Mechanisms of simian gamma delta T cell cytotoxicity against tumor and immunodeficiency virus-infected cells

Phenotype and function of peripheral blood γδ T cells in HIV infection with tuberculosis

Background

Although γδ T cells play an essential role in immunity against Human Immunodeficiency Virus (HIV) or Mycobacterium tuberculosis (MTB), they are poorly described in HIV infection with tuberculosis (TB).

Methods

The phenotypic and functional properties of peripheral blood γδ T cells in patients with HIV/TB co-infection were analyzed compared to healthy controls and patients with HIV mono-infection or TB by direct intracellular cytokine staining (ICS).

Results

The percentage of Vδ₁ subset in HIV/TB group was significantly higher than that in TB group, while the decreased frequency of the Vδ₂ and Vγ₂Vδ₂ subsets were observed in HIV/TB group than in TB group. The percentage of CD4⁺CD8^- Vδ₂ subset in HIV/TB group was markedly lower than in TB group. However, the percentage of CD4⁺CD8⁺ Vδ₂ subset in HIV/TB group was markedly higher than HIV group or TB group. A lower percentage TNF-α and a higher percentage of IL-17A of Vδ₂ subset were observed in HIV/TB group than that in HIV mono-infection. The percentage of perforin-producing Vδ₂ subset was significantly lower in HIV/TB group than that in HIV group and TB group.

Conclusions

Our data suggested that HIV/TB co-infection altered the balance of γδ T cell subsets. The influence of HIV/TB co-infection on the function of γδ T cells to produce cytokines was complicated, which will shed light on further investigations on the mechanisms of the immune response against HIV and/or MTB infection.

CD8β Depletion Does Not Prevent Control of Viral Replication or Protection from Challenge in Macaques Chronically Infected with a Live Attenuated Simian Immunodeficiency Virus

We evaluated the contribution of CD8αβ+ T cells to control of live-attenuated simian immunodeficiency virus (LASIV) replication during chronic infection and subsequent protection from pathogenic SIV challenge. Unlike previous reports with a CD8α-specific depleting monoclonal antibody (mAb), the CD8β-specific mAb CD8β255R1 selectively depleted CD8αβ+ T cells without also depleting non-CD8+ T cell populations that express CD8α, such as natural killer (NK) cells and γδ T cells. Following infusion with CD8β255R1, plasma viremia transiently increased coincident with declining peripheral CD8αβ+ T cells. Interestingly, plasma viremia returned to predepletion levels even when peripheral CD8αβ+ T cells did not. Although depletion of CD8αβ+ T cells in the lymph node (LN) was incomplete, frequencies of these cells were 3-fold lower (P = 0.006) in animals that received CD8β255R1 than in those that received control IgG. It is possible that these residual SIV-specific CD8αβ+ T cells may have contributed to suppression of viremia during chronic infection. We also determined whether infusion of CD8β255R1 in the LASIV-vaccinated animals increased their susceptibility to infection following intravenous challenge with pathogenic SIVmac239. We found that 7/8 animals infused with CD8β255R1, and 3/4 animals infused with the control IgG, were resistant to SIVmac239 infection. These results suggest that infusion with CD8β255R1 did not eliminate the protection afforded to LASIV vaccination. This provides a comprehensive description of the impact of CD8β255R1 infusion on the immunological composition in cynomolgus macaques, compared to an isotype-matched control IgG, while showing that the control of LASIV viremia and protection from challenge can occur even after CD8β255R1 administration.IMPORTANCE Studies of SIV-infected macaques that deplete CD8+ T cells in vivo with monoclonal antibodies have provided compelling evidence for their direct antiviral role. These studies utilized CD8α-specific mAbs that target both the major (CD8αβ+) and minor (CD8αα+) populations of CD8+ T cells but additionally deplete non-CD8+ T cell populations that express CD8α, such as NK cells and γδ T cells. In the current study, we administered the CD8β-specific depleting mAb CD8β255R1 to cynomolgus macaques chronically infected with a LASIV to selectively deplete CD8αβ+ T cells without removing CD8αα+ lymphocytes. We evaluated the impact on control of virus replication and protection from pathogenic SIVmac239 challenge. These results underscore the utility of CD8β255R1 for studying the direct contribution of CD8αβ+ T cells in various disease states.

Bovine peripheral blood WC1+ and WC1neg γδ T lymphocytes modulate monocyte-derived macrophage effector functions during in vitro Mycobacterium avium subspecies paratuberculosis infection

The importance of bovine γδ T lymphocytes during anti-mycobacterial immunity is recognized; however, the role of major subsets of γδ T lymphocytes (WC1⁺ and WC1^neg) in this process remains unclear. We investigated how WC1⁺ and WC1^neg γδ T lymphocyte subsets of calves modulate monocyte-derived macrophage (MDM) functions during Map infection in vitro. To achieve this, Map-infected or uninfected MDMs from young calves were co-cultured with autologous WC1⁺ or WC1^neg γδ T lymphocytes. Our data indicate that WC1⁺ and WC1^neg γδ T lymphocytes of young calves modulate effector functions of MDMs with respect to Map killing, CD11b and MHC-II expression. We observed differences in IFN-γ production and CD25 expression on γδ T lymphocyte subsets, as well as MDM expression of CD1b when in contact with WC1^neg γδ T lymphocytes.

Gammadelta T cell immune manipulation during chronic phase of simian-human immunodeficiency virus infection [corrected] confers immunological benefits

Vgamma2Vdelta2 T cells, a major human gammadelta T cell subset, recognize the phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) produced by mycobacteria and some opportunistic pathogens, and they contribute to innate/adaptive/homeostatic and anticancer immunity. As initial efforts to explore Vgamma2Vdelta2 T cell-based therapeutics against HIV/AIDS-associated bacterial/protozoal infections and neoplasms, we investigated whether a well-defined HMBPP/IL-2 therapeutic regimen could overcome HIV-mediated immune suppression to massively expand polyfunctional Vgamma2Vdelta2 T cells, and whether such activation/expansion could impact AIDS pathogenesis in simian HIV (SHIV)-infected Chinese rhesus macaques. While HMBPP/IL-2 coadministration during acute or chronic phase of SHIV infection induced massive activation/expansion of Vgamma2Vdelta2 T cells, the consequences of such activation/expansions were different between these two treatment settings. HMBPP/IL-2 cotreatment during acute SHIV infection did not prevent the increases in peak and set-point viral loads or the accelerated disease progression seen with IL-2 treatment alone. In contrast, HMBPP/IL-2 cotreatment during chronic infection did not exacerbate disease, and more importantly it could confer immunological benefits. Surprisingly, although viral antigenic loads were not increased upon HMBPP/IL-2 cotreatment during chronic SHIV infection, HMBPP activation of Vgamma2Vdelta2 T cells boosted HIV Env-specific Ab titers. Such increases in Abs were sustained for >170 days and were immediately preceded by increased production of IFN-gamma, TNF-alpha, IL-4, and IL-10 during peak expansion of Vgamma2Vdelta2 T cells displaying memory phenotypes, as well as the short-term increased effector function of Vgamma2Vdelta2 T cells and CD4(+) and CD8(+) alphabeta T cells producing antimicrobial cytokines. Thus, HMBPP/Vgamma2Vdelta2 T cell-based intervention may potentially be useful for combating neoplasms and HMBPP-producing opportunistic pathogens in chronically HIV-infected individuals.

Human gamma delta T cells: candidates for the development of immunotherapeutic strategies

A numerically small subset of human T lymphocytes expresses a gamma delta T cell receptor (TCR). These gamma delta T cells share certain effector functions with alpha beta T cells as well as with NK cells and NKT cells. The major peripheral blood gamma delta T cell subset in healthy adults expresses a Vgamma9Vdelta2 TCR, which recognizes small phosphorylated metabolites referred to as phosphoantigens. Vdelta1 gamma delta T cells mainly occur in the intestine. They recognize the stress-induced MICA/B and CD1c. Furthermore, gamma delta T cells express a variety of NK cell and pattern-recognition receptors which are responsible for the "fine-tuning" of effector functions. In recent years, gamma delta T cells start to emerge as a rewarding target for immunotherapeutic strategies against viral infections and cancer. A better understanding of factors that modulate gamma gamma delta T cell function will further eluminate the potential of these cells.

Vaccinia virus inhibits T cell receptor-dependent responses by human gammadelta T cells

Vaccinia virus (VV) is an effective vaccine and vector but has evolved multiple mechanisms for evading host immunity. We characterized the interactions of VV (TianTan and New York City Board of Health strains) with human gammadelta T cells because of the role they play in immune control of this virus. Exposure to VV failed to trigger proliferative responses in gammadelta T cells from unprimed individuals, but it was an unexpected finding that VV blocked responses to model antigens by the Vgamma2Vdelta2 T cell subset. Infectious or ultraviolet light-inactivated VV inhibited proliferative Vgamma2Vdelta2 T cell responses to phosphoantigens and tumor cells, prevented cytolysis of Daudi B cells, and reduced cytokine production. Inhibiting Vgamma2Vdelta2 T cells may be a mechanism for evading host immunity and increasing VV virulence. Increased VV replication or expression in the absence of gammadelta T cell responses might contribute to its potency as a vaccine against poxvirus and recombinant antigens.

Antiviral reactivities of gammadelta T cells

The complex antiviral immune mechanisms involve both adaptive and innate reactions mediated by γδ T lymphocytes, whose unique immunosurveillance contributions are analyzed here in different clinical and experimental settings. It is beyond any doubt that the fast, potent, cytotoxic as well as non-cytolytic antiviral activities of γδ T cells are critical in protecting the host against diverse viral pathogens.

Granule-dependent cytolysis of Mycobacterium tuberculosis-infected macrophages by human gammadelta+ T cells has no effect on intracellular mycobacterial viability

One of the most important effector functions of activated gammadelta+ T cells in tuberculosis is their strong cytolytic activity against a variety of target cells, including M. tuberculosis-infected macrophages. In the present study, we investigated the relationship between the mechanism of cytolysis utilized by gammadelta+ CTL and intracellular M. tuberculosis survival using a panel of cytolytic human M. tuberculosis-specific gammadelta+ CTL clones. Cytolysis mediated by the gammadelta+ T-cell clones was found to be Ca2+-dependent, sensitive to Cyclosporin A, and was completely abrogated following Sr2+-induced de-granulation of the gammadelta+ T cell effectors. These data demonstrate that gammadelta+ T-cell-mediated cytoxicity was mediated via the granule exocytosis/perforin pathway. Despite significant cytolytic activity against mycobacteria infected U937 cells, the gammadelta+ CTL clones had no impact on the survival of intracellular M. tuberculosis.

gammadelta(+) T-Lp6phocyte cytotoxicity against envelope-expressing target cells is unique to the alymphocytic state of bovine leukemia virus infection in the natural host

Bovine leukemia virus (BLV) is a complex B-lymphotrophic retrovirus of cattle and the causative agent of enzootic bovine leukosis. Serum antibody in infected animals does not correlate with protection from disease, yet only some animals develop severe disease. While a cytotoxic T-lymphocyte response may be responsible for directing BLV pathogenesis, this possibility has been left largely unexplored, in part since the lack of readily established cytotoxic target cells in cattle has hampered such studies. Using long-term naturally infected alymphocytic (AL) cattle, we have established the existence of cytotoxic T-lymphocyte response against BLV envelope proteins (Env; gp51/gp30). In vitro-expanded peripheral blood mononuclear (PBM) cell effector populations consisted mainly of gammadelta(+) (>40%), CD4(+) (>35%), and CD8(+) (>10%) T lymphocytes. Specific lysis of autologous fibroblasts infected with recombinant vaccinia virus (rVV) delivering the BLV env gene ranged from 30 to 65%. Depletion studies indicated that gammadelta(+) and not CD8(+) T cells were responsible for the cytotoxicity against autologous rVVenv-expressing fibroblasts. Additionally, cultured effector cells lysed rVVenv-expressing autologous fibroblasts and rVVenv-expressing xenogeneic targets similarly, suggesting a lack of genetic restricted killing. Restimulation of effector populations increased the proportion of gammadelta(+) T cells and concomitantly Env-specific cytolysis. Interestingly, culture of cells from BLV-negative or persistently lymphocytic cattle failed to elicit such cytotoxic responses or increase in gammadelta(+) T-cell numbers. These results imply that cytotoxic gammadelta(+) T lymphocytes from only AL cattle recognize BLV Env without a requirement for classical major histocompatibility complex interactions. It is known that gammadelta(+) T lymphocytes are diverse and numerous in cattle, and here we show that they may serve a surveillance role during natural BLV infection.

The role of intrahepatic gammadelta-T cells for liver injury induced by Salmonella infection in mouse

Liver injury was induced after infection with Salmonella choleraesuis 31N-1. In T-cell receptor-delta knockout mice, serum alanine transferase level was significantly decreased in comparison with normal control mice after Salmonella infection. On the contrary, in vivo administration of anti-gammadelta T-cell receptor monoclonal antibody (UC7-13D5) to stimulate gammadelta-T cells in infected mice significantly increased serum alanine transferase level but decreased bacterial growth compared with infected mice given control antibody (UC8; hamster IgG). These data suggest that gammadelta-T cells have effector activities not only for protection but also for liver injury during Salmonella infection.

Depletion of IL-10- and TGF-β-Producing Regulatory γδ T Cells by Administering a Daunomycin-Conjugated Specific Monoclonal Antibody in Early Tumor Lesions Augments the Activity of CTLs and NK Cells

It has been demonstrated that γδ T cells accumulating in early tumor lesions and those purified from spleen cells of tumor-bearing mice attenuate the activity of CTLs and NK cells. We, therefore, investigated whether depletion of γδ T cells from early lesions of tumors results in restoration of CTL and NK cell activities and subsequent regression of tumors. A daunomycin-conjugated anti-γδTCR mAb UC7-13D5 (Dau-UC7) was prepared to efficiently deplete γδ T cells. An in vitro study revealed that Dau-UC7 specifically lysed γδTCR+ cells and effectively inhibited splenic γδ T cells from tumor-bearing mice to produce cytotoxic cell-suppressive factors. Furthermore, intralesional injections of Dau-UC7 at an early stage of tumor development led to augmentation of tumor-specific CTL as well as NK cell activities and to the resultant regression or growth inhibition of the tumors. On analysis of cytokine profile, γδ T cells transcribed mRNAs for IL-10 and TGF-β, but not IL-4 or IFN-γ, suggesting the T regulatory 1-like phenotype. Finally, a blocking study with mAbs showed that the inhibitory action of γδ T cells on CTLs and NK cells was at least partly mediated by IL-10 and TGF-β. These results clearly demonstrated the novel mechanism by which T regulatory 1-like γδ T cells suppress anti-tumor CTL and NK activities by their regulatory cytokines in early tumor formation.

Gammadelta receptor bearing T cells in scleroderma: enhanced interaction with vascular endothelial cells in vitro

In view of the documented perivascular mononuclear cell infiltration in the involved organs in scleroderma (SSc) and the reported accumulation of gammadelta-T cells in SSc skin and lung, we evaluated gammadelta-T cell interaction with endothelial cells (EC) in vitro. gammadelta- and alphabeta-T cells were isolated from BPMN of SSc patients with early diffuse disease and of matched control subjects by an immunomagnetic method after stimulation with mycobacterium lysate and interleukin-2 for 2 weeks. Lymphocyte adhesion, proliferation, and cytotoxicity to EC were investigated. SSc gammadelta-T cells adhered to cultured EC and proliferated at higher rates than control cells. Furthermore, significant EC cytotoxicity by SSc gammadelta was seen. The cytotoxicity was blocked by addition of anti-gammadelta-TCR antibody and by anti-granzyme A antibody but not by anti-MHC class I and II antibodies. Expression of granzyme A mRNA was seen in five/five SSc gammadelta-T cells and in one/five control cells. alphabeta-T cells from both SSc and control subjects were significantly less interactive with EC than gammadelta-T cells. The data demonstrate EC recognition by SSc gammadelta-T cells and propose gammadelta-T cells as a possible effector cell type in the immune pathogenesis of SSc.

Pathogenesis of Marek's disease (MD) and possible mechanisms of immunity induced by MD vaccine

Marek's disease (MD) is a lymphoproliferative disease of chicken, which is characterized by malignant T cell-lymphoma formation. This disease can be effectively prevented by vaccination with attenuated MD virus (MDV), apathogenic MDV or herpesvirus of turkey. MD vaccines are ones of a few vaccines which can prevent virus-induced tumor among mammalian and avian species. To determine the roles of T cell subsets in the protection mechanism, chickens vaccinated with an attenuated MDV (CVI988) were depleted of either CD4+ or CD8+ T cells by neonatal thymectomy and injections of monoclonal antibodies against chicken CD4 or CD8 molecules and then challenged with an oncogenic MDV. These birds were effectively protected from MDV-induced tumors. However, virus titers in CD4+ T cells, which are the main target cells for MDV-latent infection and subsequent transformation, were much higher in CD8-deficient vaccinated chickens than in untreated vaccinated chickens at the early stage of the latent phase. These results suggested that CD8+ T cell responses induced by the MD vaccine are essential for anti-virus but not anti-tumor effects. Here, we will discuss how the attenuated vaccine prevents chickens from lymphoma-formation by an oncogenic MDV.