The antituberculous Mycobacterium bovis BCG vaccine is an attenuated mycobacterial producer of phosphorylated nonpeptidic antigens for human gamma delta T cells

Intravesical Ty21a treatment of non-muscle invasive bladder cancer induces immune responses that correlate with safety and may be associated to therapy potential

BACKGROUND

Standard of care treatment of non-muscle invasive bladder cancer (NMIBC) with intravesical Bacillus Calmette Guérin (BCG) is associated with side effects, disease recurrence/progression and supply shortages. We recently showed in a phase I trial (NCT03421236) that intravesical instillation in patients with NMIBC with the maximal tolerated dose of Ty21a/Vivotif, the oral vaccine against typhoid fever, might have a better safety profile. In the present report, we assessed the immunogenicity of intravesical Ty21a in patients of the clinical trial that had received the maximal tolerated dose and compared it with data obtained in patients that had received standard BCG.

METHODS

Urinary cytokines and immune cells of patients with NMIBC treated with intravesical instillations of Ty21a (n=13, groups A and F in NCT03421236) or with standard BCG in a concomitant observational study (n=12, UROV1) were determined by Luminex and flow cytometry, respectively. Serum anti-lipopolysaccharide Typhi antibodies and circulating Ty21a-specific T-cell responses were also determined in the Ty21a patients. Multiple comparisons of different paired variables were performed with a mixed-effect analysis, followed by Sidak post-test. Single comparisons were performed with a paired or an unpaired Student's t-test.

RESULTS

As compared with BCG, Ty21a induced lower levels of inflammatory urinary cytokines, which correlated to the milder adverse events (AEs) observed in Ty21a patients. However, both Ty21a and BCG induced a Th1 tumor environment. Peripheral Ty21a-specific T-cell responses and/or antibodies were observed in most Ty21a patients, pointing the bladder as an efficient local immune inductive site. Besides, Ty21a-mediated stimulation of unconventional Vδ2 T cells was also observed, which turned out more efficient than BCG. Finally, few Ty21a instillations were sufficient for increasing urinary infiltration of dendritic cells and T cells, which were previously associated with therapeutic efficacy in the orthotopic mouse model of NMIBC.

CONCLUSIONS

Ty21a immunotherapy of patient with NMIBC is promising with fewer inflammatory cytokines and mild AE, but induction of immune responses with possible antitumor potentials. Future phase II clinical trials are necessary to explore possible efficacy of intravesical Ty21a.

Role of MHC class I pathways in Mycobacterium tuberculosis antigen presentation

MHC class I antigen processing is an underappreciated area of nonviral host–pathogen interactions, bridging both immunology and cell biology, where the pathogen’s natural life cycle involves little presence in the cytoplasm. The effective response to MHC-I foreign antigen presentation is not only cell death but also phenotypic changes in other cells and stimulation of the memory cells ready for the next antigen reoccurrence. This review looks at the MHC-I antigen processing pathway and potential alternative sources of the antigens, focusing on Mycobacterium tuberculosis (Mtb) as an intracellular pathogen that co-evolved with humans and developed an array of decoy strategies to survive in a hostile environment by manipulating host immunity to its own advantage. As that happens via the selective antigen presentation process, reinforcement of the effective antigen recognition on MHC-I molecules may stimulate subsets of effector cells that act earlier and more locally. Vaccines against tuberculosis (TB) could potentially eliminate this disease, yet their development has been slow, and success is limited in the context of this global disease’s spread. This review’s conclusions set out potential directions for MHC-I-focused approaches for the next generation of vaccines.

Placentа of BCG-Vaccinated Women in early Pregnancy is Colonized with Non-Immunogenic Mycobacterial L-forms

PROBLEM

Long-lived mycobacterial L-forms (mL-forms) could be detected in the blood of BCG-vaccinated people. We have previously found mL-forms in term placentas and blood of neonates, delivered by healthy BCG-vaccinated mothers as first formal demonstration that BCG vaccination in the childhood of the woman could affect her placentobiome during pregnancy. Of note, the isolated mL-forms reverted to the cell-walled state of the parental BCG bacilli in vitro.

METHOD OF STUDY

Here, we analyzed triple samples of blood, decidua and chorion taken from BCG-vaccinated pregnant women, directed to elective abortions (6-12 gestation weeks). The colonization of the primary samples with mycobacterial L-forms (mL-forms) was evaluated using microbiological isolation and subsequent identification by real time PCR and morphological characterization by light microscopy and SEM. The potential of early placenta-derived mL-forms to expand mycobacteria-reactive γδ T cells in vitro was assessed using FACS, whereas their immunogenicity in vivo was followed up after i.p. inoculation in rats.

RESULTS

Our results showed two important findings: 1) viable filterable mL-forms varying in size, shape and proliferation modes are capable of colonizing the gestational tissues of BCG-vaccinated women early in pregnancy and 2) early placenta-derived mL-forms are not as immunogenic as walled M. bovis BCG bacilli, shown by lack of stimulation of mycobacteria-reactive γδ T cells co-cultured with early placenta-derived mL-forms and inefficient internalization of mL-forms by rat's peritoneal phagocytes in vivo.

CONCLUSION

Although generally thought to be reduced in virulence, mL-forms could provide a reservoir, hidden from the immune system especially in an immune privileged niche like placenta.

Vδ2 T cells are associated with favorable clinical outcomes in patients with bladder cancer and their tumor reactivity can be boosted by BCG and zoledronate treatments

Background Bladder cancer is an important public health concern due to its prevalence, high risk of recurrence and associated cost of management. Although BCG instillation for urothelial cancer treatment is the gold-standard treatment for this indication, repeated BCG treatments are associated with significant toxicity and failure, underlining the necessity for alternative or complementary immunotherapy and overall for better understanding of T-cell responses generated within bladder mucosa. Tumor-infiltrating lymphocytes (TIL) have long been recognized as a crucial component of the tumor microenvironment for the control of tumor. Among TIL, unconventional γδ T cells sparked interest due to their potent antitumor functions. Although preclinical mouse xenograft models demonstrated the relevance of using γδ T cells as a novel therapy for bladder cancer (BCa), the contribution of γδ T cells in BCa patients’ pathology remains unaddressed.

Methods Therefore, we first determined the proportion of intratumor γδ T cells in muscle-invasive patients with BCa by deconvoluting data from The Cancer Genome Atlas (TCGA) and the frequency of blood Vδ1, Vδ2, and total γδ T cells, by flow cytometry, from 80 patients with BCa (40 non-muscle and 40 muscle-invasive patients with BCa), as well as from 20 age-matched non-tumor patients. Then we investigated in vitro which treatment may promote BCa tumor cell recognition by γδ T cells.

Results We observed a decrease of γδ T-cell abundance in the tumor compared with corresponding normal adjacent tissue, suggesting that the tumor microenvironment may alter γδ T cells. Yet, high intratumor γδ T-cell proportions were significantly associated with better patient survival outcomes, potentially due to Vδ2 T cells. In the blood of patients with BCa, we observed a lower frequency of total γδ, Vδ1, and Vδ2 T cells compared with non-tumor patients, similarly to the TCGA analysis. In addition, a favorable clinical outcome is associated with a high frequency of circulating γδ T cells, which might be mainly attributed to the Vδ2 T-cell subset. Furthermore, in vitro assays revealed that either BCG, Zoledronate, or anti-BTN3 agonistic antibody treatment of bladder tumor cells induced Vδ2 T-cell cytolytic (CD107a⁺) and cytokine-production (IFN-γ and TNF-α). Strikingly, combining BCG and Zoledronate treatments significantly elicited the most quantitative and qualitative response by increasing the frequency and the polyfunctionality of bladder tumor-reactive Vδ2 T cells.

Conclusions Overall, our results suggest that (1) Vδ2 T cells might play a prominent role in bladder tumor control and (2) non-muscle invasive patients with BCa undergoing BCG therapy may benefit from Zoledronate administration by boosting Vδ2 T cells’ antitumor activity.

γδ T Cells Support Antigen-Specific αβ T cell-Mediated Antitumor Responses during BCG Treatment for Bladder Cancer

Bacillus Calmette-Guérin (BCG) is the most effective intravesical agent at reducing recurrence for patients with high-grade, non-muscle-invasive bladder cancer. Nevertheless, response to BCG is variable and strategies to boost BCG efficacy have not materialized. Prior work demonstrated a requirement for either conventional αβ or nonconventional γδ T cells in mediating BCG treatment efficacy, yet the importance of T-cell antigen specificity for BCG's treatment effect is unclear. Here, we provide direct evidence to show that BCG increases the number of tumor antigen-specific αβ T cells in patients with bladder cancer and protects mice from subsequent same-tumor challenge, supporting BCG induction of tumor-specific memory and protection. Adoptive T-cell transfers of antigen-specific αβ T cells into immunodeficient mice challenged with syngeneic MB49 bladder tumors showed that both tumor and BCG antigen-specific αβ T cells contributed to BCG efficacy. BCG-specific antitumor immunity, however, also required nonconventional γδ T cells. Prior work shows that the mTOR inhibitor rapamycin induces the proliferation and effector function of γδ T cells. Here, rapamycin increased BCG efficacy against both mouse and human bladder cancer in vivo in a γδ T cell-dependent manner. Thus, γδ T cells augment antitumor adaptive immune effects of BCG and support rapamycin as a promising approach to boost BCG efficacy in the treatment of non-muscle-invasive bladder cancer.

A Cell for the Ages: Human γδ T Cells across the Lifespan

The complexity of the human immune system is exacerbated by age-related changes to immune cell functionality. Many of these age-related effects remain undescribed or driven by mechanisms that are poorly understood. γδ T cells, while considered an adaptive subset based on immunological ontogeny, retain both innate-like and adaptive-like characteristics. This T cell population is small but mighty, and has been implicated in both homeostatic and disease-induced immunity within tissues and throughout the periphery. In this review, we outline what is known about the effect of age on human peripheral γδ T cells, and call attention to areas of the field where further research is needed.

Fetal public Vγ9Vδ2 T cells expand and gain potent cytotoxic functions early after birth

Vγ9Vδ2 T cells are a major human blood γδ T cell population that respond in a T cell receptor (TCR)-dependent manner to phosphoantigens which are generated by a variety of microorganisms. It is not clear how Vγ9Vδ2 T cells react toward the sudden microbial exposure early after birth. We found that human Vγ9Vδ2 T cells with a public/shared fetal-derived TCR repertoire expanded within 10 wk postpartum. Such an expansion was not observed in non-Vγ9Vδ2 γδ T cells, which possessed a private TCR repertoire. Furthermore, only the Vγ9Vδ2 T cells differentiated into potent cytotoxic effector cells by 10 wk of age, despite their fetal origin. Both the expansion of public fetal Vγ9Vδ2 T cells and their functional differentiation were not affected by newborn vaccination with the phosphoantigen-containing bacillus Calmette-Guérin (BCG) vaccine. These findings suggest a strong and early priming of the public fetal-derived Vγ9Vδ2 T cells promptly after birth, likely upon environmental phosphoantigen exposure.

Emerging role of γδ T cells in vaccine-mediated protection from infectious diseases

γδ T cells are fascinating cells that bridge the innate and adaptive immune systems. They have long been known to proliferate rapidly following infection; however, the identity of the specific γδ T cell subsets proliferating and the role of this expansion in protection from disease have only been explored more recently. Several recent studies have investigated γδ T‐cell responses to vaccines targeting infections such as Mycobacterium, Plasmodium and influenza, and studies in animal models have provided further insight into the association of these responses with improved clinical outcomes. In this review, we examine the evidence for a role for γδ T cells in vaccine‐induced protection against various bacterial, protozoan and viral infections. We further discuss results suggesting potential mechanisms for protection, including cytokine‐mediated direct and indirect killing of infected cells, and highlight remaining open questions in the field. Finally, building on current efforts to integrate strategies targeting γδ T cells into immunotherapies for cancer, we discuss potential approaches to improve vaccines for infectious diseases by inducing γδ T‐cell activation and cytotoxicity.

Gamma Delta T Cell Therapy for Cancer: It Is Good to be Local

Human gamma delta T cells have extraordinary properties including the capacity for tumor cell killing. The major gamma delta T cell subset in human beings is designated Vγ9Vδ2 and is activated by intermediates of isoprenoid biosynthesis or aminobisphosphonate inhibitors of farnesyldiphosphate synthase. Activated cells are potent for killing a broad range of tumor cells and demonstrated the capacity for tumor reduction in murine xenotransplant tumor models. Translating these findings to the clinic produced promising initial results but greater potency is needed. Here, we review the literature on gamma delta T cells in cancer therapy with emphasis on the Vγ9Vδ2 T cell subset. Our goal was to examine obstacles preventing effective Vγ9Vδ2 T cell therapy and strategies for overcoming them. We focus on the potential for local activation of Vγ9Vδ2 T cells within the tumor environment to increase potency and achieve objective responses during cancer therapy. The gamma delta T cells and especially the Vγ9Vδ2 T cell subset, have the potential to overcome many problems in cancer therapy especially for tumors with no known treatment, lacking tumor-specific antigens for targeting by antibodies and CAR-T, or unresponsive to immune checkpoint inhibitors. Translation of amazing work from many laboratories studying gamma delta T cells is needed to fulfill the promise of effective and safe cancer immunotherapy.

Mother-to-newborn transmission of mycobacterial L-forms and Vδ2 T-cell response in placentobiome of BCG-vaccinated pregnant women

The ability of bacteria to exist as a population of self-replicating forms with defective or entirely missing cell wall (L-forms) is an adaptive mechanism for their survival and reproduction under unfavorable conditions. Bacterial mother-to-fetus transfer is a universal phenomenon in the animal kingdom. However, data about vertical transfer of L bacterial forms are extremely scarce. Bacille Calmette-Guérin is an attenuated strain of M. bovis and the only licensed vaccine used for tuberculosis prevention. We already have shown that filterable L-forms of BCG exist freely in the vaccine and are able to reproduce and to form colonies. The present study was focused on the placental microbiome in the context of mother's BCG vaccination. Here we report an isolation of filterable mycobacterial L-form cultures from gestational tissues and blood of healthy newborns delivered by healthy BCG-vaccinated mothers after normal pregnancy. Of note, vertically transmitted mycobacterial L-forms as a part of placentobiome of the pregnant women didn't influence the number of resident pathogen-reactive Vδ2 cells. Placenta colonization with mycobacterial L-forms occurs by maternal blood-to-decidua transfer very early in gestation. Together, these data showed that BCG L-forms have the capacity to pass trans-placental barrier and that maternal BCG vaccination affects the placentobiome.

Metabolic engineering of Salmonella vaccine bacteria to boost human Vγ2Vδ2 T cell immunity

Human Vγ2Vδ2 T cells monitor isoprenoid metabolism by recognizing foreign (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), a metabolite in the 2-C-methyl-D-erythritol-4-phosphate pathway used by most eubacteria and apicomplexan parasites, and self isopentenyl pyrophosphate, a metabolite in the mevalonate pathway used by humans. Whereas microbial infections elicit prolonged expansion of memory Vγ2Vδ2 T cells, immunization with prenyl pyrophosphates or aminobisphosphonates elicit short-term Vγ2Vδ2 expansion with rapid anergy and deletion upon subsequent immunizations. We hypothesized that a live, attenuated bacterial vaccine that overproduces HMBPP would elicit long-lasting Vγ2Vδ2 T cell immunity by mimicking a natural infection. Therefore, we metabolically engineered the avirulent aroA(-) Salmonella enterica serovar Typhimurium SL7207 strain by deleting the gene for LytB (the downstream enzyme from HMBPP) and functionally complementing for this loss with genes encoding mevalonate pathway enzymes. LytB(-) Salmonella SL7207 had high HMBPP levels, infected human cells as efficiently as did the wild-type bacteria, and stimulated large ex vivo expansions of Vγ2Vδ2 T cells from human donors. Importantly, vaccination of a rhesus monkey with live lytB(-) Salmonella SL7207 stimulated a prolonged expansion of Vγ2Vδ2 T cells without significant side effects or anergy induction. These studies provide proof-of-principle that metabolic engineering can be used to derive live bacterial vaccines that boost Vγ2Vδ2 T cell immunity. Similar engineering of metabolic pathways to produce lipid Ags or B vitamin metabolite Ags could be used to derive live bacterial vaccine for other unconventional T cells that recognize nonpeptide Ags.

Tripartite immune cell co-operation in the Bacillus Calmette Guérin-induced activation of γδ T cells

γδ T cells contribute to immunosurveillance of pathogenic infections and malignant transformations; however, mechanisms of activation have yet to be fully defined. In this study we demonstrate a novel mechanism by which human Vδ2(+) γδ T cells are activated by the model pathogen Bacillus Calmette Guérin (BCG). We show in vitro that Vδ2 cell cytokine production and cytotoxic activity in response to BCG are dependent on both dendritic cells (DCs) and memory CD4(+) αβ T cells (CD4 T cells). We found that Vδ2 cells are indirectly activated by BCG in an interleukin (IL)-12p70-dependent manner, and that DC production of the IL-12p70 responsible for Vδ2 cell activation requires Toll-like receptor 2/4 ligands from BCG and interferon (IFN)-γ from memory CD4 T cells. Our data suggest that Vδ2 cell responses to BCG are dependent on the activation of IFN-γ-producing memory CD4 T cells, and provide novel insight into the complex interplay between cells of the innate and adaptive immune response.

WC1+ gammadelta T cell memory population is induced by killed bacterial vaccine

Limited studies have addressed the ability of gammadelta T cells to become memory populations. We previously demonstrated that WC1.1(+) gammadelta T cells from ruminants vaccinated with killed Leptospira borgpetersenii proliferate and produce IFN-gamma in recall responses. Here we show that this response is dependent upon antigen-responsive CD4 T cells, at least across transwell membranes; this requirement cannot be replaced by IL-2. The response was also dependent upon in vivo priming, since gammadelta T cells from leptospira vaccine-naive animals did not respond to antigen even when co-cultured across membranes from antigen-responsive PBMC. Gammadelta T cells were the major antigen-responding T cell population for the first 4 wks following vaccination and replicated more rapidly than CD4 T cells. Primed WC1(+) gammadelta T cells circulated as CD62L(hi)/CD45RO(int)/CD44(lo), characteristics of T(CM) cells. When stimulated with antigen, they decreased CD62L, increased CD44 and CD25, and had no change in CD45RO expression. These changes paralleled those of the leptospira antigen-responsive CD4 T cells but differed from those of gammadelta T cells proliferating to mitogen stimulation. This system for in vivo gammadelta T cell priming is unique, since it relies on a killed antigen to induce memory and may be pertinent to designing vaccines that require type 1 pro-inflammatory cytokines.

A tuberculosis vaccine based on phosphoantigens and fusion proteins induces distinct gammadelta and alphabeta T cell responses in primates

Phosphoantigens are mycobacterial non-peptide antigens that might enhance the immunogenicity of current subunit candidate vaccines for tuberculosis. However, their testing requires monkeys, the only animal models suitable for gammadelta T cell responses to mycobacteria. Thus here, the immunogenicity of 6-kDa early secretory antigenic target-mycolyl transferase complex antigen 85B (ESAT-6-Ag85B) (H-1 hybrid) fusion protein associated or not to a synthetic phosphoantigen was compared by a prime-boost regimen of two groups of eight cynomolgus. Although phosphoantigen activated immediately a strong release of systemic Th1 cytokines (IL-2, IL-6, IFN-gamma, TNF-alpha), it further anergized blood gammadelta T lymphocytes selectively. By contrast, the hybrid H-1 induced only memory alphabeta T cell responses, regardless of phosphoantigen. These latter essentially comprised cytotoxic T lymphocytes specific for Ag85B (on average + 430 cells/million PBMC) and few IFN-gamma-secreting cells (+ 40 cells/million PBMC, equally specific for ESAT-6 and for Ag85B). Hence, in macaques, a prime-boost with the H-1/phosphoantigen subunit combination induces two waves of immune responses, successively by gammadelta T and alphabeta T lymphocytes.

Potentiation of antigen-stimulated V gamma 9V delta 2 T cell cytokine production by immature dendritic cells (DC) and reciprocal effect on DC maturation

Vgamma9Vdelta2 T cells, a major gammadelta PBL subset in human adults, have been previously implicated in dendritic cell (DC) licensing, owing to their high frequency in peripheral tissues and their ability to produce inflammatory cytokines upon recognition of a broad array of conserved Ags. Although these observations implied efficient recognition of Ag-expressing immature DC (iDC) by Vgamma9Vdelta2 T cells, the role played by DC subsets in activation of these lymphocytes has not been carefully studied so far. We show that iDC, and to a lesser extent mature DC, potentiated Th1 and Th2 cytokine, but not cytolytic or proliferative responses, of established Vgamma9Vdelta2 T cell clones and ex vivo memory Vgamma9Vdelta2 PBL stimulated by synthetic agonists. The ability of iDC to potentiate Vgamma9Vdelta2 production of inflammatory cytokines required for their own maturation suggested that Vgamma9Vdelta2 T cells, despite their strong lytic activity, could promote efficient iDC licensing without killing at suboptimal Ag doses. Accordingly Vgamma9Vdelta2 cells induced accelerated maturation of Ag-expressing iDC but not "bystander" DC, even within mixed cell populations comprising both Ag-expressing and nonexpressing iDC. Furthermore Vgamma9Vdelta2 cells induced full differentiation into IL-12-producing cells of iDC infected by Vgamma9Vdelta2-stimulating mycobacteria that were otherwise unable to induce complete DC maturation. In conclusion the ability of iDC to selectively potentiate cytokine response of memory Vgamma9Vdelta2 T cells could underlie the adjuvant effect of these lymphocytes, and possibly other natural memory T cells, on conventional T cell responses.

Non-peptide antigens activating human Vγ9/Vδ2 T lymphocytes

Various non-peptidic ligands which specifically activate most of circulating human Vgamma9/Vdelta2 T lymphocytes are now known. Most of these are so-called phosphoantigens and directly trigger the Vgamma9/Vdelta2 TCR expressing cells, without need for MHC-restricted presentation molecules. Although some potent phosphoantigens currently involved in clinical trials are chemically-synthesized molecules, most of the natural antigens were isolated from microbial cultures. The structures and biosynthesis of phosphoantigens are reviewed here and the possible physiological significance of their recognition by gammadelta T lymphocytes is discussed.

Gamma interferon production by bovine gamma delta T cells following stimulation with mycobacterial mycolylarabinogalactan peptidoglycan

A large percentage of lymphocytes in the blood of cattle express the gamma delta T-cell receptor, but specific functions for these cells have not yet been clearly defined. There is evidence, however, that human, murine, and bovine gamma delta T cells have a role in the immune response to mycobacteria. This study investigated the ability of bovine gamma delta T cells to expand and produce gamma interferon (IFN-gamma) in response to stimulation with mycobacterial products. Bovine gamma delta T cells, isolated from the peripheral blood of healthy cattle, expanded following in vitro stimulation with live mycobacteria, mycobacterial crude cell wall extract, and Mycobacterium bovis culture filtrate proteins. In addition, purified gamma delta T cells, cocultured with purified monocytes and interleukin-2, consistently produced significant amounts of IFN-gamma in response to mycobacterial cell wall. The IFN-gamma-inducing component of the cell wall was further identified as a proteolytically resistant, non-sodium dodecyl sulfate-soluble component of the mycolylarabinogalactan peptidoglycan.

Antigens in tea-beverage prime human Vgamma 2Vdelta 2 T cells in vitro and in vivo for memory and nonmemory antibacterial cytokine responses

Human gammadelta T cells mediate innate immunity to microbes via T cell receptor-dependent recognition of unprocessed antigens with conserved molecular patterns. These nonpeptide alkylamine antigens are shared by tumor cells, bacteria, parasites, and fungi but also by edible plant products such as tea, apples, mushrooms, and wine. Here we show that priming of gammadelta T cells with alkylamine antigens in vitro results in a memory response to these antigens. Such priming results also in a nonmemory response to whole bacteria and to lipopolysaccharide, characterized by IL-12-dependent secretion of IFN-gamma by gammadelta T cells and by gammadelta T cell proliferation. Drinking tea, which contains l-theanine, a precursor of the nonpeptide antigen ethylamine, primed peripheral blood gammadelta T cells to mediate a memory response on reexposure to ethylamine and to secrete IFN-gamma in response to bacteria. This unique combination of innate immune response and immunologic memory shows that gammadelta T cells can function as a bridge between innate and acquired immunity. In addition, these data provide an explanation for the health benefits of tea.

Evaluation of type 1 immune response in naïve and vaccinated animals following challenge with Leptospira borgpetersenii serovar Hardjo: involvement of WC1(+) gammadelta and CD4 T cells

Organisms within the Hardjo serovar of Leptospira species are harbored in cattle throughout the world, causing abortion in pregnant animals as well as being shed in the urine, thereby providing sources of zoonotic infection for humans. We recently showed that sterile immunity in vaccinated cattle is associated with induction of a type 1 (Th1) cell-mediated immune response. Here naïve and previously vaccinated pregnant cattle were challenged with a virulent strain of serovar Hardjo and subsequently evaluated for expression of a type 1 immune response. Lymphocytes that responded in a recall response to antigen by undergoing blast transformation were evident in cultures of peripheral blood mononuclear cells (PBMC) from vaccinated cattle throughout the postchallenge test period while those from naïve cattle were evident at one time point only. Nevertheless, beginning at 2 weeks after challenge, gamma interferon (IFN-gamma) was measured in supernatants of antigen-stimulated PBMC cultures from nonvaccinated animals although the amount produced was always less than that in cultures of PBMC from vaccinated animals. IFN-gamma(+) cells were also evident in antigen-stimulated cultures of PBMC from vaccinated but not from nonvaccinated animals throughout the postchallenge period. The IFN-gamma(+) cells included CD4(+) and WC1(+) gammadelta T cells, and a similar proportion of these two subpopulations were found among the dividing cells in antigen-stimulated cultures as ascertained by carboxyfluorescein succinimidyl ester loading. Finally, while naïve and vaccinated animals had similar levels of antigen-specific immunoglobulin G1 (IgG1) following challenge, vaccinated animals had twofold-more IgG2. In conclusion, while infection may induce a type 1 response we suggest that it is too weak to prevent establishment of chronic infection.

Quantitative structure--activity relations for gammadelta T cell activation by phosphoantigens

gammadelta T cells help contribute to innate immunity and are activated by the natural phosphoantigens produced by the organisms responsible for causing, for example, tuberculosis, malaria, tularemia, and plague. They are also activated by synthetic phosphoantigens and are cytotoxic to tumor cells. Here, we show that it is now possible to accurately predict gammadelta T cell activation by both natural and synthetic phosphoantigens by using the quantitative structure-activity relationship (QSAR) techniques commonly used in drug design. This approach should be of use in developing novel immunotherapeutic agents as well as contributing to a better understanding of the immune system's response to infectious agents.

Phosphoantigen presentation by macrophages to mycobacterium tuberculosis--reactive Vgamma9Vdelta2+ T cells: modulation by chloroquine

Vgamma9Vdelta2+ T cells (gammadelta T cells) are activated by Mycobacterium tuberculosis and recognize mycobacterial nonpeptide phosphoantigens. The role of antigen-presenting cells in the processing and presentation of phosphoantigens to Vgamma9Vdelta2+ T cells is not understood. We analyzed the role of macrophages for activation of gammadelta T cells by a new synthetic phosphoantigen bromohydrin pyrophosphate (BrHPP) and M. tuberculosis. Macrophages greatly increased gammadelta T-cell activation by both BrHPP and M. tuberculosis. Fixation of macrophages before infection demonstrated that uptake of M. tuberculosis was required for presentation to gammadelta T cells. Antigens of M. tuberculosis remained stably associated with macrophage surface and were not removed by paraformaldehyde fixation or washing. Macrophages processed M. tuberculosis for gammadelta T cells through a brefeldin A-insensitive pathway, suggesting that transport through the endoplasmic reticulum and Golgi complex of a putative presenting molecule is not important in the early processing of M. tuberculosis antigens for gammadelta T cells. Processing of M. tuberculosis was not eliminated by chloroquine, indicating that processing of gammadelta antigens is not dependent on acidic pH in the lysosomes. Chloroquine treatment of BrHPP-pulsed macrophages increased activation of gammadelta T cells. Ammonium chloride treatment of macrophages did not increase reactivity of gammadelta T cells to BrHPP, indicating that the effect of chloroquine was independent of pH changes in endosomes. Chloroquine, by inhibiting membrane traffic, may increase association and retention of phosphoantigens with cell surface membrane molecules on macrophages.

Immunological characterization of a gammadelta T-cell stimulatory ligand on autologous monocytes

Bovine gammadelta T cells are stimulated to proliferate by autologous monocytes. This is referred to as the autologous mixed leucocyte reaction (AMLR). It has been shown previously that the stimulatory component is constitutively expressed on the monocyte plasma membrane and is a protein or has a protein moiety. Here we showed that gammadelta T-cell responses to the monocytes requires interaction with the T-cell receptor because Fab1 fragments of a monoclonal antibody (mAb) that reacts with the delta chain of the T-cell receptor blocked proliferation in the AMLR. Monocyte molecules involved in stimulation were also characterized further by biochemical and immunological methods. A mAb, named M5, was generated by immunizing mice with bovine monocytes and shown to block the ability of monocytes to stimulate in the AMLR. Treatment of monocytes or monocyte membranes with high salt, chelating agents or phospholipase C did not affect their ability to stimulate gammadelta T-cell proliferation or reactivity with mAb M5 indicating the ability of monocytes to stimulate does not involve peripheral membrane components or a glycosyl-phosphatidylinsositol (GPI)-anchored components. Hence it was concluded that the stimulation occurred as a result of intergral membrane proteins including that recognized by mAb M5. The ligand for mAb M5 was on all bovine monocytes and to a lower level on granulocytes but not on lymphocytes. MAb M5 also reacted with sheep monocytes but not with human monocytes or murine macrophages, in agreement with a previous reports that sheep monocytes but not human or mouse mononuclear phagocytes have the capacity to stimulate bovine gammadelta T cells in in vitro cultures. The level of expression of the M5 ligand was not altered by gamma-irradiation or culture of monocytes with lipopolysaccharide but it was decreased following culture with interferon-gamma-containing cell culture supernatants.

Escherichia coli produces phosphoantigens activating human gamma delta T cells

Human Vgamma9delta2 T lymphocytes are suggested to play an important role in the immune response to various microbial pathogens. In contrast to alphabeta T cells, gammadelta T lymphocytes recognize small, non-protein, phosphate-bearing antigens (phosphoantigens) in a major histocompatibility complex-independent manner. Four different phosphoantigens termed TUBag1 to TUBag4 with a common 3-formyl-1-butyl-pyrophosphate moiety and isopentenyl-pyrophosphate have been isolated and identified from mycobacteria. However, natural occurring gammadelta T cell ligands from other bacterial species were not characterized so far. Here, we describe the structural identification of the two compounds responsible for the gammadelta T cell-stimulating capacity of Escherichia coli as similar to the mycobacterial phosphoantigens 3-formyl-1-butyl-pyrophosphate and its M(r) 275 homologue TUBag2. In addition, E. coli phosphoantigens exert bioactivities on gammadelta T cells with similar potencies to the mycobacterial phosphoantigens at 5-15 nm concentration. Furthermore, our results clearly prove that the deoxyxylulose 5-phophate pathway (also referred to as Rohmer metabolic route of isoprenoid biosynthesis) is essential for the biosynthesis of the phosphoantigens in E. coli. Because this pathway is absent from human cells, it proves an ideal target for focusing efficiently the antimicrobial selectivity of human gammadelta T lymphocytes.

Protective killed Leptospira borgpetersenii vaccine induces potent Th1 immunity comprising responses by CD4 and gammadelta T lymphocytes

Leptospira borgpetersenii serovar hardjo is the most common cause of bovine leptospirosis and also causes zoonotic infections of humans. A protective killed vaccine against serovar hardjo was shown to induce strong antigen-specific proliferative responses by peripheral blood mononuclear cells (PBMC) from vaccinated cattle by 2 months after the first dose of vaccine. This response was absent from nonvaccinated control cattle. The mean response peaked by 2 months after completion of the two-dose vaccination regimen, and substantial proliferation was measured in in vitro cultures throughout the 7 months of the study period. Variations in magnitude of the response occurred among the vaccinated animals, but by 7 months postvaccination there was a substantial antigen-specific response with PBMC from all vaccinated animals. Up to one-third of the PBMC from vaccinated animals produced gamma interferon (IFN-gamma) after 7 days in culture with antigen, as ascertained by flow cytometric analysis, and significant levels of IFN-gamma were measured in culture supernatants by enzyme-linked immunosorbent assay. Two-color immunofluorescence revealed that one-third of the IFN-gamma-producing cells were gammadelta T cells, with the remaining cells being CD4(+) T cells. The significance of this study is the very potent Th1-type immune response induced and sustained following vaccination with a killed bacterial vaccine adjuvanted with aluminum hydroxide and the involvement of gammadelta T cells in the response. Moreover, induction of this Th1-type cellular immune response is associated with the protection afforded by the bovine leptospiral vaccine against L. borgpetersenii serovar hardjo.

In vitro responsiveness of gammadelta T cells from Mycobacterium bovis-infected cattle to mycobacterial antigens: predominant involvement of WC1(+) cells

It is generally accepted that protective immunity against tuberculosis is generated through the cell-mediated immune (CMI) system, and a greater understanding of such responses is required if better vaccines and diagnostic tests are to be developed. gammadelta T cells form a major proportion of the peripheral blood mononuclear cells (PBMC) in the ruminant system and, considering data from other species, may have a significant role in CMI responses in bovine tuberculosis. This study compared the in vitro responses of alphabeta and gammadelta T cells from Mycobacterium bovis-infected and uninfected cattle. The results showed that, following 24 h of culture of PBMC with M. bovis-derived antigens, the majority of gammadelta T cells from infected animals became highly activated (upregulation of interleukin-2R), while a lower proportion of the alphabeta T-cell population showed activation. Similar responses were evident to a lesser degree in uninfected animals. Study of the kinetics of this response showed that gammadelta T cells remained significantly activated for at least 7 days in culture, while activation of alphabeta T cells declined during that period. Subsequent analysis revealed that the majority of activated gammadelta T cells expressed WC1, a 215-kDa surface molecule which is not expressed on human or murine gammadelta T cells. Furthermore, in comparison with what was found for CD4(+) T cells, M. bovis antigen was found to induce strong cellular proliferation but relatively little gamma interferon release by purified WC1(+) gammadelta T cells. Overall, while the role of these cells in protective immunity remains unclear, their highly activated status in response to M. bovis suggests an important role in antimycobacterial immunity, and the ability of gammadelta T cells to influence other immune cell functions remains to be elucidated, particularly in relation to CMI-based diagnostic tests.

Rapid changes occur in the percentage of circulating bovine WC1(+)gamma delta Th1 cells

gamma delta T cells found in the peripheral blood of cattle include a major subpopulation distinguished by expression of WC1. These cells are distinct from the WC1(-)gamma delta T cell population based on T cell receptor gene usage. We documented that a group of 6-month-old calves allowed free-range grazing and access to their mothers had a significantly greater proportion of total gamma delta T cells in their blood, attributable to the WC1(+)gamma delta T cell subpopulation, compared to age and breed-matched calves held in conventional housing. When the animals with the greater proportion of gamma delta T cells were transferred to conventional housing there was a decrease in the WC1(+)population so that by 3 weeks after transfer there was no longer a significant difference between the two groups. To investigate the biological activities of WC1(+)gamma delta T cells, the cells were purified by flow cytometric sorting. In vitro, they responded to stimulation by irradiated monocytes in autologous mixed leukocyte reaction (AMLR) cultures but not to direct stimulation through the T cell receptor (T c R) by anti-delta monoclonal antibody. After stimulation in the AMLR, WC1(+)gamma delta T cells had a Th1 cytokine profile characterised by production of IFN -gamma and lack of IL -4. Thus we propose that higher levels of the WC1(+)gamma delta T cells may provide calves with a mechanism to produce Th1 cytokines and that the level of these cells may be modulated according to environment or stress since both groups of calves were apparently disease-free.

Identification of distinct lymphocyte subsets responding to subcellular fractions of Mycobacterium bovis bacille calmette-Guérin (BCG)

In order to investigate the ability of Mycobacterium bovis BCG vaccination to induce immune responses toward different classes of mycobacterial antigens and the cell populations involved in such responses, proliferation of distinct human lymphocyte subsets from BCG-vaccinated donors in response to different subcellular fractions of BCG was analysed and compared with that of not sensitized subjects. Proliferation of different cell subsets was evaluated by flow cytometric determination of bromodeoxyuridine incorporated into DNA of dividing cells and simultaneous identification of cell surface markers. Although a certain degree of variability was observed among different donors, after 6 days of in vitro stimulation BCG-vaccinated subjects displayed, as a mean, a stronger blastogenic response to all the classes of antigens compared with non-sensitized ones. PPD, culture filtrates and membrane antigens induced a predominant proliferation of CD4+ T cells. In contrast, preparations enriched in cytosolic antigens elicited strong proliferation of gammadelta+ T cells which, as a mean, represented 55% of the proliferating cells. Although to a lesser extent, proliferation of gammadelta+ T cells was also elicited by preparations enriched in membrane and cell wall antigens. In response to the latter preparation proliferation of CD4+ T cells and CD16+/CD3- (natural killer (NK)) cells was observed, as well. In particular, cell wall antigens were found to induce significantly higher levels of proliferation of NK cells compared with all the other classes of antigens.

Regulation of human CD4(+) alphabeta T-cell-receptor-positive (TCR(+)) and gammadelta TCR(+) T-cell responses to Mycobacterium tuberculosis by interleukin-10 and transforming growth factor beta

Mycobacterium tuberculosis is the etiologic agent of human tuberculosis and is estimated to infect one-third of the world's population. Control of M. tuberculosis requires T cells and macrophages. T-cell function is modulated by the cytokine environment, which in mycobacterial infection is a balance of proinflammatory (interleukin-1 [IL-1], IL-6, IL-8, IL-12, and tumor necrosis factor alpha) and inhibitory (IL-10 and transforming growth factor beta [TGF-beta]) cytokines. IL-10 and TGF-beta are produced by M. tuberculosis-infected macrophages. The effect of IL-10 and TGF-beta on M. tuberculosis-reactive human CD4(+) and gammadelta T cells, the two major human T-cell subsets activated by M. tuberculosis, was investigated. Both IL-10 and TGF-beta inhibited proliferation and gamma interferon production by CD4(+) and gammadelta T cells. IL-10 was a more potent inhibitor than TGF-beta for both T-cell subsets. Combinations of IL-10 and TGF-beta did not result in additive or synergistic inhibition. IL-10 inhibited gammadelta and CD4(+) T cells directly and inhibited monocyte antigen-presenting cell (APC) function for CD4(+) T cells and, to a lesser extent, for gammadelta T cells. TGF-beta inhibited both CD4(+) and gammadelta T cells directly and had little effect on APC function for gammadelta and CD4(+) T cells. IL-10 down-regulated major histocompatibility complex (MHC) class I, MHC class II, CD40, B7-1, and B7-2 expression on M. tuberculosis-infected monocytes to a greater extent than TGF-beta. Neither cytokine affected the uptake of M. tuberculosis by monocytes. Thus, IL-10 and TGF-beta both inhibited CD4(+) and gammadelta T cells but differed in the mechanism used to inhibit T-cell responses to M. tuberculosis.

Expansion of circulating V gamma 9/V delta 1 T cells in a patient with a syndrome of recurrent fever: evidence for an unusual antigen-driven process leading to selection of recurrent motifs within TCR junctional loops of diverse lengths

Polyclonal expansions of human Vdelta1 T cells have been described in diverse physiopathological situations without strong TCR structural data for an antigen-driven selection. Here, we have analyzed the phenotype and TCR repertoire of gamma delta T cells obtained from the peripheral blood of a 19-year-old patient with a syndrome of recurrent fever, which accounted for up to 40% of CD3(+) T cells and expressed predominantly Vgamma9 and Vdelta1 TCR regions and a memory phenotype. Sequence analysis of Vdelta1-Jdelta1 transcripts derived from peripheral blood lymphocytes (PBL) indicated that, while Vdelta1-Jdelta1 junctional sequences were diverse in length, all but one contained several recurrent motifs at conserved positions from both the 5'- and 3'-ends of the complementarity-determining region (CDR)3 loop. Analysis of gamma delta T cell clones derived from patient PBL demonstrated that Vgamma9(+) but not Vgamma9(-) T cell clones frequently expressed Vdelta1 chains with these characteristics and unveiled a hierarchy between the constraints imposed on the 5'- vs. the 3' motifs of the Vdelta1 CDR3 loops. These results constitute the first strong evidence for a nominal antigen-driven selection of Vdelta1 T cells in vivo and also suggest that the hierarchy of the constraints imposed by antigens respectively on the length and amino acid composition of TCR CDR3 loops differs between alpha beta and gamma delta T cells.

Gammadelta T cells increase with Mycobacterium avium complex infection but not with tuberculosis in AIDS patients

The aim of the present study was to better characterize the expansion of double-negative (DN) T cells in vivo in AIDS patients and to ascertain the discrepant response of an immunodepressed immune system towards two distinct mycobacterial infections. In a large cohort of HIV-1 seropositive patients with low CD4(+) T cell counts (<100/mm(3)), we have recently reported on an expansion of DN T cells which was observed only in patients with disseminated Mycobacterium avium infection, toxoplasmosis and Kaposi sarcoma, but not in patients with tuberculosis. The potential differential gammadelta T cells response observed in vivo in AIDS patients with tuberculosis or disseminated M. avium complex infection was investigated by collecting the concomitant or the closest T lymphocyte counts performed within 2 weeks of bacterial diagnosis of 112 disseminated M. avium infection and 41 tuberculosis patients. The DN and gammadelta T cell percentages were different between the two groups (P < 10(-4)) and the expansion of this compartment was found only with disseminated M. avium infections. An analysis of the variable delta2 segment versus pan-delta bearing T cells ratio disclosed a predominance of non-V(delta)2 T cells in these patients whose average values were identical in both groups. It is therefore concluded that the difference seen between these two types of mycobacterial infections concerning the DN T cells only involved the gammadelta T cells although the mechanism of their preferential expansion in disseminated M. avium infections remains a matter of speculation.

Tuberculosis II: the failure of the BCG vaccine

BCG (bacille Calmette-Guerin) is an attenuated pathogen characterized by its capacity to induce cellular and humoral immune responses primarily against a nonpeptidic antigen, lipoarabinomannan. Immune responses against this substance contribute to the immunoprotection of the patient if the production of IL-2 and INF-gamma is not impaired. The most adequate production of INF-gamma and IL-2 is obtained by immunoreactivity against proteinic antigens. The formation of IgG-type antibodies and of cellular immunity against mycobacterial peptidic and proteinic antigens is an additional immunological response essential for a good protection. This is achieved by the BCG vaccine in only a small proportion of the vaccinees. A vaccine adjuvant that also finds application as an immunotherapeutic agent is composed of proteinic antigens such as sonicates of Mycobacterium vaccae and antigen 60 of Mycobacterium bovis. These enhance the beneficial Th1-pole of the immune response. In addition, A60 induces the formation of antibodies against species-specific proteinic antigens. Despite the questioning of its innocuousness and efficacy, the BCG vaccine was imposed worldwide in 1950 by medical and political organizations that showed no concern for these questions. The contemporary structures of research administration in this area make it unlikely that the efficacious means recently developed to complement the action of the vaccine and of chemotherapies to face the surge of tuberculosis (TB) will be readily adopted.

Bovine gammadelta T-cell responses to the intracellular protozoan parasite Theileria parva

T cells bearing the gammadelta antigen receptor (gammadelta T cells) can constitute up to 50% of T cells in the peripheral blood and lymphoid organs of young cattle. We present data showing that gammadelta T cells are involved in immune responses against Theileria parva. gammadelta T cells isolated from peripheral blood mononuclear cells (PBMC) of T. parva-naive and -immune cattle proliferated in the presence of fixed or unfixed autologous T. parva-infected lymphoblasts (TpL) and heat-stressed concanavalin A (ConA)-induced blasts (ConA blasts) but not untreated ConA blasts. The specificity of response was further evaluated with a panel of gammadelta T-cell lines and clones. T-cell reactivity was blocked by GB21A, a monoclonal antibody (MAb) specific for the gammadelta T-cell receptor, but not by MAbs specific for class I and class II major histocompatibility complex (MHC) molecules. In addition, TpL but not ConA blasts from a variety of MHC-mismatched animals induced proliferation of the gammadelta T-cell lines and clones. These gammadelta T cells were found to respond to TpL infected with several different parasite stocks and failed to recognize TpL after elimination of the parasite by the theilericidal drug BW 720C. Assays for cytotoxic activity of gammadelta T cells sorted from bulk cultures of immune PBMC restimulated several times with autologous TpL demonstrated that effector cells whose specificity is similar to that of proliferating cells are generated. These results suggest that bovine gammadelta T cells are activated by and lyse T. parva-infected cells by recognizing conserved parasite-induced or parasite-derived antigens in an MHC-unrestricted fashion.

Gammadelta T cells and Mycobacterium tuberculosis

Since the first descriptions of mycobacterial reactivity for gammadelta T cells in 1989, studies of gammadelta T-cell responses to M. tuberculosis in humans and animal models have increased our understanding of the complex role(s) of this T-cell subset not only in the immune response to M. tuberculosis, but also to microbial pathogens in general. Although CD4+ T cells remain the dominant and critical T-cell subset in protection against M. tuberculosis, gammadelta T cells appear to have an important complementary role, which may be primarily expressed in and around maturing granulomas. This is a difficult area to study in humans. Gammadelta T cells are potent sources of IFN-gamma and competent cytotoxic effector cells, but differ from CD4+ T cells in the antigens they recognize and the manner in which M. tuberculosis-infected macrophages process and present antigens to these two subsets. One of the most fascinating features of Vgamma9/Vgamma2+ gammadelta T cells is their responsiveness to non-peptidic molecules. Solving the mechanism(s) of antigen recognition and presentation of these molecules to gammadelta T cells should help determine whether gammadelta T cells are responding to universal 'supernatigen'-like motifs expressed by a broad range of microbes or in fact discriminate among a diversity of peptidic and nonpeptidic microbial antigens. Enhanced understanding of the function of and antigen recognition by Vgamma9+/Vgamma2+ T cells is not only important for immunity to M. tuberculosis but also for T-cell responses to microbial pathogens in general.

Expansion of Vgamma9 Vdelta2 T cells is triggered by Francisella tularensis-derived phosphoantigens in tularemia but not after tularemia vaccination

Tularemia is a disease caused by the facultative intracellular bacterium Francisella tularensis. Here we demonstrate that during the first weeks of infection, a significant increase in levels of Vgamma9 Vdelta2 cells occurred in peripheral blood: in 13 patients analyzed 7 to 18 days after the onset of disease, these lymphocytes represented, on average, 30.5% of CD3+ cells and nearly 100% of gammadelta+ T cells. By contrast, after vaccination with the live vaccine strain (LVS) of F. tularensis, only a minor increase occurred. Eleven days after vaccination, gammadelta T cells represented an average of 6.7% and Vgamma9 Vdelta2 cells represented an average of 5.3% of T cells, as in control subjects. Since derivatives of nonpeptidic pyrophosphorylated molecules, referred to as phosphoantigens, are powerful stimuli for Vgamma9 Vdelta2 cells, this observation prompted an investigation of phosphoantigens in F. tularensis strains. The F. tularensis phosphoantigens triggered in vitro a proliferative response of human Vgamma9 Vdelta2 peripheral blood leukocytes as well as a cytotoxic response and tumor necrosis factor release from a Vgamma9 Vdelta2 T-cell clone. Quantitatively similar phosphoantigenic activity was detected in acellular extracts from two clinical isolates (FSC171 and Schu) and from LVS. Taken together, the chemical nature of the stimulus from the clinical isolates and the significant increase in levels of Vgamma9 Vdelta2 cells in peripheral blood of tularemia patients indicate that phosphoantigens produced by virulent strains of F. tularensis trigger in vivo expansion of gammadelta T cells in tularemia.

Gammadelta+ and CD4+ alphabeta+ human T cell subset responses upon stimulation with various Mycobacterium tuberculosis soluble extracts

By using a flow cytometric technique which allows direct identification of proliferating cells within mixed cell populations, we have previously described that soluble extracts obtained from Mycobacterium tuberculosis or M. avium represent strong stimuli for human gammadelta+ T cells. In the present study, we demonstrate that the protocol used for the preparation of M. tuberculosis soluble extracts may have an impact on their gammadelta+ T cell stimulatory capacity. In agreement with our previous data, soluble extracts prepared from bacteria killed at 85 degrees C and directly disrupted by prolonged sonication (TBe), elicited a strong proliferation of gammadelta+ T cells after 6-7 days of stimulation. In contrast, when soluble extracts were obtained from bacteria autoclaved (121 degrees C, 25 min) and then washed by centrifugation, a predominant proportion of CD4+ alphabeta+ T cells was achieved in the responding population. The stimulatory activity for gammadelta+ T cells was recovered in the supernatant of the autoclaved bacteria, indicating that autoclaving of M. tuberculosis bacilli releases an antigen(s) into the supernatant which stimulates human gammadelta+ T cells. While protease digestion of TBe only partially reduced its stimulatory capacity on gammadelta+ T cells, the stimulatory component(s) released into the supernatant after autoclavation of bacilli was found to be sensitive to protease digestion. Interestingly, in contrast to the preponderant proportion of gammadelta+ T cells induced in the responding population by unfractionated TBe, when the extract was fractionated by fast performance liquid chromatography (FPLC), most of the fractions exhibited a strong stimulatory capacity on CD4+ alphabeta+ T cells only. The gammadelta+ T cell stimulatory activity was confined to the low molecular weight range FPLC fractions. Such results may suggest a possible regulatory role of gammadelta+ T cells on CD4+ alphabeta+ T cells.

Processing of Mycobacterium tuberculosis bacilli by human monocytes for CD4+ alphabeta and gammadelta T cells: role of particulate antigen

Mycobacterium tuberculosis readily activates both CD4+ and Vdelta2+ gammadelta T cells. Despite similarity in function, these T-cell subsets differ in the antigens they recognize and the manners in which these antigens are presented by M. tuberculosis-infected monocytes. We investigated mechanisms of antigen processing of M. tuberculosis antigens to human CD4 and gammadelta T cells by monocytes. Initial uptake of M. tuberculosis bacilli and subsequent processing were required for efficient presentation not only to CD4 T cells but also to Vdelta2+ gammadelta T cells. For gammadelta T cells, recognition of M. tuberculosis-infected monocytes was dependent on Vdelta2+ T-cell-receptor expression. Recognition of M. tuberculosis antigens by CD4+ T cells was restricted by the class II major histocompatibility complex molecule HLA-DR. Processing of M. tuberculosis bacilli for Vdelta2+ gammadelta T cells was inhibitable by Brefeldin A, whereas processing of soluble mycobacterial antigens for gammadelta T cells was not sensitive to Brefeldin A. Processing of M. tuberculosis bacilli for CD4+ T cells was unaffected by Brefeldin A. Lysosomotropic agents such as chloroquine and ammonium chloride did not affect the processing of M. tuberculosis bacilli for CD4+ and gammadelta T cells. In contrast, both inhibitors blocked processing of soluble mycobacterial antigens for CD4+ T cells. Chloroquine and ammonium chloride insensitivity of processing of M. tuberculosis bacilli was not dependent on the viability of the bacteria, since processing of both formaldehyde-fixed dead bacteria and mycobacterial antigens covalently coupled to latex beads was chloroquine insensitive. Thus, the manner in which mycobacterial antigens were taken up by monocytes (particulate versus soluble) influenced the antigen processing pathway for CD4+ and gammadelta T cells.

An innate view of gamma delta T cells

Findings made during the past few years demonstrate that gamma delta T cells apparently share with macrophages a propensity to recognize nonpeptidic molecules of the kind most commonly associated with microorganisms and stressed cells. In general, recognition of these antigens by gamma delta T cells involves the antigen receptor but does not require antigen presenting cells to express MHC gene products or to have a functional antigen processing machinery. Other recent advances continue to support the notion that gamma delta T cells can perform specialized functions related to the repair of tissue damage.

A novel nucleotide-containing antigen for human blood gamma delta T lymphocytes

The stimulation of human gamma delta T cells by mycobacteria occurs through recognition of four distinct nonpeptide phosphorylated antigens termed TUBag1-4. Among these latter, TUBag4 has already been biochemically characterized as a gamma-X derivative of 5'-deoxythymidine triphosphate (Constant, P., Davodeau, F., Peyrat, M. A., Poquet, Y., Puzo, G., Bonneville, M. and Fournié, J.-J., Science 1994. 264: 267). However, despite chemical synthesis of weakly stimulatory nucleotide-containing analogs, these mycobacterial compounds remained the sole nucleotide-containing antigens actually isolated from natural sources. Here, we present the complete isolation of the TUBag3 antigen from Mycobacterium fortuitum and demonstrate that this nonpeptide molecule contains a 5'-UTP nucleotide moiety. On selected V gamma 9/V delta 2 clones, T cell responses can be triggered with nanomolar concentrations of TUBag3. Like crude mycobacterial extracts, this purified nucleotide conjugate elicits a strong polyclonal response of gamma delta PBL from healthy donors. Furthermore, we present evidence that this compound is distinct from the recently synthesized gamma-isopentenyl 5'-UTP, a nucleotide conjugate of isopentenyl pyrophosphate that was found to be stimulatory for human gamma delta T cells (Tanaka, Y., Morita, C.T., Tanaka, Y., Nieves, E., Brenner, M. B. and Bloom, B. R., Nature 1995. 375: 155). Since it appears that both mycobacterial nucleotide antigens are molecules structurally related to peculiar precursors of nucleic acid synthesis, we propose that TUBag-reactive T cells might be specifically devoted to surveillance of proliferating cells.

Plasmodium falciparum stimuli for human gammadelta T cells are related to phosphorylated antigens of mycobacteria

The presence in Plasmodium falciparum of a mitogenic factor for the major human blood gammadelta T-cell subset has been known for years. These gammadelta T cells bearing T-cell receptor Vgamma9 and Vdelta2 variable regions also respond to Mycobacterium tuberculosis, through recognition of several phosphorylated nonpeptidic antigens. In this study, we undertook a better characterization of the malarial stimulus and show that the polygonal activation of Vgamma9/Vdelta2 gammadelta T cells by P. falciparum schizonts is also and exclusively attributable to two phosphorylated malarial compounds. The finding of such stimuli in eukaryotic cells evidence an antigenic link between intracellular parasites as different as Plasmodium and Mycobacterium species. Hence, phosphorylated antigens could be involved in a common pattern of transdisease T-cell responses against various human pathogens.