Patent Grant
10406219
The invention generally relates to recombinant Brucella strains as vaccines and methods of administering the same for Brucella and mycobacterial infections in mammals. For example, the invention provides a leucine auxotrophic strain RB51leuB as an attenuated vaccine able to express at least one of the Mycobacterium tuberculosis protective antigens Ag85B, RV2660c and ESAT6.
This application claims the benefit of U.S. application 62/047,945, filed Sep. 9, 2014. This application is incorporated herein by reference in its entirety.
This document incorporates by reference an electronic sequence listing text file, which was electronically submitted along with this document. The text file is named 01640672 ST25.txt, is 14.4 kilobytes, and was created on Sep. 8, 2015.
Brucellosis is an infectious disease caused by bacteria of the genus Brucella. There are various Brucella species that are capable of infecting both wildlife and livestock. The principal cause of brucellosis in cattle is the bacterium B. abortus. Infected cattle commonly have high incidences of spontaneous abortions, arthritic joints, and retained placenta following calving. In the United States, infected cows are often killed. Sheep and goats are the preferred hosts of B. melitensis, which is the Brucella species most virulent for humans. Humans can become infected by coming in contact with infected animals or animal products, such as unpasteurized milk, that are contaminated with these bacteria.
Vaccines are used to protect against diseases, which are caused by pathogens. These pathogens are microbial organisms, such as bacteria and viruses, which affect animals, including humans. Vaccines are primarily derived from a pathogen by producing and administering either: a) an attenuated or avirulent version of the pathogen; b) the killed pathogen; c) extracted protective antigens or antigen mixes of the pathogen (homologous antigens); or d) a micro-organism expressing one or more protective antigens encoded by cloned genes originating in a microbial pathogen different from the vaccine strain (heterologous antigens).
Vaccines for both bacteria and viruses are engineered from microorganisms expressing one or more protective antigens, as described by K. Jones and M. Sheppard in Designer Vaccines, CRC Press (1997). Vaccines are intended to produce an immune response in the recipient consisting of at least one of an antibody mediated or T cell mediated immune response, thereby preventing future infection by a pathogen, or fighting a current pathogenic infection. In particular, vaccines against facultative intracellular pathogens, those growing inside the cells of the infected host, need to induce a strong and appropriate cell mediated immune response. In contrast, vaccines against obligate extracellular pathogens need to induce an appropriate antibody mediated immune response. Often, regardless of the pathogen, an appropriate combined antibody and cellular mediated immune response leads to sufficient protection or relief from infection. In order to achieve this protection or relief from infection, vaccines may express one or more homologous antigens, heterologous antigens, or a combination of both.
Vaccines may be administered to vertebrates both to prevent and treat infection by pathogens. Thus, vaccines are frequently administered to prevent the spread of a disease caused by a pathogen. In particular, herd animals, such as cows, goats, sheep and swine, are often vaccinated to prevent the spread of a disease among members of the herd. Further, because certain diseases may travel between vertebrates, including travel between various animals and between animals and humans, vaccines are used to prevent the spread of disease between various species, usually by administration to the infected animal and other uninfected animals in the immediate vicinity. However, other animals in the area which are less likely to contract the disease may also be vaccinated as a prophylactic measure. For example, an infected cow and its as yet uninfected herd may be vaccinated to treat a disease and prevent its further spread. As a prophylactic measure, other animals which are likely to contract the disease from the infected cow, such as neighboring cows, sheep or humans, may be vaccinated as well.
B. abortus strain RB51 is a stable rough mutant derived from the wild-type virulent strain B. abortus 2308 [1]. This strain is currently the official USDA approved vaccine against cattle brucellosis in the United States and elsewhere. The safety and protective efficacy of strain RB51 have been well demonstrated under laboratory and field conditions [2, 3]. Protection afforded by strain RB51 vaccination is due to induction of cell-mediated immune mechanisms including antigen-specific induction of IFN-γ production [4-6]. Multiple studies have exploited the advantageous vaccinal qualities of strain RB51 as a host for the delivery of protective antigens of other intracellular pathogens in which a Th1 type immune response or cell-mediated immunity is essential for protection [7, 8].
Previously, plasmid-based expression systems have been utilized to express heterologous proteins in strain RB51 [5, 8-13]. However, these expression vectors usually encode antibiotic resistance markers. Moreover, the U.S. Food and Drug Administration strongly discourages and strictly regulates the introduction of antibiotic resistance genes into live attenuated vaccines [14]. In addition, often such expression systems are unstable in the absence of antibiotic selection pressure. To overcome this hurdle, an environmentally safe leucine auxotroph strain of RB51 (RB51leuB) was created to over-express foreign antigens without using antibiotic resistance marked plasmids [15]. The production of this strain is described in US 2010/0226942 herein incorporated by reference. This auxotrophic strain can be complemented with the pNS4 vector expressing the wild-type leuB gene. This complementation allows for survival of the strain in leucine-deficient minimal medium and under nutrient-limiting conditions in vivo, thus providing selective pressure for plasmid maintenance without using antibiotic selection markers [16].
Although the creation of the strain RB51leuB and pNS4 has led to a safer and more stable platform for expression of other foreign antigens, additional modifications are necessary to allow for better and more consistent expression in this host-vector system. Additionally, a need remains in the art for immunogenic compositions and multivalent vaccines to combat Brucella and other bacterial infections such as those caused by mycobacteria. Similar to Brucella, humans can become infected with M. tuberculosis by coming in contact with infected animals or animal products, such as unpasteurized milk, that are contaminated with these bacteria. Additionally, the available Brucella vaccines can be effective in controlling brucellosis, but they can have numerous drawbacks, such as interference with diagnostic tests, pathogenicity for humans, and potential to cause abortion in pregnant animals.
One aspect of the invention provides a multivalent Brucella vaccine strain expressing at least one heterologous Mycobacterium antigen. In exemplary embodiments, the Mycobacterium is M. tuberculosis. In some embodiments, the vaccine improves upon the RB51leuB and pNS4 platform such that the transcriptional activity of genes carried on this plasmid is strengthened by utilizing a stronger promoter and the codon usage is modified to that of Brucella. These modifications to pNS4 allow for better expression of antigens of other intracellular pathogens in which cell-mediated immunity is essential for protection e.g. M. tuberculosis. The vaccines described herein serve as an environmentally safe bivalent vaccine for protection against Brucella and Mycobacterium infections simultaneously.
An embodiment of the invention provides a multivalent vaccine or immunogenic composition comprising at least one Brucella strain transformed with a vector expressing at least one Mycobacterium antigen, wherein said at least one Mycobacterium antigen is codon optimized for expression in said at least one Brucella strain and a vehicle or carrier suitable for administration to a subject. In exemplary embodiments, the Brucella strain is B. abortus strain RB51leuB and the Mycobacterium antigen is a M. tuberculosis antigen. In some embodiments, the M. tuberculosis antigen is selected from the group consisting of Ag85B, Rv2660c, and ESAT6. The antigens Rv2660c and ESAT6 can expressed as a fusion protein. In exemplary embodiments, the vaccine or immunogenic composition includes a first Brucella strain that is transformed with a vector expressing Ag85B and a second Brucella strain that is transformed with a vector expressing Rv2660c and ESAT6. In preferred embodiments, the M. tuberculosis antigen is codon optimized for the at least one Brucella strain.
Another aspect of the invention provides a chimeric Brucella strain and one or more sequences coding for at least one Mycobacterium antigen wherein said at least one Mycobacterium antigen is codon optimized for expression in said Brucella. In some embodiments, the Brucella is B. abortus strain RB51leuB. In exemplary embodiments, the chimeric Brucella strain is XXXX, having NRRL accession number YYY-1111 Additional embodiments of the invention provide a pNS4leuB plasmid comprising one or more sequences of heterologous Mycobacterium antigens.
An additional aspect of the invention relates to a method for protecting or treating a subject at risk of or suffering from at least one disease caused by one or more bacterium, said method comprising administering to the subject an effective amount of a vaccine or immunogenic composition according to the invention. In some embodiments, the method further comprises the step of administering at least one purified polypeptide comprising at least one of Ag85B, Rv2660c, and ESAT6 as a booster to the vaccine. In exemplary embodiments, the subject is administered a first purified polypeptide comprising Ag84B and a second purified polypeptide comprising ESAT6. In some embodiments, a live vaccine is first administered and then the vaccination can be boosted with purified polypeptide antigens or another dose of the engineered RB51leuB expressing the Mycobacterial antigens. The disease can be brucellosis and/or tuberculosis and the bacterium can be B. abortus and/or M. tuberculosis. In some embodiments, the subject is selected from the group consisting of humans, cows, sheep, goats, pigs, bison, elk, and camels. In exemplary embodiments, the animal is a cow.
A further aspect of the invention provides a method of raising an immune response to both Mycobacterium and Brucella in a subject, said method comprising the step of administering to the subject a chimeric Brucella as described herein. In some embodiments, the method further comprises a step of administering to said subject a booster a period of time after said administering step, said booster including one or more Mycobacterium antigens or one or more nucleotides coding for said one or more Mycobacterium antigens.
One aspect of the invention provides vaccines and immunogenic compositions that, when administered to a subject, elicit an immune response to Brucella and Mycobacterium in the subject, e.g. a protective immune response. Methods for using the immunogenic compositions/vaccines to prevent or attenuate the spread of Brucella and M. tuberculosis infection in susceptible individuals and in groups of susceptible individuals are also provided. In some embodiments, the expression of mycobacterial antigens does not alter the efficacy of the Brucella vaccine strain. In further embodiments, a vaccine as provided herein will not turn the subject diagnostically positive to a tuberculin skin test.
The vaccines provided herein can be in the form of recombinant polypeptides involved in evoking an immune response to bacterium of the genus Brucella and/or Mycobacterium, nucleic acid vectors (e.g., plasmids) designed to express such recombinant polypeptides, and bacteria transformed with such nucleic acids. The vaccines provided herein can be used to immunize or treat any type of animal including, without limitation, cows, sheep, goats, pigs, bison, elk, camels, dogs, poultry or any vertebrate species that contracts brucellosis and/or tuberculosis, such as humans.
The vaccines provided herein can be used to induce an immune response against any species of Brucella including, without limitation, B. abortus, B. canis, B melitensis, B. neotaomae, B. ovis, B. suis and B. pinnipediae. For example, a vaccine provided herein can protect against more than one species of Brucella. In some cases the vaccines provided by this invention can be used to induce an immune response against a pathogen that causes spontaneous abortion in cattle (e.g., Neospora caninum). The vaccines provided can be used to reduce the risk of developing symptoms associated with the disease known as brucellosis.
The vaccines provided herein can be used to induce an immune response against any species of Mycobacterium including, without limitation, M. tuberculosis, M. bovis, M. africanum, M. canetti, and M. caprae.
One aspect of the invention relates to methods of administering a vaccine as described herein. The methods involve administering an effective amount of a vaccine, where the effective amount is sufficient to prevent the development of or lessen the extent of the development of symptoms of a Brucella and/or Mycobacterium infection in the subject, when the subject is later exposed to the bacterium or contracts a bacterial infection.
Embodiments of this invention also provide methods and materials relating to isolated nucleic acid molecules, substantially pure polypeptides, and bacteria that contain an isolated nucleic acid molecule. The term “nucleic acid” as used herein encompasses both RNA and DNA, including cDNA, genomic DNA, and synthetic (e.g., chemically synthesized) DNA. The nucleic acid can be double-stranded or single stranded. Where single-stranded, the nucleic acid can be the sense strand or the antisense strand. In addition, nucleic acid can be circular or linear. The term “isolated” as used herein with reference to nucleic acid refers to a naturally-occurring nucleic acid that is not immediately contiguous with both of the sequences with which it is immediately contiguous (one of the 5′ end and one on the 3′ end) in the naturally-occurring genome of the organism from which it is derived. For example, an isolated nucleic acid can be, without limitation, a recombinant DNA molecule of any length, provided one of the nucleic acid sequences normally found immediately flanking that recombinant DNA molecule in a naturally-occurring genome is removed or absent. Thus, an isolated nucleic acid includes, without limitation, a recombinant DNA that exists as a separate molecule (e.g., a cDNA or a genomic DNA fragment produced by PCR or restriction endonuclease treatment) independent of other sequences as well as recombinant DNA that is incorporated into a vector, an autonomously replicating plasmid, a virus (e.g., a retro virus, adenovirus, or herpes virus), or into the genomic DNA of a prokaryote or eukaryote. In addition, an isolated nucleic acid can include a recombinant DNA molecule that is part of a hybrid or fusion nucleic acid sequence.
The term “isolated” as used herein with reference to nucleic acid also includes any non-naturally-occurring nucleic acid since non-naturally-occurring nucleic acid sequences are not found in nature and do not have immediately contiguous sequences in a naturally-occurring genome. For example, non-naturally-occurring nucleic acid such as an engineered nucleic acid is considered to be isolated nucleic acid. Engineered nucleic acid can be made using common molecular cloning or chemical nucleic acid synthesis techniques. Isolated non-naturally-occurring nucleic acid can be independent of other sequences, or incorporated into a vector, an autonomously replicating plasmid, a virus (e.g., a retrovirus, adenovirus, or herpes virus) or the genomic DNA of a prokaryote or eukaryote. In addition, a non-naturally-occurring nucleic acid can include a nucleic acid molecule that is part of a hybrid or fusion nucleic acid sequence. It will be apparent to those of ordinary skill in the art that a nucleic acid existing among hundreds to millions of other nucleic acid molecules within, for example, cDNA or genomic libraries, or gel slices containing a genomic DNA restriction digest is not to be considered an isolated nucleic acid.
The terms “peptide”, “polypeptide” and “protein” may be used interchangeably herein. Chimeric or fusion peptide or polypeptide refers to a recombinant or synthetic peptide or polypeptide whose primary sequence comprises two or more linear amino acid sequences which do not both occur in a single molecule in nature, or at least are not linearly contiguous in a single molecule in nature. (For example, they may both be present in a single molecule which comprises e.g. amino acids 1-15, but in the fusion or chimera, “amino acids 1-5” and amino acids 10-15″ are present but amino acids 6-9 are not present between the sequence represented by amino acids 1-5 and the sequence represented by amino acids 10-15.) The two or more sequences may be, for example, a peptide (e.g. an epitope or antigenic region) and a linker sequence, or two or more peptides (which may be the same or different) which are either contiguous or separated by a linker sequence, etc.
A polypeptide as described herein can be an antigen that produces an immune response in an animal (e.g., antibody production). In some cases a polypeptide provided herein can be expressed as a homologous or heterologous antigen. For example a polypeptide can be an antigen, which is recognized as foreign when expressed in an animal, or a polypeptide can be an enzyme that produces an antigen, which is recognized as foreign when expressed in an animal. For example, a polypeptide provided herein can be an antigen that produces an immune response against Brucella (e.g., a ribosomal protein, an outer membrane protein, a periplasmic protein, or a lipopolysaccharide isolated from a species of Brucella). In some cases, a polypeptide can produce an immune response effective against one species of Brucella and another polypeptide can produce an immune response effective against a different species of Brucella or against a species of a different bacterial genus such as Mycobacterium. For example, a polypeptide provided herein can be a heterologous antigen that produces an immune response against M. tuberculosis, such as ESAT6 (GenBank accession number DQ451152.1), Ag85B (GenBank accession number AY207396), and Rv2660c (NCBI Reference Sequence: NC_000962.3). In exemplary embodiments, the heterologous antigens are codon-optimized for expression in the Brucella strain. For example, the ESAT6, Ag85B, and Rv2660c antigens codon-optimized for expression in RB51leuB are represented by SEQ ID NO: 1, SEQ ID NO: 2, and SEQ ID NO: 3, respectively (see
Antigen is a term used historically to designate an entity that is bound by an antibody, and also to designate the entity that induces the production of the antibody. More current usage limits the meaning of antigen to that entity bound by an antibody, while the word “immunogen” is used for the entity that induces antibody production. Where an entity discussed herein is both immunogenic and antigenic, reference to it as either an immunogen or antigen will typically be made according to its intended utility. The terms “antigen”, “antigenic region” “immunogen” and “epitope” may be used interchangeably herein. As used herein, an antigen, immunogen or epitope is generally a portion of a protein (e.g. a peptide or polypeptide).
In some embodiments, a vaccine provided herein can be delivered as a prophylactic vaccine to reduce the risk of developing brucellosis should a Brucella infection occur. In some cases, a vaccine provided herein can reduce the risk of developing brucellosis from infection by B. abortus, B. canis, B. melitensis, B. neotomae, B. ovis, B. suis or B. pinnepediae bacteria. A vaccine provided herein can also be delivered as a prophylactic vaccine to reduce the risk of developing tuberculosis should a M. tuberculosis infection occur.
Another aspect of this invention provides methods for preparing a vaccine provided herein. Such methods can include transforming bacteria with an amount of a nucleic acid vector (e.g., plasmid). Transformation can be achieved by any appropriate method, including, for example, electroporation or chemical transformation. A vaccine can be produced using an isolated nucleic acid to transform a bacterial culture. For example, a transformed bacterial culture can over-express antigens to produce an immune response. In some cases an isolated nucleic acid provided herein can include a nucleic acid encoding one or more than one (a plurality) of antigens. For example, an isolated nucleic acid can encode one or more of an Ag85B, ESAT6, and/or Rv2660c polypeptide. As a further example, an ESAT6 polypeptide and an Rv2660c polypeptide may be encoded. Therefore, in some cases the vaccines disclosed herein can include one or more nucleic acids that encode, for example, two, three, or four (or more) polypeptides.
In some cases, a vaccine provided herein can include a marker of delivery and expression. For example, a vaccine can include a nucleic acid that encodes a fluorescent polypeptide (e.g., a green fluorescent protein, GFP) as a marker of expression and delivery of the vaccine to an animal. For example, a marker of delivery and expression can be detected e.g. as antibodies to the marker. For example, GFP antibodies may be detected in sera from immunized animals.
Some embodiments of the invention relate to an isolated pNS4leuB plasmid comprising one or more Mycobacterial antigen sequences, such as one or more sequences selected from the group consisting of SEQ ID NO: 1, SEQ ID NO: 2, and SEQ ID NO: 3. In exemplary embodiments, the pNS4leuB plasmid contains a sequence selected from the group consisting of SEQ ID NO:4-7. Other exemplary plasmids include pNSch (GenBank accession number DQ412050) and pNSTrcD (GenBank accession number DQ412056). Exemplary sequences of protein products produced from said plasmins include SEQ ID NO: 8 and SEQ ID NO:9. In some cases, an isolated nucleic acid provided herein can include a promoter for driving expression of a polypeptide. For example, an isolated nucleic acid can include a nucleic acid encoding a polypeptide operably linked to a promoter sequence.
A nucleic acid as provided herein may comprise at least one “core” sequence or segment consisting of a sequence from one or more of Ag85B, ESAT6, and Rv2660c. In such constructs, which can be chimeric or fusion polypeptides or proteins, the core sequence(s) is/are flanked on at least one of the amino terminus and carboxy terminus (i.e. at one or the other or both termini) by a sequence which is not found adjacent to the core sequence in nature. The sequence which is not found adjacent to the core sequence in nature may be a heterologous sequence (e.g. synthetic and/or from another species or strain) or may be a repeat or duplication of the same sequence. In some constructs, one core sequence is present alone; in other constructs, multiple core sequences of a single type (i.e. Ag85B, ESAT6, or Rv2660c) are present. In yet other constructs, one core sequence from at least two of Ag85B, ESAT6, and Rv2660c are present. In yet other constructions, multiple copies of one or more core sequence from at least two of Ag85B, ESAT6, and Rv2660c are present. For example, a single recombinant polypeptide may comprise one copy, or more than one copy (a plurality, two or more) of each of these different sequences. A single polypeptide may contain two or more copies of a single sequence, a single copy of one sequence and two or more copies of one or more different sequences, or two or more copies of at least two different sequences. Another aspect of the disclosure provides a mixture of at least two of any of the peptides and/or polypeptides described herein.
It is contemplated that virtually any protein sequence, as well as its corresponding nucleic acid sequence coding for the protein sequence that is or includes Ag85B, ESAT6, or Rv2660c may be used as described herein. This includes the full length sequence as well as any sequence of, for example from about 5-50 (or less than 5 or more than 50) amino acids at the beginning (amino terminus) or at the end (carboxy terminus) of the amino acid sequence of Ag85B, ESAT6, or Rv2660c. The polypeptide sequences as described herein may also be shortened on either the amino or carboxy terminus (or both) by one, two, or more amino acids to produce fragments within the context of the invention wherein the fragments produce the same or a similar protective effect. Alternatively, the polypeptide may be a chimera or fusion protein which comprises flanking amino acids sequences which are not adjacent to the native sequence in nature. For example, the adjacent sequences may be corresponding amino acids which are from different but related species; or amino acids which are from different species (e.g. from other bacteria or eukaryotes of interest, e.g. from infectious agents); or from a synthetic sequence, e.g. various tags such as histidine or glutathione S-transferase (GST) tags, linkers, spacers, targeting sequences, etc.).
A nucleic acid encoding an antigen such as Ag85B can be operably linked to a TrcD promoter sequence (e.g.
In addition to polypeptide sequences from M. tuberculosis antigens, other sequences may be included in the polypeptides of the invention. Such sequences include but are not limited to: antigenic peptide sequences such as linker sequences which in and of themselves can be antigenic and/or various sequences which serve as markers of delivery and expression, as discussed above. Examples of recombinant protein tags that may be useful in practicing the invention include but are not limited to glutathione-S-transferease (GST), poly-histidine, maltose binding protein (MBP), FLAG, V5, halo, myc, hemaglutinin (HA), S-tag, calmodulin, tag, streptavidin binding protein (SBP), Softagl™, Softag3™, Xpress tag, isopeptag, Spy Tag, biotin carboxyl carrier protein (BCCP), GFP, Nus-tag, strep-tag, thioredoxin tag, TC tag, and Ty tag. Examples of linker sequences include but are not limited to an amino acid spacer, an amino acid linker, a signal sequence, a stop transfer sequence, a transmembrane domain, and a protein purification ligand. It should also be recognized that a multitude of other such sequences are known to those of skill in the art, and inclusion of other antigenic, linker, or tag sequences is contemplated.
In some embodiments of the invention, individual linear epitopes in a chimeric vaccinogen are separated from one another by intervening sequences that are more or less neutral in character, i.e. they do not in and of themselves elicit an immune response to Mycobacteriaceae. Such sequences may or may not be present between the epitopes of a chimera. If present, they may, for example, serve to separate the epitopes and contribute to the steric isolation of the epitopes from each other. Alternatively, such sequences may be simply artifacts of recombinant processing procedures, e.g. cloning procedures. Such sequences are typically known as linker or spacer peptides, many examples of which are known to those of skill in the art. See, for example, Crasto, C. J. and J. A. Feng. 2000.
Those of skill in the art will recognize that, while in some embodiments of the invention, the amino acid sequences that are chosen for inclusion in the polypeptides of the invention correspond exactly to the primary amino acid sequence of the original or native sequences of an Ag85B, ESAT6, or Rv2660c protein, this need not always be the case. The amino acid sequence of an epitope that is included in the polypeptides of the invention may be altered somewhat and still be suitable for use in the present invention. For example, certain conservative amino acid substitutions may be made without having a deleterious effect on the ability of the polypeptides to elicit an immune response. Those of skill in the art will recognize the nature of such conservative substitutions, for example, substitution of a positively charged amino acid for another positively charged amino acid (e.g. K for R or vice versa); substitution of a negatively charged amino acid for another negatively charged amino acid (e.g. D for E or vice versa); substitution of a hydrophobic amino acid for another hydrophobic amino acid (e.g. substitution of A, V, L, I, W, etc. for one another); etc. All such substitutions or alterations of the sequences of the polypeptides that are disclosed herein are intended to be encompassed by the present invention, so long as the resulting polypeptides still function to elicit a suitable immune response. In addition, the amino acid sequences that are included in the polypeptides or any chimeric proteins of the invention need not encompass a full length native polypeptide. Those of skill in the art will recognize that truncated versions of amino acid sequences that are known to be or to contain antigenic polypeptides may, for a variety of reasons, be preferable for use in the practice of the invention, so long as the criteria set forth for an epitope is fulfilled by the sequence. Amino acid sequences that are so substituted or otherwise altered may be referred to herein as “based on” or “derived from” the original wild type or native sequence. In general, the Ag85B, ESAT6, or Rv2660c proteins or polypeptide fragments from which the linear epitopes are “derived” or on which the linear epitopes are “based” are the Ag85B, ESAT6, or Rv2660c proteins or peptide fragments as they occur in nature. These natural Ag85B, ESAT6, or Rv2660c proteins may alternatively be referred to as native or wild type proteins.
Such changes to the primary sequence may be introduced for any of a variety of reasons, for example, to eliminate or introduce a protease cleavage site, to increase or decrease solubility, to promote or discourage intra- or inter-molecular interactions such as folding, ionic interactions, salt bridges, etc., which might otherwise interfere with the presentation and accessibility of the individual epitopes along the length of a peptide or polypeptide. All such changes are intended to be encompassed by the present invention, so long as the resulting amino acid sequence functions to elicit a protective antibody response in a host to whom it is administered. In general, such substituted sequences will be at least about 50% identical to the corresponding sequence in the native protein, preferably about 60 to 70, or even 70 to 80, or 80 to 90% identical to the wild type sequence, and preferably at least about 95, 96, 97, 98, 99, or even 100% identical to a native Ag85B, ESAT6, or Rv2660c sequence or peptide fragment. The reference native Ag85B, ESAT6, or Rv2660c sequence or peptide fragment may be from any suitable type of Mycobacteriaceae, e.g. from any Mycobacteriaceae which is known to infect mammals.
A vaccine for producing an immune response against Brucella can be produced using any bacteria. For example, a bacterial strain such as B. abortus RB51 or RB51leuB can be used. The RB51leuB strain of bacterium exhibits leucine auxotrophy, having a mutation (i.e. deletion) at the leuB locus that disrupts expression of leuB (isopropyl malate dehydrogenase is necessary for leucine biosynthesis). In some embodiments, a leucine auxotrophic bacterial strain can be transformed with an isolated nucleic acid to restore leucine biosynthesis as described in US 2010/0226942, herein incorporated by reference.
The vaccines provided herein can be administered using any appropriate method. Administration can be, for example, topical (e.g. transdermal, ophthalmic or intranasal); pulmonary (e.g., by inhalation or insufflation or powders or aerosols); oral, or parenteral (e.g. by subcutaneous, intrathecal, intraventricular, intramuscular, or intraperitoneal injection, or by intravenous drip). Administration can be rapid (e.g., by injection) or can occur over a period of time (e.g., by slow infusion or administration of slow release formulations). In exemplary embodiments, the mode of administration is intraperitoneal. For application in livestock, the preferred mode of administration is subcutaneous or intramuscular.
In some embodiments, at least one booster vaccine, which may be a subunit booster vaccine, is administered after the initial administration of the vaccine of the invention. The booster vaccine may be identical to the vaccine that is initially used to vaccinate the subject Alternatively, the booster vaccine may be a subunit vaccine comprising isolated antigens or suitable antigenic fragments thereof, or nucleic acids encoding the protein or fragments, which are used to elicit an immunogenic response, e.g. a protective immunogenic response, in a subject. The booster vaccine may be administered between as early as four weeks after initial vaccination. In some embodiments, the booster vaccine may be administered one year or later after initial vaccination. In exemplary embodiments, the booster vaccine is administered between six weeks and 6 months after initial vaccination.
The immunogenic response from the initial or booster vaccine may protect a naive subject from subsequent full-blown Brucella and/or M. tuberculosis infection when exposed to the bacterium. Alternatively, administration of the initial or booster vaccine is used to provide treatment for an existing Brucella or M. tuberculosis infection, e.g. an active or latent TB infection. The protective response either wholly or partially prevents or arrests the development of symptoms related to disease or bacterial infection, in comparison to a non-vaccinated control organism, in which disease progression is not prevented.
The vaccines of the invention can include a pharmacologically suitable vehicle or 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. The liquid may be an aqueous liquid. 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. The vaccine preparations of the present invention may further comprise an adjuvant, suitable examples of which include but are not limited to Seppic, Quil A, Alhydrogel, etc. 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 polypeptides or chimeric peptides in the formulations may vary. However, in general, the amount in the formulations will be from about 0.01-99%, weight/volume.
In addition, the compositions may be administered in conjunction with other treatment modalities such as substances that boost the immune system, various anti-bacterial chemotherapeutic agents, antibiotics, and the like.
Before exemplary embodiments of the present invention are described in greater detail, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.
All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.
It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation.
As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any other order which is logically possible.
The invention is further described by the following non-limiting examples which further illustrate the invention, and are not intended, nor should they be interpreted to, limit the scope of the invention.
Summary
Brucella abortus strain RB51 is the official USDA approved vaccine against cattle brucellosis in the United States and other countries. Protection conferred by strain RB51 vaccination is due to induction of cell-mediated immune mechanisms, including production of IFN-γ. In this study, the feasibility of using the leucine auxotrophic strain RB51leuB as an attenuated vaccine able to express Mycobacterium tuberculosis protective antigens (Ag85B, RV2660c and ESAT6) was evaluated. Two expression vectors were designed: pNS4TrcD-Ag85B, and pNS4TrcD-Rv2660c::ESAT6 (fusion construct). These vectors enabled strain RB51leuB to express the M. tuberculosis antigens Ag85B and fusion protein Rv2660c::ESAT6. In vivo and in vitro studies indicated that the recombinant vaccines were stable and continued to express the heterologous antigens in both selective and non-selective environments. The objective of this study was to develop and test the efficacy of the B. abortus vaccine strain RB51 as a platform for expression of M. tuberculosis antigens (Ag85B, ESAT6 and Rv2660c) and simultaneous induction of a protective immune response against M. tuberculosis and B. abortus challenge in mice.
The present studies show that expression of mycobacterial antigens in strain RB51leuB lead to strong induction of antigen-specific immune response characterized in this study by secretion of IgG2a antibodies as well as of IFN-γ and TNF-α. Mice immunized with an equal mix of two RB51leuB vaccines, one expressing fusion Rv2660c::ESAT6 and another expressing Ag85B led to borderline (p=0.052) protection against infection with M. tuberculosis. However, when mice were primed with these RB51leuB vaccines and boosted thereafter with proteins Ag85B and ESAT6, significant protection against a M. tuberculosis challenge was achieved and the protection level conferred was similar to that conferred by the Bacillus Calmette-Guerin (BCG) vaccine. Importantly, mice vaccinated with the RB51leuB vaccines did not become positive to the tuberculin skin test, indicating that they remained negative to the official diagnostic test for tuberculosis. Vaccination with purified Ag85B and ESAT6 engendered significant immunity but less than the protection engendered by the RB51leuB vaccines boosted with the purified antigens or BCG. The RB51leuB vaccine carrying the Rv2660c::ESAT6 antigens protected against infection against Brucella abortus as well as the RB51leuB vaccine. In conclusion, it was shown that recombinant RB51leuB strains expressing mycobacterial protective antigens result in stimulation of mycobacterial antigens specific immune responses without turning them positive in a tuberculosis infection diagnostic test. These vaccines can be used to prime animals for protection against M. tuberculosis infection and can simultaneously protect against B. abortus infection.
Promoter Selection: Replacement of groE with trcD Promoter
The starting point for construction of the expression vectors was the pNS4GroE plasmid [13]. The groE promoter was excised from pNS4GroE expression plasmid with SalI and BamHI restriction enzymes and replaced with either trcD promoter [17] or a synthetic trcD promoter sequence to create the expression vector pNS4TrcD (
Construction of Vectors Expressing Ag85B and Fusion Protein Rv2660c::ESAT6
The genes encoding M. tuberculosis protective antigens Ag85B, ESAT6 and Rv2660c (18) were optimized using Brucella codons and were commercially synthesized by Genscript (Piscataway, N.J., USA). Brucella codon optimization of these three protective antigens of M. tuberculosis has not been previously reported (see below). BamHI and XbaI restriction sites were engineered into the forward and reverse primers, respectively, to facilitate directional cloning into pNS4TrcD expression vector. A BglII restriction site was also designed in the reverse primers of Rv2660C, upstream of XbaI restriction site, for subsequent cloning of esat6 downstream of rv2660c. The amplified DNA regions (ag85B and rv2660c) were digested with BamHI and XbaI restriction enzymes and subcloned into the same sites of pNS4TrcD plasmid to generate pNS4TrcD-Ag85B and pNS4TrcD-Rv2660c, expression vectors (
The construction of the Rv2660c::ESAT6 fusion vector was accomplished in two steps. In the first step, rv2660c was cloned as described earlier. In the second step, Esat6 gene containing BglII and XbaI restriction sites was amplified and then digested with BglII and XbaI restriction enzymes and subcloned into the same sites of pNS4TrcD-Rv2660c to generate pNS4TrcD-Rv2660c::ESAT6 expression chimeric vector (
pNS4: Was generated using the origin of replication and promoter of pNSGroE; details of pNSGroE as described in (http://www.ncbi.nlm.nih.gov/nuccore/49659742) The leuB gene of the strain RB51 along with its own promoter (1412 bp) was amplified by PCR using the primers (leuBForward, 5′GGG-AAG-CTT-GGG-TCT-AGA-AGT-TTC-GCT-CGC-GGT-GAG-TGG-CGA 3′3′ SEQ ID NO:10 and leuBReverse, 5′GGG-ACT-AGT-TCA-GGC-CGA-AAG-TGC-CTT-GAA3′ SEQ ID NO:11). The “origin of replication” (1700 bp) and 259 bp expression segment (Brucella groE promoter+multiple cloning site+6His tag) of the plasmid pNSGroE were amplified using the primers as described before as they have cloning sites as well as the minimal sequence necessary for plasmid replication (28); the groE promoter is up regulated following Brucella uptake into macrophages (31). After the restriction enzyme digestion, the 3 fragments were purified and ligated to form plasmid pNS4; note that this plasmid does not have an antibiotic resistance gene (
Details of the Constructs of the Two Protective Antigens from Mycobacterium tuberculosis for Expression in Brucella abortus RB51
The GroE promoter was replaced with TrcD promoter and the codons of the M. tuberculosis antigen were optimized for expression in Brucella species and cloned into pNS4 downstream of TrcD promoter. Expression of the M. tuberculosis antigens using our expression vector in strain RB51 was confirmed by western blotting.
Evaluation of Plasmid Stability In Vitro
To evaluate the stability of the two vectors expressing tuberculosis protective antigens, the gene for the green fluorescent protein (GFP) was cloned in-frame downstream of the mycobacterial genes. Strain RB51leuB was transformed with the GFP containing vectors and three random colonies containing each construct were subcultured onto agar made with either non-selective-enriched medium (TSA) or selective (leucine deficient) Brucella minimal medium (BMMleu). The subcultures were evaluated for GFP expression under UV light and, subsequently, subcultured onto BMMleu agar plates every 4 days until fluorescence was no longer observed.
Evaluation of Plasmid Stability in BALB/c Mice (In Vivo)
Five groups of 4-6 week old female BALB/c mice (n=9) were vaccinated with approximately 2-5×108 colony forming units (CFUs) of strain RB51leuB carrying one of following vectors pNS4TrcD-Rv2660c::ESAT6, pNS4TrcD-Ag85B, or pNS4TrcD (negative control). Three mice from each group were euthanized on weeks 3, 6, and 8 post-vaccination. Spleens and livers were aseptically harvested, homogenized, serially diluted and plated on TSA (non-selective medium) and BMMleu (selective medium) agar plates for CFU determination. The numbers of CFUs determined from growth on BMMleu were compared to the CFUs determined from growth on TSA to measure plasmid stability in vivo. Colonies isolated on BMMleu at week 6 were subject to western blotting for confirmation of protein expression i.e. mycobacterial antigens.
Preparation of the Protein Extract and Immunoblotting
Western blotting was performed on each recombinant strain using His tag antibodies to confirm expression and secretion of Ag85B and fusion protein Rv2660c::ESAT6. Briefly, cultures of strain RB51leuB carrying expression vectors were grown in BMMleu to mid-log phase. For cytoplasmic expression of Ag85B and the fusion protein Rv2660c-ESAT6, 100 ul of each culture was pelleted for 5 minutes in a micro centrifuge tube at 12,000×G. The pellet was lysed with β-mercaptoethanol in the presence of 10 mM Tris-base and heated in a water bath at 95° C. for 10 minutes. Western blot analysis was carried on proteins transferred onto nitrocellulose membranes and probed with 1:4000 dilutions of mouse IgG2a anti-His tag, horseradish peroxidase (HRP) conjugated sera (Life Sciences, Inc., Grand Island, N.Y., USA).
Mice:
Female BALB/c mice (6-8 weeks purchased from Harlan Laboratories, Indianapolis, Ind.)) were used in all experiments to evaluate the immune response to the two recombinant RB51leuB vaccine strains. All animal experimental protocols were approved by Institutional Animal Care and Use Committee (protocol # CVM-13-070) at Virginia Tech and carried out in CDC approved ABSL-3 facilities that are also AAALAC approved. For retro-orbital bleeding, mice were anaesthetized under isoflurane using Mobile Laboratory Animal Anesthesia System (Ohmeda, Madison, Wis. 53707). Mice were euthanized using overdose of carbon dioxide in-cage followed by cervical dislocation.
Preparation of Bacterial Strains:
The strains used in this study were obtained from the Brucella collection housed in the BSL-3 laboratory in Veterinary Medicine at Virginia Tech. The Mycobacterium tuberculosis strain H37Rv (ATCC 25618) and M Bovis BCG (ATCC 35734) were purchased from the American Type Culture Collection (Manassas, Va.). For preparation of the vaccine strains, four plates of leucine deficient Brucella minimal medium (15) were seeded with 100 ul of each strain and incubated for four days at 37° C. in 5% CO2. A similar procedure using trypticase soy agar (Difco) TSA was followed for B. abortus 2308. Lawns of bacteria were scraped off the agar with a sterile loop and suspended in 20 ml of phosphate buffer saline (PBS). The suspensions were centrifuged at 1,962×G for 30 minutes at 4° C., washed twice with PBS, resuspended in 15% glycerol, aliquoted and stored at −80° C. until use.
For preparation of M. tuberculosis challenge dose, 25 ml of 7H9 Middlebrook Mycobacteria base supplemented with ADC Enrichment Medium (Difco, Becton, Dickinson and Company, Sparks, Md. 21152) were inoculated with a single colony of H37Rv strain. Culture was grown in a shaking incubator at 37° C. till the density reached 100 Klett units (mid-log phase). The strains were recovered by pelleting each culture at 1962×G for 30 minutes at 4° C. Strains were then washed twice with PBS, resuspended in 5 ml of 15% glycerol, aliquoted and stored at −80° C. until use. All strains were delivered to mice via an intraperitoneal (IP) route.
Mouse Experiment 1: Enzyme-Linked Immunoabsorbent Assay (ELISA)
A total of 9 BALB/c mice were divided into 3 experimental groups (n=3) and vaccinated IP. Group 1 was immunized with strain RB51leuB (control). Group 2 was immunized with RB51leuB expressing Ag85B. Group 3 was immunized with strain RB51leuB expressing the Rv2660c::ESAT6 fusion protein. Blood was collected from the different groups of mice by retro-orbital bleeding at weeks 3 and 6. Levels of immunoglobulin (total IgG) as well as IgG1 and IgG2a, with specificity to Ag85B and ESAT6, in serum were determined by indirect ELISA as described before [19, 20].
Mouse Experiment 2: Cytokine Proliferation Assay:
A total of 12 BALB/c mice were divided into 4 experimental groups (n=3) and vaccinated IP. Group 1 was vaccinated with 100 μl PBS (control). Group 2 was vaccinated with strain RB51leuB (control). Group 3 was vaccinated with M. bovis BCG. Group 4 was inoculated with an equal mix of the two RB51leuB vaccine strains (one carrying Ag85B and another carrying Rv2660c::ESAT6). The inoculation titer for the BCG group was 1×106 CFU, whereas in all RB51leuB vaccinated groups the titer was 2-4×108 CFU. Six weeks post vaccination mice were euthanized and spleens were collected for splenocyte proliferation assay as described before [21].
Mouse Experiment 3: B. abortus 2308 Protection Assay:
Thirty BALB/c mice were divided into 6 experimental groups (n=5) and immunized IP. Group 1 was immunized with 100 μl PBS (control). Group 2 was immunized with RB51leuB (control). Group 3 was immunized with M. bovis BCG strain. Group 4 was immunized with RB51leuB expressing Ag85B. Group 5 was immunized with RB51leuB expressing Rv2660c::ESAT6. Group 6 was immunized with an equal mix of the two strains of RB51leuB (one expressing Rv2660c::ESAT6 and other expressing Ag85B). The inoculation titer for the BCG group was 1×105 CFU, whereas in all strain RB51leuB vaccinated groups the titer was 2-4×108 CFU. Six weeks post vaccination, all six groups were challenged with 5×104 CFU of B. abortus 2308 (i.p.). Two weeks post challenge all mice were killed by CO2 and cervical dislocation. Spleens and livers were removed aseptically, homogenized, serially diluted, plated on TSA agar, and incubated for four days at 37° C. in 5% CO2.
Mouse Experiment 4: M. tuberculosis Protection Assay:
Thirty BALB/c mice were divided into 6 experimental groups (n=5). All groups were vaccinated IP with same strains and doses as those in the mouse experiment 3 study. Eight weeks post-vaccination, all nine groups were challenged with 2×105 CFU of M. tuberculosis (i.p.). Four weeks post-challenge all mice were killed by CO2 and cervical dislocation. Spleens and lungs were removed aseptically, homogenized, serially diluted and plated on 7H10 selective media and incubated for 2-3 weeks at 37° C. in 5% CO2 Mouse experiment 5: M. tuberculosis protection assay following subunit boosting:
Twenty BALB/c mice were divided into 4 experimental groups (n=5). Groups 1 & 2 were immunized IP with 100 μl PBS (control). Group 3 was immunized with M. bovis BCG strain. Group 4 with an equal mix of the two RB51leuB vaccine strains (one expressing Rv2660c::ESAT6 and another expressing Ag85B). Six weeks post-vaccination; groups 2 & 4 were boosted i.p. with 20 μg of Ag85B and 20 μg of ESAT6 in dimethyl dioctadecylammonium bromide [(DDA) (250 μg/dose; Avanti Polar Lipids, Inc.)] with 25 μg of monophosphoryl lipid A [(MPL) (Avanti Polar Lipids, Inc.)] in a volume of 100 Blood was collected from the different groups of mice by retro-orbital bleeding one week pre-boosting and post-boosting. Levels of immunoglobulin (total IgG) as well as IgG1 and IgG2a, with specificity to Ag85B and ESAT6, in serum were determined by indirect ELISA as described earlier. Two weeks post-boosting, all groups were challenged with 2×105 CFU of M. tuberculosis (IP). Four weeks post challenge all mice were killed by CO2 and cervical dislocation. Spleens and lungs were removed aseptically, homogenized, serially diluted and plated on 7H10 selective media and incubated for 2-3 weeks at 37° C. in 5% CO?
Mouse Experiment 6: Tuberculin Skin Test & In Vitro Interferon-Gamma (INFγ) Production Responses of BALB/c Mice to Vaccination with RB51leuB Expressing M. tuberculosis Antigens:
Fifteen BALB/c mice were divided into 5 groups of 3 mice each (n=3) and immunized IP. Group one received PBS (control); group 2 received strain RB51leuB; group 3 received strain RB51leuB expressing Ag85B, group 4 received strain RB51leuB expressing Rv2660c::ESAT6; group 5 received an equal mix of the vaccines used in group 2 and 3. Eight weeks after vaccination, each mouse was injected with 50 ug tuberculin (PPD) into the hind leg foot-pad and swelling was measured at 24, 48 and 72 hours post exposure. Swelling was compared to the other hind leg foot-pad injected with PBS. At 96 hours mice were killed, and spleen cells were exposed to antigens in vitro to detect INF-g production using a commercially available ELISA kit (B.D. Biosciences, San Diego, Calif. 92121).
Statistical Analysis
Analysis of variance (ANOVA) was used to evaluate the differences in the protection and the production of cytokines and antibodies. Comparisons between two groups were performed with the Student's T-test. Unless otherwise stated the level of statistical significance was set at 0.05.
Results
Construction and Evaluation of Recombinant RB51 Strain Stability In Vitro
Synthesized genes encoding M. tuberculosis protective antigens using Brucella codons were successfully cloned into the two expression vectors to create pNS4TrcD-rv2660c::esat6, and pNS4TrcD-ag85B for cytoplasmic expression of M. tuberculosis protective antigens. Western blotting confirmed expression of the synthesized genes. The GFP reporter gene cloned in frame and downstream of the synthesized mycobacterial genes was used to monitor the expression and stability of the recombinant proteins in vitro. [mycobacterial antigens::GFP] Through evaluation of GFP expression under UV light, it was found that all expression vectors were maintained for more than 15 passages or 60 days on selective medium (Table 1). When grown on non-selective enriched medium the same recombinant strains maintained the expression vector in a stable fashion up to 7-8 passages or 28-32 days (Table 1).
Evaluation of Recombinant RB51 Strains Stability in Mice
To evaluate the stability of the newly constructed vectors expressing mycobacterial antigens in strain RB51, five groups of female BALB/c mice (9 mice per group) were vaccinated IP with approximately 2-5×108 CFUs of strain RB51leuB carrying the constructed vectors. Three mice of each group were euthanized at 3, 6 and 8 weeks post-vaccination. All vaccinated mice cleared the vaccine strains within 6 to 8 weeks post-vaccination. The recombinant strain of RB51leuB expressing the fusion Rv2660c::ESAT6 and Ag85B maintained the vectors during the entire course of vaccine persistence, 6-8 weeks (
Generation of Specific Immune Responses
In mouse experiment 1, sera were collected from mice vaccinated at weeks three and six, and tested for the presence of serum immunoglobulin G and their isotypes (IgG, IgG1, and IgG2a) with specificity to Ag85B and ESAT6 via indirect ELISA. As expected, mice vaccinated with strain RB51leuB carrying Ag85B, but not those vaccinated with strain RB51leuB or saline, developed Ag85B-specific IgG (
In Mouse experiment 2, total splenocytes were isolated from vaccinated mice and stimulated with heat-killed M. tuberculosis, heat-killed B. abortus RB51leuB six weeks post-vaccination. As expected, significant levels of interferon gamma (IFN-γ) were detected in mice vaccinated with RB51leuB strains and BCG when stimulated with heat killed B. abortus RB51leuB or M. tuberculosis, respectively (
When the same splenocytes were stimulated with Ag85B, antigen specific IFN-γ and
TNF-α were produced at higher levels in mice vaccinated with BCG, the mix of RB51leuB-Ag85B and RB51leuB-Rv2660c::ESAT6 than in mice vaccinated with strain RB51leuB alone (
B. abortus 2308 Protection Study
Based on colony forming units (CFU) count from homogenized spleens in Mouse Experiment 3, strains RB51leuB, RB51leuB-Rv2660c::ESAT6, and the mix of the two RB51leuB vaccine strains were able to provide significant levels of protection against subsequent challenge with B. abortus 2308 when compared to the unvaccinated group. Mice vaccinated with RB51leuB-Ag85B produced a 1.3 log reduction by the infection challenge with strain 2308; however this reduction was not statistically significant (p=0.09). The M. bovis BCG vaccinated group did not show any protection against B. abortus 2308 challenge (
M. tuberculosis Protection Study
Mouse Experiment 4: Based on CFU count from homogenized spleens, only the BCG vaccinated group showed significant protection against M. tuberculosis challenge after one vaccination. Individual strains of RB51leuB expressing the Ag85B or the fusion Rv2660c::ESAT6 did not result in any level of significant protection compared to non-vaccinated group. Mice vaccinated with the mix of the two strains of RB51leuB vaccines carrying Ag85B and fusion Rv2660c::ESAT6 (Group 8) led to borderline protection (p=0.052;
M. tuberculosis Protection Study Post-Boosting with Subunit Vaccine
Mouse Experiment 5: Serum from vaccinated mice was collected one week before and one week after boosting with Ag85B and ESAT6 to test for the presence of immunoglobulin G and its isotypes (IgG1, and IgG2a) with specificity to Ag85B and ESAT6 via indirect ELISA. Increased levels of antigens specific IgG and IgG2a were observed in mice boosted with subunit vaccines (
Based on CFU count from homogenized spleens, mice vaccinated with the mix of strain RB51leuB vaccines expressing Ag85B and Rv2660c::ESAT6 and subsequently boosted with proteins Ag85B and ESAT6 resulted in significant protection when compared to the PBS vaccinated group. Mice vaccinated with BCG alone gave a similar level of protection. Mice vaccinated with proteins Ag85B and ESAT6 alone demonstrated protection but it was statistically less than the protection induced by the mix of the strain RB51leuB vaccines followed by purified antigen booster (
Mouse Experiment 6: The mice had no skin test response to tuberculin at 24, 48 and 72 hr post-injection. The results indicate that mice do not become tuberculin skin test positive after one vaccination with RB51leuB (group II) or one vaccination with the RB51leuB vaccine expressing 85B (group III) or ESAT-6 M. tuberculosis antigens (group IV) or a combination of the two heterologous expressing vaccine strains (group 5). The following antigens were used for the in-vitro stimulation of the spleen cells of each mouse to measure INF-g production: Purified 85B antigen. purified ESAT-6 antigen, heat killed RB51leuB, Con-A (positive control) and culture medium [(negative control) see
Discussion
B. abortus vaccine strain RB51 is a potent stimulator of cell-mediated immunity response. This vaccine strain acts as an immunomodulator by promoting a strong Th1 type and simultaneously inhibiting the Th2 type of immune response (5). These vaccine qualities of strain RB51 make it a good platform candidate for the development of multivalent vaccines with strong Th1 immunizing abilities. Such vaccines can confer protection against Brucella and other intracellular pathogens that require cell-mediated immunity for protection such as M. tuberculosis. In an effort to enhance these qualities, expression vector, pNS4TrcD, was created for cytoplasmic expression of mycobacterial proteins in strain RB51leuB.
Replacement of groE promoter with the trcD promoter was based on the findings of Seleem et al., [13], who showed that expression of LacZ under the trcD promoter was 2-3 times stronger than that under the groE promoter in B. suis. The strength of this expression was attributed to the placement of an A tract, an A+T rich upstream element, between the −38 and the −59 of the core trc promoter [22]. This enhancement in expression appeared to be due to the ability of the A tract to provide a binding site for the RNA polymerase [22, 23].
To test the functionality of the newly designed expression vector, genes encoding M. tuberculosis proteins; Ag85B and Rv2660c and ESAT6; were cloned into pNS4TrcD expression vector. Initially, expression of these recombinant proteins was not achieved using the original DNA sequences of M. tuberculosis. This lack of expression was attributed to the difference in codon usage between Mycobacterium species and Brucella species [24]. The Codon Adaptation Index (CAI) [25] was used to predict the expression level of mycobacterial proteins in strain RB51. Using CAI, it was shown that the predicted levels of expression of Ag85B, Rv2660c and ESAT6, using original DNA sequences of M. tuberculosis, were 0.51, 0.29 and 0.47, respectively. It has been well documented that the rate of translation of foreign antigens in high expression vectors can be influenced by their codon usage [26]. Brucella species have a G+C content of 57%, whereas the genomes of Mycobacterium species have a higher G+C content of 65.9% [27]. As a result, there is a high degree of bias for codons with G and C at the third nucleotide position, effectively, leading to codons that are rare in Brucella species. This use of rare codons usually compromises expression of heterologous proteins by inducing translational errors such as stalling, termination, amino acid substitution and possibly frame shifting [28]. In our study, genes coding for the intended mycobacterial genes were synthesized commercially using Brucella codons. Upon optimizing these codons for Brucella expression, the predicted levels of expression of Ag85B, Rv2660c and ESAT6 became 0.94, 0.94 and 0.93, respectively. This optimization of codon usage resulted in stable expression vectors and successful expression of M. tuberculosis proteins in strain RB51leuB without showing any signs of lethality or toxicity. This is the first report describing the expression of genes adapted with Brucella codons encoding mycobacterial proteins 85B, Rv2660c and ESAT6 in Brucella.
Unlike mutant strains of bacteria that are engineered for protein synthesis i.e. Escherichia coli HB101, expression of heterologous antigens within pathogenic strains, such as strain RB51leuB, can impose a metabolic burden. A portion of the host bacterium's energy and materials are required to maintain the foreign DNA and express foreign protein as well as maintain it without imposing toxicity on its self. In the case of recombinant vaccines, it is crucial for such strains to maintain plasmid and expression of foreign antigens in order to develop a strong immune response against the targeted antigens. One of the techniques used to assess the stability of recombinant strains in vivo and in vitro is through estimating the percentage of recombinant colonies retaining selective markers, which is used as an indicator of retention of the plasmid. However, this approach has limitations; for example, retention of selection markers does not distinguish between retention of intact vector or retention of vectors which have lost the foreign gene but retained the selective marker. Therefore a more robust confirmation is necessary not only to test for the presence of the intact expression vectors along with the foreign DNA, but also for expression of such foreign antigens. In this study, GFP was used as a reporter protein to evaluate the stability of expression vectors and expression of mycobacterial antigens in vitro. Cloning GFP in-frame downstream of the mycobacterial genes, addressed plasmid stability and mRNA translation. The ATG start codon of GFP was deleted and replaced by a linker to allow for in-frame translation and flexibility for proper GFP folding. Using this reporter system, it was shown that the recombinant strains were very stable when grown under selective pressure i.e. BMMleu. However, when grown using non-selective enriched medium, the recombinant strains were also stable up to 7-8 passages.
The stability of the constructed expression vectors was also assessed in vivo by vaccinating mice with each construct. It was apparent that recombinant strains of RB51leuB were stable for 6-8 weeks post vaccination. An immunoblot of extracts from isolated colonies at week 6 showed stable expression of the mycobacterial antigens.
In summary, the feasibility of high-level expression of heterologous proteins in strain RB51leuB has been exploited. The expression vectors constructed in this current study proved to be easily transformed into and stably maintained in strain RB51leuB. These data strongly suggest that strain RB51leuB could be used as a host for expression and delivery of protective antigens of Mycobacterium species. These new RB51leuB vaccine strains carrying mycobacterial antigens will serve as an environmentally safe bivalent vaccine for protection against Brucella and Mycobacterium infections simultaneously.
In an attempt to test the protective efficacy of these recombinant vaccines, a series of animal experiments were conducted; BALB/c mouse was the model of choice. This model is one of the best rodent models that can be used to evaluate both brucellosis and tuberculosis infections [29, 30]. Since Brucella protection studies are based on intraperitoneal vaccination followed by intraperitoneal challenge with the virulent strains, it was decided to follow the same route of vaccination and challenge for the M. tuberculosis protection study. Although this is not the natural route of tuberculosis infection, this route results in chronic infection in mouse spleens and lungs similar to that observed during low dose aerosol infection [31]. Additionally, this route of challenge ensures that a proper dose of the bacterium is given and also results in low levels of cross contamination between animals [31].
Using the BALB/c mouse model, a novel vaccine strategy was presented that conferred protection similar to the official tuberculosis vaccine BCG. It was hypothesized that the B. abortus vaccine RB51leuB carrying mycobacterial protective antigens could lead to protection against M. tuberculosis challenge in a murine model. Strain RB51 was chosen based on its ability to stimulate cell-mediated immunity not only against B. abortus challenge, but also against other heterologous proteins expressed by the strain [32-37]. However, these vaccinal qualities of strain RB51 had to be optimized for better induction of immune response against mycobacterial antigens.
Expression of mycobacterial antigens Rv2660c and ESAT6 as a fusion protein in strain RB51leuB did not affect its protective efficacy against B. abortus 2308 challenge. The B. abortus protection studies conducted showed that this recombinant RB51leuB vaccine strain induced protection against B. abortus 2308 challenge at levels similar to those induced by vaccine strain RB51, indicating that the expression of the heterologous fusion protein did not alter the protective efficacy of the strain. Surprisingly strain RB51leuB-85B did not protect against Brucella challenge at the same level.
None of the individual strains of RB51leuB carrying mycobacterial antigens or a combination thereof was able to elicit protective immunity against mycobacterial challenge on their own after one vaccination. However, when the two strains of RB51leuB carrying Ag85B and Rv2660c::ESAT6 were combined, a close to significant protection level was achieved against M. tuberculosis challenge (
Recent reports from a number of vaccine studies have shown that prime-boost protocols of immunization provide an effective strategy to promote long-term memory and strong cellular Th1 responses to M. tuberculosis [38-42]. In an attempt to test this strategy, another TB protection study was conducted where mice were primed with the two vaccine strains of RB51leuB carrying Ag85B and Rv2660c::ESAT6, and later boosted with a subunit vaccine consisting of purified Ag85B and ESAT6 emulsified in DDA-MPL adjuvant formulation. The protection level conferred by this vaccination strategy was essentially the same as the protection level conferred by BCG, and was higher than the protection level conferred by the subunit vaccine alone (
Methods
It is important that vaccines designed to protect cattle against tuberculosis and brucellosis do not interfere with official diagnostic methodologies (i.e. vaccinated animals should not respond diagnostically in a positive way to tuberculin). The skin tuberculin test is the official diagnostic test employed by USDA. Therefore, mice were administered the new vaccines as described in Example 1 and were then tested for a response to tuberculin in vivo (official diagnostic test) and INF-γ production in vitro in order to predict a possible response to the vaccine in cattle. All work was carried out under BSL3 conditions at the CVM-BSL3 facilities of VT. Groups of 3 mice each were vaccinated with 5×10(8) viable organisms of the following vaccine strains along with controls (see table 2).
Eight weeks after vaccination, each mouse was injected with tuberculin (PPD) into the hind leg foot-pad and swelling was measured at 24, 48, and 72 hours post exposure. Swelling was compared to the other hind leg foot-pad injected with PBS. At 96 hours mice were killed, and spleen cells were exposed to antigens in vitro to detect INF-g production using a commercially available ELISA kit.
Results
1. Skin test: The mice had no skin test response to tuberculin at 24, 48, and 72 hrs post-injection. The results indicate that mice do not become tuberculin skin test positive after one vaccination with strain RB51 (group II) or one vaccination with the strain RB51 vaccine expressing 85B (group III) or ESAT-6 Mycobacterium tuberculosis antigens (group IV) or a combination of the two heterologous expressing vaccines (group V).
2. INF-g production: The following antigens were used for the in vitro stimulation of the spleen cells of each mouse: Purified 85B antigen. purified ESAT-6 antigen, heat killed RB51, Con-A (positive control) and culture media (negative control). As expected culture media (negative control) gave no stimulation and Con-A (positive control) gave the highest response. Purified ESAT-6 and 85B antigens stimulated the spleen cells from all vaccinated groups to produce INF-g above levels obtained with the PBS vaccinated mice (
Conclusions
The INF-γ results indicate that vaccinated mice, including those vaccinated only with strain RB51, respond to the M. tuberculosis antigens 85B and ESAT-6 and would be considered positive to Mycobacterium exposure from a diagnostic point of view. Interestingly, mice vaccinated only with strain RB51 also responded to the TB antigens suggesting that these reactions may be non-specific and that the in vitro INF-γ test is not useful diagnostically if carried out 8-9 weeks post immunization. Alternatively, although unlikely, the mice may have become sensitized to the tuberculin utilized in the foot-pad test and therefore responded in the INF-γ assay. Tuberculin contains both, 85B and ESAT-6 antigens. Assuming that cattle would have a response similar to mice, the use of an in vitro INF-γ test (like the commercially available Bovigam test) would not be diagnostically accurate. The in vitro INF-γ test is not recognized as an official diagnostic test by USDA. Without being bound by theory, the production of INF-γ could be due to a non-specific reaction, as mice vaccinated with normal RB51 also produced INF-γ. Alternatively, the response could be due to the previous tuberculin testing.
The results presented herein suggest that one vaccination of cattle with these new vaccines will not turn them diagnostically positive to the skin test with tuberculin and therefore, these vaccines are commercially viable for use in cattle. In Example 1, it was shown that recombinant strain RB51leuB vaccines carrying mycobacterial protective antigens RV2660c and ESAT-6 as a fusion protein result in stimulation of antigens specific immune responses to mycobacterial antigens without altering the strain RB51leuB efficacy in protecting against the virulent strain of B. abortus 2308. In Example 2, it was shown that mice vaccinated with the recombinant strain RB51leuB vaccines did not develop a tuberculin positive skin test indicating that one vaccination does not induce a false positive diagnostic tuberculin test. The mice immunized with the recombinant strain RB51leuB vaccines were protected against M. tuberculosis challenge if boosted with Ag85B-EAST6 subunit vaccine along with an adjuvant. Moreover, this protection was similar to the protection obtained with BCG and better than the protection induced by one vaccination of the purified antigens. Therefore, these vaccines can protect animals such as cattle against brucellosis and prime for protection against tuberculosis without diagnostic interference with vaccine RB51leuB-RV2660c::ESAT6 and/or vaccine RB51leuB-Ag85B.
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.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2015/048841 | 9/8/2015 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2016/040258 | 3/17/2016 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20100183677 | Skeiky et al. | Jul 2010 | A1 |
| Entry |
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| Number | Date | Country | |
|---|---|---|---|
| 20170246282 A1 | Aug 2017 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62047945 | Sep 2014 | US |
