Patent Application
20090136534
1. Field of the Invention
The invention generally relates to improved Mycobacterium tuberculosis (Mtb) vaccines that are successful in preventing the development of symptoms of tuberculosis, both pre- and post-exposure to Mtb. In particular, the invention provides an improved recombinant Bacille Calmette-Guerin (BCG) subunit-based vaccine in which one or more Mtb antigens and one or more Mtb resuscitation or reactivation antigens are overexpressed, and in which at least a portion of the DosR regulon is up-regulated.
2. Background of the Invention
The current prophylactic (pre-exposure) Mycobacterium tuberculosis (Mtb) vaccine Mycobacterium bovis (M. bovis) BCG, introduced over 60 years ago, efficiently protects against severe disease manifestation in children but fails to prevent the establishment of latent TB or disease reactivation of infection in adolescents and adults. Moreover, essentially all novel Mtb vaccines currently in clinical trials are designed as prophylactic rather than both prophylactic and therapeutic (post exposure) vaccines.
It is believed that Mtb progresses through a series of stages during its infectious cycle in man as a reaction to human immune responses and that each stage is orchestrated by a distinct genetic program which directs the expression of stage-specific antigens. If this concept is valid, then a truly comprehensive tuberculosis vaccine should include antigens representing each stage as well as antigens that are stage-independent. Latent tuberculosis (LTBI/latency) appears to be one such stage and current evidence suggests that Mtb adopts a unique physiological phenotype during latency characterized by bacteriostasis (non-replicating persistence), a switch from aerobic to anaerobic respiration, expression of the α-crystalline small chaperone protein (Acr/HspX) and increased resistance to several mycobacterial antibiotics.
Maintenance of the non-replicating persistence state, believed to be typical of Mtb in latent lesions, appears to depend on the continuous production of Th1 cytokines (IFNγ, IL-12 and TNFα) and nitric oxide and the localization of MTB within stable granulomas. However, the reactivation of latent Mtb infection, characterized by resumption of bacterial replication, inflammation and cavitation, can be promptly precipitated by immunosuppressive regimens (e.g., corticosterioids or TNFα-antagonist) and occurs in 5-10% of latently infected individuals, perhaps due to acquired tolerance to environmental mycobacteria, age, and, more significantly, HIV disease. This common clinical scenario and the proven role of the cellular immune system for the maintenance of latency lead to the conclusion that non-replicating persistence is a metastable phenotype determined by three interacting processes: bacterial replication within latent lesions is constrained by effectors of the cellular immune system; bacteria within latent lesions monitor the production of immune effectors; and, decreased production of immune effectors results in resumption of replication.
To date, no successful vaccines have been developed which confer immunity to infection by Mtb and at the same time treat or prevent the development of symptoms of TB after exposure to Mtb, or as a result of reactivation of latent infection. A recombinant BCG vaccine, engineered to elicit an immune response of this kind, might reduce reactivation rates in persons with subtle degrees of immunosuppression produced, for example, by senescence, diabetes, HIV disease, acquired tolerance to environmental mycobacteria or malnutrition. There is thus an ongoing need to develop new TB vaccines, and it would be particularly useful to develop a vaccine that can be used both prophylactically and for post-exposure treatment.
The present invention is based on the development of a novel recombinant Bacille Calmette-Guerin (rBCG) for use as a vaccine. The vaccine may be used prophylactically to prevent Mtb infection in naive individuals. However, the vaccine is also effective for treating individuals who have already been exposed to and/or infected by Mtb. The vaccine prevents the establishment of infection and likewise prevents the reactivation of latent Mtb in individuals that have been previously infected. The rBCG that is used in the vaccine preparations is genetically engineered to express “classical” Mtb antigens and antigens that are relevant to several stages of the Mtb life cycle, e.g. latency, reactivation and resuscitation. Thus, the immune response that is generated as a result of immunization with the vaccine protects the vaccinated individual from developing an active Mtb infection at any and all stages of exposure to Mtb. In particular, the rBCG overexpresses 1) one or more genes encoding Mycobacterium tuberculosis (Mtb) antigens that are known to elicit potent, protective immune responses to Mtb; and 2) one or more genes encoding at least one Mtb resuscitation or reactivation antigen. The antigen encoding sequences are located on an extrachromosomal element or are integrated into the chromosome of the recombinant BCG. In addition, expression of all or part of the Dos R regulon is up-regulated in the novel rBCG. The embodiment of the invention in which the antigen encoding sequences are integrated into the chromosome is depicted schematically in
The present invention provides a novel rBCG for use in Mtb vaccine preparations. The rBCG is genetically engineered to overexpress 1) one or more Mtb antigens, which may include so-called “classical” Mtb antigens such as Rv1886c-Ag85B (“85B”) and Rv3804c-Ag85A (“85A”), among others; and 2) at least one Mtb resuscitation/reactivation antigen. In addition, in the rBCG of the invention, the DosR regulon, or a portion thereof, is up-regulated. The DosR regulon, comprised of 48 genes, is typically activated in Mtb as a result of a post-infection drop in O2 tension (hypoxia).
The Mtb antigens that are selected for inclusion in the rBCG of the invention are generally those which are known or predicted to elicit a protective immune response in individuals exposed to the antigens. Various criteria may be used to select suitable antigens, including but not limited to: the observation that individuals with immune responses to the antigen are able to control Mtb infection, determination that the antigen contains one or more T-cell epitopes via an immunoinformatics analysis (e.g. using a program such as that which is found at the website of the Technical University of Denmark: cbs.dtu.dk/services/NetCTL, in which the analysis is based on the identification of proteosome cleavage sites, endoplasmic reticulum (ER) transport efficiency, major histocompatibility (MHC) class 1 binding affinity, etc.); an analysis of experimental evidence based on an in-depth literature search; sorting or ranking of results according to various parameters such as macrophage survival/persistence; up-regulation of expression by the two-component system MprAB; response to hypoxia; involvement in dormancy; expression in lung tissue; genes with promoters that are co-regulated with Rv2031 (Acr); proteins that are secreted (which are more accessible to the immune system); presence of repeats (many virulence associated proteins have amino acid repeat domains); ability to act as a B-cell immunogen; cell wall associated or cell walls biogenesis (membrane-exposed/associated proteins are considered to be more accessible to the immune system; existing vaccine efficacy data; uniqueness to Mtb; etc.) Thus, antigens may be selected based on experimental data demonstrating their efficacy, or alternatively (or in addition) such antigens may be selected based on their predicted abilities. Those of skill in the art are familiar with the implementation of such analyses, and with developing scoring or ranking systems in order to assign a weighted comparative score to candidate antigens. For example, numeric scores may be assigned for each attribute under consideration, and the antigens with the highest cumulative totals may be selected for use. In addition, other considerations may play a role in the decision making process, some of which are practical in nature (e.g. the availability of the antigen, the ease of expressing the antigen, the ease of measuring immune responses to the antigen, etc.)
The starting pool of antigens may be any or all known Mtb open reading frame (ORF) products. Those of skill in the art are familiar with sources for identifying Mtb ORF products, e.g. the “Tuberculist” website sponsored by the Pasteur Institute. In one embodiment of the invention, the antigens from which a selection may be made include but are not limited to all ORF products of M. tuberculosis H37Rv as identified in GenBank Accession #AL123456 (NC 000962).
In a preferred embodiment of the invention, the antigens that are expressed by the rBCG are selected from but are not limited to an initial group of 189 antigens presented in Table 1.
(a)NCBI annotation is based on Accession # AL123456 (NC_000962); updated annotation is based on bioinformatic analyses, data from MTB-related servers and experimental evidence.
In a more preferred embodiment of the invention, the antigens that are expressed by the rBCG are the 45 antigens presented in Tables 2 and 3.
(a)NCBI annotation is based on Accession # AL123456 (NC_000962); updated annotation is based on bioinformatic analyses, data from MTB-related servers and experimental evidence.
The list of 45 high-ranking antigens were classified according to the following classes:
(a)NCBI annotation is based on Accession # AL123456 (NC_000962); updated annotation is based on bioinformatic analyses, data from MTB-related servers and experimental evidence.
The list of 45 high-ranking antigens were sorted by the qualitative score and then by the quantitative score according to this invention and as discussed in Example 1. This method leads to 3 groups as follows:
In general, at least one such antigen will be overexpressed and several different antigens may be overexpressed. For example, about 1-20 or more of such antigens, or alternatively about 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or only 1 of such antigens will be overexpressed by the rBCG. Further, multiple copies of one or more of the antigens may be encoded and overexpressed in the rBCG. The amino acid sequences of selected antigens, and the nucleic acid sequences that encode them, are depicted in
In addition, the rBCG contains nucleic acid sequences comprising one or more genes that encodes and overexpresses at least one Mtb resuscitation/reactivation antigen. Those of skill in the art will be aware that the precise definition of “resuscitation” and “reactivation” antigens may vary somewhat within the field, and in some cases, the definitions may overlap. For the purposes of the invention, it is not necessary to separate resuscitation and reactivation antigens as all are identified as being of significance in the outgrowth of Mtb from the latent state. In the most accurate sense, resuscitation antigens (i.e. resuscitation promoting factors) are a subset of reactivation antigens defined as having significant sequence or functional homology to the resuscitation promoting factor of Micrococcus luteus (G Mukamolova et al, Archives of Microbiology, Volume 172, 1999). For the purposes of the present application, a “reactivation” antigen is a protein expressed by M. tuberculosis which elicits an immune response in humans with active tuberculosis but not latent Mtb infection. They may also be identified as immunogens expressed by Mtb during outgrowth from a non-replicative stationary phase in the Wayne model of latent tuberculosis. This may include molecules that are expressed during the emergence of Mtb from the dormant latent state into active tubercle bacilli. Examples of suitable reactivation/resuscitation antigens include Rv0867c, Rv0288, Rv1009, Rv0685, Rv0824c, Rv2744c, Rv3347c, Rv1130, Rv1169c, Rv1009, Rv1884c, Rv2389c, and Rv2450c. In a preferred embodiment, the reactivation/resuscitation antigens expressed are Rv0867c, Rv1884c, and Rv2389c.
In addition, in the rBCG of the invention the genes of the DosR (Dormancy Survival Regulator) regulon, or a portion thereof, are upregulated and expressed. The entire regulon may be upregulated, or a suitable portion thereof. For example, genes that encode antigens that are recognized by individuals with latent TB may be the most suitable for upregulation. Examples of DosR upregulated antigens include Rv1738, Rv2623, Rv2031c, Rv2032, Rv2626c, Rv2005c, Rv3127, Rv1733c, Rv1996, Rv2628, Rv0079, Rv3130c, Rv3131, Rv1813c, Rv2006, Rv2029c, Rv2627c, Rv2030c, Rv3132c, and Rv2629. It is noteworthy that some overlap exists between latency and reactivation antigens, possibly reflecting the extended presence of latency related antigens in previously dormant organisms re-entering an active growth phase or their function in both the dormant and actively replicating state after reactivation in the mammalian host. Antigens that may be considered to overlap between latency and reactivation are listed in Table 4.
By “up-regulate” we mean that expression of each of the individual genes of the regulon or their translated proteins is increased above the level at which they are expressed when the regulon is in a “repressed” state. Proteins of the DosR regulon are normally expressed at a relatively low level. Upon oxygen starvation and/or the presence of oxidative nitrogen compounds the DosS and DosT proteins of TB complex organisms autophosphorylate and transfer this phosphate to DosR. DosR then binds to discrete sequences upstream of DosR regulated genes thereby activating their transcription and upregulating this group of genes and gene products which constitute the DosR regulon. Upregulation within the practice of this invention mimics this oxygen starvation effect where the DosR genes have increased transcription.
Those of skill in the art are familiar with approaches to genetically engineering an organism in order to up-regulate selected genes of interest, or selected regulons of interest. Such approaches include but are not limited to overexpression of the regulator, introduction of mutations in the regulator or sensor which render them constitutively active, the introduction of regulators which mimic the function of the regulator in question, introduction of kinases or feedback loop products which activate the sensor or regulator, or the introduction of genes/gene products which mimic the environmental state which causes activation of the sensor or regulator. In a preferred embodiment, the DosR regulon is up-regulated by over expressing the response regulator DosR (Rv3133c) of the DosRST “two component” regulatory system.
In another preferred embodiment, the vaccine includes one or more of Rv1908, Rv3873, Rv2780 and Rv1349. These are immunopotent antigens which were identified in silico and/or by experimentation.
In addition, the rBCG of the invention may encode antigens selected based on other criteria, such as demonstrated protective efficacy in an animal model or the expression of the antigen by Mtb but not BCG (J Mattow et al., Electrophoresis, 22:2936-2946, 2001, P. R. Jungblut, Molecular Microbiology, 33:1103-1117, 1999, H. J. Mollenkopf et al, Infection and Immunity, 72:6471-6479, 2004). In a preferred embodiment, the rBCG of the invention expresses Rv3407, which is normally expressed by Mtb but not BCG and has been shown to protect against tuberculosis in a mouse model.
The BCG that is genetically engineered as described herein may be of any BCG strain considered suitable, including but not limited to BCG strains BCG1331, BCG Pasteur, BCG Tokyo, BCG Copenhagen, BCG Moreau, or BCG Moscow.
In a preferred embodiment, the strain is BCG1331. In addition, the rBCG may be further genetically engineered to possess other traits, for example: a perfringolysin O (pfo) gene (in order to facilitate escape from the endosome); to express various selection markers such as antibiotic resistance or an auxotrophic selection marker in which a gene critical to the rBCG (e.g. for leucine or lysine synthesis) is deleted and must be complemented (e.g. by an extrachromsomal element that encodes the missing crucial gene) in order for the bacterium to survive; by deletion of genes or inhibition of the function of gene products which suppress apoptosis, etc.
In general, the rBCG of the invention is genetically engineered to overexpress selected antigens by introduction of genes encoding the antigens of interest into the chromosome of the rBCG under the transcriptional control of highly active expression control sequences, which may include those which are most active during mammalian infection. However, the genes encoding the antigens of interest could also be expressed from an extrachromosomal plasmid under the transcriptional control of highly active expression control sequences. Expression control sequences include but are not limited to promoters, ribosomal entry sites, etc.
The present invention further provides compositions for use in eliciting an immune response in and/or vaccinating a mammal. The compositions may be utilized as a vaccine against Mtb. The compositions of the invention include genetically engineered rBCG as described herein, and a pharmacologically suitable carrier. The preparation of such compositions for use as vaccines is well known to those of skill in the art. Typically, such compositions are prepared either as liquid solutions or suspensions, however solid forms such as tablets, pills, powders and the like are also contemplated. Solid forms suitable for solution in, or suspension in, liquids prior to administration may also be prepared. The preparation may also be emulsified. The active ingredients may be mixed with excipients which are pharmaceutically acceptable and compatible with the active ingredients. Suitable excipients are, for example, water, saline, dextrose, glycerol, ethanol and the like, or combinations thereof. In addition, the composition may contain minor amounts of auxiliary substances such as wetting or emulsifying agents, pH buffering agents, and the like. In addition, the composition may contain other adjuvants. If it is desired to administer an oral form of the composition, various thickeners, flavorings, diluents, emulsifiers, dispersing aids or binders and the like may be added. The composition of the present invention may contain any such additional ingredients so as to provide the composition in a form suitable for administration. The final amount of rBCG in the formulations may vary. However, in general, the amount in the formulations will be from about 1-99%. The compositions may further comprise additional adjuvants, suitable examples of which include but are not limited to Seppic, Quil A, Alhydrogel, etc.
Vaccine formulation also involves studies to determine maximum bacterial viability and stability throughout the manufacturing process. This includes determination of maximum organism viability (live to dead) during culture utilizing a variety of commonly used medium for the culture of Mycobacteria to include the addition of glycerol, sugars, amino acids, and detergents or salts. After culture cells are harvested by centrifugation or tangential flow filtration and resuspended in a stabilizing medium that allows for protection of cells during freezing or freeze-drying process. Commonly used stabilizing agents include sodium glutamate, amino acids or amino acid derivatives, glycerol, sugars or commonly used salts. The final formulation will provide sufficient viable organisms to be delivered by intradermal, percutaneous injection, perfusion or oral delivery with sufficient stability to maintain and adequate shelf life for distribution and use.
The methods of the present invention involve administering a composition comprising the rBCG of the invention in a pharmacologically acceptable carrier to a subject, usually a human mammal. The vaccine preparations of the present invention may be administered by any of the many suitable means which are well known to those of skill in the art, including but not limited to by injection, orally, intranasally, by ingestion of a food product containing the antigen, etc. However, in a preferred embodiment, the mode of administration is intradermal injection. In addition, the compositions may be administered alone or in combination with other medicaments or immunogenic compositions, e.g. as part of a multi-component vaccine. Further, administration may be a single event, or multiple booster doses may be administered at various timed intervals to augment the immune response. In one embodiment, the vaccine preparation of the invention is used for an initial immunization, and the individual receiving the initial vaccine is then “boosted” with one or more different vaccine compositions, e.g. a known attenuated BCG vaccine. Alternatively, an individual may be vaccinated with another vaccine preparation and boosted one or more times with the vaccine preparation of the present invention. In some embodiments of the invention, the boosting compositions include nucleic acids encoding one or more Mtb antigens, for example: i) one or more antigens such as Rv1738, Rv2623, Rv2031c, Rv2032, Rv2626c, Rv2005c, Rv3127, Rv1733c, Rv1996, Rv2628, Rv0079, Rv3130c, Rv3131, Rv1813c, Rv2006, Rv2029c, Rv2627c, Rv2030c, Rv2629, Rv2450c, Rv1009, Rv0867c, Rv2389c, Rv1884c, Rv0288, Rv0685, Rv0824c, Rv2744, Rv3347c, Rv130, Rv1169c, Rv1886, Rv1980c, Rv3804c, Rv3875, Rv1926c, Rv0467, Rv3873, Rv1908c, Rv1174c, Rv2780, Rv2620c, Rv1793, Rv1349 and Rv3132; ii) one or more antigens such as Rv1996, Rv2005, Rv2029, Rv2623, Rv2626 and Rv2727; iii) one or more antigens such as Rv2626, Rv1738, Rv2623, Rv1733, Rv2032, Rv3131, Rv3127, Rv3130c, Rv3804c and Rv1886c; a or more antigens including at least one of a dosR antigen, a reactivation antigen and/or a resuscitation antigen e.g., one antigen from each stage (latency, reactivation and resuscitation) of the life cycle of M. tuberculosis.
A particular advantage of the vaccine preparation of the present invention is that administration may be prophylactic, i.e. before exposure to the bacteria has occurred, or is suspected to have occurred, or after the fact, i.e. after a known or suspected exposure, or therapeutically, e.g. after the occurrence of disease symptoms associated with bacterial infection. This is because antigens that are involved in Mtb life cycle or infection and disease processes such as resuscitation and reactivation are included in the vaccine. Thus, the vaccine is useful not only for preventing the initial establishment of an Mtb infection, but also for preventing the reactivation of a latent Mtb infection.
Prior to administration to humans as a vaccine, the genetically engineered rBCG strains of the present are tested according to methods that are well-known to those of skill in the art. For example, tests for toxicity, virulence, safety, etc. are carried out in suitable animal models, e.g. in mice, guinea pigs, etc., some of which are immunocompromised. The ability of the vaccine preparations to elicit an immune response is likewise typically tested in suitable animal models, e.g. mice, guinea pigs, etc. In addition, protection studies involving vaccination, boosting, and subsequent challenge with live Mtb may be carried out using suitable animal models such as mice, guinea pigs, and non-human primates. Finally, those of skill in the art are familiar with the arrangements for carrying out clinical trials in consenting humans, in order to test the efficacy of the vaccine preparations. For details, see, for example, United States patent application 20060121054 (Sun et al.) published Jun. 8, 2006, and references cited therein.
By “eliciting an immune response” we mean that administration of the vaccine preparation of the present invention causes the synthesis of specific antibodies (at a titer in the range of 1 to 1×106, preferably 1×103, more preferable in the range of about 1×103 to about 1×106, and most preferably greater than 1×106) and/or cellular proliferation, as measured, e.g. via cellular assays in which IFN-γ production is assessed, for example, by 3H thymidine incorporation, or other suitable means. In a preferred embodiment, the immune response is a protective immune response, i.e. the immune response protects the vaccinated individual from future challenge with Mtb. However, those of skill in the art will recognize that a vaccine or immunostimulating preparation need not provide total protection in order to convey some benefit to a patient. For example, the preparations may elicit immune responses that slow or lessen the progress of disease symptoms, without fully eradicating them.
The following non-limiting Examples serve to illustrate the practice of this invention.
Selection of suitable antigens and design of rBCG based on this selection An initial group of Mtb proteins (189 antigens, see Table 1) was selected from all possible 3989 Mtb ORFs, according to the following selection procedure:
The 189 candidate antigens were ranked in order of likely importance by the following 14 analyses:
The presence or absence of each of these traits was scored for each of the 189 genes and a qualitative score was determined and employed as a measure to rank the list of 189 antigens and choose for the 45 best hits.
The 45 candidates were then further ranked using the same 13 criteria, by assigning internal numerical scores to each of the criteria, according to the intensity of the results and/or relevance to vaccine development. A list of the top-ranking 45 antigens is given in Table 2, along with their subgrouping according to the class/phase of infection (latency/dormancy, resuscitation/reactivation, classical and others); within the classes, the antigens are sorted by their scores. Table 3 presents the 45 antigens prioritization into 3 subset groups according to their quantitative, and subsequently—qualitative scores.
Based on this analysis, final selections of groups of antigens for use in the rBCGs were made, usually based on the antigens with the highest overall scores. In addition, for the final selection, antigens were grouped according to “type” in that the rBCG includes at least
In addition, antigens were selected based on other criteria such as demonstrated protective efficacy in an animal model, the expression of the antigen by Mtb but not BCG, or diminished expression of the antigen in BCG (J Mattow et al., Electrophoresis, 22:2936-2946, 2001, P. R. Jungblut, Molecular Microbiology, 33:1103-1117, 1999, H. J. Mollenkopfet al, Infection and Immunity, 72:6471-6479). Such Mtb-specific antigens include Rv1511, Rv2520c, Rv3407, Rv2802c and Rv3710.
Preferred combinations of antigens to be expressed in an rBCG include the following:
Construction of a recombinant BCG genetically engineered to express at least one classical Mtb antigen, at least one Mtb resuscitation/reactivation antigen and in which the DosR regulon is upregulated.
For the construction of an rBCG described in the following sections, restriction endonucleases (herein “REs”); New England Biolabs Beverly, Mass.), T4 DNA ligase (New England Biolabs, Beverly, Mass.) and Taq polymerase (Invitrogen, Carlsbad, Calif.) were used according to the manufacturers' protocols; Plasmid DNA was prepared using small-scale (Qiagen MiniprepR kit, Santa Clara, Calif.) or large-scale (Qiagen Maxiprep® kit, Santa Clara, Calif.) plasmids DNA purification kits according to the manufacturer's protocols (Qiagen, Santa Clara, Calif.); Nuclease-free, molecular biology grade Milli-Q water, Tris-HCl (pH 7.5), EDTA pH 8.0, 1M MgCl−2, 100% (v/v) ethanol, ultra-pure agarose, and agarose gel electrophoresis buffer were purchased from Invitrogen, Carlsbad, Calif. RE digestions, PCRs, DNA ligation reactions and agarose gel electrophoresis were conducted according to well-known procedures (Sambrook, et al., Molecular Cloning: A Laboratory Manual. 1, 2, 3; 1989); (Straus, et al., Proc Natl Acad Sci USA. March; 87(5): 1889-93; 1990). Nucleotide sequencing to verify the DNA sequence of each recombinant plasmid described in the following sections was accomplished by conventional automated DNA sequencing techniques using an Applied Biosystems automated sequencer, model 373A.
PCR primers were purchased from commercial vendors such as Sigma (St. Louis, Mo.) or synthesized using an Applied Biosystems DNA synthesizer (model 373A). PCR primers were used at a concentration of 150-250 μM and annealing temperatures for the PCR reactions were determined using Clone manager software version 4.1 (Scientific and Educational Software Inc., Durham, N.C.). PCRs were conducted in a BioRad thermocycler (BioRad, Hercules, Calif.). The PCR primers for the amplifications were designed using Clone Manager® software version 4.1 (Scientific and Educational Software Inc., Durham N.C.). The RE digestions and the PCRs were subsequently analyzed by agarose gel electrophoresis using standard procedures (Straus et al, supra 1990; and Sambrook et al., supra 1989). A positive clone is defined as one that displays the appropriate RE pattern and/or PCR pattern. Plasmids identified through this procedure were further evaluated using standard DNA sequencing procedures, as described above.
Escherichia coli strains, such as DH5α and Stable2®, were purchased from Invitrogen (Carlsbad, Calif.) and served as initial host of the recombinant plasmids. Recombinant plasmids were introduced into E. coli strains by electroporation using a high-voltage eletropulse device, such as the Gene Pulser (BioRad Laboratories, Hercules, Calif.), set at 100-200Ω, 15-25 μF and 1.0-2.5 kV, as described (Straus et al, supra 1990). Optimal electroporation conditions were identified by determining settings that resulted in maximum transformation rates per mcg DNA per bacterium.
E. coli strains are typically grown on tryptic soy agar (Difco, Detroit, Mich.) or in tryptic soy broth (Difco, Detroit, Mich.), which was made according to the manufacturer's directions. Unless stated otherwise, all bacteria were grown at 37° C. in 5% (v/v) CO2 with gentle agitation. When appropriate, the media was supplemented with antibiotics (Sigma, St. Louis, Mo.). Bacterial strains were typically stored at −80° C. suspended in (Difco) containing 30% (v/v) glycerol (Sigma, St. Louis, Mo.) at ca. 109 colony-forming units (herein referred to as “cfu”) per ml.
Mycobacterial strains were cultured in liquid media, such as Middlebrook 7H9 or Saulton Synthetic Medium, preferably at 37° C. The strains can be maintained as static or agitated cultures. In addition, the growth rate of BCG can be enhanced by the addition of oleic acid (0.06% v/v; Research Diagnostics Cat. No. 01257) and detergents such as Tyloxapol (0.05% v/v; Research Diagnostics Cat. No. 70400). The purity of BCG cultures can be evaluated by evenly spreading 100 mcl aliquots of the BCG culture serially diluted (e.g. 10-fold steps from Neat—10−8) in phosphate buffered saline (herein referred to PBS) onto 3.5 inch plates containing 25-30 ml of solid media, such as Middlebrook 7H10. In addition, the purity of the culture can be further assessed using commercially available medium such as thioglycolate medium (Science Lab, catalogue number 1891) and soybean-casein medium (BD, catalogue number 211768).
In order to insert the desired antigen expression cassettes into the chromosome of the perfringolysin expressing BCG1331 derivative described elsewhere, a plasmid was designed in silico and synthesized by DNA2.0 (Menlo Park, Calif.). The salient features of this vector (pJFINT) include an E. coli colE1 origin of replication, 3 multiple cloning sites separated by transcriptional terminators rmBT1, T2 of pEX18gm, and mhA, the attP phage integration region of bacteriophage L5 and the integrase gene of bacteriophage L5 (GenBank #Z18946). Immediately upstream of the L5 sequence, a selectable marker cassette consisting of a kanamycin resistance allele aphA from Tn10 (GenBank #AAM97345) and a sacB gene (Genbank # NP—391325) were included. This marker cassette was flanked by direct repeats of the γΔ resolvase binding site from transposon Tn1000. This plasmid is incapable of replication in mycobacterial species and the L5 attP sequence allows for high frequency recombination with the attB region of mycobacterial chromosomes to facilitate integration of the plasmid sequence into the chromosome. The marker cassette can then be removed from the chromosome of the integrant by the introduction of γΔ resolvase and selection of markerless strains on solid media containing 10% sucrose.
An antigen expression cassette was designed in silico to encode Rv0867c, Rv1884c, and Rv2389c separated by optimized ribosomal sites under the transcriptional control of the hsp60 promoter of Mycobacterium bovis and synthesized by DNA2.0 (Carlsbad Calif.). A second expression cassette was similarly designed and constructed to encode Rv1886c, Rv3804c and Rv3407c under transcriptional control of the hsp60 promoter. Finally, a third cassette encoding Rv3133c (DosR) under the transcriptional control of the hsp60 promoter was designed and constructed. These three antigen expression cassettes were ligated into pJFINT such that each was separated by a transcriptional terminator (
The pRC108 plasmid was isolated from a 100 ml E. coli culture and electroporated into a pfo expressing derivative of BCG Danish 1331. After electroporation, the cells were cultured overnight in 7H9 medium with 10% (v/v) OADC and 0.05% (v/v) of Tyloxapol supplementation and plated on 7H10 agar containing 50 ug/ml of kanamycin. As the plasmid does not encode a mycobacterial origin of replication, kanamycin resistance in all colonies tested was conferred by integration of the plasmid into the attB site of the BCG genome. Individual colonies were picked for PCR analysis and inoculated into 7H9 medium with 10% (v/v) OADC and 0.05% (v/v) tyloxapol for analysis of antigen expression. PCR characterization of the kanamycin resistant colonies demonstrated the presence of the entire plasmid sequence in the chromosome of the recombinant BCG, designated AFV-102pRC108. AFV-102pRC108 cultures were washed with 7H9 and used to inoculate protein-free 7H9tyloxapol cultures. Supernatants of the AFV-102pRC108 cultures were harvested by centrifugation and immunoblotted with rabbit polyclonal antisera to the transglycolase domain of the Rpf protein. Rv1009, which is cross reactive with the transglycosylase domains of all Rpf's or rabbit polyclonal antisera raised against peptides of Rv0867c. This demonstrated the enhanced production of Rv0867c, Rv1884c, and Rv2389c above the background of the BCG homologs of these proteins (
In order to complete the construction of this vaccine to make it suitable for human use, the marker cassette of the integrated plasmid was then removed. Electrocompetent AFV-102pRC108 cells were electroporated with plasmid pYUB870hyg, which encodes the γΔ resolvase of Tn1000, a sacB allele, and a hygromycin resistance gene (GenBank #ABD64366). Transformants resistant to both kanamycin and hygromycin were selected on 7H10 media and inoculated into 7H9 liquid media with 10% (v/v) OADC and 0.05% (v/v) tyloxapol and no antibiotics. After seven days growth, dilutions of these liquid cultures were plated on 7H10 containing 10% sucrose to select for recombinants from which the aphA-sacB marker has been excised and the pYUB870hyg plasmid has been lost by dilution and selection against the sacB allele.
Sucrose-resistant transformants were picked for PCR analysis of the integrated antigen cassettes and were inoculated into 7H9 liquid media for immunoblot analysis as before. PCR analysis revealed that the antigen expression cassettes were still present in the chromosome and that the hygromycin resistance marker and sacB gene had been excised. Immunoblotting of supernatants and cell pellets with antisera to Rpf, Ag85 complex, Rv3407, and DosR confirmed that excision of the marker cassette from the chromosome did not effect the expression of the inserted antigen cassettes.
Strain AERAS-407 was constructed by removal of the anti-biotic resistance marker from AFV-102pRC108.
To illustrate the immune responses elicited by AERAS-407 and to demonstrate its protective efficacy against tuberculosis, four groups of 10 C57/BL6 mice are vaccinated subcutaneously with either 1) saline, 2) BCG, 3) BCG-PfoA or 4) AERAS-407. Mice in groups 2, 3, and 4 receive 5×105 cfu of BCG or recombinant BCG. After 10 weeks, five mice from each group are sacrificed for immune assays and the remaining animals are challenged with 100 cfu aerosolized M. tuberculosis Erdman.
To measure humoral immune responses, a peptide microarray chip has been designed. The chip is spotted with overlapping 50 amino acid peptides generated from the sequences of Rv1886c, Rv3804c, Rv3407c, Rv0867c, Rv1884c, Rv2389c, Rv3133c, and all BCG encoded DosR-regulated proteins which are at least 2 fold induced by the overexpression of DosR (i.e. DosR regulated genes for which transcription is at least 2 fold greater in BCG constitutively expressing the DosR regulon than the wild-type parent strains under aerobic conditions). Pooled sera from each group is incubated with 3 peptide chips for 1 hr at 37° C. The chips are then washed with phosphate-buffered saline (PBS) pH 7.2 and incubated with fluorescein isothiocyanate (FITC) conjugated goat anti-mouse IgG sera (Abcam, Cambridge, Mass.) for 1 hour at 37° C. The chips are then washed again with PBS and the immunofluorescence is read with a Genepix 4000B Array Scanner (Molecular Devices, Sunnyvale, Calif.). Values for each peptide spot are averaged for the 3 chips in each group. Mice receiving AERAS-407 show greater antibody responses to peptides derived from Rv1886c, Rv3804c, Rv3407c, Rv0867c, Rv1884c, Rv2389c and DosR regulated proteins than unvaccinated mice or mice vaccinated with BCG or BCG-PfoA.
To measure cellular immune responses elicited by AERAS-407, spleens are harvested from each and homogenized. Splenocyte concentrations are adjusted to 5×105 cells/well in R10 media in multichamber plates and are incubated for 3 days at 37° C. with purified Rv1886c, Rv3804c, Rv3407c, Rv0867c, Rv1884c, or Rv2389c at a concentration of 1 μg/ml. In addition, splenocytes from each mouse are incubated with Rv2623 and Rv3130c as these proteins are known to be highly upregulated in DosR overexpressing strains and are known to be potent T cell immunogens. After the 3 day incubation, supernatants are harvested from the splenocyte cultures and assayed by ELISA for interferon-γ produced in response to antigen stimulation. Control cultures of unstimulated splenocytes or PMA/PHA stimulated splenocytes are included as negative and positive controls, respectively.
To quantify protection afforded by vaccination with AERAS-407, the 5 remaining mice from each group are sacrificed 10 weeks after challenge with M. tuberculosis and lungs and spleens are aseptically harvested from each animal. Lungs and spleens are homogenized in PBS and dilutions are plated on 7H10 agar. After 4 weeks of incubation, the number of M. tuberculosis colonies are enumerated for each animals lungs and spleen and corrected for the dilution factor. This value is the number of live tubercle bacilli present in the lungs and spleen of each animal. BCG vaccination typically results in approximately a 1 log reduction in cfu/lung and spleen versus saline vaccination. AERAS-407 vaccination results in a greater reduction of Mtb load in the lungs and spleens of mice.
Construction of a Second Recombinant BCG Vaccine Genetically Engineered to Over Express Selected Classical M. tb Antigens and the DosR Regulon
A second combination of antigens (TB10.4, Ag85B, Ag85A and Rv3407) was also overexpressed in the rBCG AFV102 strain by integration into the chromosome at the attB site. This was carried out in a manner similar to that described in Example 2 for the Aeras 407 construct. To integrate this second antigen set, the integration plasmid pAF707 (depicted schematically in
The protective efficacy of AERAS-407, particularly in relation to the enhanced capacity to prevent latent infection and reactivation of disease, is best tested in rhesus macaques as mice do not create granulomatous latent foci as humans and other primates do. To evaluate the protective efficacy of AERAS407 in NHP's, four groups of six weight and sex-matched rhesus macaques are vaccinated with 1) saline, 2) BCG 1331, 3) BCG-Pfo, or 4) AERAS-407. Each animal in groups 2-4 receives 5×105 cfu of the respective BCG or rBCG by intradermal injection. Fifteen weeks after vaccination, all animals are challenged by bronchial installation of approximately 300 cfu of M. tuberculosis Erdman. All animals are evaluated monthly for six months for clinical symptoms of tuberculosis by chest X-ray, weight, feeding, cough, lethargy, and immune responses to TB specific proteins. All animals that die during the six month observation period are necropsied and tissue pathology and Mtb burden by organ is measured as in Example 3. All moribund animals are humanely euthanized and similarly examined. Six months post-challenge all surviving animals are euthanized and necropsied for tissue pathology and Mtb burden in lungs, liver and spleen. AERAS-407 vaccination results in decreased mortality, decreased tissue damage and lower counts of viable Mtb organisms in the lungs of experimentally infected animals.
While the invention has been described in terms of its preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims. Accordingly, the present invention should not be limited to the embodiments as described above, but should further include all modifications and equivalents thereof within the spirit and scope of the description provided herein.
