Gamma delta T cells in rhesus monkeys and their response to simian immunodeficiency virus (SIV) infection

The BLT Humanized Mouse Model as a Tool for Studying Human Gamma Delta T Cell-HIV Interactions In Vivo

Gamma-delta (γδ) T cells recognize antigens in a major histocompatibility complex (MHC) independent and have cytotoxic capability. Human immunodeficiency virus (HIV) infection reduces the proportion of the Vδ2 cell subset compared to the Vδ1 cell subset of γδ T cells in the blood in most infected individuals, except for elite controllers. The capacity of Vδ2 T cells to kill HIV-infected targets has been demonstrated in vitro, albeit in vivo confirmatory studies are lacking. Here, we provide the first characterization of γδ T cell-HIV interactions in bone marrow-liver-thymus (BLT) humanized mice and examined the immunotherapeutic potential of Vδ2 T cells in controlling HIV replication in vivo. We demonstrate a reduced proportion of Vδ2 T cells and an increased proportion of Vδ1 T cells in HIV-infected BLT humanized mice, like in HIV-positive individuals. HIV infection in BLT humanized mice also impaired the ex vivo expansion of Vδ2 T cells, like in HIV-positive individuals. Adoptive transfer of activated Vδ2 T cells did not control HIV replication during cell-associated HIV transmission in BLT humanized mice but instead exacerbated viremia, suggesting that Vδ2 T cells may serve as early targets for HIV replication. Our findings demonstrate that BLT humanized mice can model γδ T cell-HIV interactions in vivo.

Localization of infection in neonatal rhesus macaques after oral viral challenge

Vertical transmission of human immunodeficiency virus (HIV) can occur in utero, during delivery, and through breastfeeding. We utilized Positron Emission Tomography (PET) imaging coupled with fluorescent microscopy of ⁶⁴Cu-labeled photoactivatable-GFP-HIV (PA-GFP-BaL) to determine how HIV virions distribute and localize in neonatal rhesus macaques two and four hours after oral viral challenge. Our results show that by four hours after oral viral exposure, HIV virions localize to and penetrate the rectal mucosa. We also used a dual viral challenge with a non-replicative viral vector and a replication competent SHIV-1157ipd3N4 to examine viral transduction and dissemination at 96 hours. Our data show that while SHIV-1157ipd3N4 infection can be found in the oral cavity and upper gastrointestinal (GI) tract, the small and large intestine contained the largest number of infected cells. Moreover, we found that T cells were the biggest population of infected immune cells. Thus, thanks to these novel technologies, we are able to visualize and delineate of viral distribution and infection throughout the entire neonatal GI tract during acute viral infection.

Approximately 1.8 million children are currently living with human immunodeficiency virus (HIV). While mother-to-child HIV transmission can occur in utero and during delivery, it most commonly occurs through breastfeeding, creating the need to understand how the virus moves throughout the body and infects the infant once breast milk is consumed. Here, we used multiple imaging techniques and PCR to determine how HIV distributes throughout the gastrointestinal tract after oral viral exposure and in which tissues and cell types become acutely infected. We found that HIV rapidly spreads throughout and penetrates the entire gastrointestinal tract as early as four hours after exposure. We also found that the intestine contained the largest number of infected cells at 96 hours and that most cells infected were T cells. Our study shows that these imaging technologies allow for the examination of viral distribution and infection in a rhesus macaque model.

Dysregulation of IL-17/IL-22 Effector Functions in Blood and Gut Mucosal Gamma Delta T Cells Correlates With Increase in Circulating Leaky Gut and Inflammatory Markers During cART-Treated Chronic SIV Infection in Macaques

HIV-associated inflammation has been implicated in the premature aging and increased risk of age-associated comorbidities in cART-treated individuals. However, the immune mechanisms underlying the chronic inflammatory state of cART-suppressed HIV infection remain unclear. Here, we investigated the role of γδT cells, a group of innate IL-17 producing T lymphocytes, in the development of systemic inflammation and leaky gut phenotype during cART-suppressed SIV infection of macaques. Plasma levels of inflammatory mediators, intestinal epithelial barrier disruption (IEBD) and microbial translocation (MT) biomarkers, and Th1/Th17-type cytokine functions were longitudinally assessed in blood and gut mucosa of SIV-infected, cART-suppressed macaques. Among the various gut mucosal IL-17/IL-22-producing T lymphocyte subsets including Th17, γδT, CD161+ CD8+ T, and MAIT cells, a specific decline in the Vδ2 subset of γδT cells and impaired IL-17/IL-22 production in γδT cells significantly correlated with the subsequent increase in plasma IEBD/MT markers (IFABP, LPS-binding protein, and sCD14) and pro-inflammatory cytokines (IL-6, IL-1β, IP10, etc.) despite continued viral suppression during long-term cART. Further, the plasma inflammatory cytokine signature during long-term cART was distinct from acute SIV infection and resembled the inflammatory cytokine profile of uninfected aging (inflammaging) macaques. Overall, our data suggest that during cART-suppressed chronic SIV infection, dysregulation of IL-17/IL-22 cytokine effector functions and decline of Vδ2 γδT cell subsets may contribute to gut epithelial barrier disruption and development of a distinct plasma inflammatory signature characteristic of inflammaging. Our results advance the current understanding of the impact of chronic HIV/SIV infection on γδT cell functions and demonstrate that in the setting of long-term cART, the loss of epithelial barrier-protective functions of Vδ2 T cells and ensuing IEBD/MT occurs before the hallmark expansion of Vδ1 subsets and skewed Vδ2/Vδ1 ratio. Thus, our work suggests that novel therapeutic approaches toward restoring IL-17/IL-22 cytokine functions of intestinal Vδ2 T cells may be beneficial in preserving gut epithelial barrier function and reducing chronic inflammation in HIV-infected individuals.

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.

Mucosal and Systemic γδ+ T Cells Associated with Control of Simian Immunodeficiency Virus Infection

γδ T cells act as a first line of defense against invading pathogens. However, despite their abundance in mucosal tissue, little information is available about their functionality in this compartment in the context of HIV/SIV infection. In this study, we evaluated the frequency, phenotype, and functionality of Vδ1 and Vδ2 T cells from blood, rectum, and the female reproductive tract (FRT) of rhesus macaques to determine whether these cells contribute to control of SIV infection. No alteration in the peripheral Vδ1/Vδ2 ratio in SIV-infected macaques was observed. However, CD8⁺ and CD4⁺CD8⁺ Vδ1 T cells were expanded along with upregulation of NKG2D, CD107, and granzyme B, suggesting cytotoxic function. In contrast, Vδ2 T cells showed a reduced ability to produce the inflammatory cytokine IFN-γ. In the FRT of SIV⁺ macaques, Vδ1 and Vδ2 showed comparable levels across vaginal, ectocervical, and endocervical tissues; however, endocervical Vδ2 T cells showed higher inflammatory profiles than the two other regions. No sex difference was seen in the rectal Vδ1/Vδ2 ratio. Several peripheral Vδ1 and/or Vδ2 T cell subpopulations expressing IFN-γ and/or NKG2D were positively correlated with decreased plasma viremia. Notably, Vδ2 CD8⁺ T cells of the endocervix were negatively correlated with chronic viremia. Overall, our results suggest that a robust Vδ1 and Vδ2 T cell response in blood and the FRT of SIV-infected macaques contribute to control of viremia.

γδ T Cells in HIV Disease: Past, Present, and Future

Human immunodeficiency virus (HIV) type 1 dysregulates γδ T cells as part of an immune evasion mechanism. Nearly three decades of research defined the effects of HIV on γδ T cells and how this impacts disease. With highly effective antiretroviral therapy providing virus suppression and longer survival, we expected a return to normal for γδ T cells. This is not the case. Even in patients with CD4 T cell reconstitution, normal γδ T cell levels and function are not recovered. The durable damage to Vδ2 T cells is paralleled by defects in NK, CD8 T cells, and dendritic cells. Whether these consequences of HIV stem from similar or distinct mechanisms are not known and effective means for recovering the full range of cellular immunity have not been discovered. These unanswered questions receive too little attention in the overall program of efforts to cure HIV this disease. Approved drugs capable of increasing Vδ2 T cell function are being tested in clinical trials for cancer and hold promise for restoring normal function in patients with HIV disease. The impetus for conducting clinical trials will come from understanding the significance of γδ T cells in HIV disease and what might be gained from targeted immunotherapy. This review traces the history and current progress of AIDS-related research on γδ T cells. We emphasize the damage to γδ T cells that persists despite effective virus suppression. These chronic immune deficits may be linked to the comorbidities of AIDS (cancer, cardiovascular disease, metabolic disease, and others) and will hinder efforts to eradicate HIV by cytotoxic T or NK cell killing. Here, we focus on one subset of T cells that may be critical in the pathogenesis of HIV and an attractive target for new immune-based therapies.

Localized populations of CD8 MHC class I tetramer SIV-specific T cells in lymphoid follicles and genital epithelium

CD8 T cells play an important role in controlling viral infections. We investigated the in situ localization of simian immunodeficiency virus (SIV)-specific T cells in lymph and genital tissues from SIV-infected macaques using MHC-class I tetramers. The majority of tetramer-binding cells localized in T cell zones and were CD8⁺. Curiously, small subpopulations of tetramer-binding cells that had little to no surface CD8 were detected in situ both early and late post-infection, and in both vaginally and rectally inoculated macaques. These tetramer⁺CD8^low/− cells were more often localized in apparent B cell follicles relative to T cell zones and more often found near or within the genital epithelium than the submucosa. Cells analyzed by flow cytometry showed similar populations of cells. Further immunohistological characterization revealed small populations of tetramer⁺CD20⁻ cells inside B cell follicles and that tetramer⁺ cells did not stain with γδ-TCR nor CD4 antibodies. Negative control tetramer staining indicated that tetramer⁺CD8^low/− cells were not likely NK cells non-specifically binding to MHC tetramers. These findings have important implications for SIV-specific and other antigen-specific T cell function in these specific tissue locations, and suggest a model in which antigen-specific CD8+ T cells down modulate CD8 upon entering B cell follicles or the epithelial layer of tissues, or alternatively a model in which only antigen-specific CD8 T cells that down-modulate CD8 can enter B cell follicles or the epithelium.

Association between Vgamma2Vdelta2 T cells and disease progression after infection with closely related strains of HIV in China

BACKGROUND

Human immunodeficiency virus (HIV) infection and disease are accompanied by decreases in the absolute number and function of Vgamma2Vdelta2 T cells, suggesting that this subset of cells may play an important role in controlling disease. We performed a cross-sectional study involving HIV-infected former blood donors and assessed the association between Vgamma2Vdelta2 T cells and markers of disease progression.

METHODS

Changes in Vgamma2Vdelta2 T cell count and function were compared between HIV-infected individuals and healthy blood donors using the Mann-Whitney U test. The relationships between Vgamma2Vdelta2 T cell count, plasma viral load, and CD4 T cell count were analyzed using the Spearman correlation.

RESULTS

We found significant positive correlations between CD4 T cell count and both total Vgamma2Vdelta2 T cell count (P<.001) and functional (isopentenyl pyrophosphate-responsive) Vgamma2Vdelta2 T cell count (P<.001). We found significant reverse correlations between viral load and both total Vgamma2Vdelta2 T cell count (P<.05) and functional Vgamma2Vdelta2 T cell count (P<.05).

CONCLUSIONS

The association of Vgamma2Vdelta2 T cells with disease progression in 146 HIV-infected participants supports the view that intact Vgamma2Vdelta2 T cell populations are important for controlling HIV disease.

Impacts of HIV infection on Vgamma2Vdelta2 T cell phenotype and function: a mechanism for reduced tumor immunity in AIDS

HIV infection causes rapid and lasting defects in the population of Vgamma2Vdelta2 T cells. To fully describe the impact of HIV, we examined PBMC samples from HIV+ patients receiving highly active antiretroviral therapy, who had displayed prolonged viral control and CD4 counts above 300 cells/mm3. We observed lower frequencies of CD27-/CD45RA- Vgamma2Vdelta2 cells in HIV+ individuals when compared with controls, coupled with an increased proportion of CD45RA+ cells. These changes were common among 24 HIV+ patients and were not related to CD4 cell count or viral RNA burden. Vgamma2 cells from HIV+ individuals had lower expression of Granzyme B and displayed reduced cytotoxicity against Daudi targets after in vitro stimulation. There was increased expression of FasR (CD95) on Vgamma2 cells from HIV+ PBMC that may be a mechanism for depletion of Vgamma2 cells during disease. In addition to the well-characterized defects in the Vgamma2 repertoire and functional responses to phosphoantigen, the proportion of CD27-/CD45RA- Vgamma2Vdelta2 T cells after isopentenyl pyrophosphate stimulation was reduced sharply in HIV+ donors versus controls. Thus, HIV infection has multiple impacts on the circulating Vgamma2Vdelta2 T cell population that combine to reduce the potential effector activity in terms of tumor cytotoxicity. Changes in Vgamma2Vdelta2 T cells, along with concomitant effects on NK and NKT cells that also contribute to tumor surveillance, may be important factors for elevating the risk of malignancy during AIDS.

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.

Vdelta2+ gammadelta T cell function in Mycobacterium tuberculosis- and HIV-1-positive patients in the United States and Uganda: application of a whole-blood assay

BACKGROUND

Vgamma9(+)Vdelta2(+) gammadelta T cells (Vdelta 2(+) T cells) are activated by Mycobacterium tuberculosis and secrete interferon (IFN)-gamma. Vdelta 2(+) T cells recognize phosphoantigens, such as bromohydrin pyrophosphate (BrHPP), and link innate and adaptive immunity.

METHODS

A whole-blood assay was developed that used IFN-gamma secretion in response to BrHPP as a measurement of Vdelta2(+) T cell function.

RESULTS

Peak IFN-gamma levels were detected after stimulating whole blood with BrHPP for 7-9 days. IFN- gamma production in whole blood in response to BrHPP paralleled IFN-gamma production and Vdelta2(+) T cell expansion of peripheral-blood mononuclear cells. The assay was used to evaluate Vdelta2(+) T cell function in subjects in the United States (n = 24) and Uganda (n = 178) who were or were not infected with M. tuberculosis and/or human immunodeficiency virus (HIV) type 1. When 50 micromol/L BrHPP was used, 100% of healthy subjects produced IFN-gamma. The Vdelta2(+) T cell response was independent of the tuberculin skin test response. In Uganda, Vdelta2(+) T cell responses were decreased in patients with tuberculosis (n = 73) compared with responses in household contacts (n = 105). HIV-1-positive household contacts had lower responses than did HIV-1-negative household contacts. HIV-1-positive patients with tuberculosis had the lowest V delta 2(+) T cell responses.

CONCLUSIONS

Tuberculosis and HIV-1 infection are associated with decreased Velta2(+) T cell function. Decreased Vdelta2(+) T cell function may contribute to increased risk for tuberculosis in HIV-1-positive patients.

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.

Vgamma2Vdelta2+ T cells and anti-microbial immune responses

Vgamma2Vdelta2(+) T cells exist only in primates and constitute the majority of circulating human gammadelta T cells. Recent studies have demonstrated that this unique gammadelta T cell subpopulation can be a component of adaptive immune responses and contribute to anti-microbial immunity to infections.

Immunological changes in simian immunodeficiency virus (SIV(agm))-infected African green monkeys (AGM): expanded cytotoxic T lymphocyte, natural killer and B cell subsets in the natural host of SIV(agm)

The African green monkey (AGM) model system for simian immunodeficiency virus (SIV(agm)) has been used to examine why prolonged infection with the relevant virus does not result in the development of immunodeficiency in its natural host. Blood lymphocyte subset values were determined in uninfected (n=88) and naturally SIV(agm)-infected AGMs (n=74). A number of blood cell subsets, such as CD8alpha(+)CD3(+)CD28(neg), CD8alpha(+)CD3(neg) and CD20(+) cells, were expanded significantly in clinically asymptomatic animals carrying a relatively high plasma load of viral RNA (10(4)-10(7) RNA copies/ml plasma). The expanded CD8alpha(+)CD3(+)CD28(neg) subpopulation (1094 +/- 986 cells/microl blood in infected animals versus 402 +/- 364 cells/microl blood, P=0.03) comprised cells that resembled terminally differentiated effector CD8 T cells (CD27(neg) and CD11a(+)). In SIV(agm)-infected animals, the expanded CD8alpha(+)CD3(neg) cell subset shared identity with the CD16(+) population (natural killer cells). These results demonstrate for the first time that apathogenic SIV(agm) infection causes significant changes in the immune system of its natural host. Although previous studies had indicated that noncytotoxic mechanisms might play an important role in the suppression of virus replication in the natural host of SIV(agm), this study sheds new light on the possible role of cytotoxic T lymphocytes, the innate immune system and double-positive T helper cells (CD4(+)CD8alpha(+)CD3(+)) in suppressing virus replication in this animal model of AIDS.

Functional gamma delta T-lymphocyte defect associated with human immunodeficiency virus infections

BACKGROUND

Antiviral cellular immune responses may influence immunological homeostasis in HIV-infected persons. Recent data indicate that V gamma 9/V delta 2 T lymphocytes display potent cytotoxic activities against human cells infected with certain viruses including HIV. Understanding the role of gamma delta T cells in the course of HIV infection may be helpful for designing novel treatment strategies for HIV-associated disorders.

MATERIALS AND METHODS

The constitutive recognition of Daudi cells and monoethyl pyrophosphate (Etpp) by peripheral blood V gamma 9/V delta 2 T cells was assessed using a proliferation assay. The cytotoxicity of Daudi-stimulated lymphocyte populations was measured by chromium release assays. The HIV infectivity for gamma delta T cell clones was determined by measuring the levels of HIV p24 in cell supernatants. The effect of in vitro HIV-infection on cytokine mRNA production by gamma delta T cell clones was assessed by PCR.

RESULTS

The constitutive proliferative responses of peripheral blood V gamma 9/V delta 2 T cells and the lytic functions of Daudi-expanded lymphoid cells from HIV+ persons were substantially diminished in comparison with those of HIV-seronegative persons. These alterations were present in asymptomatic HIV+ persons prior to substantial alpha beta CD4+ T cell loss. Productive HIV infection of gamma delta T cells in vitro had no measurable effect either on their proliferative response to Daudi stimuli or on the expression of cytokine mRNAs for IFN-gamma, IL-2, IL-4, IL-5, IL-6, IL-10, and IL-13.

CONCLUSIONS

The constitutive responsiveness of V gamma 9/V delta 2 T lymphocytes to Daudi and Etpp is severely altered in HIV+ persons. HIV infection of gamma delta T cells in vitro does not substantially change their cytokine expression or antigenic response.

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

The mechanisms of cytotoxic killing of various tumor cell lines and immunodeficiency virus-infected T cell lines by simian gamma delta T cells were examined. The lysis of the majority of the target cell lines by gamma delta effectors was calcium-dependent, indicating that cytotoxicity is mediated by the perforin/granzyme pathway rather than the Fas-FasL pathway, with the exception of Jurkat cells. The gamma delta T cells were able to suppress SIV replication as measured by the p27 ELISA and the suppression was contact-dependent. We further determined that the target cells were induced to undergo apoptosis by the gamma delta T cell effectors. These results contribute to our understanding of the function of simian gamma delta T cells and their similarities to human gamma delta T cells, and extend our knowledge on the cytotoxic mechanisms employed by gamma delta T cells in general.