Patent Application
20150224188
Throughout this application various publications are referred to by number in parentheses. Full citations for the references may be found at the end of the specification. The disclosures of each of these publications, and also the disclosures of all patents, patent application publications and books recited herein, are hereby incorporated by reference in their entirety into the subject application to more fully describe the art to which the subject invention pertains.
Mycobacterium tuberculosis, the causative agent of Tuberculosis (TB), remains a leading human pathogen and tuberculosis is a major health problem in the developing world. In 2010 there were 8.8 million incident cases of TB, 1.1 million deaths from TB among HIV-negative people and an additional 0.35 million deaths from HIV-associated TB (1). Efforts to control the disease include the development of “point-of-care” tests, new TB drugs, the use of the Bacillus Calmette-Guerin (BCG) vaccine and the development of new vaccines. Most of the new vaccine candidates against TB that have entered in clinical trials fall into one of the following groups: (I) live attenuated vaccines to replace BCG; (II) subunit vaccines to be given on after initial BCG vaccination (2); and (III) single immunodominant antigens, usually secreted, such as ESAT-6, Cfp10 and Ag85b (2).
Bacterial pathogens have developed different secretion systems to release their products to the extracellular environment, tissues or bloodstream of the host organism (3). Some microorganisms including bacteria and fungi use membrane vesicles (MVs), to release a complex group of proteins, polysaccharides and lipids into the extracellular milieu (3-7). Both pathogenic and nonpathogenic species bacteria secrete vesicles consistent with the notion that they are means by which bacteria interact with prokaryotic and eukaryotic cells in their environment (3). Typically, vesicles from pathogenic bacteria contain virulence factors including toxins, adhesins or immunomodulatory compounds. The packaging of virulence factors in vesicles allows microorganisms to deliver host cell damaging materials in a concentrated manner. This laboratory has recently demonstrated the production of MVs in many mycobacterium species, including the medically important BCG and Mtb (7). It was shown that mycobacterial MVs transport lipids and proteins previously known to be involved in the subversion of the immune response of the host. In addition, it has been demonstrated that these vesicles trigger an inflammatory response in a TLR2 dependent manner that directly modulates the outcome of the interaction with the host, contributing to virulence and pathogenesis in Mtb infection (7).
Despite the intimate connection between bacterial vesicles and virulence, they have also been used as a vaccine, eliciting immune responses that protect against mucosal and systemic bacterial infections such as Neisseria meningitidis (8), Bordetella pertussis (9), Salmonella typhimurium (10), Vibrio chloerae (11) and Bacillus anthracis (12). Artificially produced membrane vesicles from the gram-negative bacteria N. meningitidis constitute the basis of one the few licensed vesicle-based vaccines (VA-MENGOC-BCTM) (13). Recently, the immune response to artificial membrane vesicles from M. smegmatis was tested in mice, showing cross-reactivity against Mtb antigens (14).
The present invention address the need for improved vaccines and vaccination methods for tuberculosis.
This invention provides a composition comprising a plurality of isolated mycobacterium membrane vesicles.
The invention also provides a method of eliciting an immune response in a subject comprising administering to the subject any of the vesicle compositions described herein an amount effective to elicit an immune response.
The invention also provides a method of improving the efficacy of an anti-mycobacterial immunization administered to a subject, comprising administering to the subject any of the compositions described herein in an amount effective to improve efficacy of an anti-mycobacterial immunization administered to a subject.
The invention also provides a method of immunizing a subject against tuberculosis comprising administering to the subject an amount of any of the instant compositions in an amount effective to immunize a subject against tuberculosis.
Also provided is a composition comprising a plurality of isolated bacterium membrane vesicles isolated from a pathogenic bacterium that produces membrane vesicles. In an embodiment, the composition further comprises an immunological adjuvant. In an embodiment, the composition further comprises a pharmaceutically acceptable carrier.
Also provided is a method of eliciting an immune response in a subject comprising administering to the subject any of the instant compositions in an amount effective to elicit an immune response.
Also provided is a method of preparing an isolated mycobacterium membrane vesicles preparation comprising centrifuging a culture of mycobacterium and treating the resultant product so as to remove live mycobacteria and recover the vesicles, thereby preparing the isolated mycobacterium membrane vesicles preparation.
Additional objects of the invention will be apparent from the description which follows.
This invention provides a composition comprising a plurality of isolated mycobacterium membrane vesicles.
As used herein, “isolated” means not as existing in the natural state or not as existing in the natural environment. For example, a plurality of mycobacterium membrane vesicles recovered and suspended in a sterile carrier is not a natural state or natural environment. In an embodiment, the composition is synthetic in that it does not occur in nature.
In an embodiment, the composition further comprises an immunological adjuvant. In an embodiment, the composition further comprises a pharmacologically acceptable carrier. In an embodiment, the composition is sterile in not containing live bacteria.
In an embodiment, the composition comprises purified mycobacterium membrane vesicles.
In an embodiment, the composition is a vaccine for inducing an immune response against the mycobacterium in a mammal. In an embodiment, the composition is a vaccine adjuvant for enhancing or modulating an immune response against the mycobacterium when used with a vaccine against the mycobacterium in a mammal.
In a preferred embodiment, the isolated mycobacterium membrane vesicles are M. tuberculosis membrane vesicles. In an embodiment, the mycobacterium is an H37Rv strain M. tuberculosis.
In an embodiment, the isolated mycobacterium membrane vesicles are M. bovis Bacille Calmette Guerin (BCG) Pasteur membrane vesicles. In an embodiment, the isolated mycobacterium membrane vesicles are from Mycobacterium avium, Mycobacterium bovis, Mycobacterium diphtheria, Mycobacterium intracellulare, Mycobacterium leprae, Mycobacterium lepraemurium, Mycobacterium phlei, Mycobacterium smegmatis, Mycobacterium fortuitum, Mycobacterium lufu, Mycobacterium paratuberculosis, Mycobacterium habana, Mycobacterium scrofulacium, or Mycobacterium kansasii.
In an embodiment, the composition further comprises a tuberculosis vaccine active agent. The active agent may be a mycobacterium, for example an attenuated mycobacterium, or a mycobacterium subunit, for example of a M. tuberculosis. In an embodiment, the active agent is an H1 or H4 subunit vaccine or comprises Ag85B antigen. In an embodiment, the tuberculosis vaccine active agent is a M. bovis BCG Pasteur, or a portion thereof.
The invention also provides a method of eliciting an immune response in a subject comprising administering to the subject any of the vesicle compositions described herein an amount effective to elicit an immune response. In an embodiment, the immune response comprises a Th1 response.
The invention also provides a method of improving the efficacy of an anti-mycobacterial immunization administered to a subject, comprising administering to the subject any of the compositions described herein in an amount effective to improve efficacy of an anti-mycobacterial immunization administered to a subject.
In an embodiment, the anti-mycobacterial immunization is an anti-tuberculosis immunization. In an embodiment, the tuberculosis vaccine active agent is a M. tuberculosis BCG Pasteur, or a portion thereof. In an embodiment, the composition is administered to the subject via the same route as the anti-mycobacterial immunization is administered. In an embodiment, the composition is administered subcutaneously.
The invention also provides a method of immunizing a subject against tuberculosis comprising administering to the subject an amount of any of the instant compositions in an amount effective to immunize a subject against tuberculosis.
In an embodiment, the subject is immunocompromised. In an embodiment, the composition is administered subcutaneously.
Also provided is a composition comprising a plurality of isolated bacterium membrane vesicles isolated from a pathogenic bacterium that produces membrane vesicles. In an embodiment, the composition further comprises an immunological adjuvant. In an embodiment, the composition further comprises a pharmaceutically acceptable carrier.
Also provided is a method of eliciting an immune response in a subject comprising administering to the subject any of the instant compositions in an amount effective to elicit an immune response.
Also provided is a method of preparing an isolated mycobacterium membrane vesicles preparation comprising centrifuging a culture of mycobacterium and treating the resultant product so as to remove live mycobacteria and recover the vesicles, thereby preparing the isolated mycobacterium membrane vesicles preparation. In an embodiment, the isolated mycobacterium membrane vesicles are M. tuberculosis membrane vesicles. In an embodiment, the isolated mycobacterium membrane vesicles are purified. In an embodiment, the isolated mycobacterium membrane vesicles are admixed with a pharmaceutically acceptable carrier.
In an embodiment, the isolated mycobacterium membrane vesicles are M. bovis Bacille Calmette Guerin (BCG) Pasteur membrane vesicles. In an embodiment, the isolated mycobacterium membrane vesicles are from Mycobacterium avium, Mycobacterium bovis, Mycobacterium diphtheria, Mycobacterium intracellulare, Mycobacterium leprae, Mycobacterium lepraemurium, Mycobacterium phlei, Mycobacterium smegmatis, Mycobacterium fortuitum, Mycobacterium lufu, Mycobacterium paratuberculosis, Mycobacterium habana, Mycobacterium scrofulacium, or Mycobacterium kansasii. In an embodiment, the mycobacterium is an H37Rv strain M. tuberculosis.
In an embodiment of the inventions described herein, the mycobacterium vesicles are mycobacterium tuberculosis vesicles, and the mycobacterium tuberculosis is one of the following: Mycobacterium tuberculosis H37Rv, BTB05-552, BTB05-559, CDC1551, CTRI-2, F11, H37, H37Ra, HN878, KZN 1435, KZN 4207, KZN R506, KZN V2475, R1207, RGTB327, S96-129, X122, ‘98-R604 INH-RIF-EM’, 02—1987, 210, 94_M4241A, C, CDC1551A, CPHL_A, CTRI-4, EAS054, GM 1503, K85, KZN 605, OSDD071, OSDD504, OSDD518, SUMu001, SUMu002, SUMu003, SUMu004, SUMu005, SUMu006, SUMu007, SUMu008, SUMu009, SUMu010, SUMu011, SUMu012, T17, T46, T85, T92, W-148, str. Haarlem, 210—16C2—24C1, 210—16C2—24C2, 210—32C4, 210—4C15, 210—4C15—16C1, 210—4C15—16C1—48C1, 210—4C15—16C1—48C2, 210—4C15—16C1—56C1, 210—4C15—16C1—56C2, 210—4C31, 210—4C31—16C1, 210—4C31—16C1—24C1, 210—4C31—16C1—40C1, 210—4C31—16C2, 210—8C1, 210—8C6, BC, CTRI-3, H37Rv—2009, NJT210GTG, str. Erdman=ATCC 35801, str. Erdman WHO, CCDC5079, CCDC5180, RGTB423, UT205, CTRI-1, H37RvAE, H37RvCO, H37RvHA, H37RvJO, H37RvLP, H37RvMA, LAM7, NCGM2209, RGTB306, WX1, WX3, XDR1219, XDR1221, str. Beijing/W BT1, or str. Erdman (ATCC 35801). In a preferred embodiment, the mutant is a mutant of M. tuberculosis H37Rv strain.
In an embodiment, wherein the composition is intended for administration to a subject, the composition can further comprise an immunological adjuvant. Immunological adjuvants encompassed within the compositions and methods of the invention are widely known in the art and include alum, other aluminum salts (e.g. aluminum phosphate and aluminum hydroxide) and squalene. Other immunological adjuvants encompassed within the compositions and methods of the invention include the compounds QS21 and MF59. In an embodiment, the composition is vaccine. In an embodiment, the vaccine comprises a live attenuated mycobacterium. In an embodiment, the vaccine comprises a portion of a mycobacterium but does not comprise the whole of the mycobacterium. In an embodiment, the vaccine comprises a pharmaceutically acceptable carrier. In an embodiment, the vaccine further comprises an immunological adjuvant.
Any of the compositions of the invention can be used to evoke an immune response in a subject. In an embodiment, administration of a composition of the invention, or the isolated mycobacteria membrane vesicles of the invention, is used to elicit an immune response in the subject. In an embodiment, the eliciting an immune response in a subject is effected by a method comprising administering to the subject the composition or isolated mycobacterium vesicles in an amount effective to elicit an immune response.
In a preferred embodiment of the mutants, compositions and methods of the invention, the mutant is a mutant M. tuberculosis H37Rv strain. For H37Rv genome, see NCBI Reference Sequence: NC—000962.2, see GenBank: AL123456.2.
The methods disclosed herein involving subjects can be used with any species capable of being infected by mycobacteria, preferably M. Tuberculosis. In a preferred embodiment, the subject is a mammalian subject. Most preferably, the mammal is a human.
All combinations of the various elements described herein are within the scope of the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
This invention will be better understood from the Experimental Details, which follow. However, one skilled in the art will readily appreciate that the specific methods and results discussed are merely illustrative of the invention as described more fully in the claims that follow thereafter.
Here, it was investigated whether systemic administration of MV preparations could induce protective immune against an Mtb pulmonary infection. It is demonstrated that systemic administration of isolated mycobacterial vesicles elicits a protective response protection against an Mtb aerosol infection.
Mycobacterial culture: Mycobacteria (Mycobacterium bovis Bacillus Calmette-Guerin (BCG, Pasteur strain), M. tuberculosis strains H37Rv (Mtb) and M. smegmatis) were grown in a minimal medium (MM) consisting of KH2PO4 1 g/l, Na2HPO4 2.5 g/l, asparagine 0.5 g/l, ferric ammonium citrate 50 mg/l, MgSO4×7 H2O 0.5 g/l, CaCl2 0.5 mg/l, ZnSO4 0.1 mg/l, with or without Tyloxapol 0.05% (v/v), containing 0.1% (v/v) glycerol, pH 7.0. The M. bovis BCG strain lacking the 19 kDa protein (D19) was a gift from D. Young. This strain was grown in the presence of 50 μg/ml of hygromicin. Cultures were grown for up to 10 days for slow growers and 4 days for fast growers in roller bottles at 37° C. In some experiments as stated, cultures were grown in Middlebrook 7H9 medium (M7H9) supplemented with 10% (v/v) OADC enrichment (Becton Dickinson Microbiology Systems, Spark, Md.), 0.5% (v/v) glycerol and with or without Tyloxapol 0.05% (v/v; Sigma). M. tuberculosis H37Rv subcellular fractions were prepared as described (15).
Vesicle isolation and purification: Vesicles were isolated as described (7). Briefly, cells were pelleted (3,450 g for 15 min, 4° C.) from 1000 ml cultures and the supernatants were filtered through a 0.45-mm-pore size polyvinylidene difluoride filter (Millipore, Billerica, Mass.). The supernatant volumes were then concentrated approximately 20-fold using an Amicon (Millipore) ultrafiltration system with a 100 kDa exclusion filter. The concentrate was then sequentially centrifuged at 4,000 and 15,000 g (15 min, 4° C.) to remove cell debris and aggregates and the remaining supernatant was then centrifuged at 100,000 g for 1 h at 4° C. to sediment the vesicular fraction into a pellet. The supernatant was then discarded, the pellet was suspended in 1 ml of 10 mM HEPES, 0.15 M NaCl and mixed with 2 ml of Optiprep solution (Sigma) in 10 mM HEPES and 0.15 M NaCl (yielding 35% (w/v) Optiprep final concentration). The crude vesicle sample was then overlaid with a series of Optiprep gradient layers with concentrations ranging from 30-5% (w/v). The gradients were centrifuged (100,000×g, 16 h) and 1 ml fractions were removed from the top. The fractions were then dialyzed separately in PBS overnight and again recovered by sedimentation at 100,000×g for 1 h. Finally, the vesicles were suspended in LPS-free PBS. Vesicles quantitation was performed using the BCA protein assay (Thermo Scientific, Rockford, Ill.).
Immunizations and Mtb challenge: Six to 8-week-old female wild type (C57BL/6) mice were purchased from the National Cancer Institute (NCI, Frederick, Md.). All mice were maintained in specific pathogen-free conditions, and were transferred to biosafety level 3 conditions for infection with M. tuberculosis. All procedures involving the use of animals were in compliance with protocols approved by the Albert Einstein College of Medicine Institutional Animal Use and Biosafety Committees. BCG cultures were grown to mid-log phase, washed, suspended in PBS+0.05% Tyloxapol (PBS/T) and sonicated before infection. Mice were vaccinated with BCG subcutaneously (SC) at the scruff of the neck with 1×106 CFU in 100 μl for four or eight weeks. Approximately 2.5 micrograms of vesicles were administered per mouse intraperitoneally (IP) or subcutaneously (SC) in a final volume of 200 μl PBS. In the boosting experiments the vesicles were given on top of BCG after 4 weeks IP or SC. For aerosol challenge with Mtb, a low-density freezer stock of H37Rv was grown in 7H9 liquid medium to an A600 of 0.4-0.8. 2×106 CFU ml−1 of bacteria in PBS/T plus 0.04% (vol/vol) Antifoam Y-30 (Sigma) was placed in a nebulizer attached to an airborne infection system (University of Wisconsin Mechanical Engineering Workshop). Mice were exposed to aerosol for 40 min, during which approximately 100 bacteria were deposited in the lungs of each animal. Tissue bacterial loads in tissues for aerosol infections were determined by plating organ homogenates onto 7H11 agar OADC plates. Colonies were counted after 21 d of incubation at 37° C.
ELISA: Vaccinated mice were bled by an orbital bleed. Serum was collected by centrifugation at 10,000×g for 20 min and stored at −20° C. until use. Serum reactivity was measured by ELISA against a whole cell lysate preparation of Mtb. ELISA plates (96 wells) were coated with 20 μg ml−1 Mtb lysate in PBS and incubated at 37° C. for 1 h and then blocked in PBS+3% BSA for 1 h at 37° C. or overnight at 4° C. Wells were washed three times in PBS with 0.05% (PBS/T) Tween-20 and then incubated with a 1:300 diluted mouse serum for 1 h at 37° C. After washing three times with PBS/T wells were incubated with an alkaline-phosphatase conjugated goat antibody to mouse immunoglobulin G (Southern biotechnologies) for 1 h at 37° C. Color was developed with p-nitrophenyl phosphate. The titer was defined as the dilution of sera resulting in an A405 2 times greater than the background.
Immunoblot: Serum reactivity against an Mtb lysate was also tested by immunobloting (16). To find the identity of the 19 kDa band, serum reactivity was also measured against a whole cell lysate preparation of a Δ19 kDa mutant strain of BCG. Electrophoresis was done with a 12% resolving gel at 100 V. Gels were transferred to nitrocellulose membranes, which were then blocked overnight in a buffer containing 5% milk in PBS with 0.1% Tween 20. Individual channels on a blotting frame were incubated with diluted serum (1:400) sera for 1 h at room temperature or overnight at 4° C. Channels were washed three times with blocking buffer and then incubated with a horseradish peroxidase-conjugated goat antibody to mouse immunoglobulin G (Sigma) for 1 h at RT. Membranes were developed using luminol (Pierce).
IFNγ ELISPOT assay: Splenocytes were cultured in ELISPOT plates (1×106/well; Millipore, Danvers, Mass.) coated with IFNγ capture antibody (clone R4.6A2; BD Biosciences). Mtb sonicate (BEI Resources, VA) was added (20 μg/ml) and plates were for 24 h at 37° C. After removal of cells, plates were washed with PBS followed by PBS with 0.05% Tween 20 (PBST). Biotinylated anti-IFNγ detection antibody (clone 4S.B3; BD Biosciences) was added for 2 h at 37° C., followed by washing with PBST. Streptavidin-alkaline phosphatase (Sigma-Aldrich) was added to the plates for 1 h (37° C.), followed by washing and addition of BCIP/NBT substrate (Sigma-Aldrich). The reaction was stopped by washing the wells with water, and spots were counted using an ELISPOT reader (Autoimmun Diagnostika, Strasberg, Germany).
Intracellular cytokine analysis: For analysis of cytokine-producing CD4+ T and CD8+ T cells, spleen cell suspensions were isolated and placed in 96-well plates in RPMI-1640 with 10% FCS. The samples were stimulated with 10 μg ml−1 a whole cell lysate Mtb preparation (BEI Resources, VA) plate-bound monoclonal antibody to mouse CD3ε (clone 145-2C11), with unstimulated wells serving as negative controls. Samples were combined with 1 μg ml−1 soluble antibody to mouse CD28 (clone 37.51). After 2 h at 37° C., 10 μg ml−1 of Brefeldin-A (Sigma) was added to all samples, followed by incubation for 4 h. Cells were stained with Blue LIVE/DEAD viability dye (Invitrogen) followed by antibody to FcγRI/III (clone 2.4G2; American Type Culture Collection), with fluorochrome-conjugated monoclonal antibodies for surface staining: antibody to CD3ε (clone 145-2C11; eBioscience), antibody to CD44 (clone IM7; eBioscience), antibody to CD8α (clone 53-6.7; BD Bioscience) and antibody to CD4 (clone GK1.5; BD Bioscience). Cells were fixed with 2% (vol/vol) paraformaldehyde, washed with permeabilization buffer (PBS with 1 mM Ca2+, 1 mM Mg2+, 1 mM HEPES, 2% (vol/vol) FCS and 0.1% (wt/vol) saponin) and then blocked in permeabilization buffer plus 5% (vol/vol) normal mouse serum (Jackson ImmunoResearch Laboratories). Intracellular cytokines were detected with fluorochrome-conjugated antibodies to IL-2 (clone JES6-5H4; eBioscience), IFN-γ (clone XMG1.2) and TNF-α (MP6-XT22) (both from BD Biosciences). Data were acquired on an LSR II flow cytometer (BD Biosciences), and data analysis was performed using FlowJo software (Tree Star).
Histology: Lungs and spleens were removed and fixed in 10% neutral buffered formalin (Fisher Scientific, Fair Lawn, N.J.). Tissues were embedded with paraffin, sectioned at 5 μm thickness, and stained with hematoxylin and eosin and by Kinyoun's acid fast (AF) stain. Area of lung lesions was calculated in Image J and expressed as percentage of total lung area. Five different lung sections per mouse were counted.
In an attempt to characterize the immune response, if any, of MVs in mice we immunized C57BL/6 mice with 2.5 μg of BCG, H37Rv and M. smegmatis MVs (based on protein concentration) intraperitoneally (IP) with no adjuvant. After 30 d the serum antibody response was measured by ELISA against a whole cell Mtb lysate (
Since lipoproteins are located at the mycobacterial cell membrane (18), and MVs originate primarily from this cellular compartment (7), antibodies from BCG or H37Rv MVs immunized sera should preferentially recognize the membrane fraction of M. tuberculosis. When ELISA was performed on plates coated with a mycobacterium membrane fractions the measured serum titers were significantly greater (
Mycobacteria MVs induce a high Th1 response: A T helper type 1 (Th1) cell response is crucial in protective immunity to many intracellular pathogens and Th1-polarized responses play an important role in the control of Mtb infection (19). As above, mice were immunized with a single dose of 2.5 μg of BCG, H37Rv or M. smegmatis MVs via IP and total T cell responses on ex vivo Mtb sonicate-stimulated spleens were studied by IFNγ ELISPOT at day 30. Among the MVs tested, the H37Rv MVs triggered the highest T cell response, being two-fold higher than that elicited by BCG MVs and almost on 1.5-fold that observed with BCG immunization (
Next, it was investigated whether the splenic responses obtained upon MVs stimulation were also biased for the mycobacterial membrane fraction, as occurred with antibody responses. Since there was not access to specific vesicle associated antigens like the lipoproteins 19 kDa or LprG, it was not practical to dissect T cell responses as done with antibodies (
Next, the multifunctionality of the CD4+ T cell in response in MVs-immunized mice was examined Mice were immunized as above and cytokine production by splenic CD4+ T cells was analyzed at day 30. Upon re-stimulation in vitro with an Mtb sonicate, a substantial increase in INFγ, TNFα and IL-2 production was observed between naive and BCG or MVs-immunized mice with no remarkable differences (
Mycobacterial vesicles induce protective immune responses in mice: To test the protective efficacy of MV, mice were immunized with 2.5 μg of BCG MVs via IP. Mice were challenged 4 weeks later with a low dose (50-100 bacilli) of Mtb via aerosol and CFUs were determined at 4 weeks after infection in lungs and spleens. For controls mice were vaccinated with either one million of bacilli of BCG Pasteur strain or sham (PBS) immunized. It was found that immunization of mice with BCG MVs without adjuvant was associated with marked reductions in lung CFUs comparable to those of mice immunized with BCG (
Boosting BCG vaccine with mycobacterial vesicles: the ability of mycobacterial MVs to boost BCG vaccine was investigated. Consequently, BCG vaccinated mice were boosted at 2 months with a single dose of BCG, H37Rv and M. smegmatis MVs and after two weeks Mtb-specific antibodies and T cell responses were analyzed in serum and spleen, respectively. The response was compared to that of mice vaccinated with BCG alone for three months and sham (PBS) vaccinated mice. A low antibody response including IgM and IgG1 was detected in serum of BCG-vaccinated mice (
As in single vesicle stimulation experiments (
BCG or H37Rv MVs boosting increased 1.5-fold the number of Mtb specific splenic T cells compared to BCG vaccinated mice (
Four weeks after boosting with BCG MVs mice were challenged with a low dose of Mtb via aerosol and lung and spleen mycobacterial counts were enumerated 4 weeks after challenge. All mice in the BCG-vaccinated groups had significantly fewer bacilli in the lungs than the control mice (1.12±0.04 log 10 CFU reduction, P<0.001). BCG MVs-boosted mice had slightly lower bacterial counts than the BCG-vaccinated mice (1.24±0.08 log 10 CFU reduction, P<0.001) (
In agreement with these results, the lung histological analysis showed a marked reduction in inflammation between PBS and BCG or BCG MVs-vaccinated mice (
The elucidation of the M. tuberculosis genome highlighted a remarkable capacity for lipid biosynthesis (20). Subsequent studies have shown that many genes involved in lipid biosynthesis are essential for virulence in animal models. Recently, two independent groups have described the Mtb lipidome using high resolution mass spectrometry (21, 22). Despite these advances, little is known about the mechanisms by which Mtb release lipids to the extracellular milieu. This laboratory has recently shown that M. tuberculosis, and other mycobacterial strains, including the vaccine strain BCG and the environmental strain M. smegmatis, produce membrane vesicles that are released to the extracellular space (7). Remarkably, only vesicles from the virulent strains are enriched in lipoproteins, which are well known TLR2 agonists involved in modulation of host immune response (17). Lipid analysis indicated prevalence for polar lipids, consistent with origin from the cellular membrane. Intratracheal administration of vesicles to mice followed by aerosol challenge resulted in an increase of bacterial burden in the lungs (7), suggesting a Koch phenomenon where an immune response to the vesicles in the lung worsened the outcome of infection. The contribution of bacterial vesicles to virulence has been demonstrated for other bacterial pathogens, including B. anthracis (12), N. meningitidis (23), E. coli (3) or P. aeruginosa (3). However, when these vesicles were tested as vaccine preparations and administered systemically they elicited immune responses that were associated with significant protection. Moreover, the immune response of bacterial MVs-based vaccines neutralizes bacterial toxins or is directed to the bacteria surface and membrane antigens, promoting bacterial opsonization and complement-mediate killing.
In this report, isolated MVs from three mycobacterial strains: BCG, H37Rv M. tuberculosis and M. smegmatis were studies as an anti-tuberculosis vaccine. Both antibodies and T cells appeared to be responsible for the protective efficacy of BCG and H37Rv MVs. Furthermore, antibodies were preferentially produced to membrane compounds, and specifically to lipoproteins LprG and LpqH, suggesting that they may determine the mycobacterial MVs antigenicity. Enhanced antibody reactivity to a mycobacterial membrane fraction confirmed this hypothesis. Moreover, when antigenicity of serum BCG vaccinated mice was tested, a unique band, possibly corresponding to LprG, was detected, indicating that lipoproteins strongly determine antigenicity in the current anti-tuberculosis vaccine. Interestingly, a global analysis of antibody response to Mtb reported that LprG is among the most reactive proteins (24). M. tuberculosis uses lipoproteins such as LpqH or LprG to inhibit antigen processing and presentation, induce proinflammatory or inhibitory cytokines, and control of costimulatory molecule expression in APCs leading to the modulation of T cell function (17, 25, 26). Thus, it is believed that specific antibodies produced upon mycobacterial MVs vaccination may interact with lipoproteins inactivating or neutralizing their immunomodulatory effect. Interestingly, LprG and LpqH were recently shown to activate and module CD4+T cells effector functions in a TLR2 dependent manner, independently from antigen presenting cells, suggesting that M. tuberculosis lipoproteins can regulate adaptive immunity not only by inducing cytokine secretion and costimulatory molecules in innate immune cells but also through directly regulating the activation T lymphocytes (27). Moreover, this finding indicates that mycobacterial MVs can serve as an adjuvant since these molecules directly enhance CD4+ T cell memory responses. Recently, some mycobacterial lipids associated to MVs, such as PIM2 or PIM6, were used as an adjuvant showing their capacity to modulate the immune response and efficacy of a protective vaccine against M. bovis infection (28)
The enhanced splenic T cell responses, including higher total T cell responses and increased levels of multifunctional T cells of MVs-vaccinated mice, indicate that they may also contribute to the protection efficacy. In agreement with antibody studies responses were also enhanced after stimulation with M. tuberculosis membrane and cell wall fractions. The protective host response to mycobacterial infection is believed to be mainly mediated by a cell-based immunity (29). On the other hand, antibody responses are generally believed to have no protective role (30) despite considerable evidence that protective antibodies can be generated against M. tuberculosis and that B cells contribute to host protection (31-33). Remarkably, most of the current subunit vaccines in clinical trials are composed of immunodominant antigens like ESAT-6, Ag85b, and Ag85A, each of which have been shown to produce mixed humoral and cellular responses (34-37).
The necessity of a long-term protection in anti-tuberculosis vaccines is likely to be an important quality to prevent reactivation of latent infection. This does not seem to be the case for BCG MVs using the present scheme of immunization and mice may require several doses to keep the immunization status to control the infection, as it is true for most of the subunit vaccines (34-37). On the other hand, immunization with a single dose of H37Rv MVs promoted containment of bacilli in lungs at later time points. Although BCG and H37Rv MVs have a similar protein composition (7), subtle differences may determine their differential contribution to protection. Consistently, a differential recognition for LprG and LpqH was found between these two sets of MVs. It is also noted that this immune response was obtained with MVs preparations alone without the presence of adjuvant Ongoing experiments including multiple doses and co-administration with adjuvants will elucidate the potential capacity of MVs to enhance the current vaccine BCG.
The fact that almost 80% of the current pre-exposure vaccines in clinical trials are subunit booster vaccines to be given on top of an initial BCG prime suggests the necessity of improving the immune response triggered by BCG (2). Analysis of the immune response of BCG vaccinated and MVs-boosted mice showed an increase in antibody titers and the levels of all CD4+ T cells producing single and multiple cytokines increase in BCG and H37Rv boosted mice. Although BCG MVs administration did not reach a higher level of protection when given on top of a BCG vaccine at 4 weeks, their administration did not worsen the previously established immune response. However, re-stimulation with H37Rv MVs promoted a more robust protective efficacy at later time points after challenge. These observations indicate that MVs preparations have considerable promise as vaccine components alone and/or in combination with BCG. This study shows mycobacterial MVs as an alternative vaccine to BCG in protection against Mtb in mice. This is first effective anti-tuberculosis vaccine containing lipoproteins.
Immunol 27:393-422.
This application claims benefit of U.S. Provisional Application No. 61/704,874, filed Sep. 24, 2012, the contents of which are hereby incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US13/61120 | 9/23/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61704874 | Sep 2012 | US |
