Long-lasting T-cell reactivity to Mycobacterium leprae antigens in human volunteers vaccinated with killed M. leprae

Cytokine response to selected MTB antigens in Ghanaian TB patients, before and at 2 weeks of anti-TB therapy is characterized by high expression of IFN-γ and Granzyme B and inter- individual variation

BACKGROUND

There has been a long held belief that patients with drug-susceptible TB are non-infectious after two weeks of therapy. Recent microbiological and epidemiological evidence has challenged this dogma, however, the nature of the Mtb-specific cellular immune response during this period has not been adequately investigated. This knowledge could be exploited in the development of immunological biomarkers of early treatment response.

METHODS

Cellular response to four Mtb infection phase-dependent antigens, ESAT-6/CFP-10 fusion protein and three DosR encoded proteins (Rv1733c, Rv2029c, Rv2628) were evaluated in a Ghanaian TB cohort (n=20) before and after 2 weeks of anti TB therapy. After 6-days in vitro stimulation, Peripheral blood mononuclear cell (PBMC) culture supernatant was harvested and the concentration of IFN-γ, Granzyme B, IL-10, IL-17, sIL2Rα and TNF-α were determined in a 6-plex Luminex assay. Frequencies of IFN-γ + CD4 and CD8 T cells were also determined in an intracellular cytokine assay.

RESULTS

All antigens induced higher levels of IFN-γ, followed by Granzyme B, TNF-α and IL-17 and low levels of IL-10 and sIL-2R-α in PBMC before treatment and after 2 weeks of treatment. Median cytokine levels of IFN-γ, Granzyme B, IL-17 and sIL-2R-α increased during week two, but it was significant for only Rv1733-specific production of Granzyme B (P = 0. 013). The median frequency of antigen specific IFN-γ + CD4 T cells increased at week two; however, only the increase in the ESAT-6/CFP-10-specific response was significant (P = 0. 0008). In contrast, the median frequency of ESAT-6/CFP-10- specific IFN-γ + CD8 T cell responses declined during week two (P = 0. 0024). Additionally, wide inter-individual variation with three distinct patterns were observed; increase in all cytokine levels, decrease in all cytokine levels and fluctuating cytokine levels after 2 weeks of treatment.

CONCLUSION

The second week of effective chemotherapy was characterized by a general increase in cytokine response to Mtb-specific antigens suggestive of an improvement in cellular response with therapy. However, the wide inter-individual variation observed would limit the utility of cytokine biomarkers during this period.

Characterization of a cross-reactive, immunodominant and HLA-promiscuous epitope of Mycobacterium tuberculosis-specific major antigenic protein PPE68

PPE68 (Rv3873), a major antignic protein encoded by Mycobacteriun tuberculosis-specific genomic region of difference (RD)1, is a strong stimulator of peripheral blood mononuclear cells (PBMCs) obtained from tuberculosis patients and Mycobacterium bovis bacillus Calmette Guerin (BCG)-vaccianted healthy subjects in T helper (Th)1 cell assays, i.e. antigen-induced proliferation and interferon-gamma (IFN-γ) secretion. To confirm the antigen-specific recognition of PPE68 by T cells in IFN-γ assays, antigen-induced human T-cell lines were established from PBMCs of M. Bovis BCG-vaccinated and HLA-heterogeneous healthy subjects and tested with peptide pools of RD1 proteins. The results showed that PPE68 was recognized by antigen-specific T-cell lines from HLA-heteregeneous subjects. To further identify the immunodominant and HLA-promiscuous Th1-1 cell epitopes present in PPE68, 24 synthetic peptides covering the sequence of PPE68 were indivdually analyzed for HLA-DR binding prediction analysis and tested with PBMCs from M. bovis BCG-vaccinated and HLA-heterogeuous healthy subjects in IFN-γ assays. The results identified the peptide P9, i.e. aa 121-VLTATNFFGINTIPIALTEMDYFIR-145, as an immunodominant and HLA-DR promiscuous peptide of PPE68. Furthermore, by using deletion peptides, the immunodominant and HLA-DR promiscuous core sequence was mapped to aa 127-FFGINTIPIA-136. Interestingly, the core sequence is present in several PPE proteins of M. tuberculosis, and conserved in all sequenced strains/species of M. tuberculosis and M. tuberculosis complex, and several other pathogenic mycobacterial species, including M. leprae and M. avium-intracellulalae complex. These results suggest that the peptide aa 121-145 may be exploited as a peptide-based vaccine candidate against tuberculosis and other mycobacterial diseases.

In silico analysis and experimental validation of Mycobacterium tuberculosis -specific proteins and peptides of Mycobacterium tuberculosis for immunological diagnosis and vaccine development

Comparative analyses of the Mycobacterium tuberculosis genome with the genomes of other mycobacteria have led to the identification of several genomic regions of difference (RDs) between M. tuberculosis and M. bovis BCG. The identification of immunodominant and HLA-promiscuous antigens and peptides encoded by these RDs could be useful for diagnosis and the development of new vaccines against tuberculosis. The analysis of RD proteins and peptides by in silico methods (using computational programs to predict major and HLA-promiscuous antigenic proteins and peptides) and experimental validations (using peripheral blood mononuclear cells and sera from tuberculosis patients and BCG-vaccinated healthy subjects to assess antigen-specific cellular and humoral immune responses in vitro) identified several major antigens and peptides. To evaluate the in vivo potentials, the genes of immunodominant antigens were cloned and expressed in DNA vaccine vectors. Immunizations of experimental animals with the recombinant constructs induced antigen-specific cellular responses. Further experiments showed that each of these proteins had several T and B cell epitopes scattered throughout their sequence, which confirmed their strong immunogenicity. In conclusion, the bioinformatics-based in silico identification of promiscuous antigens and peptides of M. tuberculosis is a useful approach to identify new candidates important for diagnosis and vaccine applications.

Mycobacterial gene cloning and expression, comparative genomics, bioinformatics and proteomics in relation to the development of new vaccines and diagnostic reagents

Recent advances in molecular and genomic techniques have facilitated research on several aspects of mycobacteriology, such as diagnosis and the identification of new vaccines and therapeutic targets for various diseases, including tuberculosis. The aim of this review was to analyze the implications of advances in molecular and genomic techniques on the development of new vaccines for tuberculosis as well as immunological reagents to diagnose the disease. Gene cloning and expression, DNA and protein sequencing, polymerase chain reaction, comparative genomics, bioinformatics, proteomics and DNA and peptide synthesis coupled with the application of cellular immunology techniques have led to the identification of several antigens of Mycobacterium tuberculosis, which have potential for diagnosis and vaccine applications. For example, cross-reactive mycobacterial antigens like heat shock proteins, MTB32 and MTB39, have been identified as new vaccine candidates, and antigens encoded by M. tuberculosis-specific genomic regions as new reagents for diagnosis.

In vitro cellular immune responses to complex and newly defined recombinant antigens of Mycobacterium tuberculosis

The immunological diagnosis and development of new antituberculosis vaccines require the characterization of Mycobacterium tuberculosis antigens inducing cell-mediated immune responses. In this study, we have tested peripheral blood mononuclear cells (PBMC) from tuberculosis (TB) patients (n = 43) and Bacille Calmette-Guérin (BCG)-vaccinated healthy subjects (n = 24) for in vitro cellular immune responses, as indicated by antigen-induced proliferation and interferon (IFN)-gamma secretion, in response to a panel of complex (culture filtrate and cell wall preparations) and single recombinant antigens (Mtb8.4, Mtb9.8, Mtb9.9, Mtb32A, Mtb39A, Mtb40, Mtb41 and Ag85B) of M. tuberculosis. The results of cellular responses showed that the majority (ranging from 70 to 98%) of TB patients and healthy donors responded to the complex antigens in antigen-induced proliferation and IFN-gamma secretion assays. However, when PBMC from the same groups of patients and healthy donors were tested with the recombinant antigens, TB patients showed strong recognition (>50% responders) of Mtb9.8 and Mtb39A in proliferation assays (median SI = 6.2 and 6.4, respectively) and of Mtb9.8, Mtb39A, Mtb40 and Ag85B in IFN-gamma assays (median delta IFN-gamma= 15.5, 10.8, 7.8 and 8.1 U/ml, respectively). BCG-vaccinated healthy donors showed weak (<30% responders) to moderate (31-50% responders) responses to all of the recombinant antigens in both assays. When PBMC of a subset of TB patients (n = 11) were tested for secretion of protective Th1 cytokines [IFN-gamma, tumour necrosis factor (TNF)-alpha and interleukin (IL)-12] and the immunosuppressive cytokine IL-10, the complex CF and CW antigens as well as the recombinant Mtb9.8, Mtb9.9, Mtb40 and Ag85B induced the secretion of both types of cytokines. On the other hand, Mtb41 induced only IL-10, while Mtb8.4, Mtb32Aand Mtb39A induced the secretion of one or more of Th1 cytokines, but not IL-10. In conclusion, the recombinant antigens inducing the secretion of Th1 cytokines could be useful as subunit vaccine candidates against TB.

Computer-assisted prediction of HLA-DR binding and experimental analysis for human promiscuous Th1-cell peptides in the 24 kDa secreted lipoprotein (LppX) of Mycobacterium tuberculosis

The secreted 24 kDa lipoprotein (LppX) is an antigen that is specific for Mycobacterium tuberculosis complex and M. leprae. The present study was carried out to identify the promiscuous T helper 1 (Th1)-cell epitopes of the M. tuberculosis LppX (MT24, Rv2945c) antigen by using 15 overlapping synthetic peptides (25 mers overlapping by 10 residues) covering the sequence of the complete protein. The analysis of Rv2945c sequence for binding to 51 alleles of nine serologically defined HLA-DR molecules, by using a virtual matrix-based prediction program (propred), showed that eight of the 15 peptides of Rv2945c were predicted to bind promiscuously to >/=10 alleles from more than or equal to three serologically defined HLA-DR molecules. The Th1-cell reactivity of all the peptides was assessed in antigen-induced proliferation and interferon-gamma (IFN-gamma)-secretion assays with peripheral blood mononuclear cells (PBMCs) from 37 bacille Calmette-Guérin (BCG)-vaccinated healthy subjects. The results showed that 17 of the 37 donors, which represented an HLA-DR-heterogeneous group, responded to one or more peptides of Rv2945c in the Th1-cell assays. Although each peptide stimulated PBMCs from one or more donors in the above assays, the best positive responses (12/17 (71%) responders) were observed with the peptide p14 (aa 196-220). This suggested a highly promiscuous presentation of p14 to Th1 cells. In addition, the sequence of p14 is completely identical among the LppX of M. tuberculosis, M. bovis and M. leprae, which further supports the usefulness of Rv2945c and p14 in the subunit vaccine design against both tuberculosis and leprosy.

Restoration of mycobacterial antigen-induced proliferation and interferon-γ responses in peripheral blood mononuclear cells of tuberculosis patients upon effective chemotherapy

Peripheral blood mononuclear cells (PBMC) were obtained from culture-proven tuberculosis (TB) patients before and after 2 and 6 months of chemotherapy with a multi-drug regimen. PBMC were tested for cellular responses in antigen-induced proliferation and interferon-gamma (IFN-gamma) assays in response to complex mycobacterial antigens (whole cell Mycobacterium bovis BCG and M. tuberculosis, cell walls and short-term culture filtrate [ST-CF] of M. tuberculosis), fractionated ST-CF antigens (fractions F1-F10) and ESAT-6. The responses in TB patients before anti-TB treatment were low (median stimulation index (SI)=1-7, median delta IFN-gamma=0-12 U ml(-1), and percent responders=13-67%) to all the antigenic preparations. Following the administration of anti-TB chemotherapy for 2 months, there were significant (P<0.05) improvements in the cellular responses (median SI=9-76, median delta IFN-gamma=3-70 U ml(-1), and percent responders=33-100%) to most of the antigenic preparations tested. However, concanavalin A-induced proliferation responses of PBMC from the same patients before and after 2 months of chemotherapy were high and comparable (median SI=101 and 114, respectively, P>0.05, 100% responders). A further increase in IFN-gamma responses (median delta IFN-gamma=14-250 U ml(-1) and percent responders=43-100%) to mycobacterial antigens was observed in patients receiving chemotherapy for 6 months. Among the ST-CF fractions, F1 and F2 containing low molecular mass proteins resulted in the highest responses, whereas ESAT-6 showed responses comparable to these fractions only in a minority of the patients. HLA-DR typing of these patients showed heterogeneity in the expression of molecules encoded by HLA-DRB genes. These results show that effective chemotherapy restores cellular responses of TB patients to a large number of M. tuberculosis antigens, which could be useful in monitoring the efficacy of anti-TB treatment.

Identification of an I-Ad restricted peptide on the 65-kilodalton heat shock protein of Mycobacterium avium

The 65 kilodalton heat shock protein (Hsp65) from mycobacterial species elicits immune responses and in some cases protective immunity. Here we have used a DNA sublibrary approach to identify antigenic fragments of Mycobacterium avium Hsp65 and a synthetic peptide approach to delineate CD4+ T cell determinants. A panel of Hsp65 reactive CD4+ T cell clones was established from lymph node cells obtained from BALB/c mice immunized with recombinant Hsp65. The clones were tested for proliferative reactivity against the products of the DNA sublibrary of the hsp65 gene. A T cell epitope, restricted by the I-Ad molecule, was identified within the C-terminal region of Hsp65 and the minimal epitope (amino acid residues 489-503) delineated using overlapping peptides spanning the C-terminal fragment. Additionally, the CD4+ T cell clone recognizing this epitope also responded to native Hsp65 present in M. avium lysates by both proliferation and cytokine production, indicating that the epitope was present and processed similarly both in the native and the recombinant forms of Hsp65. This sequence identified in BALB/c mice (Hsp65 489-503) is identical in other mycobacteria, notably M. tuberculosis, M. bovis and M. leprae, suggesting the epitope may have wider application in murine models of other mycobacterial infections.

Development of new vaccines and diagnostic reagents against tuberculosis

Tuberculosis (TB) is a major infectious disease problem with one-third of the world population infected, 8 million people developing the active disease and 2 million dying of TB each year. The attenuated Mycobacterium bovis Bacillus Calmette Guerin (BCG) is the only available vaccine against TB. However, the trials conducted in different parts of the world have shown that this vaccine doe not provide consistent protection against TB. The purified protein derivative (PPD) of Mycobacterium tuberculosis is the commonly used reagent for the diagnosis of TB. However, PPD lacks specificity because of the presence of antigens crossreactive with M. bovis BCG and other mycobacteria. The studies to identify M. tuberculosis antigens and epitopes as candidates for new protective vaccines and specific diagnostic reagents against TB have led to the identification and characterization of several major antigens of M. tuberculosis including heat shock proteins (hsp) and secreted antigens present in the culture filtrate (CF) of M. tuberculosis. Some of these antigens have shown promise as new candidate vaccines (hsp60, Ag85 and ESAT-6, etc.) and specific diagnostic reagents (ESAT-6 and CFP10, etc.) for TB. Moreover, in the mouse model of TB, vaccination with DNA-hsp60 has immunotheraputic effects and helps in eradication of persisters. In addition, identification of proper adjuvant and delivery systems has shown the promise to overcome the problem of poor immunogenicity associated with subunit and peptide based vaccines. More recently, the comparison of the genome sequence of M. tuberculosis with M. bovis BCG and other mycobacteria has led to the identification of M. tuberculosis-specific genomic regions. Evaluation of these regions for encoding proteins with immunological reactivity can lead to the identification of additional antigens of M. tuberculosis useful as new vaccines and reagents for specific diagnosis of TB.

Identification and HLA restriction of naturally derived Th1-cell epitopes from the secreted Mycobacterium tuberculosis antigen 85B recognized by antigen-specific human CD4(+) T-cell lines

Antigen 85B (Ag85B/MPT59) is a major secreted protein from Mycobacterium tuberculosis which is a promising candidate antigen for inclusion in novel subunit vaccines against tuberculosis (TB). The present study was undertaken to map naturally derived T-cell epitopes from M. tuberculosis Ag85B in relation to major histocompatibility complex (MHC) class II restriction. Antigen-specific CD4(+) T-cell lines were established from HLA-typed TB patients and Mycobacterium bovis BCG vaccinees by stimulation of peripheral blood mononuclear cells with purified Ag85B in vitro. The established T-cell lines were then tested for proliferation and gamma interferon (IFN-gamma) secretion in response to 31 overlapping synthetic peptides (18-mers) covering the entire sequence of the mature protein. The results showed that the epitopes recognized by T-cell lines from TB patients were scattered throughout the Ag85B sequence whereas the epitopes recognized by T-cell lines from BCG vaccinees were located toward the N-terminal part of the antigen. The T-cell epitopes represented by peptides p2 (amino acids [aa] 10 to 27), p3 (aa 19 to 36), and p11 (aa 91 to 108) were frequently recognized by antigen-specific T-cell lines from BCG vaccinees in both proliferation and IFN-gamma assays. MHC restriction analysis demonstrated that individual T-cell lines specifically recognized the complete Ag85B either in association with one of the self HLA-DRB1, DRB3, or DRB4 gene products or nonspecifically in a promiscuous manner. At the epitope level, panel studies showed that peptides p2, p3, and p11 were presented to T cells by HLA-DR-matched as well as mismatched allogeneic antigen-presenting cells, thus representing promiscuous epitopes. The identification of naturally derived peptide epitopes from the M. tuberculosis Ag85B presented to Th1 cells in the context of multiple HLA-DR molecules strongly supports the relevance of this antigen to subunit vaccine design.

Multiple epitopes from the Mycobacterium tuberculosis ESAT-6 antigen are recognized by antigen-specific human T cell lines

A synthetic-peptide approach was used to map epitope regions of the Mycobacterium tuberculosis 6-kDa early secreted antigen target (ESAT-6) by testing human CD4(+) T cell lines for secretion of IFN-gamma in response to recombinant ESAT-6 (rESAT-6) and overlapping 20-mer peptides covering the antigen sequence. The results demonstrate that all of the ESAT-6 peptides screened were able to induce IFN-gamma secretion from one or more of the T cell lines tested. Some of the individual T cell lines showed the capacity to respond to all peptides. Human leukocyte antigen (HLA-DR) typing of the donors showed that rESAT-6 was presented to T cells in association with multiple HLA-DR molecules. The results suggest that frequent recognition of the M. tuberculosis ESAT-6 antigen by T cells from patients with tuberculosis is due to the presence of multiple epitopes scattered throughout the ESAT-6 sequence.

Cross-reactive epitopes and HLA-restriction elements in human T cell recognition of the Mycobacterium leprae 18-kD heat shock protein

We have previously demonstrated that the Mycobacterium leprae 18-kD heat shock protein (HSP18) is represented among the antigenic targets of human T cell responses induced by M. leprae immunization and that the peptide 38-50 serves as an immunodominant epitope recognized by CD4+ T cell clones. By using peripheral blood mononuclear cells and T cell lines from the same donor group, we have in this study shown that the M. leprae HSP18 and peptide 38-50 were recognized by memory T cells 8 years after immunization with M. leprae. The finding that M. bovis BCG-induced T cell lines responded to M. leprae HSP18, but not to the peptide 38-50, suggested the existence of additional T cell epitopes of a cross-reactive nature. Consistent with this, testing of the T cell lines for proliferative responses to the complete HSP18 molecule, truncated HSP18 (amino acid (aa) residues 38-148) and overlapping synthetic peptides, made it possible to identify two cross-reactive epitope regions defined by aa residues 1-38 and 41-55. While peptide 38-50-reactive T cell clones showed limited cross-reactivity by responding to M. leprae, M. avium and M. scrofulaceum, the T cell lines specific to the epitopes 1-38 and 41-55 were broadly cross-reactive, as demonstrated by their response to M. leprae, M. tuberculosis complex, M. avium and other mycobacteria. MHC restriction analysis of the HSP18-responding T cell lines showed that the epitopes 1-38 and 38-50 were presented by one of the two HLA-DR molecules expressed from self HLA-DRB1 genes, whereas the epitope 41-55 was recognized in the presence of autologous as well as HLA-DR and HLA-DQ mismatched allogeneic antigen-presenting cells. The results obtained in this study made it possible to identify cross-reactive T cell epitopes of the M. leprae HSP18, and provide an explanation for T cell recognition of this antigen in individuals infected with species of the M. tuberculosis complex or environmental mycobacteria.

HLA-restricted immune response to mycobacterial antigens: relevance to vaccine design

Identification of mycobacterial antigens that are recognized by CD4+ Th1 cells in HLA-nonrestricted manner or in association with multiple allelic products is required to develop universally effective vaccines against mycobacterial diseases. Our studies in this direction have shown that several recombinant mycobacterial antigens of cytosolic and culture filtrate origin are recognized by CD4+ Th1 cells. Mapping of T cell epitopes with overlapping synthetic peptides covering the entire sequence of these antigens identified peptide sequences stimulatory for Th1 cells. HLA-restriction analysis showed that in addition to HLA-DRB1 products (serologically defined HLA-DR1 to HLA-DR10), the HLA molecules encoded by HLA-DRB3 (HLA-DR52) and HLA-DRB4 (HLA-DR53) are important in presentation of mycobacterial antigens and epitopes to T cells. Depending on the T cell donor, the presentation of a given antigen or peptide could be restricted by HLA-DRB1, HLA-DRB3, and/or HLA-DRB4 products. In addition, stimulation of Th1 cells by some antigens and peptides in the presence of autologous and HLA-DR mismatched allogeneic APC suggested promiscuous presentation. These results taken together suggest that from HLA-restriction perspective, several mycobacterial antigens qualify as candidates for subunit or recombinant vaccine design against mycobacterial diseases.

Identification of promiscuous epitopes from the Mycobacterial 65-kilodalton heat shock protein recognized by human CD4(+) T cells of the Mycobacterium leprae memory repertoire

By using a synthetic peptide approach, we mapped epitopes from the mycobacterial 65-kDa heat shock protein (HSP65) recognized by human T cells belonging to the Mycobacterium leprae memory repertoire. A panel of HSP65 reactive CD4(+) T-cell lines and clones were established from healthy donors 8 years after immunization with heat-killed M. leprae and then tested for proliferative reactivity against overlapping peptides comprising both the M. leprae and Mycobacterium tuberculosis HSP65 sequences. The results showed that the antigen-specific T-cell lines and clones established responded to 12 mycobacterial HSP65 peptides, of which 9 peptides represented epitopes crossreactive between the M. tuberculosis and M. leprae HSP65 (amino acids [aa] 61 to 75, 141 to 155, 151 to 165, 331 to 345, 371 to 385, 411 to 425, 431 to 445, 441 to 455, and 501 to 515) and 3 peptides (aa 343 to 355, 417 to 429, and 522 to 534) represented M. leprae HSP65-specific epitopes. Major histocompatibility complex restriction analysis showed that presentation of 9 of the 12 peptides to T cells were restricted by one of the 2 HLA-DR molecules expressed from self HLA-DRB1 genes, whereas 3 peptides with sequences completely identical between the M. leprae and M. tuberculosis HSP65 were presented to T cells by multiple HLA-DR molecules: peptide (aa 61 to 75) was presented by HLA-DR1, -DR2, and -DR7, peptide (aa 141 to 155) was presented by HLA-DR2, -DR7, and -DR53, whereas both HLA-DR2 and -DR4 (Dw4 and Dw14) were able to present peptide (aa 501 to 515) to T cells. In addition, the T-cell lines responding to these peptides in proliferation assays showed cytotoxic activity against autologous monocytes/macrophages pulsed with the same HSP65 peptides. In conclusion, we demonstrated that promiscuous peptide epitopes from the mycobacterial HSP65 antigen can serve as targets for cytotoxic CD4(+) T cells which belong to the human memory T-cell repertoire against M. leprae. The results suggest that such epitopes might be used in the peptide-based design of subunit vaccines against mycobacterial diseases.

Human T cell recognition of the Mycobacterium leprae LSR antigen: epitopes and HLA restriction

We have in this work mapped epitopes and HLA molecules used in human T cell recognition of the Mycobacterium leprae LSR protein antigen. HLA typed healthy subjects immunized with heat killed M. leprae were used as donors to establish antigen reactive CD4+ T cell lines which were screened for proliferative responses against overlapping synthetic peptides covering the C-terminal part of the antigen sequence. By using this approach we were able to identify two epitope regions represented by peptide 2 (aa 29-40) and peptide 6 (aa 49-60), of which the former was mapped in detail by defining the N- and C-terminal amino acid positions necessary for T cell recognition of the core epitope. MHC restriction analysis showed that peptide 2 was presented to T cells by allogeneic cells coexpressing HLA-DR4 and DRw53 or DR7 and DRw53. In contrast, peptide 6 was presented to T cells only in the context of HLA-DR5 molecules. In conclusion, the M. leprae LSR protein antigen can be recognized by human T cells in the context of multiple HLA-DR molecules, of which none are reported to be associated with the susceptibility to develop leprosy. The results obtained are in support of using the LSR antigen in subunit vaccine design.

Isolation of recombinant phage clones expressing mycobacterial T cell antigens by screening a recombinant DNA library with human CD4+ Th1 clones

A lambda gt11 recombinant DNA library of Mycobacterium leprae was screened to isolate recombinant phage clones expressing mycobacterial antigens important for T cell reactivity. The library was plated on a lawn of Escherichia coli Y1090 and recombinant antigens were expressed from isolated phage clones in 96-well plates. Pools of recombinant antigens from 12 wells were tested in T cell proliferation assays with MHC class II restricted human CD4+ Th1 clones secreting interferon-gamma and cytotoxic for antigen pulsed antigen presenting cells. By screening 1750 pools of recombinant antigens with a mixture of eight Th1 clones, we identified two recombinant phage clones that expressed recombinant mycobacterial antigens stimulatory for T cells. MHC restriction analysis and reactivity to a battery of mycobacterial antigens suggested that the two responding Th1 clones recognized mycobacterial antigens/epitopes with different MHC class II (HLA-DR) restriction requirements. Our results suggest that the methodology described in this paper is suited to isolate recombinant phage clones expressing mycobacterial recombinant antigens stimulatory for T cells of protective phenotype. Such antigens may be useful in designing new vaccines and diagnostic reagents against mycobacterial diseases.

Comparison of antigen-specific T-cell responses of tuberculosis patients using complex or single antigens of Mycobacterium tuberculosis

We have screened peripheral blood mononuclear cells (PBMC) from tuberculosis (TB) patients for proliferative reactivity and interferon-gamma (IFN-gamma) secretion against a panel of purified recombinant (r) and natural (n) culture filtrate (rESAT-6, nMPT59, nMPT64 and nMPB70) and somatic-derived (rGroES, rPstS, rGroEL and rDnaK) antigens of Mycobacterium tuberculosis. The responses of PBMC to these defined antigens were compared with the corresponding results obtained with complex antigens, such as whole-cell M. tuberculosis, M. tuberculosis culture filtrate (MT-CF) and cell wall antigens, as well as the vaccine strain, Mycobacterium bovis bacillus Calmette-Guerin (BCG). In addition, M. tuberculosis and MT-CF-induced T-cell lines were tested in the same assays against the panel of purified and complex antigens. The compiled data from PBMC and T-cell lines tested for antigen-induced proliferation and IFN-gamma secretion showed that the most frequently recognized antigen was ESAT-6, followed by MPT59, GroES, MPB70, MPT64, DnaK, GroEL and PstS. The frequency of ESAT-6 responders, as measured both by proliferation (18/19) and secretion of IFN-gamma (16/19) was comparable to the results obtained with whole-cell M. tuberculosis, MT-CF and M. bovis BCG. We also observed that most of the high responders to complex antigens recognized all of the antigens tested (covariation), demonstrating that the repertoire of human T-cell specificities induced by natural infection is directed towards several unrelated culture filtrate as well as somatic-derived protein antigens. In conclusion, the results obtained suggest that the cellular immune response in humans is directed against several important target antigens of M. tuberculosis and that some antigens, such as ESAT-6, are recognized by a high number of individuals. Such antigens represent candidates to be used for development of specific diagnostic reagents or in subunit vaccines.

HLA-DR4-restricted T-cell epitopes from the mycobacterial 60,000 MW heat shock protein (hsp 60) do not map to the sequence homology regions with the human hsp 60

The mycobacterial 60,000 MW heat shock protein (hsp 60) is a major antigen recognized by mycobacteria-reactive human CD4+ T cells with lymphokine profiles and effector functions consistent with protective immunity. In addition, the presence of a large number of T-cell epitopes presented by several HLA class II molecules makes this antigen relevant to subunit vaccine design. However, the results from animal models as well as human studies suggest that the mycobacterial hsp 60 may induce T-cell-mediated autoimmune conditions. In humans, the expression of HLA-DR4 represents a risk factor for some autoimmune diseases. These observations suggest that the epitopes from the mycobacterial hsp 60 presented to T cells in the context of HLA-DR4 could be relevant to autoimmunity. This is the first report on identification of HLA-DR4-restricted T-cell epitopes from the mycobacterial antigen hsp 60. In total, five epitopes recognized in the context of HLA-DR4 by the M. leprae hsp 60-reactive CD4+ T-cell clones from a subject immunized with M. leprae were defined by synthetic peptides. Two of the epitopes were M. leprae-specific (aa 343-355, aa 522-534), whereas three epitopes were common to M. leprae and M. tuberculosis (aa 331-345, aa 441-455, aa 501-515). However, all of these epitopes belong to the regions that are highly divergent between the mycobacterial hsp 60 and the homologous human hsp 60 sequence, suggesting that the T cells recognizing the mycobacterial hsp 60 in the context of HLA-DR4 may not necessarily induce autoreactivity.

An HLA-DRw53-restricted T-cell epitope from a novel Mycobacterium leprae protein antigen important to the human memory T-cell repertoire against M. leprae

Cellular immunity mediated by T cells plays a major role in protection against intracellular infections, including leprosy, a chronic disease caused by Mycobacterium leprae. In this work, we describe CD4+ T-cell clones, isolated from healthy humans immunized with M. leprae, which recognize a novel M. leprae protein antigen previously isolated from a lambda gt11 DNA expression library. On the basis of the deduced primary structure of the carboxyl-terminal part of the antigen, we have used a synthetic-peptide approach to exactly define the T-cell epitope recognized. Importantly, major histocompatibility complex restriction studies showed that the epitope is presented by an HLA-DRw53 molecule which is frequently expressed in many populations. In addition, we have demonstrated that a long-term cell-mediated immunity response against the peptide epitope is present after immunization with M. leprae. In conclusion, the M. leprae T-cell epitope described here fulfills the primary criteria for subunit vaccine candidates against leprosy.