Recombinant BCG overexpressing phoP-phoR

Abstract

Provided are a live recombinant Mycobacterium bovis-BCG strain and a tuberculosis (TB) vaccine or immunogenic composition comprising a nucleic acid capable of overexpression, the nucleic acid encoding PhoP and PhoR proteins. A method for treatment or prophylaxis of a mammal against challenge by Mycobacterium tuberculosis or Mycobacterium bovis using the strain is also provided.

Description

INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ELECTRONICALLY

This application contains, as a separate part of disclosure, a sequence listing in computer-readable form (filename: 54507_SeqListing.txt; 10,563 bytes; created: Mar. 11, 2020) which is incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to tuberculosis (TB) vaccines. In particular, the invention provides a recombinant BCG that overexpresses the phoP-phoR two-component regulatory system and confers enhanced protection against tuberculosis.

BACKGROUND OF THE INVENTION

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tb), ranks alongside HIV/AIDS as a major cause of mortality by infectious diseases worldwide. In 2014, TB caused 1.5 million deaths and 9.6 million new infections. The lack of a protective vaccine, the emergence of drug-resistant M. tb strains, and the high rate of M. tb/HIV coinfection continue to fuel the TB epidemic. Bacille Calmette-Guérin (BCG) is the only licenced TB vaccine and although it is effective against disseminated forms of TB in children^1,2, BCG has limited protection against pulmonary TB in adults, the most common and contagious form of the disease. Clinical studies have shown variable efficacies ranging from 0 to 80%^3-5.

One hypothesis to explain the variable efficacy of BCG concerns the heterogeneity of BCG strains⁶. BCG was derived from a virulent strain of Mycobacterium bovis through in vitro passaging from 1908-1921. Subsequent worldwide distribution and continuous passaging until the 1960s resulted in a number of BCG substrains. Genetic differences among BCG strains including deletions and duplications of genomic regions and single nucleotide polymorphisms (SNPs) have been well documented^7-12. Whether these differences affect BCG effectiveness against TB is a matter of debate^6,13, and currently there are insufficient data to recommend one particular strain because of the paucity of clinical trials directly comparing multiple BCG strains¹⁴.

Current strategies to improve TB vaccines include the development of subunit and live attenuated vaccines^15,16. However, none of the subunit vaccines have proved to be superior to BCG in animal models. The lack of protective efficacy of MVA85A, the most advanced subunit vaccine, in BCG-vaccinated infants in a recent clinical trial¹⁷ further emphasizes the importance of live vaccine research¹⁸. A number of approaches have been explored to develop live vaccines including the generation of recombinant BCG and attenuated M. tb strains. Of these, only a few have proven to be superior to BCG in animal models including the three live vaccines (rBCG30, VPM1002, and MTBVAC) that have entered clinical trials¹⁶. rBCG30 is a recombinant BCG-Tice strain that overexpresses antigen Ag85B. rBCG30-vaccination of guinea pigs followed by M. tb challenge resulted in a reduction of the bacterial burden by 0.5-1.0 log₁₀ and prolonged survival compared to those immunized with the parental BCG^19,20. However, this effect was specific to BCG-Tice since overexpression of Ag85B in BCG-Connaught did not improve protection²⁰. VPM1002 is a recombinant BCG that expresses listeriolysin of Listeria monocytogenes. The rationale behind this vaccine was the notion that listeriolysin could facilitate phagosomal escape of BCG into the cytosol of macrophages, thereby increasing antigen presentation²¹. BALB/c mice vaccinated with VPM1002 showed a reduction in M. tb burden by 0.5-1.0 log₁₀ compared to the parental strain^21,22; however, this improvement in protection was not observed in the guinea pig model²³. A phoP deletion mutant of M. tb was evaluated as a vaccine candidate with the reasoning that attenuated M. tb may share more antigens with clinical strains of M. tb than BCG²⁴. M. tb ΔphoP provided similar protection as BCG in mice but better protection in guinea pigs against M. tb challenge^24,25. To ensure safety, fadD26 was deleted to further attenuate the strain (MTBVAC), which showed a comparable safety profile to BCG-Pasteur or BCG-Danish in SCID mice²⁶.

SUMMARY OF THE INVENTION

The present invention provides tuberculosis vaccines comprising a recombinant Mycobacterium strain that overexpresses phoP-phoR, a two-component regulatory system. The immunogenicity of current BCG vaccine strains is not sufficient to induce the optimal protection in host against tuberculosis. In contrast, a genetically engineered BCG strain of present invention that overexpresses phoP-phoR is more immunogenic and provides better protection against tuberculosis. Any genetically engineered Mycobacterium that overproduces phoP-phoR at a level sufficient to cause a 2-(or more) fold induction of the PhoP-PhoR regulated genes or proteins may be advantageously used in the practice of this invention. When the recombinant Mycobacterium of the invention is administered to a mammalian host, the production of IFN-γ by CD4⁺ T cells is increased in the host, and this recombinant Mycobacterium provides protection against tuberculosis.

There have been over a dozen studies comparing the immune response induced by different BCG strains in humans^14,27. However, only two or three BCG strains were included in the majority of these studies. Differences in study design such as the choice of BCG strains, age at immunization, and population size have led to inconclusive results¹⁴. Nonetheless, the largest of these studies, which was led by the WHO in the 1970s, compared 11 BCG strains in children²⁸. BCG-Prague was found to be an outlier, exhibiting lower tuberculin reactivity than the other BCG strains, including BCG-Danish, -Pasteur, -Glaxo, -Japan, -Russia, and -Moreau^28,29. Concern over its low immunogenicity resulted in its replacement by BCG-Russia in Czechoslovakia in 1981, after nearly 30 years of use³⁰. Reasons for the low tuberculin reactivity of BCG-Prague remain unknown. However, the inventor found that phoP in BCG-Prague is pseudogene, containing a 1-bp insertion that disrupts the C-terminal DNA-binding domain⁹. This mutation is specific to BCG-Prague since all other BCG strains contain a wild type (WT) phoP. PhoP is a response regulator of the PhoP-PhoR two-component system and positively regulates more than 40 genes in M. tb , including two T cell antigens (Ag85A, PPE18) that have been used to construct subunit vaccines^16,31. As such, the inventor hypothesized that the low immunogenicity of BCG-Prague is a result of phoP mutation⁹, and that overexpression of phoP in BCG may provide an effective means to enhance immunogenicity and therefore protective efficacy. Consistently, the inventor showed in WO2011/130878A1 that complementation of BCG-Prague with WT phoP or overexpression of phoP in BCG-Japan increased IFN-γ production.

The present invention is based on the inventor's discovery that overexpression of phoP-phoR in BCG strain, such as BCG-Japan, enhanced its immunogenicity and protective efficacy, suggesting that this could be a generally applicable approach to improve BCG. It was demonstrated in the present invention that vaccination of C57BL/6 mice with the recombinant strain rBCG-Japan/PhoPR induced higher levels of IFN-γ production by CD4⁺ T cells than that with the parental BCG. Guinea pigs vaccinated with rBCG-Japan/PhoPR were better protected against challenge with Mycobacterium tuberculosis, showing significantly longer survival time, reduced bacterial burdens and less severe pathology, as compared with animals immunized with the parental BCG. Taken together, the recombinant BCG of present invention that overexpresses phoP-phoR has been confirmed to confer enhanced protection against tuberculosis than current BCG.

An exemplary amino acid sequence of PhoP is presented in FIG. 1A [SEQ ID NO:1] and an exemplary nucleotide sequence encoding the same is presented in FIG. 1B [SEQ ID NO:2]. An exemplary amino acid sequence of PhoR is presented in FIG. 1C [SEQ ID NO:3] and an exemplary nucleotide sequence encoding the same is presented in FIG. 1D [SEQ ID NO:4]. These sequences represent PhoP and PhoR from BCG-Pasteur, as presented in the genome sequence available at the Pasteur Institute's Website (http://genodb.pasteur.fr/cgi-bin/WebObjects/GenoList).

The present invention relates to a recombinant Mycobacterium bovis BCG, which overexpresses DNA encoding PhoP [SEQ ID NO:1; SEQ ID NO:2] and PhoR [SEQ ID NO:3; SEQ ID NO:4].

The present invention relates to a recombinant Mycobacterium bovis BCG comprising a nucleic acid capable of overexpression, the nucleic acid encoding PhoP [SEQ ID NO:1; SEQ ID NO:2] and PhoR [SEQ ID NO:3; SEQ ID NO:4].

In one embodiment, the recombinant Mycobacterium bovis-BCG strain is selected from the group consisting of Mycobacterium bovis-BCG-Russia, Mycobacterium bovis-BCG-Moreau, Mycobacterium bovis-BCG-Japan, Mycobacterium bovis-BCG-Sweden, Mycobacterium bovis-BCG-Birkhaug, Mycobacterium bovis-BCG-Prague, Mycobacterium bovis-BCG-Glaxo, Mycobacterium bovis-BCG-Denmark, Mycobacterium bovis-BCG-Tice, Mycobacterium bovis-BCG-Frappier, Mycobacterium bovis-BCG-Connaught, Mycobacterium bovis-BCG-Phipps, Mycobacterium bovis-BCG-Pasteur, and Mycobacterium bovis-BCG-China.

In addition, the recombinant mycobacteria of the invention need not be confined to strains of BCG. Those of skill in the art will recognize that other Mycobacterium strains may also be employed including attenuated strains of M. tb.

In yet another embodiment, the vaccine of the invention may be a subunit or DNA-vaccine. In some embodiments, the vaccine would be delivered via lung pathogens. For example, the DNA sequences coding for PhoP and PhoR could be harbored within the chromosome or extra chromosomal nucleic acid of a lung pathogen such as attenuated Pseudomonas aeruginosa, or other known attenuated fungi or viruses. Alternatively, the nucleic acid encoding PhoP and PhoR regulon could be delivered by other means known to those of skill in the art, e.g., via liposomes, adenoviral vectors, etc.

Another aspect of the invention is a pharmaceutical composition comprising a live recombinant Mycobacterium bovis-BCG strain comprising a nucleic acid capable of overexpression, the nucleic acid encoding PhoP [SEQ ID NO:1; SEQ ID NO:2] and PhoR [SEQ ID NO:3; SEQ ID NO:4].

In a further aspect of the invention there is a vaccine or immunogenic composition for treatment or prophylaxis of a mammal against challenge by mycobacteria comprising a live recombinant Mycobacterium bovis-BCG strain comprising a nucleic acid capable of overexpression, the nucleic acid encoding PhoP [SEQ ID NO:1; SEQ ID NO:2] and PhoR [SEQ ID NO:3; SEQ ID NO:4].

Another aspect of this invention relates to a method for treatment or prophylaxis of a mammal against challenge by Mycobacterium tuberculosis or Mycobacterium bovis comprising administering to the mammal a vaccine or immunogenic composition of the instant invention. In one embodiment the mammal is a cow. In another embodiment the mammal is a human. In yet another embodiment the vaccine or immunogenic composition is administered in the presence of an adjuvant.

A further aspect of the invention is a method for the treatment or prophylaxis of a mammal against cancer comprising administering to the mammal a vaccine or immunogenic composition of the current invention. In one embodiment the cancer is bladder cancer. In another embodiment the vaccine or immunogenic composition is administered in the presence of an adjuvant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows PhoP-PhoR sequences. (a) Amino acid sequence of PhoP of BCG-Pasteur; (b) DNA sequence of phoP of BCG-Pasteur. (c) Amino acid sequence of PhoR of BCG-Pasteur; (d) DNA sequence of phoR of BCG-Pasteur.

FIG. 2 shows the cloning vector pME.

FIG. 3 shows the constructed expression vectors for phoP and phoP-phoR.

FIG. 4 shows that rBCG-Japan/PhoPR induces more IFN-γ production by CD4⁺ T cells than parental BCG.

FIG. 5 shows that rBCG-Japan/PhoPR prolongs the survival of guinea pigs infected with M. tb.

FIG. 6 shows that rBCG-Japan/PhoPR reduces the lung pathology of guinea pigs infected with M. tb.

FIG. 7 shows that rBCG-Japan/PhoPR is safe in SCID mice.

DETAILED DESCRIPTION OF THE INVENTION

Protection against TB requires cell-mediated immunity, which is not fully understood but involves multiple components including CD4⁺ and CD8⁺ T Cells^16,32,33. BCG induces a T helper cell 1 (Th1) type response, mostly IFN-γ production by CD4⁺ T cells³⁴. Traditionally, immunogenicity of BCG was determined by measuring the tuberculin (PPD, purified protein derivatives of M. tb) sensitivity induced by the vaccine in children who were tuberculin-negative before vaccination³⁰. While its use as a surrogate measure of protection has been questioned in recent years^35,36, tuberculin reactivity continues to be used as an in vivo assay for cell-mediated immune response and a marker for immunogenicity^19,37. Supporting this, there is a strong association between tuberculin reactivity and PPD-specific IFN-γ levels in BCG-vaccinated infants³⁸. Further, tuberculin reactivity and IFN-γ production were found to be non-redundant, complementary measures of anti-TB immunity in young people³⁹. Studies in the 1970s found that BCG-Prague consistently exhibited significantly lower tuberculin reactivity in children and guinea pigs than the other 10 BCG strains tested^28,29. Concern over its low immunogenicity resulted in its replacement by BCG-Russia in Czechoslovakia in 1981, after nearly 30 years of use³⁰.

Reasons for the reduced tuberculin reactivity of BCG-Prague are unknown. I hypothesized that the phoP mutation in BCG-Prague discovered in our previous study⁹ contributes to its reduced immunogenicity.

To test this hypothesis, we first complemented BCG-Prague with an intact phoP gene and determined its effect on immunogenicity. The WT phoP gene from BCG-Pasteur was cloned into a multicopy shuttle vector pME and introduced into BCG-Prague (rBCG-Prague/PhoP). C57BL/6 mice were vaccinated with the recombinant BCG-Prague strains and the production of PPD-specific IFN-γ was measured by ELISA. Consistently, rBCG-Prague/PhoP induced higher levels of PPD-specific IFN-γ release in C57BL/6 mice, which was ˜2.4 fold of that in mice immunized with the parental strain (FIG. 4a, p<0.05).

To test if overexpression of phoP can be used as a generally applicable method to improve BCG immunogenicity, we constructed a recombinant BCG overexpressing phoP in another BCG strain, BCG-Japan and generated rBCG-Japan/PhoP. PhoR is a histidine kinase that senses an unknown extracellular signal and phosphorylates PhoP³¹. Since BCG-Japan has an intact phoP phoR which is con-transcribed in its genome, we also generated rBCG-Japan/PhoPR, overexpressing both phoP and phoR to maintain the functional ratio of this two-component system.

Consistent with the results obtained with BCG-Prague, both rBCG-Japan/PhoP and rBCG-Japan/PhoPR induced significantly higher levels of PPD-specific IFN-γ production in C57BL/6 mice than the parental strain (FIG. 4b). Interestingly, among the three strains, rBCG-Japan/PhoPR induced the highest level of IFN-γ.

To determine the source of IFN-γ induced by the recombinant BCG strains, we also performed intracellular cytokine staining and FACS analyses. We found that CD4⁺ T cells were likely responsible for the enhanced IFN-γ release (FIG. 4c). The frequency of IFN-γ producing CD4⁺ T cells in mice vaccinated with rBCG-Japan/PhoPR was ˜3.5 fold of that in mice vaccinated with the parental strain, which is in agreement with the fold difference (˜2.6 fold) of total IFN-γ production between these two groups (FIG. 4b, c).

In contrast, neither recombinant BCG-Japan strain induced a robust CD8⁺ T cell response compared to the sham-immunized control. No significant induction of other cytokines (IL-2, TNF, IL-12, IL-4, IL-5, and IL-10) by the recombinant BCG-Japan strains was detected.

Taken together, these results suggest that the phoP mutation is partially responsible for the low immunogenicity of BCG-Prague. More importantly, overexpression of phoP-phoR in BCG-Japan further boosted IFN-γ production by CD4⁺ T cells, suggesting that this could be a generally applicable approach to enhance the protective efficacy of BCG.

To examine if overexpression of phoP-phoR improves BCG-mediated protection against M. tb infection, we performed a long-term (10 months) guinea pig survival experiment. Guinea pigs (11 per group) were vaccinated with rBCG-Japan/PhoPR, the parental strain, or PBS and were challenged aerogenically with 1,000 CFU/lung of M. tb H37Rv 8 weeks post-vaccination. Guinea pigs were euthanized at the humane end-point and survival curves were plotted using a Kaplan-Meier analysis.

The median survival time for the PBS, the parental, and the rBCG-Japan/PhoPR groups were 18, 27, and 39 weeks, respectively (FIG. 5a). Log-rank analysis revealed that the rBCG-Japan/PhoPR group survived significantly longer than the parental BCG group (p<0.05) and the PBS group (p<0.0001). The parental group also survived significantly longer than the PBS group (p<0.01).

Compared to unvaccinated animals, the parental BCG prolonged the survival of guinea pigs by 9 weeks, while rBCG-Japan/PhoPR prolonged the survival of guinea pigs by 21 weeks (133% improvement over the parental group). At week 43 post-challenge when the experiment was terminated, only one guinea pig in the parental group survived compared to four animals in the rBCG-Japan/PhoPR group. All animals in the PBS group succumbed to infection by week 25.

The guinea pig lungs and spleen were further analyzed after the animals were euthanized at the humane or experimental endpoint. Similar to previous observation, the rBCG-Japan/PhoPR group had ˜1.7 log₁₀ lower M. tb counts in the lungs than the parental BCG group (FIG. 5b, p<0.05). The M. tb burden in the spleen of the rBCG-Japan/PhoPR group was also ˜1.0 log₁₀ lower than the parental BCG group and this difference is approaching significance (p=0.066). Consistently, the rBCG-Japan/PhoPR group had the lowest lung and spleen weights compared to the other two groups (FIG. 5d, e).

The lungs of five animals were subjected to histological analysis. They include one animal from each group that reached the humane endpoint, the sole survivor of the parental group, and one of the four survivors of the rBCG-Japan/PhoPR group at week 43. Interestingly, the mortality of guinea pigs appeared to be associated with the extent of tissue damage in the caudal lobe. The three animals euthanized before the end of experiment had extensive (FIG. 6a) or partial consolidation (FIG. 6b, c) in the caudal lobes in addition to extensive consolidation in the cranial lobes. In contrast, the two survivors appeared to have healthy tissues in the caudal lobe, despite the fact that the one from the parental group also had extensive tissue damage in the cranial lobe (FIG. 6d). Strikingly, the survivor of the rBCG-Japan/PhoPR group appeared to have normal lungs with no visible lung consolidation in either lobe (FIG. 6e).

PhoP is considered a virulence factor of M. tb²⁴ partially because it positively regulates the secretion of EsxA, an important effector of M. tb virulence⁴⁰. As such, it is possible that overexpression of phoP-phoR in BCG may increase virulence and compromise safety. On the other hand, since esxA is part the region of difference 1 (RD1) that is absent in the genomes of all BCG strains¹², the extent to which overexpression of phoP-phoR contributes to BCG virulence remains unclear.

To address this, we first infected SCID mice with the recombinant BCG-Japan strains and monitored bacterial growth in target organs for up to 6 weeks. Interestingly, there was no significant difference between the growth of rBCG-Japan/PhoPR and the parental BCG in the lungs or spleen during the course of the experiment (FIG. 7a, b). However, overexpression of phoP alone increased replication of BCG-Japan in SCID mice compared to both the parental strain and rBCG-Japan/PhoPR.

Next, we performed a long-term SCID mice survival experiment. BCG-Pasteur, which is among the most virulent of the BCG strains⁴¹, was also included in this experiment for comparison. The median survival time of SCID mice infected with BCG-Pasteur, rBCG-Japan/PhoP, and rBCG-Japan/PhoPR were 7, 14, and 19 weeks, respectively (FIG. 7c). All SCID mice infected with the parental strain or PBS survived until week 20 when the experiment was terminated. Log-rank analysis revealed that the rBCG-Japan/PhoP group had significantly reduced survival compared to the rBCG-Japan/PhoPR group (p=0.02) and the parental group (p<0.001), which is consistent with the higher bacterial burdens observed in this group in the short-term infection experiment (FIG. 7a, b). The rBCG-Japan/PhoPR group also showed reduced survival compared to the parental group (p=0.02). Importantly, both rBCG-Japan/PhoPR and rBCG-Japan/PhoP were significantly less virulent than BCG-Pasteur (p<0.001) in SCID mice. Taken together, these results suggest that the overexpression of phoP-phoR in BCG-Japan does not increase its replication in SCID mice and causes only a modest increase in virulence.

Taken together, we demonstrated that recombinant BCG overexpressing phoP-phoR confers enhanced protection against tuberculosis. The superior protection of rBCG-Japan/PhoPR was demonstrated in guinea pigs, evidenced by significantly prolonged survival and reduced pathology, which is a hallmark for testing novel vaccines in animal models. Guinea pigs are the “gold standard” animal model for testing TB vaccine efficacy'. The pathogenesis of disease, pathological lesions and response to BCG vaccination are similar to those described in humans.

There is consensus that novel TB vaccine candidates must meet criteria to advance from the discovery stage into pre-clinical development. These criteria include a robust induction of IFN-γ, better protective efficacy than BCG, and a comparable safety profile to BCG in the established animal models⁴². The rBCG-Japan/PhoPR strain has already satisfied these criteria and thus is a promising candidate for future clinical development.

M. bovis BCG is also used in the treatment of bladder cancer. Numerous randomized controlled clinical trials indicate that intravesical administration of BCG can prevent or delay tumor recurrence⁴³. The details of how BCG exerts this effect remain to be determined. However, the antitumor response requires an intact T-cell response, and involves increased expression of Th1-type cytokines⁴⁴. As such, a BCG strain such as rBCG-Japan/PhoPR demonstrating increased Th1 cytokine IFN-γ may provide enhanced antitumor activity.

In summary, we use recombinant BCG strains that overexpress phoP phoR as vaccines to prevent TB and other mycobacterial infections. These recombinant BCG vaccines induce better protective immunity against tuberculosis.

In the genetically engineered (i.e., recombinant) Mycobacterium of the invention, the PhoP and PhoR proteins are overexpressed, i.e., these two proteins are expressed at a level that exceeds that of a suitable control organism, such as the same Mycobacterium that has not been genetically engineered to overexpress PhoP and PhoR. Those of skill in the art are well acquainted with comparative measurements of protein activity, and with the use of suitable standards and controls for such measurements.

The overexpression of PhoP and PhoR proteins in a Mycobacterium may be carried out by any suitable method known in the art. Generally, the method will involve linking nucleic acid sequences encoding the PhoP and PhoR proteins to expression control sequences that are not, in nature, linked to phoP and phoR genes. Those of skill in the art will recognize that many such expression-control sequences are known and would be suitable for use in the invention. For example, if constitutive expression of phoP and phoR genes is desired, expression-control sequences (e.g., promoters and associated sequences) include but are not limited to: Mycobacterium optimal promoter: hsp65, ace or msp 12 promoter, T7 promoter, etc. Alternatively, overexpression of phoP and phoR may be inducible for example, under the tetracycline inducible promoters.

The proteins, polypeptides or peptides encoded according to the invention include naturally-occurring proteins, polypeptides or peptides, or the homologs thereof which have the same function as naturally-occurring proteins, polypeptides or peptides. Such homologs include proteins, polypeptides or peptides having at least 60%, preferably about 70% or more, 80% or more, and most preferably 90% or more, e.g., 95%, 96%, 97%, 98 or 99% homology to the amino acid sequences of the naturally-occurring proteins, polypeptides or peptides, e.g., to the amino acid sequences shown in SEQ ID NO: 1 and SEQ ID NO:3. Such homologs include proteins, polypeptides or peptides with substitution, addition and deletion of one or more (e.g., 1-50, 1-20, 1-10, 1-5) amino acid residues in the amino acid sequences of the naturally-occurring proteins, polypeptides or peptides (e.g., in the amino acid sequences shown in SEQ ID NO: 1 and SEQ ID NO:3). Such homologs include especially proteins, polypeptides or peptides with conserved amino acid substitution(s).

The term “PhoP” and “PhoR”, as used therein, refer to the two-component regulatory system PhoP-PhoR. PhoP is a response regulator and PhoR is a histidine kinase. PhoP or PhoR encoded according to the invention includes naturally-occurring, functional PhoPs and PhoRs, e.g., from genus Mycobacterium, preferably from Mycobacterium tuberculosis, or Mycobacterium bovis, or the homologs thereof as described above. Exemplary amino acid sequences of PhoP and PhoR are presented in FIG. 1a SEQ ID NO:1 and FIG. 1c SEQ ID NO:3.

The term “overexpress”, “overexpressing” or “overexpression”, as used therein, refers to the protein level of a target gene expressed in a recombinant bacterium is higher than the level of the same protein expressed in the initial bacterium which is not recombinant. For example, the protein of interest expressed in a recombinant bacterium is 1.1, 1.5, 2, 4, 10, 20, 50, 100, 500, 1000 or more fold than a non-recombinant bacterium. The overexpression can be carried out by genetic engineering such as the use of a multiple copy plasmids and/or the use of strong promoters.”

Variations of Nucleic Acid Molecules

Modifications

Many modifications may be made to the nucleic acid molecule DNA sequences disclosed in this application and these will be apparent to one skilled in the art. The invention includes nucleotide modifications of the sequences disclosed in this application (or fragments thereof) that encode proteins or peptides in bacterial or mammalian cells which have the same function as the proteins or peptides disclosed in this application. Modifications include substitution, insertion or deletion of one or more (e.g., 1-50, 1-20, 1-10, 1-5) nucleotides or altering the relative positions or order of one or more (e.g., 1-50, 1-20, 1-10, 1-5) nucleotides.

Nucleic acid molecules may encode conservative amino acid changes in PhoP and PhoR proteins. The invention includes functionally equivalent nucleic acid molecules that encode conservative amino acid changes and produce silent amino acid changes in PhoP and PhoR proteins. Methods for identifying empirically conserved amino acid substitution groups are well known in the art (see for example, Wu, Thomas D. “Discovering Emperically Conserved Amino Acid Substitution Groups in Databases of Protein Families ” (http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8877 523&dopt=Abstract).

Nucleic acid molecules may encode non-conservative amino acid substitutions, additions or deletions in phoP and/or phoR gene. The invention includes functionally equivalent nucleic acid molecules that make non-conservative amino acid changes within the amino acid sequences in PhoP and PhoR proteins. Functionally equivalent nucleic acid molecules include DNA and RNA that encode peptides, peptides and proteins having non-conservative amino acid substitutions (preferably substitution of a chemically similar amino acid), additions, or deletions but which also retain the same or similar function to the PhoP and PhoR proteins or peptides disclosed in this application. The invention includes the DNAs or RNAs encoding fragments or variants of PhoP and PhoR protein.

The fragments are useful as immunogens and in immunogenic compositions.

PhoP and PhoR like-activity of such fragments and variants is identified by assays as described below.

Sequence Identity

The nucleic acid molecules of the invention also include nucleic acid molecules (or a fragment thereof) having at least about: 60% identity, at least 70% identity, at least 80% identity, at least 90% identity, at least 95% identity, at least 96% identity, at least 97% identity, at least 98% identity or, most preferred, at least 99% or 99.5% identity to a nucleic acid molecule of the invention and which are capable of expression of nucleic acid molecules in bacterial or mammalian cells. Identity refers to the similarity of two nucleotide sequences that are aligned so that the highest order match is obtained. Identity is calculated according to methods known in the art. For example, if a nucleotide sequence (called “Sequence A”) has 90% identity to a portion of SEQ ID NO: 2, then Sequence A will be identical to the referenced portion of SEQ ID NO: 2 except that Sequence A may include up to 10 point mutations (such as substitutions with other nucleotides) per each 100 nucleotides of the referenced portion of SEQ ID NO: 2.

Sequence identity (each construct preferably without a coding nucleic acid molecule insert) is preferably set at least about: 70% identity, at least 80% identity, at least 90% identity, at least 95% identity, at least 96% identity, at least 97% identity, at least 98% identity or, most preferred, at least 99% or 99.5% identity to the sequences provided in SEQ ID NO: 2 or its complementary sequence). Sequence identity will preferably be calculated with the GCG program from Bioinformatics (University of Wisconsin). Other programs are also available to calculate sequence identity, such as the Clustal W program (preferably using default parameters; Thompson, J D et al., Nucleic Acid Res. 22:4673-4680), BLAST P, BLAST X algorithms, Mycobacterium avium BLASTN at The Institute for Genomic Research (http:tigrblast.tigr.org/), Mycobacterium bovis, M. bovis BCG (Pastuer), M. marinum, M. leprae, M. tuberculosis BLASTN at the Wellcome Trust Sanger Institute (http://www.sanger.ac.uk/Projects/Microbes/), M. tuberculosis BLAST searches at Institute Pasterur (Tuberculist) (http://genolist.pasteur.fr/TubercuList/), M. leprae BLAST searches at Institute Pasteur (Leproma) (http://genolist.pasteur.fr/Leproma/), M. paratuberculosis BLASTN at Microbial Genome Project, University of Minnesota (http://www.cbc.umn.edu/ResearchProjects/Ptb/ and http://www.cbc.umn.edu/ResearchProjects/AGAC/Mptb/Mptbhome.html), various BLAST searches at the National Center for Biotechnology Information—USA (http://www.ncbi.nlm.nih.gov/BLAST/) and various BLAST searches at GenomeNet (Bioinformatics Center—Institute for Chemical Research) (http://blast.genome.ad.jp/).

Since the genetic code is degenerate, the nucleic acid sequences in SEQ ID NO:2 and SEQ ID NO:4 are not the only sequences which may code for a polypeptide having PhoP and PhoR activities. This invention includes nucleic acid molecules that have the same essential genetic information as the nucleic acid molecules described in SEQ ID NO:2 and SEQ ID NO:4. Nucleic acid molecules (including RNA) having one or more nucleic acid changes compared to the sequences described in this application and which result in production of the polypeptides shown in SEQ ID NO:1 and SEQ ID NO:3 are within the scope of the invention.

Other functional equivalent forms of PhoP and PhoR proteins-encoding nucleic acids can be isolated using conventional DNA-DNA or DNA-RNA hybridization techniques.

Hybridization

The invention includes DNA that has a sequence with sufficient identity to a nucleic acid molecule described in this application to hybridize under stringent hybridization conditions (hybridization techniques are well known in the art). The present invention also includes nucleic acid molecules that hybridize to one or more of the sequences in [SEQ ID NO:2] and SEQ ID NO:4 or their complementary sequences. Such nucleic acid molecules preferably hybridize under high stringency conditions (see Sambrook et al. Molecular Cloning: A Laboratory Manual, Most Recent Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.). High stringency washes have preferably low salt (preferably about 0.2% SSC) and a temperature of about 50-65° C.

Vaccines

One skilled in the art knows the preparation of live recombinant vaccines. Typically, such vaccines are prepared as injectable, either as liquid solutions or suspensions; solid forms suitable for solution in, or suspension in, liquid prior to injection may also be prepared. The preparation may also be emulsified, or the protein encapsulated in liposomes. The live immunogenic ingredients are often mixed with excipients that are pharmaceutically acceptable and compatible with the active ingredient. Suitable excipients are, for example, water, saline, dextrose, glycerol, ethanol, or the like and combinations thereof. In addition, if desired, the vaccine may contain minor amounts of auxiliary substances such as wetting or emulsifying agents, pH buffering agents, and/or adjuvants that enhance the effectiveness of the vaccine. Examples of adjuvants which may be effective include but are not limited to: aluminum hydroxide, N-acetyl-muramyl-L-threonyl-D-isoglutamine (thr-MDP), N-acetyl-nor-muramyl-L-alanyl-D-isoglutamine (CGP 11637, referred to as nor-MDP), N-acetylmuramyl-L-alanyl-D-isoglutaminyl-L-alanine-2-(1′-2′-dipalmitoyl-sn -glycero-3-hydroxyphosphoryloxy)-ethylamine (CGP 19835A, referred to as MTP-PE), and RIBI, which contains three components extracted from bacteria, monophosphoryl lipid A, trehalose dimycolate and cell wall skeleton (MPL+TDM+CWS) in a 2% squalene/Tween 80™ emulsion.

The effectiveness of an adjuvant may be determined by measuring the amount of antibodies directed against an immunogenic polypeptide containing a Mycobacterium tuberculosis antigenic sequence resulting from administration of the live recombinant Mycobacterium bovis-BCG vaccines that are also comprised of the various adjuvants.

The vaccines are conventionally administered parenterally, by injection, for example, either subcutaneously or intramuscularly. Additional formulations which are suitable for other modes of administration include suppositories and, in some cases, oral formulations. For suppositories, traditional binders and carriers may include, for example, polyalkylene glycols or triglycerides; such suppositories may be formed from mixtures containing the active ingredient in the range of 0.5% to 10%, preferably 1%-2%. Oral formulations include such normally employed excipients as, for example, pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate, and the like. These compositions take the form of solutions, suspensions, tablets, pills, capsules, sustained release formulations or powders and contain 10%-95% of active ingredient, preferably 25%-70%.

The vaccines are administered in a manner compatible with the dosage formulation, and in such amount as will be prophylactically and/or therapeutically effective.

The vaccine may be given in a single dose schedule, or preferably in a multiple dose schedule. A multiple dose schedule is one in which a primary course of vaccination may be with 1-10 separate doses, followed by other doses given at subsequent time intervals required to maintain and or reinforce the immune response, for example, at 1-4 months for a second dose, and if needed, a subsequent dose(s) after several months. The dosage regimen will also, at least in part, be determined by the need of the individual and be dependent upon the judgment of the practitioner.

In addition, the live recombinant Mycobacterium bovis-BCG vaccine administered in conjunction with other immuneregulatory agents, for example, immune globulins.

A subject of the present invention is also a multivalent vaccine formula comprising, as a mixture or to be mixed, a live recombinant Mycobacterium bovis-BCG vaccine as defined above with another vaccine, and in particular another recombinant live recombinant Mycobacterium bovis-BCG vaccine as defined above, these vaccines comprising different inserted sequences.

Pharmaceutical Compositions

The pharmaceutical compositions of this invention are used for the treatment or prophylaxis of a mammal against challenge by Mycobacterium tuberculosis or Mycobacterium bovis. The pharmaceutical compositions of this invention are also used to treat patients having degenerative diseases, disorders or abnormal physical states such as cancer.

The pharmaceutical compositions can be administered to humans or animals by methods such as tablets, aerosol administration, intratracheal instillation and intravenous injection.

EXAMPLES

Example 1: Cloning Vector pME

A kanamycin resistant shuttle vector which contains a T7 promoter was obtained as follows. The pDrive cloning vector (obtained from Qiagen) was cut with EcoRI and self-ligated to generate pDRI. The pDRI was digested with SspI and the 1903 bp fragment product was isolated. The pMD31 shuttle vector (Wu et al., 1993, Molecular Microbiology, 7, 407-417) was digested with SspI and the 3379 bp fragment was isolated. The two SspI generated fragments were ligated to generate pME (5282 bp), which contains the original T7 promoter of the pDRIVE. The cloning vector pME is shown in FIG. 2.

Example 2: Construction of Expression Vectors for phoP and phoP-phoR

An 1028 bp product containing phoP as well as the 257 bp upstream region of the phoP translational start site was amplified by PCR using a forward primer phoP-F (5′- AAAAAGGTACCGCTTGTTTGGCCATGTCAAC-3′ (SEQ ID NO:5)) and a reverse primer phoP-R (5′-AAAAACTGCAGGCTGCCGATCCGATTAACTAC-3′ (SEQ ID NO: 6)) which contain a KpnI and a PstI restriction site (underlined), respectively. Using these restriction sites, the PCR product was ligated to a shuttle vector pME (pME-PhoP). Similarly, a vector which expresses the phoP-phoR operon (pME-PhoPR) was constructed by cloning a 2501 bp PCR product—containing phoP and phoR (as well as the intergenic region between the two genes, 177 bp upstream of the phoP start codon, and 78 bp downstream of phoR stop codon)—into pME. This product was amplified by PCR from BCG-Pasteur genomic DNA using forward primer phoPR-F (5′-AAAAAGGTACCGGTCGCAATACCCACGAG-3′ (SEQ ID NO: 7)) and reverse primer phoPR-R (5′-AAAAACTGCAGCCTCAGTGATTTCGGCTTTG-3′ (SEQ ID NO: 8)) containing a KpnI and a PstI site (underlined), respectively. The constructs were confirmed by DNA sequencing.

The constructs as well as the empty vector pME were electroporated separately into BCG-Prague and BCG-Japan. Generation of a recombinant BCG was accomplished as follows: Cells of M. bovis BCG-Japan (ATCC 35737) and M. bovis BCG-Prague (ATCC 35742) were transformed with plasmid pME-PhoP or pME-PhoPR by electroporation, and electroporated cells were plated onto 7H11 media plates supplemented with 10% OADC (Difco) and 25 μg/ml of kanamycin. After 4 weeks of incubation at 37° C., individual colonies were selected and grown in 7H9 liquid media supplemented with 10% ADC (Difco) plus 25 μg/ml of kanamycin. After culturing for 3 weeks in this media, plasmid DNA from the selected clones was isolated and confirmed by DNA sequencing. Frozen stocks of recombinant BCG strains were subsequently made by mixing 1 ml of culture with 1 ml of 50% sterile glycerol solution and stored at −80° C.

The constructed expression vectors for phoP and phoP-phoR are shown in FIG. 3.

Example 3: rBCG-Japan/PhoPR Induces More IFN-γ Production by CD4⁺ T Cells than Parental BCG

Female C57BL/6 mice were purchased from Charles River Laboratories and were age-matched (6 weeks) within each experiment. Four mice per group were inoculated subcutaneously on the scruff of the neck with approximately 5×10⁴ CFU in 0.2 ml PBS/0.01% Tween 80 of BCG strains. Control mice were given 0.2 mL of PBS/0.01% Tween 80. After 8 weeks, mice were euthanized, splenocytes were isolated. Quantitative measurements of IFN-γ production was determined using an enzyme-linked immunosorbant assay (ELISA) using the OptEIA Mouse IFN-γ ELISA set (BD Biosciences). Samples used for ELISAs were supernatants from splenocytes stimulated by PPD (10 μg/ml) for 72 hours. Briefly, samples were added in triplicate to 96-well, flat-bottomed plates (Nunc MaxiSorp) pre-coated with capture antibody and measurements were carried out following the manufacturer's protocol. The absorbance was read at 450 nm on a microplate reader (TECAN infinite M200). IFN-γ levels were calculated based on a standard curve generated using an IFN-γ standard. The results are shown in FIGS. 4a and 4b. Data are shown as mean±SEM, after subtraction of reading from samples without PPD stimulation. In FIG. 4a, the two-tailed unpaired student t-test was performed; in FIG. 4b, One-way ANOVA and Bonferroni multiple comparison tests were performed. *p<0.05, **p<0.01, ***p<0.001.

To determine the source of IFN-γ induced by the recombinant BCG strains, we also performed intracellular cytokine staining and FACS analyses. Briefly, splenocytes were seeded at 2×10⁶ cells/well in 100 μl in triplicate and stimulated with 2.5 μg/well of purified protein derivative (PPD) (Statens Serum Institute, Denmark) or complete RPMI (cRPMI; RPMI/10% FBS/1% L-glutamine/1% penicillin/streptomycin) as a control and incubated at 37° C. and 5% CO₂. After 19 hours of stimulation, GolgiPlug (BD Biosciences) was added in a 1:1000 final dilution and incubated for an additional 5 hours. After a total of 24 hours stimulation, plates were centrifuged at 1400 rpm for 5 minutes at 4° C. The supernatant was removed and the cell pellet was washed in 200 μl FACS Buffer (0.5% BSA/PBS), and resuspended in Fc Block (eBiosciences) diluted in FACS Buffer (1:400) and incubated for 15 minutes on ice in the dark. An additional 150 μl of FACS Buffer was added, mixed, and plates were centrifuged at 1400 rpm for 5 minutes at 4° C. Supernatant was removed and cells were stained for extracellular T cell surface markers: CD3-PE, CD4-FITC, and CD8a-PercyPCy5.5 (BD Biosciences) diluted in FACS Buffer, and incubated for 30 minutes on ice in the dark. Following extracellular marker staining, the cells were washed with 150 μl FACS Buffer and permeabilized and fixed with 1× CytoFix/CytoPerm (BD Biosciences) for 20 minutes. Cells were then washed with 1× PermWash (BD Biosciences) and incubated with IFN-γ-APC (BD Biosciences) for 30 minutes to stain for intracellular IFN-γ. Cells were centrifuged as above, resuspended in 200 μl FACS Buffer, and analyzed on a BD FACSCalibur™ flow cytometer (BD Biosciences). A total of 300 000 events per sample were collected in the lymphocyte gate and analyzed using FlowJo V7.6. Gates for analysis were set based on isotype controls. Data are shown as mean±SEM, after subtraction of reading from samples without PPD stimulation. The result is shown in FIG. 4c, and one-way ANOVA and Bonferroni multiple comparison tests were performed for statistical analysis. *p<0.05, **p<0.01, ***p<0.001.

Example 4: rBCG-Japan/PhoPR Prolongs the Survival of Guinea Pies Infected with M. tb

Groups of 11 female Hartely guinea pigs (200-250 g) were purchased from Charles River Laboratories, and they were vaccinated subcutaneously with 5×10⁴ CFU of BCG-Japan containing pME (rBCG-Japan/pME), pME-PhoPR (rBCG-Japan/PhoPR) in 0.2 ml PBS/0.01% Tween80 or PBS/0.01% Tween80 alone as a control. At eight weeks post-vaccination, guinea pigs were challenged with 1,000 CFU of M. tb H37Rv by an aerosol route using a GlasCol nebulizer. Guinea pigs were euthanized at the humane end-point and survival curves were plotted using the Kaplan-Meier method. The result is shown in FIG. 5a. Log-rank test was performed to compare each pair of the survival curves. *p<0.05, **p<0.01, ***p<0.0001.

The lungs and spleen of guinea pigs euthanized at the humane end-point were harvested. The spleen and the entire right lung were homogenized separately and plated on 7H11 agar to quantify the M. tb burden in each organ. Colonies were counted after incubation at 37° C. for three weeks. The results are shown in FIGS. 5b and 5c. The organ weights of all animals in each group were measured and the results are shown in FIGS. 5d and 5e. Data in FIGS. 5b to 5e are shown as mean±SEM, and One-way ANOVA and Bonferroni multiple comparison tests were performed. *p<0.05, **p<0.01, ***p<0.001.

Example 5: rBCG-Japan/PhoPR Reduces the Lung Pathology of Guinea Pies Infected with M. tb

Six guinea pigs from the experiment described in FIG. 4 were chosen for histology analysis. These include one guinea pig from each group that reached the humane endpoint at weeks 25, 27, and 39, respectively (FIGS. 6a to 6c). The pME (FIG. 6b) and PhoPR (FIG. 6c) guinea pigs represent the sixth animal to be euthanized from each group (median). The sole survivor of the pME group (FIG. 6d) and one randomly chosen survivor of the PhoPR group (FIG. 6e) were included. For each guinea pig, sections of caudal and cranial lobes of the left lungs were analyzed by hematoxylin-eosin staining. Briefly, formalin-fixed tissues were embedded into paraffin blocks. Serial sections (5 μm thick) were prepared and they went through deparafinization process with three changes of xylene (3 minutes each) before being rehydrated with four washes of alcohol (100%, 100%, 95%, 70%, 3 minutes each). Sections were stained with hematoxylin and eosin (EMD Chemicals) and examined using Cytation™ 5 (BioTek).

Example 6: rBCG-Japan/PhoPR is Safe in SCID Mice

Short-term bacterial burden assay: Female Fox Chase CB17 SCID mice (Charles River Laboratories) were age-matched (7 weeks old). Groups of 12 mice were infected intravenously via a lateral tail vein with 10⁵ CFU of rBCG-Japan/pME, rBCG-Japan/ PhoP, or rBCG-Japan/PhoPR in 0.2 mL of PBS/0.01% Tween80 or PBS/0.01% Tween80 alone as a control. At weeks 1, 3, and 6 post-infection, mice (n=4 at each time point) were euthanized and the lungs and spleen were harvested, homogenized in PBS, and plated on 7H11 agar to determine bacterial burden in the lungs (FIG. 7a) and spleen (FIG. 7b). Data are showed as mean±SD. Two-Way ANOVA and Bonferroni multiple comparison tests were performed. *p<0.05, **p<0.01, ***p<0.001.

Long term survival assay: Groups of ten age-matched female SCID mice (7 weeks old) from Charles River Laboratories were infected intravenously via a lateral tail vein with 10⁷ CFU of BCG-Pasteur, three aforementioned recombinant BCG-Japan strains or PBS/0.01% Tween80 as described above. Three mice from each group were euthanized at day 1 post-infection (for assessing infection dose) while the remaining mice were monitored weekly until they reached a humane endpoint (loss of 20% maximal body weight). Survival curves were plotted using the Kaplan-Meier method. The results are shown in FIG. 7c. Log-rank test was performed to compare each pair of the survival curves. *p<0.05, ***p<0.001.

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Claims

1. A live recombinant Mycobacterium bovis-BCG strain comprising nucleic acids capable of overexpression and overexpressing both PhoP and PhoR proteins, the recombinant Mycobacterium bovis-BCG strain having improved immunogenicity compared to wild type nonrecombinant Mycobacterium bovis-BCG strain, the recombinant Mycobacterium bovis-BCG strain having virulence comparable with wild type nonrecombinant Mycobacterium bovis-BCG strain, and the recombinant Mycobacterium bovis-BCG strain having a decreased virulence compared to recombinant Mycobacterium bovis-BCG strain overexpressing only PhoP.

2. The live recombinant Mycobacterium bovis-BCG strain of claim 1, wherein the PhoP and PhoR proteins are from Mycobacterium tuberculosis or Mycobacterium bovis.

3. The live recombinant Mycobacterium bovis-BCG strain of claim 1, wherein the nucleic acids encode (i) the amino acid sequence shown in SEQ ID NO: 1; or(ii) a PhoP protein with the substitution, addition, or deletion of one or more amino acids in the amino acid sequence shown in SEQ ID NO: 1; or p1 (iii) the amino acid sequence shown in SEQ ID NO: 3; or(iv) a PhoR protein with the substitution, addition, or deletion of one or more amino acids in the amino acid sequence shown in SEQ ID NO: 3.

4. The live recombinant Mycobacterium bovis-BCG strain of claim 1, wherein the nucleic acids comprise (i) the nucleotide sequence shown in SEQ ID NO: 2; or(ii) a sequence that hybridizes to the nucleotide sequence of (i) under a stringent hybridization condition; or(iii) a sequence having at least 60% sequence identity to the nucleotide sequence shown in SEQ ID NO: 2; or(iv) the nucleotide sequence shown in SEQ ID NO: 4; or(v) a sequence that hybridizes to the nucleotide sequence of (iv) under a stringent hybridization condition; or(vi) a sequence having at least 60% sequence identity to the nucleotide sequence shown in SEQ ID NO: 4.

5. The live recombinant Mycobacterium bovis-BCG strain of claim 1 wherein the nucleic acid molecule has undergone modification.

6. The live recombinant Mycobacterium bovis-BCG strain of claim 1 wherein the Mycobacterium bovis-BCG strain is selected from Mycobacterium bovis-BCG-Russia (ATCC number: 35740), Mycobacterium bovis-BCG-Moreau (ATCC number: 35736), Mycobacterium bovis-BCG-Japan (ATCC number: 35737), Mycobacterium bovis-BCG-Sweden (ATCC number: 35732), Mycobacterium bovis-BCG-Birkhaug (ATCC number: 35731), Mycobacterium bovis-BCG-Prague (ATCC number: 35742), Mycobacterium bovis-BCG-Glaxo (ATCC number: 35741), Mycobacterium bovis-BCG-Denmark (ATCC number: 35733), Mycobacterium bovis-BCG-Tice (ATCC numbers: 35743, 27289), Mycobacterium bovis-BCG-Frappier (ATCC: 35746, SM-R; ATCC: 35747, INH-R), Mycobacterium bovis-BCG-Connaught (ATCC: 35745) , Mycobacterium bovis-BCG-Phipps (ATCC number: 35744), Mycobacterium bovis-BCG-Pasteur (ATCC number: 35734), BCG-Mexican (ATCC number: 35738) and Mycobacterium bovis-BCG-China (Shanghai Institute of Biological Product).

7. A pharmaceutical composition comprising the live recombinant Mycobacterium bovis-BCG strain of claim 1.

8. The recombinant Mycobacterium bovis-BCG strain of claim 1, wherein the PhoR of the recombinant Mycobacterium bovis-BCG strain is overexpressed by at least 10 fold as compared to an amount of PhoR expressed in the wild type nonrecombinant Mycobacterium bovis-BCG strain.

9. The recombinant Mycobacterium bovis-BCG strain of claim 1, wherein the PhoP of the recombinant Mycobacterium bovis-BCG strain is overexpressed by at least 10 fold as compared to an amount of PhoP expressed in the wild type nonrecombinant Mycobacterium bovis-BCG strain.