Effects of Cross-Presentation, Antigen Processing, and Peptide Binding in HIV Evasion of T Cell Immunity.

Unlike cytosolic processing and presentation of viral Ags by virus-infected cells, Ags first expressed in infected nonprofessional APCs, such as CD4+ T cells in the case of HIV, are taken up by dendritic cells and cross-presented. This generally requires entry through the endocytic pathway, where endosomal proteases have first access for processing. Thus, understanding virus escape during cross-presentation requires an understanding of resistance to endosomal proteases, such as cathepsin S (CatS). We have modified HIV-1MN gp120 by mutating a key CatS cleavage site (Thr322Thr323) in the V3 loop of the immunodominant epitope IGPGRAFYTT to IGPGRAFYVV to prevent digestion. We found this mutation to facilitate cross-presentation and provide evidence from MHC binding and X-ray crystallographic structural studies that this results from preservation of the epitope rather than an increased epitope affinity for the MHC class I molecule. In contrast, when the protein is expressed by a vaccinia virus in the cytosol, the wild-type protein is immunogenic without this mutation. These proof-of-concept results show that a virus like HIV, infecting predominantly nonprofessional presenting cells, can escape T cell recognition by incorporating a CatS cleavage site that leads to destruction of an immunodominant epitope when the Ag undergoes endosomal cross-presentation.

Paradoxical myeloid-derived suppressor cell reduction in the bone marrow of SIV chronically infected macaques.

Myeloid derived suppressor cells (MDSCs), which suppress anti-tumor or anti-viral immune responses, are expanded in the peripheral blood and tissues of patients/animals with cancer or viral infectious diseases. We here show that in chronic SIV infection of Indian rhesus macaques, the frequency of MDSCs in the bone marrow (BM) was paradoxically and unexpectedly decreased, but increased in peripheral blood. Reduction of BM MDSCs was found in both CD14+MDSC and Lin-CD15+MDSC subsets. The reduction of MDSCs correlated with high plasma viral loads and low CD4+ T cell counts, suggesting that depletion of BM MDSCs was associated with SIV/AIDS disease progression. Of note, in SHIVSF162P4-infected macaques, which naturally control viral replication within a few months of infection, the frequency of MDSCs in the bone marrow was unchanged. To investigate the mechanisms by which BM MDSCs were reduced during chronic SIV infection, we tested several hypotheses: depletion due to viral infection, alterations in MDSC trafficking, and/or poor MDSC replenishment. We found that the possible mobilization of MDSCs from BM to peripheral tissues and the slow self-replenishment of MDSCs in the BM, along with the viral infection-induced depletion, all contribute to the observed BM MDSC reduction. We first demonstrate MDSC SIV infection in vivo. Correlation between BM CD14+MDSC reduction and CD8+ T cell activation in tissues is consistent with decreased immune suppression by MDSCs. Thus, depletion of BM MDSCs may contribute to the pathologic immune activation during chronic SIV infection and by extension HIV infection.

Low Antigen Dose in Adjuvant-Based Vaccination Selectively Induces CD4 T Cells with Enhanced Functional Avidity and Protective Efficacy.

T cells with high functional avidity can sense and respond to low levels of cognate Ag, a characteristic that is associated with more potent responses against tumors and many infections, including HIV. Although an important determinant of T cell efficacy, it has proven difficult to selectively induce T cells of high functional avidity through vaccination. Attempts to induce high-avidity T cells by low-dose in vivo vaccination failed because this strategy simply gave no response. Instead, selective induction of high-avidity T cells has required in vitro culturing of specific T cells with low Ag concentrations. In this study, we combined low vaccine Ag doses with a novel potent cationic liposomal adjuvant, cationic adjuvant formulation 09, consisting of dimethyldioctadecylammonium liposomes incorporating two immunomodulators (monomycolyl glycerol analog and polyinosinic-polycytidylic acid) that efficiently induces CD4 Th cells, as well as cross-primes CD8 CTL responses. We show that vaccination with low Ag dose selectively primes CD4 T cells of higher functional avidity, whereas CD8 T cell functional avidity was unrelated to vaccine dose in mice. Importantly, CD4 T cells of higher functional avidity induced by low-dose vaccinations showed higher cytokine release per cell and lower inhibitory receptor expression (PD-1, CTLA-4, and the apoptosis-inducing Fas death receptor) compared with their lower-avidity CD4 counterparts. Notably, increased functional CD4 T cell avidity improved antiviral efficacy of CD8 T cells. These data suggest that potent adjuvants, such as cationic adjuvant formulation 09, render low-dose vaccination a feasible and promising approach for generating high-avidity T cells through vaccination.

Difference in TB10.4 T-cell epitope recognition following immunization with recombinant TB10.4, BCG or infection with Mycobacterium tuberculosis.

Most novel vaccines against infectious diseases are based on recombinant Ag; however, only few studies have compared Ag-specific immune responses induced by natural infection with that induced by the same Ag in a recombinant form. Here, we studied the epitope recognition pattern of the tuberculosis vaccine Ag, TB10.4, in a recombinant form, or when expressed by the pathogen Mycobacterium tuberculosis (M.tb), or by the current anti-tuberculosis vaccine, Mycobacterium bovis BCG. We showed that BCG and M.tb induced a similar CD4+ T-cell specific TB10.4 epitope-pattern, which differed completely from that induced by recombinant TB10.4. This difference was not due to post-translational modifications of TB10.4 or because TB10.4 is secreted from BCG and M.tb as a complex with Rv0287. In addition, BCG and TB10.4/CAF01 were both taken up by DC and macrophages in vivo, and in vitro uptake experiments revealed that both TB10.4 and BCG were transported to Lamp+-compartments. BCG and TB10.4 however, were directed to different types of Lamp+-compartments in the same APC, which may lead to different epitope recognition patterns. In conclusion, we show that different vectors can induce completely different recognition of the same protein.

Rescuing ESAT-6 Specific CD4 T Cells From Terminal Differentiation Is Critical for Long-Term Control of Murine Mtb Infection.

In most cases, Mycobacterium tuberculosis (Mtb) causes life-long chronic infections, which poses unique challenges for the immune system. Most of the current tuberculosis (TB) subunit vaccines incorporate immunodominant antigens and at this point, it is poorly understood how the CD4 T cell subsets recognizing these antigens are affected during long-term infection. Very little is known about the requirements for sustainable vaccine protection against TB. To explore this, we screened 62 human-recognized Mtb antigens during chronic murine Mtb infection and identified the four most immunodominant antigens in this setting (MPT70, Rv3020c, and Rv3019c and ESAT-6). Combined into a subunit vaccine, this fusion protein induced robust protection both in a standard short-term model and in a long-term infection model where immunity from BCG waned. Importantly, replacement of ESAT-6 with another ESAT-6-family antigen, Rv1198, led to similar short-term protection but a complete loss of bacterial control during chronic infection. This observation was further underscored, as the ESAT-6 containing vaccine mediated sustainable protection in a model of post-exposure vaccination, where the ESAT-6-replacement vaccine did not. An individual comparison of the CD4 T cell responses during Mtb infection revealed that ESAT-6-specific T cells were more terminally differentiated than the other immunodominant antigens and immunization with the ESAT-6 containing vaccine led to substantially greater reduction in the overall T cell differentiation status. Our data therefore associates long-term bacterial control with the ability of a vaccine to rescue infection-driven CD4T cell differentiation and future TB antigen discovery programs should focus on identifying antigens with the highest accompanying T cell differentiation, like ESAT-6. This also highlights the importance of long-term readouts in both preclinical and clinical studies with TB vaccines.

The effect of antigen dose on T cell-targeting vaccine outcome.

During the past 3-4 decades, an increasing amount of evidence has pointed to the complex role of the antigen dose or T cell receptor (TCR) stimulation strength on the subsequent type, duration and "flavor" or quality of the response. Antigen dose was initially shown to impact Th1/Th2 bias, and later also shown to differentially affect development and induction of Tregs, Th17, T-follicular helper (Tfh), cells, and others. In recent years the quality of both CD4/8 T cells during infections, cancer and/or autoimmunity has turned out to be critical for subsequent disease outcome. Importantly, different vaccination strategies also lead to different types of T cell responses, and the role of the antigen dose is emerging as an important factor as well as a tool for investigators to utilize in fine-tuning vaccine efficacy. This commentary will highlight essential background of how antigen dose can impact and affect the quality of T cell responses, and discuss how this translates in different vaccine settings.

High Antigen Dose Is Detrimental to Post-Exposure Vaccine Protection against Tuberculosis.

Mycobacterium tuberculosis (Mtb), the etiologic agent of tuberculosis (TB), causes 1.8M deaths annually. The current vaccine, BCG, has failed to eradicate TB leaving 25% of the world's population with latent Mtb infection (LTBI), and 5-10% of these people will reactivate and develop active TB. An efficient therapeutic vaccine targeting LTBI could have an enormous impact on global TB incidence, and could be an important aid in fighting multidrug resistance, which is increasing globally. Here we show in a mouse model using the H56 (Ag85B-ESAT-6-Rv2660) TB vaccine candidate that post-exposure, but not preventive, vaccine protection requires low vaccine antigen doses for optimal protection. Loss of protection from high dose post-exposure vaccination was not associated with a loss of overall vaccine response magnitude, but rather with greater differentiation and lower functional avidity of vaccine-specific CD4 T cells. High vaccine antigen dose also led to a decreased ability of vaccine-specific CD4 T cells to home into the Mtb-infected lung parenchyma, a recently discovered important feature of T cell protection in mice. These results underscore the importance of T cell quality rather than magnitude in TB-vaccine protection, and the significant role that antigen dosing plays in vaccine-mediated protection.

Lack of the programmed death-1 receptor renders host susceptible to enteric microbial infection through impairing the production of the mucosal natural killer cell effector molecules.

The programmed death-1 receptor is expressed on a wide range of immune effector cells, including T cells, natural killer T cells, dendritic cells, macrophages, and natural killer cells. In malignancies and chronic viral infections, increased expression of programmed death-1 by T cells is generally associated with a poor prognosis. However, its role in early host microbial defense at the intestinal mucosa is not well understood. We report that programmed death-1 expression is increased on conventional natural killer cells but not on CD4(+), CD8(+) or natural killer T cells, or CD11b(+) or CD11c(+) macrophages or dendritic cells after infection with the mouse pathogen Citrobacter rodentium. Mice genetically deficient in programmed death-1 or treated with anti-programmed death-1 antibody were more susceptible to acute enteric and systemic infection with Citrobacter rodentium. Wild-type but not programmed death-1-deficient mice infected with Citrobacter rodentium showed significantly increased expression of the conventional mucosal NK cell effector molecules granzyme B and perforin. In contrast, natural killer cells from programmed death-1-deficient mice had impaired expression of those mediators. Consistent with programmed death-1 being important for intracellular expression of natural killer cell effector molecules, mice depleted of natural killer cells and perforin-deficient mice manifested increased susceptibility to acute enteric infection with Citrobacter rodentium. Our findings suggest that increased programmed death-1 signaling pathway expression by conventional natural killer cells promotes host protection at the intestinal mucosa during acute infection with a bacterial gut pathogen by enhancing the expression and production of important effectors of natural killer cell function.

Testing the H56 Vaccine Delivered in 4 Different Adjuvants as a BCG-Booster in a Non-Human Primate Model of Tuberculosis.

The search for new and improved tuberculosis (TB) vaccines has focused on IFN-γ both for selecting antigens and for evaluating vaccine delivery strategies. The essential role of IFN-γ in endogenous host protection is well established, but it is still uncertain whether this also holds true for vaccine protection. Here we evaluate the H56 fusion protein vaccine as a BCG booster in a non-human primate (NHP) model of TB that closely recapitulates human TB pathogenesis. To date, only a handful of novel adjuvants have been tested in the NHP model of TB, and therefore we administered H56 in 3 novel cationic liposome adjuvants of increasing immunogenicity (CAF01, CAF04, CAF05) and compared them to H56 in the IC31® adjuvant previously reported to promote protection in this model. The individual clinical parameters monitored during infection (weight, ESR, X-ray) all correlated with survival, and boosting BCG with H56 in all adjuvants resulted in better survival rates compared to BCG alone. The adjuvants promoted IFN-γ-responses of increasing intensity as measured by ELISPOT in the peripheral blood, but the level of vaccine-specific IFN-γ production did not correlate with or predict disease outcome. This study's main outcome underscores the importance of the choice of adjuvant for TB subunit vaccines, and secondly it highlights the need for better correlates of protection in preclinical models of TB.

Different human vaccine adjuvants promote distinct antigen-independent immunological signatures tailored to different pathogens.

The majority of vaccine candidates in clinical development are highly purified proteins and peptides relying on adjuvants to enhance and/or direct immune responses. Despite the acknowledged need for novel adjuvants, there are still very few adjuvants in licensed human vaccines. A vast number of adjuvants have been tested pre-clinically using different experimental conditions, rendering it impossible to directly compare their activity. We performed a head-to-head comparison of five different adjuvants Alum, MF59®, GLA-SE, IC31® and CAF01 in mice and combined these with antigens from M. tuberculosis, influenza, and chlamydia to test immune-profiles and efficacy in infection models using standardized protocols. Regardless of antigen, each adjuvant had a unique immunological signature suggesting that the adjuvants have potential for different disease targets. Alum increased antibody titers; MF59® induced strong antibody and IL-5 responses; GLA-SE induced antibodies and Th1; CAF01 showed a mixed Th1/Th17 profile and IC31® induced strong Th1 responses. MF59® and GLA-SE were strong inducers of influenza HI titers while CAF01, GLA-SE and IC31® enhanced protection to TB and chlamydia. Importantly, this is the first extensive attempt to categorize clinical-grade adjuvants based on their immune profiles and protective efficacy to inform a rational development of next generation vaccines for human use.

Comparing adjuvanted H28 and modified vaccinia virus ankara expressingH28 in a mouse and a non-human primate tuberculosis model.

Here we report for the first time on the immunogenicity and protective efficacy of a vaccine strategy involving the adjuvanted fusion protein "H28" (consisting of Ag85B-TB10.4-Rv2660c) and Modified Vaccinia Virus Ankara expressing H28. We show that a heterologous prime-boost regimen involving priming with H28 in a Th1 adjuvant followed by boosting with H28 expressed by MVA (H28/MVA28) induced the highest percentage of IFN-γ expressing T cells, the highest production of IFN-γ per single cell and the highest induction of CD8 T cells compared to either of the vaccines given alone. In contrast, in mice vaccinated with adjuvanted recombinant H28 alone (H28/H28) we observed the highest production of IL-2 per single cell and the highest frequency of antigen specific TNF-α/IL-2 expressing CD4 T cells pre and post infection. Interestingly, TNF-α/IL-2 expressing central memory-like CD4 T cells showed a significant positive correlation with protection at week 6 post infection, whereas the opposite was observed for post infection CD4 T cells producing only IFN-γ. Moreover, as a BCG booster vaccine in a clinically relevant non-human primate TB model, the H28/H28 vaccine strategy induced a slightly more prominent reduction of clinical disease and pathology for up to one year post infection compared to H28/MVA28. Taken together, our data showed that the adjuvanted subunit and MVA strategies led to different T cell subset combinations pre and post infection and that TNF-α/IL-2 double producing but not IFN-γ single producing CD4 T cell subsets correlated with protection in the mouse TB model. Moreover, our data demonstrated that the H28 vaccine antigen was able to induce strong protection in both a mouse and a non-human primate TB model.

The HyVac4 subunit vaccine efficiently boosts BCG-primed anti-mycobacterial protective immunity.

BACKGROUND: The current vaccine against tuberculosis (TB), BCG, has failed to control TB worldwide and the protective efficacy is moreover limited to 10-15 years. A vaccine that could efficiently boost a BCG-induced immune response and thus prolong protective immunity would therefore have a significant impact on the global TB-burden. METHODS/FINDINGS: In the present study we show that the fusion protein HyVac4 (H4), consisting of the mycobacterial antigens Ag85B and TB10.4, given in the adjuvant IC31® or DDA/MPL effectively boosted and prolonged immunity induced by BCG, leading to improved protection against infection with virulent M. tuberculosis (M.tb). Increased protection correlated with an increased percentage of TB10.4 specific IFNγ/TNFα/IL-2 or TNFα/IL-2 producing CD4 T cells at the site of infection. Moreover, this vaccine strategy did not compromise the use of ESAT-6 as an accurate correlate of disease development/vaccine efficacy. Indeed both CD4 and CD8 ESAT-6 specific T cells showed significant correlation with bacterial levels. CONCLUSIONS/SIGNIFICANCE: H4-IC31® can efficiently boost BCG-primed immunity leading to an increased protective anti-M.tb immune response dominated by IFNγ/TNFα/IL-2 or TNFα/IL2 producing CD4 T cells. H4 in the CD4 T cell inducing adjuvant IC31® is presently in clinical trials.

A multistage tuberculosis vaccine that confers efficient protection before and after exposure.

All tuberculosis vaccines currently in clinical trials are designed as prophylactic vaccines based on early expressed antigens. We have developed a multistage vaccination strategy in which the early antigens Ag85B and 6-kDa early secretory antigenic target (ESAT-6) are combined with the latency-associated protein Rv2660c (H56 vaccine). In CB6F1 mice we show that Rv2660c is stably expressed in late stages of infection despite an overall reduced transcription. The H56 vaccine promotes a T cell response against all protein components that is characterized by a high proportion of polyfunctional CD4(+) T cells. In three different pre-exposure mouse models, H56 confers protective immunity characterized by a more efficient containment of late-stage infection than the Ag85B-ESAT6 vaccine (H1) and BCG. In two mouse models of latent tuberculosis, we show that H56 vaccination after exposure is able to control reactivation and significantly lower the bacterial load compared to adjuvant control mice.

Distinct differences in the expansion and phenotype of TB10.4 specific CD8 and CD4 T cells after infection with Mycobacterium tuberculosis.

BACKGROUND: Recently we and others have identified CD8 and CD4 T cell epitopes within the highly expressed M. tuberculosis protein TB10.4. This has enabled, for the first time, a comparative study of the dynamics and function of CD4 and CD8 T cells specific for epitopes within the same protein in various stages of TB infection. METHODS AND FINDINGS: We focused on T cells directed to two epitopes in TB10.4; the MHC class I restricted epitope TB10.4 (3-11) (CD8/10.4 T cells) and the MHC class II restricted epitope TB10.4 (74-88) (CD4/10.4 T cells). CD4/10.4 and CD8/10.4 T cells displayed marked differences in terms of expansion and contraction in a mouse TB model. CD4/10.4 T cells dominated in the early phase of infection whereas CD8/10.4 T cells were expanded after week 16 and reached 5-8 fold higher numbers in the late phase of infection. In the early phase of infection both CD4/10.4 and CD8/10.4 T cells were characterized by 20-25% polyfunctional cells (IL-2(+), IFN-gamma(+), TNF-alpha(+)), but whereas the majority of CD4/10.4 T cells were maintained as polyfunctional T cells throughout infection, CD8/10.4 T cells differentiated almost exclusively into effector cells (IFN-gamma(+), TNF-alpha(+)). Both CD4/10.4 and CD8/10.4 T cells exhibited cytotoxicity in vivo in the early phase of infection, but whereas CD4/10.4 cell mediated cytotoxicity waned during the infection, CD8/10.4 T cells exhibited increasing cytotoxic potential throughout the infection. CONCLUSIONS/SIGNIFICANCE: Our results show that CD4 and CD8 T cells directed to epitopes in the same antigen differ both in their kinetics and functional characteristics throughout an infection with M. tuberculosis. In addition, the observed strong expansion of CD8 T cells in the late stages of infection could have implications for the development of post exposure vaccines against latent TB.

CD4 and CD8 T cell responses to the M. tuberculosis Ag85B-TB10.4 promoted by adjuvanted subunit, adenovector or heterologous prime boost vaccination.

BACKGROUND: Although CD4 T cells are crucial for defense against M.tb, it is still not clear whether the optimal response against M.tb in fact involves both CD4 and CD8 T cells. To test this, we used a new vaccine strategy that generated a strong balanced T cell response consisting of both CD4 and CD8 T cells. METHODS AND FINDINGS: To compare CD4 and CD8 responses against Ag85B-TB10.4 (H4), H4 was delivered as a subunit vaccine in cationic liposomes (CAF01), expressed in Ad5 (Ad-H4) or as a heterologous prime boost vaccination. H4/CAF01 induced primarily CD4 T cells and Ad-H4 gave predominantly a CD8 T cell response. In contrast, the heterologous prime boost combination resulted in augmentation of both the CD4 and CD8 response. The majority (>40%) of the CD4 T cells induced by the heterologous prime boost protocol were polyfunctional, and expressed IFN-gamma(+), IL-2(+), and TNF-alpha(+), whereas most of the CD8 T cells expressed IFN-gamma(+) and TNF-alpha(+) and possessed strong cytotoxic potential. The heterologous prime boost protocol also gave an increase in protective efficacy against M.tb challenge compared to H4/CAF01 and Ad-H4. Both the H4 specific CD4 and CD8 T cells were recruited to the site of infection, at the onset of infection. However, compared to CD8 T cells, CD4 T cells showed more extensive recruitment and were the main T cell subset proliferating at the site of infection. CONCLUSIONS/SIGNIFICANCE: Heterologous prime boost based on H4, produced an additive effect on the priming of CD4 and CD8 cells and in terms of the protective capacity of the vaccine, and therefore represent an interesting new vaccine strategy against M.tb. However, CD4 and CD8 T cells respond very differently to live M.tb challenge, in a manner which supports the consensus that CD4 T cells do play the major role during the early stages of an M.tb infection.

Protection and polyfunctional T cells induced by Ag85B-TB10.4/IC31 against Mycobacterium tuberculosis is highly dependent on the antigen dose.

BACKGROUND: Previously we have shown that Ag85B-TB10.4 is a highly efficient vaccine against tuberculosis when delivered in a Th1 inducing adjuvant based on cationic liposomes. Another Th1 inducing adjuvant, which has shown a very promising profile in both preclinical and clinical trials, is IC31. In this study, we examined the potential of Ag85B-TB10.4 delivered in the adjuvant IC31 for the ability to induce protection against infection with Mycobacterium tuberculosis. In addition, we examined if the antigen dose could influence the phenotype of the induced T cells. METHODS AND FINDINGS: We found that vaccination with the combination of Ag85B-TB10.4 and IC31 resulted in high numbers of polyfunctional CD4 T cells co-expressing IL-2, IFN-gamma and TNF-alpha. This correlated with protection against subsequent challenge with M.tb in the mouse TB model. Importantly, our results also showed that both the vaccine induced T cell response, and the protective efficacy, was highly dependent on the antigen dose. Thus, whereas antigen doses of 5 and 15 microg did not induce significant protection against M.tb, reducing the dose to 0.5 microg selectively increased the number of polyfunctional T cells and induced a strong protection against infection with M.tb. The influence of antigen dose was also observed in the guinea pig model of aerosol infection with M.tb. In this model a 2.5 fold increase in the antigen dose reduced the protection against infection with M.tb to the level observed in non-vaccinated animals. CONCLUSIONS/SIGNIFICANCE: Small changes in the antigen dose can greatly influence the induction of specific T cell subpopulations and the dose is therefore a crucial factor when testing new vaccines. However, the adjuvant IC31 can, with the optimal dose of Ag85B-TB10.4, induce strong protection against Mycobacterium tuberculosis. This vaccine has now entered clinical trials.

Tuberculosis subunit vaccines: from basic science to clinical testing.

More than 80 years after the introduction of Bacillus Calmette-GuErin, the first tuberculosis vaccine, new vaccines for tuberculosis are finally in clinical trials. The selection of antigens on which new subunit vaccines are based represent the first fulfillment of the promise of proteomics and genomics, and the delivery systems for these antigens are likewise the first fruits of the improved understanding of how the host immune system recognizes pathogens. However, clinical trials are still at Phase I and there remain formidable obstacles to the registration of the first new TB vaccines. Here the authors review the vaccines in clinical trials and discuss the different approaches they take to stimulating immunity to Mycobacterium tuberculosis infection, focusing on recombinant subunit vaccines. The challenges that confront these approaches and how they are being addressed are then discussed.

Synergistic effect of bacillus calmette guerin and a tuberculosis subunit vaccine in cationic liposomes: increased immunogenicity and protection.

In the present work, we evaluated a new TB vaccine approach based on a combination of the Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccine and a subunit vaccine consisting of the proteins Ag85B and ESAT-6. We demonstrate that in addition to its vaccine efficacy BCG is an immune modulator that can potentiate a Th1 immune response better than the well-known adjuvant mono phosphoryl lipid A, leading to enhanced recognition of the subunit vaccine Ag85B-ESAT-6. Importantly, adding a vehicle to the vaccine, such as the cationic liposome dimethyl dioctadecyl ammonium bromide (DDA), significantly increased the potentiating effect of BCG. This synergistic effect between BCG and Ag85B-ESAT-6/liposome required drainage to the same lymph node of all vaccine components but did not require direct mixing of the components and was therefore also observed when BCG and Ag85B-ESAT-6/liposome were given as separate injections at sites draining to the same lymph node. The resulting optimized vaccine protocol consisting of BCG and subunit in liposomes (injected side by side) followed by boosting with the subunit in conventional adjuvant resulted in an impressive increase in the protective efficacy of up to 7-fold compared with BCG alone and 3-fold compared with unaugmented BCG boosted by the subunit vaccine. Thus, these studies suggest an immunization strategy where a novel TB subunit vaccine is administered as part of the child vaccination program together with BCG in neonates and followed by subunit boosting.

Induction of CD8 T cells against a novel epitope in TB10.4: correlation with mycobacterial virulence and the presence of a functional region of difference-1.

Although infection with Mycobacterium tuberculosis (M.tb) induces a robust CD8 T cell response, the role of CD8 T cells in the defense against M.tb, and the mechanisms behind the induction of CD8 T cells, is still not clear. TB10.4 is a recently described Ag that is expressed by both bacillus Calmette-Guérin (BCG) and M.tb. In the present study, we describe a novel CD8 T cell epitope in TB10.4, TB10.4(3-11). We show that TB10.4(3-11)-specific CD8 T cells are induced at the onset of infection and are present throughout the infection in high numbers. TB10.4(3-11) CD8 T cells were recruited to the site of infection and expressed CD44, TNF-alpha, and IFN-gamma. In addition, TB10.4(3-11) CD8 T cells showed an up-regulation of FasL and LAMP-1/2 (CD107A/B), which correlated with a strong in vivo cytolytic activity. The induction of TB10.4(3-11)-specific CD8 T cells was less pronounced following infection with BCG compared to infection with M.tb. By using a rBCG expressing the genetic region of difference-1 (RD1), we show that the presence of a functional RD1 region increases the induction of TB10.4(3-11)-specific CD8 T cells as well as the bacterial virulence. Finally, as an M.tb variant lacking the genetic region RD1 also induced a significant amount of TB10.4(3-11)-specific CD8 T cells, and exhibited increased virulence compared with BCG, our data suggest that virulence in itself is also involved in generating a robust CD8 T cell response against mycobacterial epitopes, such as TB10.4(3-11).