Functional simian immunodeficiency virus Gag-specific CD8+ intraepithelial lymphocytes in the mucosae of SIVmac251- or simian-human immunodeficiency virus KU2-infected macaques

Correlation between CD4+ T-cell loss and Gag-specific T cells in different intestinal sites of chronically SIV-infected rhesus monkeys

OBJECTIVE

To determine the loss of CD4+ T cells and virus-specific cytotoxic T cells (CTL) in different mucosal sites of rhesus monkeys infected with simian immunodeficiency virus (SIV).

DESIGN

A cross-sectional comparative investigation of seven different mucosal sites from chronically SIV-infected rhesus monkeys was performed by analyzing blood and mucosal lymphocytes.

METHODS

Mucosal lymphocytes were isolated from duodenum, jejunum, ileum and colon as well as from vagina, cervix and uterus of SIV-infected rhesus monkeys at necropsy. CD4+ T cells and SIV-Gag-specific CTL were determined in blood and mucosal samples by flow cytometry.

RESULTS

A significant depletion of CD4+ T cells was observed in blood and all mucosal sites of SIV-infected rhesus monkeys compared to uninfected animals. But the mean percentage loss of CD4+ T cells varied between 66 and 95% between the different mucosal tissues. The frequency of CTL ranged between 0.4 and 2.4% with the highest proportions in vagina and cervix. Among the intestinal sites the mean levels of CTL correlated with mean percentage loss of CD4+ T cells.

CONCLUSION

A discriminative pronounced loss of CD4+ T cells among the mucosal tissues confirmed that viral replication affects different mucosal sites in a distinct way. Despite high levels of CTL, especially in vagina and cervix, the severe loss of mucosal CD4+ T cells could not be prevented during chronic SIV infection. However, within the four sites of the intestine a high virus-specific cellular immune response correlated with better preservation of CD4+ T cells.

Mucosa and vaccine-induced immune protection in nonhuman primates

PURPOSE OF REVIEW

The purpose of this article is to review some of the recent progress in the development of HIV vaccines that induce immune responses in mucosal tissues that may correlate with protection of the mucosal CD4 T cell compartment.

RECENT FINDINGS

Mucosal tissues are the primary sites for viral entry and the resident CD4 T cells serve as readily available target cells for active infection. Viral entry is associated with a massive destruction of these cells. The resident CD4 cells are memory T cells and hence play an important role in the generation of secondary immune responses. Protecting these CD4 T cells is critical for controlling viral infection and for preserving immune competence. Numerous mucosal vaccine regimens currently under development have been shown to induce both B and T cell responses in mucosal tissues. Though induction of neutralizing antibodies still remains an elusive goal, the demonstration that antibodies can have a protective role through alternative mechanisms offers hope that humoral responses can be harnessed to yield a protective response in mucosal tissues.

SUMMARY

The mucosal immune system is highly compartmentalized and hence immunization regimens need to target mucosal tissues to be successful in inducing protective immune responses in mucosal tissues.

Long-term vaccine protection from AIDS and clearance of viral DNA following SHIV89.6P challenge

In an earlier study, our group vaccinated rhesus macaques with vesicular stomatitis virus (VSV) vectors expressing Gag, Pol, and Env proteins from a hybrid simian/human immunodeficiency virus (SHIV). This was followed by a single boost with modified vaccinia virus Ankara (MVA) vectors expressing the same proteins. Following challenge with SHIV89.6P, vaccinated animals cleared challenge virus RNA from the blood by day 150 and maintained normal CD4 T cell counts for 8 months. Here we report on the long-term (>5-year post-challenge) status of these animals and the immunological correlates of long-term protection. Using real-time PCR, we found that viral DNA in peripheral blood mononuclear cells (PBMCs) of the vaccinees declined continuously and fell to below detection (<5copies/10(5)cells) by approximately 3 years post-challenge. SHIV DNA was also below the limit of detection in the lymph nodes of two of the four animals at 5 years post-challenge. We detected long-term persistence of multi-functional Gag-specific CD8(+) T cells in both PBMCs and lymph nodes of the two protected animals with the Mamu A01(+) MHC I allele. All animals also maintained SHIV89.6P neutralizing antibody titers for 5 years. Our results show that this vaccine approach generates solid, long-term control of SHIV infection, and suggest that it is mediated by both cytotoxic T lymphocytes and neutralizing antibody.

The efficacy of T cell-mediated immune responses is reduced by the envelope protein of the chimeric HIV-1/SIV-KB9 virus in vivo

Gp120 is a critical component of the envelope of HIV-1. Its role in viral entry is well described. In view of its position on the viral envelope, gp120 is a part of the retrovirus that immune cells encounter first and has the potential to influence antiretroviral immune responses. We propose that high levels of gp120 are present in tissues and may contribute to the failure of the immune system to fully control and ultimately clear the virus. Herein, we show for the first time that lymphoid tissues from acutely HIV-1/SIV (SHIV)-KB9-infected macaques contain deposits of gp120 at concentrations that are high enough to induce suppressive effects on T cells, thus negatively regulating the antiviral CTL response and contributing to virus survival and persistence. We also demonstrate that SHIV-KB9 gp120 influences functional T cell responses during SHIV infection in a manner that suppresses degranulation and cytokine secretion by CTLs. Finally, we show that regulatory T cells accumulate in lymphoid tissues during acute infection and that they respond to gp120 by producing TGFbeta, a known suppressant of cytotoxic T cell activity. These findings have significant implications for our understanding of the contribution of non-entry-related functions of HIV-1 gp120 to the pathogenesis of HIV/AIDS.

Decreased number of CD4+ and CD8+ T cells that express the interleukin-7 receptor in blood and tissues of SIV-infected macaques

Acute HIV/SIV (human/simian immunodeficiency virus) infection results in severe CD4(+) T cell depletion in lymphoid compartments. During the chronic phase of infection, CD4(+) T cell numbers rebound in blood but remain low in the gut-associated lymphoid tissue (GALT), even when viral replication is suppressed by antiretroviral therapy (ART). Thus, strategies to repopulate lymphoid compartments may ameliorate the clinical outcome of HIV/SIV infection. Interleukin (IL)-7 is a key cytokine for the maintenance of homeostatic proliferation of T cells. In HIV/SIV infection, IL-7 expression is increased, likely to compensate for T cell loss, suggesting that supraphysiological administration of IL-7 could provide additional benefit. However, the ability of T cells to respond to IL-7 is dependent on the level of expression of the IL-7 receptor (IL-7R) in T cells in various body compartments. In here, we investigated the proportion of IL-7R(+) T cells in blood, spleen, gut, and genitourinary tract of healthy and SIV-infected macaques with various degrees of CD4(+) T cell depletion. We found that the percentage of T cells expressing IL-7R was significantly lower in both CD4(+) and CD8(+) T cell subsets in SIV-infected macaques than in healthy animals and this decrease directly correlated with the CD4(+) T cell number. Importantly, the proportion of CD4(+) and CD8(+) T cells expressing IL-7R in blood paralleled that found in tissues. IL-7R(+) T cells within the SIV-specific CD8(+) T cells varied and were lowest in most tissues of viremic macaques, likely reflecting continuous antigen stimulation of effector cells.

The importance of mucosal immunity in defense against epithelial cancers

Many cancers arise in epithelial mucosa. These mucosal surfaces are characterized by the induction of divergent immune responses, as they are both the main portal of entry for pathogens and a large niche of commensal bacteria and tolerized antigens. In addition, mucosa located in different anatomical sites harbor distinct typical features. Exploiting the different requirements for inducing an effective immune response at mucosal sites might help to define new immunotherapeutic approaches against epithelial cancers, at least in the case of differentiated tumors that have retained their mucosal characteristics.

Molecular and Functional Characterization of NKG2D, NKp80, and NKG2C Triggering NK Cell Receptors in Rhesus and Cynomolgus Macaques: Monitoring of NK Cell Function during Simian HIV Infection

An involvement of innate immunity and of NK cells during the priming of adaptive immune responses has been recently suggested in normal and disease conditions such as HIV infection and acute myelogenous leukemia. The analysis of NK cell-triggering receptor expression has been so far restricted to only NKp46 and NKp30 in Macaca fascicularis. In this study, we extended the molecular and functional characterization to the various NK cell-triggering receptors using PBMC and to the in vitro-derived NK cell populations by cytofluorometry and by cytolytic activity assays. In addition, RT-PCR strategy, cDNA cloning/sequencing, and transient transfections were used to identify and characterize NKp80, NKG2D, CD94/NKG2C, and CD94/NKG2A in M. fascicularis and Macaca mulatta as well as in the signal transducing polypeptide DNAX-activating protein DAP-10. Both M. fascicularis and M. mulatta NK cells express NKp80, NKG2D, and NKG2C molecules, which displayed a high degree of sequence homology with their human counterpart. Analysis of NK cells in simian HIV-infected M. fascicularis revealed reduced surface expression of selected NK cell-triggering receptors associated with a decreased NK cell function only in some animals. Overall surface density of NK cell-triggering receptors on peripheral blood cells and their triggering function on NK cell populations derived in vitro was not decreased compared with uninfected animals. Thus, triggering NK cell receptor monitoring on macaque NK cells is possible and could provide a valuable tool for assessing NK cell function during experimental infections and for exploring possible differences in immune correlates of protection in humans compared with cynomolgus and rhesus macaques undergoing different vaccination strategies.

In situ staining using MHC class I tetramers

The invention of MHC-tetramer technology to label antigen-specific T cells has lead to a greatly enhanced understanding of T lymphocyte biology. This protocol describes the use of MHC class I tetramers to stain antigen-specific T cells in tissue sections. In situ tetramer staining (IST) can be used to determine the localization, abundance, and phenotype of antigen-specific T cells in native environments and in three-dimensional space. IST is broadly applicable because it can be used to stain essentially any antigen-specific T cell in any tissue for which MHC tetramers are available. IST can be combined with histochemistry and/or immunohistochemistry to permit visualization and characterization of antigen-specific T cells relative to other cell types in stained tissue sections. Thus, IST is a useful and valuable component of MHC-tetramer technology.