transcription of operably linked sequences in any of those cell types are sufficiently low so as not to affect the physiological functioning of the cell. Several examples of photoreceptor cell specific promoters include, the rhodopsin promoter (Chen et al. (1996) The Journal of Biological Chemistry 271(45) 8:28549-28557), the promoter of the β subunit of cGMP-phosphodiesterase (Di Polo et al. (1997) Nucleic Acid Research 25(19):3863-3867; Ogueta et al. (2000) Investigative Ophthalmology and Visual Science 41(13):4059-4063; Lerner et al. (2001) The Journal of Biological Chemistry 276(37) 14:34999-35007; Lerner et al. (2002) The Journal of Biological Chemistry 277(29) 19:25877-25883, the Retinitis Pigmentosa 1 promoter (Qian et al. (2005) Nucleic Acid Research 33(11):3479-3491; Liu et al. (2004) The Journal of Neuroscience 24(29):6427-6436, the peripherin/rds promoter (Moritz et al. (2002) Gene 298:173-182), and guanylate cyclase-E (Duda et al. (1998) Mol Cell Biochem. 189:63-70; Johnston et al. (1997) Gene 193:219-227), the alpha subunit of rod transducin promoter (Ahmad et al. (1994) J. Neurochem. 62:396-399), promoter sequences of red and green visual pigment (Shaaban and Deeb (1998), Invest. Ophthalmol. Vis. Sci. 39:885-896), and the cone arrestin promoter (Zhu et al. (2002) FEBS Lett. 524:116-122) or variants or homologs thereof. The sequences of the promoters are well known in the art and may be found, for example, using the DBTSS website (Database of Transcriptional Start Sites, http://dbtss.hgc.jp/).
The promoter used in the present invention comprises at least one nucleotide sequence capable of activating photoreceptor cell specific expression of operably linked sequences and in some embodiments the nucleotide sequence will retain the minimum binding site(s) for transcription factor(s) required for the sequence to act as a promoter. In some embodiments, the recombinant nucleic acid comprises multiple copies of the same sequence or two or more different nucleotide sequences each of which is effective to activate the transcription activity. For various promoters which may be used, transcription factor binding sites may be known or identified by one of ordinary skill using methods known in the art as described above.
Preferred promoters for use in the invention are human photoreceptor cell specific promoter sequences or variants or homologs thereof
Particularly preferred promoters for use in the invention are the rhodopsin promoter (Rho), the promoter of the β subunit of cGMP-phosphodiesterase (PDE6b) and the Retinitis Pigmentosa 1 promoters. In a particularly preferred embodiment, the photoreceptor cell specific promoter used in the present invention is the promoter of the cGMP-phosphodiesterase β subunit.
As mentioned above, a preferred promoter used in the present invention is the β subunit cGMP-phosphodiesterase promoter. Preferably, the promoter of the β subunit of cGMP-phosphodiesterase is the promoter of the β subunit of cGMP-phosphodiesterase which is expressed in retinal or photoreceptor cells. In one embodiment, the promoter of the β subunit of cGMP-phosphodiesterase is the promoter of the β subunit of cGMP-phosphodiesterase which is expressed in rod cells. Preferably, the promoter of the β subunit of cGMP-phosphodiesterase is the promoter of the β subunit of type 6 cGMP-phosphodiesterase (PDE6B). One of the key components of the phototransduction cascade that takes place in rod photoreceptors is the heterotetrameric (αβγ2) cGMP-phosphodiesterase (Fung et al. (1990) Biochemistry 29:2657-2664). The gene encoding the β-subunit of the human enzyme (β-PDE) has been well characterized and consists of 22 exons encompassing ˜43 kb of genomic DNA (Weber et al. (1991) Nucleic Acids Res. 19:6263-6268). Genetic defects in this gene have been linked to retinal degeneration in several animal species and in humans. Ogueta et al. (2000) Investigative Ophthalmology and Visual Science 41(13):4059-4063 demonstrated that the -297 to +53 fragment of the human β-PDE gene efficiently directed expression of the reporter gene to the photoreceptors.
Mutational analysis of the β-PDE promoter tested both in vitro and ex vivo, and confirmed by the generation of transgenic Xenopus expressing mutant β-PDE promoter/green fluorescent protein fusion constructs in vivo, revealed a minimal promoter region, from −93 to +53, that supports high levels of rod-specific transcription (Lerner et al. (2001) J. Biol. Chem. 276:34999-35007). Two enhancer elements were localized within this minimal promoter, βAp1/NRE and β/GC, that interact with nuclear factors and activate transcription from the β-PDE promoter.
Transient transfection assays using a retinoblastoma cell line demonstrated that deletion of the sequence −167 to −34 upstream of the first transcribed nucleotide reduced reporter gene expression by 90%, indicating the presence of important regulatory elements in this region (Di Polo et al. (1997) Nucleic Acid Research 25(]9):3863-3867). This sequence contained several potential sites for DNA-protein interactions, including an AP-1 consensus motif located at −69 to −63 bp. This putative AP-1 element is highly conserved among the human, bovine and mouse β-PDE genes. Transfection experiments demonstrated that the human β-PDE gene sequence from −72 to +53 bp, is a good candidate to comprise the minimal promoter of the human β-PDE gene. This sequence, which contained the AP-1 motif, was sufficient to support high levels of reporter gene expression in a retinoblastoma-specific fashion. The transcriptional activity of this construct was three orders of magnitude higher in retinoblastoma cells than in HeLa or 293 cells.
As mentioned above, in one embodiment the promoter used in the present invention is the rhodopsin promoter. Rhodopsin, the visual pigment of rod photoreceptors, provides a useful model system for the study of late-stage photoreceptor cell-specific markers. It consists of a 348-amino acid residue protein moiety, rod opsin, covalently joined through a Schiff-base linkage to the chromophore 11-cis-retinal. Upon photon capture, it undergoes a conformational change, which results in activation of the trimeric GTP-binding protein transducin, and this in turn activates the phototransduction cascade. In addition to its intrinsic biologic importance, rhodopsin is also important because structural mutations in its gene can cause the sight-threatening retinal degeneration, retinitis pigmentosa, and other retinal diseases.
Regulatory sequences from rhodopsin genes are recognized by trans-acting factors in photoreceptor cells across species. For example, both bovine and human rhodopsin regulatory elements have been shown to direct expression of transgenes to mouse photoreceptor cells (Zack et al. (1991) Neuron 6:187-199; Nie et al. (1996) J. Biol. Chem. 271:2667-2675). Moreover, rhodopsin regulatory sequences have been characterized in a number of species, including Xenopus (Mani et al. (2001) J. Biol. Chem. 28:36557-36565), mouse (Lem et al. (1991) Neuron 6:201-210) and bovine (Nie et al. (1996) J. Biol. Chem. 271:2667-2675). These studies have indicated that fragments from −2174 to +70 bp; from −735 to +70 bp; from −222 to +70 bp; and from −176 to +70 bp, relative to the rhodopsin mRNA start site, are able to direct photoreceptor-specific gene expression in transgenic mice (Nie et al. (1996) supra), indicating that the minimal cell-specific promoter lies within the region −176 to +70 bp of the bovine rhodopsin transcription start site. Likewise, 4.4 kb and 0.5 kb fragments from the mouse rhodopsin gene are able to direct photoreceptor-specific gene expression in transgenic mice (Lem et al. (1991) supra), indicating that the minimal cell-specific promoter lies within about 500 bp 5′ of the mouse rhodopsin transcription start site.
Examples of the rhodopsin promoter (Rho), the β subunit cGMP-phosphodiesterase promoter (PDE6b) and the Retinitis Pigmentosa 1 promoters may be found via the DBTSS website using the access numbers below:
In a specific embodiment, the rhodopsin promoter sequence comprises the nucleotides −228 to +91, the cGMP-phosphodiesterase promoter comprises nucleotides −115 to +78 and the Retinitis Pigmentosa 1 promoter comprises nucleotides −95 to +50 (relative to the human mRNA transcription start site) or homologues or variants of these sequences.
The promoter may also comprise allelic variants, homologues and derivatives (such as deletions, insertions, inversion, substitutions or addition of sequences) of the above mentioned promoter sequences provided such variants, homologues and derivatives activate photoreceptor specific transcription of operably linked sequences.
Enhancer Element
The nucleic acid molecule of the invention comprises a photoreceptor cell specific promoter operably linked to one or more enhancer elements wherein the enhancer elements modify the photoreceptor cell specific transcriptional activity of the promoter.
Thus, the enhancer may be any nucleotide sequence which is not naturally operably linked to the photoreceptor cell specific promoter and which, when so operably linked, modifies the photoreceptor cell specific transcriptional activity of the photoreceptor cell specific promoter. Preferably the enhancer element increases the transcriptional activity of the photoreceptor cell specific promoter. Reference to modifying the transcriptional activity is meant to refer to any detectable modification, e.g. increase, in the level of transcription of operably linked sequences compared to the level of the transcription observed with a photoreceptor cell specific promoter alone, as may be detected in standard transcriptional assays, including using a reporter gene construct as described in the Examples. Reference to increasing the transcriptional activity is meant to refer to any detectable increase in the level of transcription of operably linked sequences compared to the level of the transcription observed with a photoreceptor cell specific promoter alone, as may be detected in standard transcriptional assays.
In some embodiments, the nucleotide sequence effective to modify the transcriptional activity will retain the minimum binding site(s) for transcription factor(s) required for the sequence to act as an enhancer. As may be necessary to modify transcription of operably linked sequences to the desired extent, in some embodiments, the recombinant nucleic acid may comprise multiple copies of the same sequence or two or more different nucleotide sequences each of which is effective to modify the transcription. Thus, by using multiple enhancer elements the transcription can be fine-tuned to the desired level. For various enhancers which may be used, transcription factor binding sites may be known or identified by one of ordinary skill using methods known in the art, for example by DNA footprinting, gel mobility shift assays, and the like. The factors may also be predicted on the basis of known consensus sequence motifs.
Preferably the enhancer is a human enhancer sequence or a variant or homologue thereof.
In a specific embodiment, the enhancer is the interphotoreceptor retinoid-binding protein (IRBP) enhancer element or a variant or homologue thereof. IIRBP is the major protein component of the interphotoreceptor matrix. IRBP has a highly restricted tissue-specific expression in retinal photoreceptor cells and in a subgroup of pinealocytes (Babola et al. (1995) J Biol Chem. January 20 270(3):1289-94). IRBP is a large lipoglycoprotein that constitutes approximately 70% of the protein component of the interphotoreceptor matrix. Although widely distributed among the vertebrates, it has a highly restricted tissue-specific expression and is found in the interphotoreceptor matrix of the retina. IRBP mRNA is present in photoreceptor cells of the retina, prevalently in rod cells, and, at very low levels, in a subgroup of pinealocytes. IRBP is also expressed by retinoblastoma-derived cell lines in vitro, and the level of IRBP expression can be altered by agents that affect retinoblastoma cell differentiation. The bovine and human IRBP genes have been cloned (Borst et al. (1989) J. Biol. Chem. 264:1115-1123; Liou et al. (1989) J. Biol. Chem. 264:8200-8206) and the human IRBP gene has been mapped to the centromeric region of chromosome 10 (Liou et al.(1987) Somatic Cell. Mol. Genet. 13 ;315-323). The upstream IRBP enhancer element between -1620 and -1411 has been shown to have enhancer properties (Fong et al. (1999) Curr Eye Res. 18(4):283-9 1; May et al. (2003) Clin Experiment Ophthalmol 31(5):445-50).
An example of a sequence of an IRBP enhancer element for use in the present invention may be found via the DBTSS website (Database of Transcriptional Start Sites, http://dbtss.hgc.jp/) using the access numbers shown below:
In a specific embodiment, the IRBP enhancer element comprises the nucleotides −1653 to −1403 (relative to the mRNA transcription start site).
The enhancer may also be allelic variants, homologs and derivatives (such as deletions, insertions, inversion, substitutions or addition of sequences) of this nucleotide sequence and other known IRBP sequences provided such variants, homologs or derivatives modify, and preferably increase, photoreceptor cell-specific transcription of operably linked sequences.
NOI
The polynucleotides of the present invention may be used to deliver one or more NOI(s) useful in the treatment of ocular disorders. That is the nucleic acid molecule may comprise at least one operably linked NOI. The NOI may be DNA or RNA.
In various embodiments, the operably linked sequence may encode a reporter protein such as luciferase or green fluorescence protein or may be a therapeutic gene sequence.
In a preferred embodiment, the NOI encodes a protein implicated in an ocular disorder.
Where the disease is caused by the absence or inappropriate expression of a normal gene, the NOI may encode for the normal (non-muted) gene product.
Where the NOI encodes a polypeptide, the NOI may be codon optimized (see below).
Moreover, where the disease is caused by the build up of a gene product, the NOI may reduce the build up of the gene product (e.g., by cleaving mutant transcripts). This is particularly preferable where the gene product is a mutant gene product which disturbs metabolism or causes the death of cells, as seen, for example, by the degeneration of photoreceptors in many forms of autosomal dominant retinitis pigmentosa.
The NOI may encode or comprise regulatory sequences such as, an antisense nucleotide, a ribozyme, a siRNA, shRNA or microRNA (Dickins et al. (2005) Nature Genetics 37:1289-1295; Silva et al. (2005) Nature Genetics 37:1281-1288) which will inhibit or modulate the expression of a protein. Thus, for example, ocular cells may express undesirable proteins, and the methods of the present invention allow for the addition of such regulatory sequences to regulate the expression of the undesirable proteins. Similarly, the expression of mutant forms of a protein may cause ocular disease. It is possible to incorporate such regulatory sequences to reduce the level of expression of the mutant endogeneous gene as well as nucleic acid encoding a correct copy of the gene.
Ribozyme-directed cleavage of mutant mRNAs has been shown to be a potentially effective, long-term therapy for autosomal dominant retinal degenerations. For example, the NOI may encode or comprise a ribozyme targeted to the P23H mutation in rhodopsin, which is implicated in retinitis pigmentosa, and which has been shown to slow photoreceptor degeneration in transgenic rats (LaVail et al. (200)) Proc Natl Acad Sci USA. 97(21): 11488-93).
Post-transcriptional gene silencing (PTGS) mediated by double-stranded RNA (dsRNA) is a conserved cellular defense mechanism for controlling the expression of foreign genes. It is thought that the random integration of elements such as transposons or viruses causes the expression of dsRNA which activates sequence-specific degradation of homologous single-stranded mRNA or viral genomic RNA. The silencing effect is known as RNA interference (RNAi) (Ralph et al. (2005): Nature Medicine 11:429-433). The mechanism of RNAi involves the processing of long dsRNAs into duplexes of about 21-25 nucleotide (nt) RNAs. These products are called small interfering or silencing RNAs (siRNAs) which are the sequence-specific mediators of mRNA degradation. In differentiated mammalian cells dsRNA >30 bp has been found to activate the interferon response leading to shut-down of protein synthesis and non-specific mRNA degradation (Stark et al. (1998)). However this response can be bypassed by using 21nt siRNA duplexes (Elbashir et al. (2001), Hutvagner et al. (2001)) allowing gene function to be analyzed in cultured mammalian cells.
MicroRNAs are a very large group of small RNAs produced naturally in organisms, at least some of which regulate the expression of target genes. Founding members of the microRNA family are let-7 and lin-4. The let-7 gene encodes a small, highly conserved RNA species that regulates the expression of endogenous protein-coding genes during worm development. The active RNA species is transcribed initially as a ˜70nt precursor, which is post-transcriptionally processed into a mature ˜21nt form. Both let-7 and lin-4 are transcribed as hairpin RNA precursors which are processed to their mature forms by the Dicer enzyme.
Examples of genes implicated in ocular disorders which may be encoded or targeted by the NOI of the present invention can be found at the Retinal Informational Network website located at http://www.sph.uth.tmc.edu/Retnet/. Examples of such sequences include RPE65, arylhydrocarbon-interacting receptor protein like 1 (AIPL1), CRB1, lecithin retinal acetyltransferase (LRAT), photoreceptor-specific homeo box (CRX), retinal guanylate cyclase (GUCY2D), RPGR Interacting Protein 1 (RPGRIP1), LCA2, LCA3, LCA5, dystrophin, PRPH2, CNTF, ABCR, EMP1, TIMP3, MERTCK and ELOVL4.
As a specific example, the NOI may encode the ABCR/ABCA4 gene product (Sing et al. (2006) Am. J. Ophthalmol. 141(5):906-13 Epub Mar. 20, 2006). The membrane-associated protein encoded by this gene is a member of the superfamily of ATP-binding cassette (ABC) transporters. This protein is a retina-specific ABC transporter with N-retinylidene-PE as a substrate. It is expressed exclusively in retina photoreceptor cells and mediates transport of an essential molecule across the photoreceptor cell membrane. Mutations in this gene are found in patients diagnosed with Stargardt's disease and are associated with retinitis pigmentosa-and macular degeneration
As another specific example, the NOI may encode the Prph2 gene product, also known as peripherin or rds (Ali et al. (2000) Nat. Genet. 25(3):306-10). The gene Prph2 encodes a photoreceptor-specific membrane glycoprotein, peripherin-2 (also known as peripherin/rds), which is inserted into the rims of photoreceptor outer segment discs in a complex with rom-1. The complex is necessary for the stabilization of the discs, which are renewed constantly throughout life, and which contain the visual pigments necessary for photon capture. Mutations in Prph2 have been shown to result in a variety of photoreceptor dystrophies, including autosomal dominant retinitis pigmentosa and macular dystrophy.
As another specific example, the NOI may encode the ciliary neurotrophic factor (CNTF). Neurotrophin gene therapy using recombinant adenovirus carrying a CNTF cDNA has led to structural rescue of photoreceptors for several months in mouse models of retinitis pigmentosa (Cayouette et al. (1997) Hum Gene Ther 8:423-430).
As another example, the NOI may encode the RPE65 gene product. Mutations in this gene have been associated with Leber congenital amaurosis type 2 (LCA2) and retinitis pigmentosa.
As another example, the NOI may encode the CRX gene product. The protein encoded by this gene is a photoreceptor-specific transcription factor which plays a role in the differentiation of photoreceptor cells. This homeodomain protein is necessary for the maintenance of normal cone and rod function. Mutations in this gene are associated with photoreceptor degeneration, Leber congenital amaurosis type III and the autosomal dominant cone-rod dystrophy 2.
Derivatives
The term “derived from” is used in its normal sense as meaning the sequence need not necessarily be obtained from a sequence but instead could be derived therefrom. By way of example, a sequence may be prepared synthetically or by use of recombinant DNA techniques.
Mutants, Variants and Homologs
The term “wild type” is used to mean a polypeptide having a primary amino acid sequence which is identical with the native protein.
The term “mutant” is used to mean a polypeptide having a primary amino acid sequence which differs from the wild type sequence by one or more amino acid additions, substitutions or deletions. A mutant may arise naturally, or may be created artificially (for example by site-directed mutagenesis). Preferably the mutant has at least 90% sequence identity with the wild type sequence. Preferably the mutant has 20 mutations or less over the whole wild-type sequence. More preferably the mutant has 10 mutations or less, most preferably 5 mutations or less over the whole wild-type sequence.
The term “variant” is used to mean a naturally occurring polypeptide or polynucleotide sequence which differs from a wild-type sequence. Preferably the variant has at least 90% sequence identity with the wild type sequence. Preferably the variant has 20 mutations or less over the whole wild-type sequence. More preferably the variant has 10 mutations or less, most preferably 5 mutations or less over the whole wild-type sequence.
Here, the term “homolog” means an entity having a certain homology with the wild type amino acid sequence and the wild type nucleotide sequence. Here, the term “homology” can be equated with “identity”.
In the present context, a homologous sequence is taken to include an amino acid sequence which may be at least 75, 85 or 90% identical, preferably at least 95 or 97 or 99% identical to the subject sequence. Typically, the homologs will comprise the same active sites etc. as the subject amino acid sequence. Although homology can also be considered in terms of similarity (i.e. amino acid residues having similar chemical properties/functions), in the context of the present invention it is preferred to express homology in terms of sequence identity.
In the present context, a homologous sequence is taken to include a nucleotide sequence which may be at least 75, 85 or 90% identical, preferably at least 95 or 97 or 99 % identical to the subject sequence. Although homology can also be considered in terms of similarity, in the context of the present invention it is preferred to express homology in terms of sequence identity.
Homology comparisons can be conducted by eye, or more usually, with the aid of readily available sequence comparison programs. These commercially available computer programs can calculate % homology between two or more sequences.
% homology may be calculated over contiguous sequences, i.e. one sequence is aligned with the other sequence and each amino acid in one sequence is directly compared with the corresponding amino acid in the other sequence, one residue at a time. This is called an “ungapped” alignment. Typically, such ungapped alignments are performed only over a relatively short number of residues.
Although this is a very simple and consistent method, it fails to take into consideration that, for example, in an otherwise identical pair of sequences, one insertion or deletion will cause the following amino acid residues to be put out of alignment, thus potentially resulting in a large reduction in % homology when a global alignment is performed. Consequently, most sequence comparison methods are designed to produce optimal alignments that take into consideration possible insertions and deletions without penalizing unduly the overall homology score. This is achieved by inserting “gaps” in the sequence alignment to try to maximize local homology.
However, these more complex methods assign “gap penalties” to each gap that occurs in the alignment so that, for the same number of identical amino acids, a sequence alignment with as few gaps as possible—reflecting higher relatedness between the two compared sequences—will achieve a higher score than one with many gaps. “Affine gap costs” are typically used that charge a relatively high cost for the existence of a gap and a smaller penalty for each subsequent residue in the gap. This is the most commonly used gap scoring system. High gap penalties will of course produce optimized alignments with fewer gaps. Most alignment programs allow the gap penalties to be modified. However, it is preferred to use the default values when using such software for sequence comparisons. For example when using the GCG Wisconsin Bestfit package the default gap penalty for amino acid sequences is −12 for a gap and −4 for each extension.
Calculation of maximum % homology therefore firstly requires the production of an optimal alignment, taking into consideration gap penalties. A suitable computer program for carrying out such an alignment is the GCG Wisconsin Bestfit package (University of Wisconsin, U.S.A.; Devereux et al. (1984) Nucleic Acids Research 12:387). Examples of other software that can perform sequence comparisons include, but are not limited to, the BLAST package (see Ausubel et al. (1999) ibid—Ch. 18), FASTA (Atschul et al. (1990) J. Mol. Biol. 403-410) and the GENEWORKS suite of comparison tools. Both BLAST and FASTA are available for offline and online searching (see Ausubel et al. (1999) ibid, pages 7-58 to 7-60). However, for some applications, it is preferred to use the GCG Bestfit program. A new tool, called BLAST 2 Sequences is also available for comparing protein and nucleotide sequence (see FEMS Microbiol Lett (1999) 174(2):247-50; FEMS Microbiol Lett (1999) 177(1): 187-8).
Although the final % homology can be measured in terms of identity, the alignment process itself is typically not based on an all-or-nothing pair comparison. Instead, a scaled similarity score matrix is generally used that assigns scores to each pairwise comparison based on chemical similarity or evolutionary distance. An example of such a matrix commonly used is the BLOSUM62 matrix—the default matrix for the BLAST suite of programs. GCG Wisconsin programs generally use either the public default values or a custom symbol comparison table if supplied (see user manual for further details). For some applications, it is preferred to use the public default values for the GCG package, or in the case of other software, the default matrix, such as BLOSUM62.
Once the software has produced an optimal alignment, it is possible to calculate % homology, preferably % sequence identity. The software typically does this as part of the sequence comparison and generates a numerical result.
The sequences may also have deletions, insertions or substitutions of amino acid residues which produce a silent change and result in a functionally equivalent substance. Deliberate amino acid substitutions may be made on the basis of similarity in polarity, charge, solubility, hydrophobicity, hydrophilicity, and/or the amphipathic nature of the residues as long as the secondary binding activity of the substance is retained. For example, negatively charged amino acids include aspartic acid and glutamic acid; positively charged amino acids include lysine and arginine; and amino acids with uncharged polar head groups having similar hydrophilicity values include leucine, isoleucine, valine, glycine, alanine, asparagine, glutamine, serine, threonine, phenylalanine, and tyrosine.
Conservative substitutions may be made, for example according to the Table below. Amino acids in the same block in the second column and preferably in the same line in the third column may be substituted for each other:
The present invention also encompasses homologous substitution (substitution and replacement are both used herein to mean the interchange of an existing amino acid residue, with an alternative residue) may occur i.e. like-for-like substitution such as basic for basic, acidic for acidic, polar for polar etc. Non-homologous substitution may also occur i.e. from one class of residue to another or alternatively involving the inclusion of unnatural amino acids such as ornithine (hereinafter referred to as Z), diaminobutyric acid ornithine (hereinafter referred to as B), norleucine ornithine (hereinafter referred to as O), pyriylalanine, thienylalanine, naphthylalanine and phenylglycine.
Replacements may also be made by unnatural amino acids include; alpha* and alpha-disubstituted* amino acids, N-alkyl amino acids*, lactic acid*, halide derivatives of natural amino acids such as trifluorotyrosine*, p-Cl-phenylalanine*, p-Br-phenylalanine*, p-I-phenylalanine*, L-allyl-glycine*, β-alanine*, L-α-amino butyric acid*, L-γ-amino butyric acid*, L-α-amino isobutyric acid*, L-ε-amino caproic acid#, 7-amino heptanoic acid*, L-methionine sulfone#*, L-norleucine*, L-norvaline*, p-nitro-L-phenylalanine*, L-hydroxyproline#, L-thioproline*, methyl derivatives of phenylalanine (Phe) such as 4-methyl-Phe*, pentamethyl-Phe*, L-Phe (4-amino)#, L-Tyr (methyl)*, L-Phe (4-isopropyl)*, L-Tic (1,2,3,4-tetrahydroisoquinoline-3-carboxyl acid)*, L-diaminopropionic acid# and L-Phe (4-benzyl)*. The notation * has been utilized for the purpose of the discussion above (relating to homologous or non-homologous substitution), to indicate the hydrophobic nature of the derivative whereas # has been utilized to indicate the hydrophilic nature of the derivative, #* indicates amphipathic characteristics.
Variant amino acid sequences may include suitable spacer groups that may be inserted between any two amino acid residues of the sequence including alkyl groups such as methyl, ethyl or propyl groups in addition to amino acid spacers such as glycine or β-alanine residues. A further form of variation, involves the presence of one or more amino acid residues in peptoid form, will be well understood by those skilled in the art. For the avoidance of doubt, “the peptoid form” is used to refer to variant amino acid residues wherein the α-carbon substituent group is on the residue's nitrogen atom rather than the α-carbon. Processes for preparing peptides in the peptoid form are known in the art, for example Simon R J et al.(1992) PNAS 89(20):9367-9371 and Horwell D C (1995) Trends Biotechnol. 13(4):132-134.
Vectors
Polynucleotides used in the invention are preferably incorporated into a vector. As it is well known in the art, a vector is a tool that allows or facilitates the transfer of an entity from one environment to another. In accordance with the present invention, and by way of example, some vectors used in recombinant DNA techniques allow entities, such as a segment of DNA (such as a heterologous DNA segment, such as a heterologous cDNA segment), to be transferred into a host cell for the purpose of replicating the vectors comprising a segment of DNA. Examples of vectors used in recombinant DNA techniques include but are not limited to plasmids, chromosomes, artificial chromosomes or viruses.
The vectors used in the present invention may be for example, plasmid or virus vectors provided with an origin of replication. The vectors may contain one or more selectable marker genes, and/or a traceable marker such as GFP. Vectors may be used, for example, to transfect or transform a host cell.
Preferably the vector is a viral vector such as, but not limited to, a retroviral vector, a lentiviral vector, an adenoviral vector, a pox viral vector or a vaccinia viral vector.
Preferably the viral vector is a retroviral vector, more preferably a lentiviral vector.
Retroviral and Lentiviral Vectors
The retroviral vector of the present invention may be derived from or may be derivable from any suitable retrovirus. A large number of different retroviruses have been identified. Examples include: murine leukemia virus (MLV), human T-cell leukemia virus (HTLV), mouse mammary tumour virus (MMTV), Rous sarcoma virus (RSV), Fujinami sarcoma virus (FuSV), Moloney murine leukemia virus (Mo-MLV), FBR murine osteosarcoma virus (FBR MSV), Moloney murine sarcoma virus (Mo-MSV), Abelson murine leukemia virus (A-MLV), Avian myelocytomatosis virus-29 (MC29), and Avian erythroblastosis virus (AEV). A detailed list of retroviruses may be found in Coffin et al. (1997) “Retroviruses”, Cold Spring Harbour Laboratory Press Eds: J M Coffin, S M Hughes, H E Varmus pp 758-763.
Retroviruses may be broadly divided into two categories: namely, “simple” and “complex”. Retroviruses may even be further divided into seven groups. Five of these groups represent retroviruses with oncogenic potential. The remaining two groups are the lentiviruses and the spumaviruses. A review of these retroviruses is presented in Coffin et al (1997) ibid.
The basic structure of retrovirus and lentivirus genomes share many common features such as a 5′ LTR and a 3′ LTR, between or within which are located a packaging signal to enable the genome to be packaged, a primer binding site, integration sites to enable integration into a host cell genome and gag, pol and env genes encoding the packaging components—these are polypeptides required for the assembly of viral particles. Lentiviruses have additional features, such as rev and RRE sequences in HIV, which enable the efficient export of RNA transcripts of the integrated provirus from the nucleus to the cytoplasm of an infected target cell.
In the provirus, these genes are flanked at both ends by regions called long terminal repeats (LTRs). The LTRs are responsible for proviral integration, and transcription. LTRs also serve as enhancer-promoter sequences and can control the expression of the viral genes.
The LTRs themselves are identical sequences that can be divided into three elements, which are called U3, R and U5. U3 is derived from the sequence unique to the 3′ end of the RNA. R is derived from a sequence repeated at both ends of the RNA and U5 is derived from the sequence unique to the 5′ end of the RNA. The sizes of the three elements can vary considerably among different retroviruses.
In a defective retroviral vector genome gag, pol and env may be absent or not functional. The R regions at both ends of the RNA are repeated sequences. U5 and U3 represent unique sequences at the 5′ and 3′ ends of the RNA genome respectively.
In a typical retroviral vector of the present invention, at least part of one or more protein coding regions essential for replication may be removed from the virus. This makes the viral vector replication-defective. Portions of the viral genome may also be replaced by a library encoding candidate modulating moieties operably linked to a regulatory control region and a reporter moiety in the vector genome in order to generate a vector comprising candidate modulating moieties which is capable of transducing a target non-dividing host cell and/or integrating its genome into a host genome.
Lentivirus vectors are part of a larger group of retroviral vectors. A detailed list of lentiviruses may be found in Coffin et al (1997) “Retroviruses” Cold Spring Harbour Laboratory Press Eds: J M Coffin, S M Hughes, H E Varmus pp 758-763). In brief, lentiviruses can be divided into primate and non-primate groups. Examples of primate lentiviruses include but are not limited to: the human immunodeficiency virus (HIV), the causative agent of human auto-immunodeficiency syndrome (AIDS), and the simian immunodeficiency virus (SIV). The non-primate lentiviral group includes the prototype “slow virus” visna/maedi virus (VMV), as well as the related caprine arthritis-encephalitis virus (CAEV), equine infectious anaemia virus (EIAV) and the more recently described feline immunodeficiency virus (FIV) and bovine immunodeficiency virus (BIV).
The lentivirus family differs from retroviruses in that lentiviruses have the capability to infect both dividing and non-dividing cells (Lewis et al. (1992); Lewis and Emerman (1994)). In contrast, other retroviruses—such as MLV—are unable to infect non-dividing or slowly dividing cells such as those that make up, for example, muscle, brain, lung and liver tissue.
A lentiviral vector, as used herein, is a vector which comprises at least one component part derivable from a lentivirus. Preferably, that component part is involved in the biological mechanisms by which the vector infects cells, expresses genes or is replicated.
The lentiviral vector may be a “non-primate” vector, i.e., derived from a virus which does not primarily infect primates, especially humans.
The examples of non-primate lentivirus may be any member of the family of lentiviridae which does not naturally infect a primate and may include a feline immunodeficiency virus (FIV), a bovine immunodeficiency virus (BIV), a caprine arthritis encephalitis virus (CAEV), a Maedi visna virus (MVV) or an equine infectious anaemia virus (EIAV).
In one embodiment the viral vector is derived from EIAV. EIAV has the simplest genomic structure of the lentiviruses and is particularly preferred for use in the present invention. In addition to the gag, pol and env genes EIAV encodes three other genes: tat, rev, and S2. Tat acts as a transcriptional activator of the viral LTR (Derse and Newbold (1993); Maury et al. (1994)) and Rev regulates and coordinates the expression of viral genes through rev-response elements (RRE) (Martarano et al (1994)). The mechanisms of action of these two proteins are thought to be broadly similar to the analogous mechanisms in the primate viruses (Martano et al. ibid). The function of S2 is unknown. In addition, an EIAV protein, Ttm, has been identified that is encoded by the first exon of tat spliced to the env coding sequence at the start of the transmembrane protein.
Preferred vectors of the present invention are recombinant retroviral or lentiviral vectors.
The term “recombinant retroviral or lentiviral vector” (RRV) refers to a vector with sufficient retroviral genetic information to allow packaging of an RNA genome, in the presence of packaging components, into a viral particle capable of infecting a target cell. Infection of the target cell may include reverse transcription and integration into the target cell genome. The RRV carries non-viral coding sequences which are to be delivered by the vector to the target cell. A RRV is incapable of independent replication to produce infectious retroviral particles within the final target cell. Usually the RRV lacks a functional gag-pol and/or env gene and/or other genes essential for replication. The vector of the present invention may be configured as a split-intron vector. A split intron vector is described in PCT patent application WO 99/15683.
Preferably the RRV vector of the present invention has a minimal viral genome.
As used herein, the term “minimal viral genome” means that the viral vector has been manipulated so as to remove the non-essential elements and to retain the essential elements in order to provide the required functionality to infect, transduce and deliver a nucleotide sequence of interest to a target host cell. Further details of this strategy can be found in our WO 98/17815.
A minimal viral genome of the present invention may comprise (5′) R—U5—one or more nucleotide of interest sequences operatively linked to a photoreceptor cell specific regulatory construct of the present invention—U3-R (3′).
However, the plasmid vector used to produce the viral genome within a host cell/packaging cell will also include transcriptional regulatory control sequences operably linked to the retroviral genome to direct transcription of the genome in a host cell/packaging cell. These regulatory sequences may be the natural sequences associated with the transcribed retroviral sequence, i.e. the 5′ U3 region, or they may be a heterologous promoter such as another viral promoter, for example the CMV promoter. Some lentiviral genomes require additional sequences for efficient virus production. For example, in the case of HIV, rev and RRE sequence are preferably included. However the requirement for rev and RRE may be reduced or eliminated by codon optimization. Further details of this strategy can be found in our WO 01/79518. Alternative sequences which perform the same function as the rev/RRE system are also known. For example, a functional analogue of the rev/RRE system is found in the Mason Pfizer monkey virus. This is known as the constitutive transport element (CTE) and comprises an RRE-type sequence in the genome which is believed to interact with a factor in the infected cell. The cellular factor can be thought of as a rev analogue. Thus, CTE may be used as an alternative to the rev/RRE system. Any other functional equivalents which are known or become available may be relevant to the invention. For example, it is also known that the Rex protein of HTLV-I can functionally replace the Rev protein of HIV-1. It is also known that Rev and Rex have similar effects to IRE-BP.
Packaging Sequence
As utilized within the context of the present invention the term “packaging signal” which is referred to interchangeably as “packaging sequence” or “psi” is used in reference to the non-coding, cis-acting sequence required for encapsidation of retroviral RNA strands during viral particle formation. In HIV-1, this sequence has been mapped to loci extending from upstream of the major splice donor site (SD) to at least the gag start codon.
As used herein, the term “extended packaging signal” or “extended packaging sequence” refers to the use of sequences around the psi sequence with further extension into the gag gene. The inclusion of these additional packaging sequences may increase the efficiency of insertion of vector RNA into viral particles. As an example, for the Murine Leukemia Virus MoMLV, the minimum core packaging signal is encoded by the sequence (counting from the 5′ LTR cap site) from approximately nucleotide 144, up through the Pst I site (nucleotide 567). The extended packaging signal of MoMLV includes the sequence beyond nucleotide 567 up through the start of the gag/pol gene (nucleotide 621), and beyond nucleotide 1040 (Bender et al. (1987)). These sequences include about a third of the gag gene sequence.
Feline immunodeficiency virus (FIV) RNA encapsidation determinants have been shown to be discrete and non-continuous, comprising one region at the 5′ end of the genomic mRNA (R-U5) and another region that mapped within the proximal 311 nt of gag. (Kaye et al. (1995)) showed that mRNAs of subgenomic vectors as well as of full-length molecular clones were optimally packaged into viral particles and resulted in high-titer FIV vectors when they contained only the proximal 230 nucleotides (nt) of gag. Further 3′ truncations of gag sequences progressively diminished encapsidation and transduction. Deletion of the initial ninety 5′ nt of the gag gene abolished mRNA packaging, demonstrating that this segment is indispensable for encapsidation.
Adenovirus Vectors
In another embodiment, the vector of the present invention may be an adenovirus vector. The adenovirus is a double-stranded, linear DNA virus that does not go through an RNA intermediate. There are over 50 different human serotypes of adenovirus divided into 6 subgroups based on the genetic sequence homology. The natural target of adenovirus is the respiratory and gastrointestinal epithelia, generally giving rise to only mild symptoms. Serotypes 2 and 5 (with 95% sequence homology) are most commonly used in adenoviral vector systems and are normally associated with upper respiratory tract infections in the young.
Adenoviruses are nonenveloped, regular icosohedrons. A typical adenovirus comprises a 140 nm encapsidated DNA virus. The icosahedral symmetry of the virus is composed of 152 capsomeres: 240 hexons and 12 pentons. The core of the particle contains the 36 kb linear duplex DNA which is covalently associated at the 5′ ends with the Terminal Protein (TP) which acts as a primer for DNA replication. The DNA has inverted terminal repeats (ITR) and the length of these varies with the serotype.
The adenovirus is a double stranded DNA nonenveloped virus that is capable of in vivo and in vitro transduction of a broad range of cell types of human and non-human origin. These cells include respiratory airway epithelial cells, hepatocytes, muscle cells, cardiac myocytes, synoviocytes, primary mammary epithelial cells and post-mitotically terminally differentiated cells such as neurons.
Adenoviral vectors are also capable of transducing non dividing cells. This is very important for diseases, such as cystic fibrosis, in which the affected cells in the lung epithelium, have a slow turnover rate. In fact, several trials are underway utilizing adenovirus-mediated transfer of cystic fibrosis transporter (CFTR) into the lungs of afflicted adult cystic fibrosis patients.
Adenoviruses have been used as vectors for gene therapy and for expression of heterologous genes. The large (36 kilobase) genome can accommodate up to 8 kb of foreign insert DNA and is able to replicate efficiently in complementing cell lines to produce very high titres of up to 1012. Adenovirus is thus one of the best systems to study the expression of genes in primary non-replicative cells.
The expression of viral or foreign genes from the adenovirus genome does not require a replicating cell. Adenoviral vectors enter cells by receptor mediated endocytosis. Once inside the cell, adenovirus vectors rarely integrate into the host chromosome. Instead, it functions episomally (independently from the host genome) as a linear genome in the host nucleus. Hence the use of recombinant adenovirus alleviates the problems associated with random integration into the host genome.
Pox Viral Vectors
Pox viral vectors may be used in accordance with the present invention, as large fragments of DNA are easily cloned into their genome and recombinant attenuated vaccinia variants have been described (Meyer et al. (1991); Smith and Moss (1983)).
Examples of pox viral vectors include but are not limited to leporipoxvirus: Upton et al. (1986), (shope fibroma virus); capripoxvirus: Gershon et al. (1989), (Kenya sheep-1); orthopoxvirus: Weir et al. (1983), (vaccinia); Esposito et al. (1984), (monkeypox and variola virus); Hruby et al. (1983), (vaccinia); Kilpatrick et al. (1985), (Yaba monkey tumour virus); avipoxvirus: Binns et al. (1988) (fowlpox); Boyle et al. (1987), (fowlpox); Schnitzlein et al. (1988), (fowlpox, quailpox); entomopox (Lytvyn et al. (1992)).
Poxvirus vectors are used extensively as expression vehicles for genes of interest in eukaryotic cells. Their ease of cloning and propagation in a variety of host cells has led, in particular, to the widespread use of poxvirus vectors for expression of foreign protein and as delivery vehicles for vaccine antigens (Moss (1991)).
Vaccinia Viral Vectors
The vector of the present invention may be a vaccinia virus vector such as MVA or NYVAC. Alternatives to vaccinia vectors include avipox vectors such as fowlpox or canarypox known as ALVAC and strains derived therefrom which can infect and express recombinant proteins in human cells but are unable to replicate.
Viral Vector Particle Production Systems
The term ‘viral vector particle production system’ refers to a system comprising the necessary components for viral particle production.
By using producer/packaging cell lines, it is possible to propagate and isolate quantities of viral vector particles (e.g. to prepare suitable titres of the retroviral vector particles) for subsequent transduction of, for example, a site of interest (such as retinal tissue). Producer cell lines are usually better for large scale production or vector particles.
As used herein, the term “packaging cell” refers to a cell which contains those elements necessary for production of infectious recombinant virus which are lacking in the RNA genome. Typically, such packaging cells contain one or more producer plasmids which are capable of expressing viral structural proteins (such as codon optimized gag-pol and env) but they do not contain a packaging signal.
Transient transfection has numerous advantages over the packaging cell method. In this regard, transient transfection avoids the longer time required to generate stable vector-producing cell lines and is used if the vector genome or retroviral packaging components are toxic to cells. If the vector genome encodes toxic genes or genes that interfere with the replication of the host cell, such as inhibitors of the cell cycle or genes that induce apoptosis, it may be difficult to generate stable vector-producing cell lines, but transient transfection can be used to produce the vector before the cells die. Also, cell lines have been developed using transient infection that produce vector titre levels that are comparable to the levels obtained from stable vector-producing cell lines (Pear et al. (1993)).
Producer cells/packaging cells can be of any suitable cell type. Producer cells are generally mammalian cells but can be, for example, insect cells.
As used herein, the term “producer cell” or “vector producing cell” refers to a cell which contains all the elements necessary for production of retroviral vector particles.
Preferably, the producer cell is obtainable from a stable producer cell line.
Preferably, the producer cell is obtainable from a derived stable producer cell line.
Preferably the envelope protein sequences, and nucleocapsid sequences are all stably integrated in the producer and/or packaging cell. However, one or more of these sequences could also exist in episomal form and gene expression could occur from the episome.
Also as discussed above, simple packaging cell lines, comprising a provirus in which the packaging signal has been deleted, have been found to lead to the rapid production of undesirable replication competent viruses through recombination. In order to improve safety, second generation cell lines have been produced wherein the 3′LTR of the provirus is deleted. In such cells, two recombinations would be necessary to produce a wild type virus. A further improvement involves the introduction of the gag-pol genes and the env gene on separate constructs so-called third generation packaging cell lines. These constructs are introduced sequentially to prevent recombination during transfection.
Preferably, the packaging cell lines are second generation packaging cell lines.
Preferably, the packaging cell lines are third generation packaging cell lines.
In these split-construct, third generation cell lines, a further reduction in recombination may be achieved by changing the codons. This technique, based on the redundancy of the genetic code, aims to reduce homology between the separate constructs, for example between the regions of overlap in the gag-pol and env open reading frames.
The packaging cell lines are useful for providing the gene products necessary to encapsidate and provide a membrane protein for a high titre vector particle production. The packaging cell may be a cell cultured in vitro such as a tissue culture cell line. Suitable cell lines include but are not limited to mammalian cells such as murine fibroblast derived cell lines or human cell lines. Preferably the packaging cell line is a human cell line.
Alternatively, the packaging cell may be a cell derived from the individual to be treated. The cell may be isolated from an individual and the packaging and vector components administered ex vivo followed by re-administration of the autologous packaging cells.
In more detail, the packaging cell may be an in vivo packaging cell in the body of an individual to be treated or it may be a cell cultured in vitro such as a tissue culture cell line.
In one embodiment the vector configurations of the present invention use as their production system, three transcription units expressing a genome, the gag-pol components and an envelope. The envelope expression cassette may include one of a number of envelopes such as VSV-G or various murine retrovirus envelopes such as 4070A.
Pseudotyping
In one preferred aspect, the viral vector of the present invention has been pseudotyped. In this regard, pseudotyping can confer one or more advantages. For example, with the lentiviral vectors, the env gene product of the HIV based vectors would restrict these vectors to infecting only cells that express a protein called CD4. But if the env gene in these vectors has been substituted with env sequences from other RNA viruses, then they may have a broader infectious spectrum (Verma and Somia (1997)). By way of example, workers have pseudotyped an HIV based vector with the glycoprotein from VSV (Verma and Somia (1997)).
In another alternative, the Env protein may be a modified Env protein such as a mutant or engineered Env protein. Modifications may be made or selected to introduce targeting ability or to reduce toxicity or for another purpose (Valsesia-Wittman et al (1996); Nilson et al (1996); Fielding et al (1998) and references cited therein).
The vector may be pseudotyped with any molecule of choice.
VSV-G:
The envelope glycoprotein (G) of Vesicular stomatitis virus (VSV), a rhabdovirus, is another envelope protein that has been shown to be capable of pseudotyping certain retroviruses.
Its ability to pseudotype MoMLV-based retroviral vectors in the absence of any retroviral envelope proteins was first shown by Emi et al. (1991) Journal of Virology 65:1202-1207). WO 94/294440 teaches that retroviral vectors may be successfully pseudotyped with VSV-G. These pseudotyped VSV-G vectors may be used to transduce a wide range of mammalian cells. Even more recently, Abe et al. (1998) J Virol 72(8) 6356-6361 teach that non-infectious retroviral particles can be made infectious by the addition of VSV-G.
Burns et al. (1993) Proc. Natl. Acad. Sci. USA 90:8033-7) successfully pseudotyped the retrovirus MLV with VSV-G and this resulted in a vector having an altered host range compared to MLV in its native form. VSV-G pseudotyped vectors have been shown to infect not only mammalian cells, but also cell lines derived from fish, reptiles and insects (Burns et al. (1993) ibid). They have also been shown to be more efficient than traditional amphotropic envelopes for a variety of cell lines (Yee et al., (1994) Proc. Natl. Acad. Sci. USA 91:9564-9568, Lin, Emi et al. (1991) Journal of Virology 65:1202-1207). VSV-G protein can be used to pseudotype certain retroviruses because its cytoplasmic tail is capable of interacting with the retroviral cores.
The provision of a non-retroviral pseudotyping envelope such as VSV-G protein gives the advantage that vector particles can be concentrated to a high titre without loss of infectivity (Akkina et al. (1996) J. Virol. 70:2581-5). Retrovirus envelope proteins are apparently unable to withstand the shearing forces during ultracentrifugation, probably because they consist of two non-covalently linked subunits. The interaction between the subunits may be disrupted by the centrifugation. In comparison the VSV glycoprotein is composed of a single unit. VSV-G protein pseudotyping can therefore offer potential advantages.
WO 00/52188 describes the generation of pseudotyped retroviral vectors, from stable producer cell lines, having vesicular stomatitis virus-G protein (VSV-G) as the membrane-associated viral envelope protein, and provides a gene sequence for the VSV-G protein.
Ross River Virus
The Ross River viral envelope has been used to pseudotype a nonprimate lentiviral vector (FIV) and following systemic administration predominantly transduced the liver (Kang et al. (2002)). Efficiency was reported to be 20-fold greater than obtained with VSV-G pseudotyped vector, and caused less cytotoxicity as measured by serum levels of liver enzymes suggestive of hepatotoxicity.
Ross River Virus (RRV) is an alphavirus spread by mosquitoes which is endemic and epidemic in tropical and temperate regions of Australia. Antibody rates in normal populations in the temperate coastal zone tend to be low (6% to 15%) although sero-prevalence reaches 27 to 37% in the plains of the Murray Valley River system. In 1979 to 1980 Ross River Virus became epidemic in the Pacific Islands. The disease is not contagious between humans and is never fatal, the first symptom being joint pain with fatigue and lethargy in about half of patients (Fields Virology).
Baculovirus GP64
The baculovirus GP64 protein has been shown to be an attractive alternative to VSV-G for viral vectors used in the large-scale production of high-titer virus required for clinical and commercial applications (Kumar M, Bradow B P, Zimmerberg J (2003) Hum Gene Ther. 14(1):67-77). Compared with VSV-G-pseudotyped vectors, GP64-pseudotyped vectors have a similar broad tropism and similar native titers. Because, GP64 expression does not kill cells, 293T-based cell lines constitutively expressing GP64 can be generated.
Alternative Envelopes
Other envelopes which give reasonable titre when used to pseudotype EIAV include Mokola, Rabies, Ebola and LCMV (lymphocytic choriomeningitis virus). Following in utero injection in mice the VSV-G envelope was found to be more efficient at transducing hepatocytes than either Ebola or Mokola (Mackenzie et al. (2002)). Intravenous infusion into mice of lentivirus pseudotyped with 4070A led to maximal gene expression in the liver (Peng et al. (2001)).
Codon Optimization
The polynucleotide of the present invention (including the NOI and/or vector components) may be codon optimized. Codon optimization has previously been described in WO 99/41397 and WO 01/79518. Different cells differ in their usage of particular codons. This codon bias corresponds to a bias in the relative abundance of particular tRNAs in the cell type. By altering the codons in the sequence so that they are tailored to match with the relative abundance of corresponding tRNAs, it is possible to increase expression. By the same token, it is possible to decrease expression by deliberately choosing codons for which the corresponding tRNAs are known to be rare in the particular cell type. Thus, an additional degree of translational control is available.
Many viruses, including HIV and other lentiviruses, use a large number of rare codons and by changing these to correspond to commonly used mammalian codons, increased expression of a gene of interest, e.g. a NOI or packaging components in mammalian producer cells, can be achieved. Codon usage tables are known in the art for mammalian cells, as well as for a variety of other organisms.
Codon optimization of viral vector components has a number of other advantages. By virtue of alterations in their sequences, the nucleotide sequences encoding the packaging components of the viral particles required for assembly of viral particles in the producer cells/packaging cells have RNA instability sequences (INS) eliminated from them. At the same time, the amino acid sequence coding sequence for the packaging components is retained so that the viral components encoded by the sequences remain the same, or at least sufficiently similar that the function of the packaging components is not compromised. Codon optimization also overcomes the Rev/RRE requirement for export, rendering optimized sequences Rev independent. Codon optimization also reduces homologous recombination between different constructs within the vector system (for example between the regions of overlap in the gag-pol and env open reading frames). The overall effect of codon optimization is therefore a notable increase in viral titer and improved safety.
In one embodiment only codons relating to INS are codon optimized. However, in a much more preferred and practical embodiment, the sequences are codon optimized in their entirety, with the exception of the sequence encompassing the frameshift site of gag-pol (see below).
The gag-pol gene comprises two overlapping reading frames encoding the gag-pol proteins. The expression of both proteins depends on a frameshift during translation. This frameshift occurs as a result of ribosome “slippage” during translation. This slippage is thought to be caused at least in part by ribosome-stalling RNA secondary structures. Such secondary structures exist downstream of the frameshift site in the gag-pol gene. For HIV, the region of overlap extends from nucleotide 1222 downstream of the beginning of gag (wherein nucleotide 1 is the A of the gag ATG) to the end of gag (nt 1503). Consequently, a 281 bp fragment spanning the frameshift site and the overlapping region of the two reading frames is preferably not codon optimized. Retaining this fragment will enable more efficient expression of the gag-pol proteins.
For EIAV the beginning of the overlap has been taken to be nt 1262 (where nucleotide 1 is the A of the gag ATG). The end of the overlap is at 1461 bp. In order to ensure that the frameshift site and the gag-pol overlap are preserved, the wild type sequence has been retained from nt 1156 to 1465.
Derivations from optimal codon usage may be made, for example, in order to accommodate convenient restriction sites, and conservative amino acid changes may be introduced into the gag-pol proteins.
In one embodiment, codon optimization is based on lightly expressed mammalian genes. The third and sometimes the second and third base may be changed.
Due to the degenerate nature of the Genetic Code, it will be appreciated that numerous gag-pol sequences can be achieved by a skilled worker. Also there are many retroviral variants described which can be used as a starting point for generating a codon optimized gag-pol sequence. Lentiviral genomes can be quite variable. For example there are many quasi-species of HIV-1 which are still functional. This is also the case for EIAV. These variants may be used to enhance particular parts of the transduction process. Examples of HIV-1 variants may be found at the HIV Databases operated by Los Alamos National Security, LLC at http://hiv-web.lanl.gov. Details of EIAV clones may be found at the National Center for Biotechnology Information (NCBI) database located at http://www.ncbi.nlm.nih.gov.
The strategy for codon optimized gag-pol sequences can be used in relation to any retrovirus. This would apply to all lentiviruses, including EIAV, FIV, BIV, CAEV, VMR, SIV, HIV-1 and HIV-2. In addition this method could be used to increase expression of genes from HTLV-1, HTLV-2, HFV, HSRV and human endogenous retroviruses (HERV), MLV and other retroviruses.
Codon optimization can render gag-pol expression Rev independent. In order to enable the use of anti-rev or RRE factors in the retroviral vector, however, it would be necessary to render the viral vector generation system totally Rev/RRE independent. Thus, the genome also needs to be modified. This is achieved by optimizing vector genome components. Advantageously, these modifications also lead to the production of a safer system absent of all additional proteins both in the producer and in the transduced cell.
Pharmaceutical Compositions and Administration
The present invention also provides a pharmaceutical composition for treating an individual by gene therapy, wherein the composition comprises a therapeutically effective amount of the polynucleotide of the present invention comprising one or more deliverable therapeutic and/or diagnostic NOI(s). The pharmaceutical composition may be for human or animal usage. Typically, a physician will determine the actual dosage which will be most suitable for an individual subject and it will vary with the age, weight and response of the particular individual.
The composition may optionally comprise a pharmaceutically acceptable carrier, diluent, excipient or adjuvant. The choice of pharmaceutical carrier, excipient or diluent can be selected with regard to the intended route of administration and standard pharmaceutical practice. The pharmaceutical compositions may comprise, or in addition to, the carrier, excipient or diluent any suitable binder(s), lubricant(s), suspending agent(s), coating agent(s), solubilizing agent(s), and other carrier agents that may aid or increase the viral entry into the target site (such as for example a lipid delivery system).
Where appropriate, the pharmaceutical compositions can be administered by any one or more of: inhalation, in the form of a suppository or pessary, topically in the form of a lotion, solution, cream, ointment or dusting powder, by use of a skin patch, orally in the form of tablets containing excipients such as starch or lactose, or in capsules or ovules either alone or in admixture with excipients, or in the form of elixirs, solutions or suspensions containing flavoring or coloring agents, or they can be injected parenterally, for example intracavernosally, intravenously, intramuscularly or subcutaneously. For parenteral administration, the compositions may be best used in the form of a sterile aqueous solution which may contain other substances, for example enough salts or monosaccharides to make the solution isotonic with blood.
For buccal or sublingual administration, the compositions may be administered in the form of tablets or lozenges which can be formulated in a conventional manner.
Preferably, the pharmaceutical composition is suitable for subretinal, intravitreal, or anterior injection. Such formulation involves the use of a pharmaceutically and/or physiologically acceptable vehicle or carrier, particular one for subretinal injection, such as buffered saline or other buffers, e.g., HEPES, to maintain pH at appropriate physiological levels. A variety of known carriers are provided in International Publication No. WO 00/15822, incorporated herein by reference.
According to the method of this invention for treating an ocular disorder characterized by the defect or absence of a normal gene in the ocular cells of a human or animal subject, the pharmaceutical composition is preferably administered by subretinal injection.
Treatment
It is to be appreciated that all references herein to treatment include curative, palliative and prophylactic treatment. The treatment of mammals is particularly preferred. Both human and veterinary treatments are within the scope of the present invention.
Various preferred features and embodiments of the invention will now be described by way of non-limiting examples with reference to the accompanying Examples.
The sequence of the photoreceptor promoters were found via the DBTSS website (Database of Transcriptional Start Sites, located at http://dbtss.hgc.jp/) using the access numbers showed in Table 1 below.
Primers to amplify and isolate the photoreceptor promoter sequences were designed to span regions from (relative to the mRNA start site):
Restriction sites were included in the primers with a view to direct subcloning into the pGL3-basic luciferase report vector (Promega).
The promoter sequences were amplified by PCR using genomic DNA isolated from 293T cells as template* and PuRe Taq Ready-to-go PCR beads (Amersham Biosciences, 27-9558-01).
* except for the bovine rho promoter where the template used was the BSG378 plasmid.
PCR products were digested with BglII/HindIlI (for the promoters) or MluI/XhoI (for the IRBP enhancer element), gel purified and subcloned into the pGL3-basic plasmid upstream of the luciferase reporter gene.
The cloning steps resulted in the creation of a series of luciferase reporter plasmids containing the different photoreceptor promoters with and without the IRBP enhancer element (see
All the promoters cloned into the pGL3-basic plasmid were sequenced by Lark Technologies to identify any possible problems arising from an incorrect sequence. All the promoter sequences were as expected.
The cell specificity of the different truncated rhodopsin promoter constructs was evaluated by DNA transfection of a human retinoblastoma-derived cell line (Y-79) and a human embryonic kidney cell line (HEK-293T). The Y-79 human retinoblastoma cell line produces mRNAs encoding proteins unique to the photoreceptors and therefore, is the most suitable in vitro model to study transcriptional regulation of photoreceptor-specific genes (Di Polo et al. (1995) Proc. Natl. Acad. Sci. 92:4016-4020; Rakoczy et al., Methods in Molecular Medicine, Humana Press, Vol. 47, pp. 31-43).
All cell lines were maintained at 37° C. with 5% CO2.
Y-79 cells were cultured in suspension in RPMI-1640 supplemented with 20% foetal bovine serum (FBS), HEPES (10 mM), sodium pyruvate (1 mM), sodium bicarbonate (1 mM) and glucose (4.5 g/L) and seeded at a density of 8×105 cells/well in 24-well plates. For cell attachment, plates were coated with 80 uL/well of poly-D-lysine (SIGMA, P-7280, 0.05 mg/mL). Two hours after seeding, transfections were performed in triplicates with Lipofectamine™ 2000 Transfection Reagent (Invitrogen) using 1.6 ug DNA (including the renilla plasmid as a transfection control) and 4 uL Lipofectamine for each well.
293T cells were maintained in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% FBS, L-Glutamine (2 mM) and MEM non-essential amino-acids and seeded, after trypsin dispersion, at 1.5×105 cells/well in 24-well plates 24 hours before transfections. When the cells were approximately 90% confluent, transfections were performed using Lipofectamine™ 2000 as described earlier.
Plates were incubated for 48 hours and a luciferase assay was performed.
This assay was based on the Dual-Luciferase® Reporter Assay System kit (Promega, Cat. No. E1910) and was performed as per manufacturer's protocol.
The plasmids used for transfections are those described in Example 2 and additional plasmids banked as:
Reporter gene expression driven by the photoreceptor-specific promoters was measured in 293T and Y-79 cell lines to assess the specificity and strength of expression of each promoter. The results obtained are shown in
Conclusions
The Y-79 cells grow naturally in suspension and in this experiment the cells were made adherent for the transfection experiment and the promoter activity was compared to that in the suspension culture.
The transfection efficiency of the adherent and suspension Y-79 cells was investigated by transfecting with a LacZ plasmid and X-gal staining the cells 48 hrs later. The results are shown in
No difference in transfection efficiencies could be observed between suspension and adherent Y-79 cells.
Reporter gene expression driven by the photoreceptor-specific promoters was compared in both suspension and adherent Y-79 cells. The results obtained are shown in
Conclusions
These results confirm the experiments above in terms of the relative strength of the different promoters being evaluated.
Transfection efficiencies are similar with suspension or adherent Y-79 cells.
Two additional IRBP elements were added by cloning to BSG397 (see
Reporter gene expression driven by the photoreceptor-specific promoters was measured in ARPE-19, D407 and Y-79 cell lines to assess the specificity and strength of expression of each promoter. The results obtained are shown in
Conclusions
Y-79 Cells
The (3*IRBP)-hPDE is the most potent photoreceptor-specific promoter showing strong activity relative to the CMV promoter (¼th of the CMV activity) and higher activity than the single IRBP version of the PDE promoter.
ARPE-19 and D407
Both these cell lines transfected very well as shown by the CMV and SV40 luciferase results. The CMV and SV40 promoters were particularly potent promoters (non specific) in these cell lines and the photoreceptor-specific promoters showed a weak activity slightly increased with the triple IRBP-PDE promoter.
An additional experiment was carried out with other multiple IRBP-hPDE constructs. In plasmid banked as BSG422 and shown in
In plasmid banked as BSG423 and shown in
Conclusions
This experiment confirmed that the (3xIRBP)-hPDE is the most potent photoreceptor-specific promoter. BSG422 in which expression of luciferase is driven by the hPDE promoter downstream of 2 IRBP enhancer elements gave improved results compared to BSG397 (single IRBP element). However, photoreceptor-specific promoters showed a weak activity in the non-photoreceptor cell lines which was slightly increased when the number of IRBP elements was increased. Interestingly, BSG423 in which the second IRBP enhancer was placed downstream of the luciferase expression cassette in BSG397 plasmid did not show any improved improved expression results compared to BSG397 transfected Y-79 cells.
EIAV vectors were manufactured using the 3 plasmid transfection system of vector genome, gag/pol (pESGPK) and env (phGK) with Lipofectamine™ 2000 (Invitrogen) as the transfecting agent in HEK293T (ATCC). The luciferase reporter was replaced with LacZ in the vector genomes.
The titres of the vectors were determined through their integration efficiency compared to a known reference standard in a quantitative PCR.
Y-79 cells along with ARPE-19 and HT1080 (ATCC) were transduced with the following vectors at an M.O.I of 10 in the presence of 8 μg/ml polybrene (Sigma) and expanded for 2 weeks.
The transduced cells were re-seeded into 24 well plates in triplicates and the Luminescent β-galactosidase reporter assay (Clontech) was performed 24 hrs later as per manufacturer's instructions. Results are shown in
Conclusions
The hPDE6b promoter coupled with three multiple copies of the IRBP enhancer element (3xIRBP hPDE6b) demonstrated significant expression in Y-79 cells which was comparable to the CMV promoter.
The non-target cell types ARPE-19 and HT1080 displayed little or no activity with the photoreceptor specific promoters.
The in vivo expression profile of the photoreceptor specific promoters were examined following subretinal delivery of recombinant EIAV vectors described in Example 8 into mouse eyes. Eyes were harvested at 14 days post injection and X-gal stained to reveal LacZ expression. Results are shown in
Conclusions
At 14 days post injection, staining for LacZ could be clearly detected in all the EIAV vector treated eyes. LacZ expression was restricted to the photoreceptor cell layer with all three vectors.
The in vivo expression profile of the photoreceptor specific promoters were examined following subretinal delivery of recombinant EIAV vectors shown in
1 μl of the vector preparation was injected subretinally into each eye of the abcr−/− (Abcr knockout) transgenic mice (Kim et al. (2004), Proc Natl Acad Sci USA. 101(32):11668-72). Then 4 months later the eyes from these animals were harvested. A2E and iso-A2E metabolites were extracted from these eyes and were quantified using reverse phase HPLC according to the procedure described in Kim et al. (2004), Proc Natl Acad Sci USA. 101(32): 11668-72.
The results are shown in
Three photoreceptor cell-specific promoters (hRho, hPDE6b, hRP1) were cloned into the pGL3-basic vector in combination with the IRBP enhancer element. These constructs were used to transfect Y-79 and 293T cells to test specificity and strength of promoter activity via a luciferase reporter assay. The assay demonstrated that:
Two of the photoreceptor specific promoters (hRho, hPDE6b) in combination with one or three IRBP enhancer elements were transferred to the EIAV lentivector platform, replacing the luciferase reporter with LacZ. These were used to transduce Y-79, ARPE-19 and HT1080 cells to evaluate their expression in vitro in a β-galactosidase reporter assay. The assay demonstrated that:
Following subretinal delivery of these EIAV vectors into mouse eyes, it was observed that:
Furthermore, following subretinal delivery of EIAV encoding ABCR into mouse eyes, it was observed that:
All publications mentioned in the above specification are herein incorporated by reference. Various modifications and variations of the described methods and system of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. Although the present invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in biochemistry and biotechnology or related fields are intended to be within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0624097.2 | Dec 2006 | GB | national |
| 0710135.5 | May 2007 | GB | national |
This application is a continuation of international patent application Serial No. PCT/GB2007/004615 filed Nov. 30, 2007, which claims priority to Great Britain patent application Serial Nos. 0624097.2 filed Dec. 1, 2006 and 0710135.5 filed May 25, 2007. The foregoing applications, and all documents cited therein or during their prosecution (“appln cited documents”) and all documents cited or referenced in the appln cited documents, and all documents cited or referenced herein (“herein cited documents”), and all documents cited or referenced in herein cited documents, together with any manufacturer's instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/GB2007/004615 | Nov 2007 | US |
| Child | 12475943 | US |
