Cervicovaginal lamina propria lymphocytes: phenotypic characterization and their importance in cytotoxic T-lymphocyte responses to simian immunodeficiency virus SIVmac251

T Cells in the Female Reproductive Tract Can Both Block and Facilitate HIV Transmission

Because HIV is sexually transmitted, there is considerable interest in defining the nature of anti-HIV immunity in the female reproductive tract (FRT) and in developing ways to elicit antiviral immunity in the FRT through vaccination. Although it is assumed that the mucosal immune system of the FRT is of central importance for protection against sexually transmitted diseases, including HIV, this arm of the immune system has only recently been studied. Here we provide a brief review of the role of T cells in the FRT in blocking and facilitating HIV transmission.

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.

ART influences HIV persistence in the female reproductive tract and cervicovaginal secretions

The recently completed HIV prevention trials network study 052 is a landmark collaboration demonstrating that HIV transmission in discordant couples can be dramatically reduced by treating the infected individual with antiretroviral therapy (ART). However, the cellular and virological events that occur in the female reproductive tract (FRT) during ART that result in such a drastic decrease in transmission were not studied and remain unknown. Here, we implemented an in vivo model of ART in BM/liver/thymus (BLT) humanized mice in order to better understand the ability of ART to prevent secondary HIV transmission. We demonstrated that the entire FRT of BLT mice is reconstituted with human CD4+ cells that are shed into cervicovaginal secretions (CVS). A high percentage of the CD4+ T cells in the FRT and CVS expressed CCR5 and therefore are potential HIV target cells. Infection with HIV increased the numbers of CD4+ and CD8+ T cells in CVS of BLT mice. Furthermore, HIV was present in CVS during infection. Finally, we evaluated the effect of ART on HIV levels in the FRT and CVS and demonstrated that ART can efficiently suppress cell-free HIV-RNA in CVS, despite residual levels of HIV-RNA+ cells in both the FRT and CVS.

Development and optimization of a non-enzymatic method of leukocyte isolation from macaque tissues

BACKGROUND AND METHODS

Cell isolation from macaque tissues involves laborious enzymatic digestion. The Medimachine provides a simpler, quicker non-enzymatic method, yielding 1.5–5 million cells/g of vaginal or rectal tissue from pigtailed macaques.

RESULTS AND CONCLUSIONS

Flow cytometry analysis of the two methods revealed similar levels of cell viability and most major cell lineage and activation markers.

Mimicking herpes simplex virus 1 and herpes simplex virus 2 mucosal behavior in a well-characterized human genital organ culture

We developed and morphologically characterized a human genital mucosa explant model (endocervix and ectocervix/vagina) to mimic genital herpes infections caused by herpes simplex virus types 1 (HSV-1) and 2 (HSV-2). Subsequent analysis of HSV entry receptor expression throughout the menstrual cycle in genital tissues was performed, and the evolution of HSV-1/-2 mucosal spread over time was assessed. Nectin-1 and -2 were expressed in all tissues during the entire menstrual cycle. Herpesvirus entry mediator expression was limited mainly to some connective tissue cells. Both HSV-1 and HSV-2 exhibited a plaque-wise mucosal spread across the basement membrane and induced prominent epithelial syncytia.

Functional diversity of human vaginal APC subsets in directing T-cell responses

Human vaginal mucosa is the major entry site of sexually transmitted pathogens and thus has long been attractive as a site for mounting mucosal immunity. It is also known as a tolerogenic microenvironment. Here, we demonstrate that immune responses in the vagina can be orchestrated by the functional diversity of four major antigen-presenting cell (APC) subsets. Langerhans cells (LCs) and CD14(-) lamina propria-dendritic cells (LP-DCs) polarize CD4(+) and CD8(+) T cells toward T-helper type 2 (Th2), whereas CD14(+) LP-DCs and macrophages polarize CD4(+) T cells toward Th1. Both LCs and CD14(-) LP-DCs are potent inducers of Th22. Owing to their functional specialties and the different expression levels of pattern-recognition receptors on the APC subsets, microbial products do not bias them to elicit common types of immune responses (Th1 or Th2). To evoke desired types of adaptive immune responses in the human vagina, antigens may need to be targeted to proper APC subsets with right adjuvants.

Spontaneous cervicovaginal lesions and immune cell infiltrates in nonhuman primates

Nonhuman primates, particularly rhesus macaques (Macaca mulatta), provide important model systems for studying human reproductive infectious diseases such as human immunodeficiency virus, human papillomavirus, and Chlamydia spp. An understanding of the spectrum of spontaneous cervical disease provides essential context for interpreting experimental disease outcomes in the female reproductive tract. This retrospective study characterizes the incidence of inflammatory and/or proliferative cervicovaginal lesions seen over a 14-year period in a multispecies nonhuman primate colony, focusing on rhesus macaques. The most common observations included a spectrum of lymphocytic accumulation from within normal limits to lymphoplasmacytic cervicitis, and suppurative inflammation with occasional squamous metaplasia or polyp formation. These inflammatory spectra frequently occurred in the context of immunosuppression following experimental simian immunodeficiency virus (SIV) infection. Cervical neoplasias were uncommon and included leiomyomas and carcinomas. Cervical sections from 13 representative cases, with an emphasis on proliferative and dysplastic lesions, were surveyed for leukocyte infiltration, abnormal epithelial proliferation, and the presence of papillomavirus antigens. Proliferative lesions showed sporadic evidence of spontaneous papillomavirus infection and variable immune cell responses. These results underscore the importance of pre screening potential experimental animals for the presence of preexisting reproductive tract disease, and the consideration of normal variability within cycling reproductive tracts in interpretation of cervical lesions.

HIV pathogenesis: the host

Human immunodeficiency virus (HIV) pathogenesis has proven to be quite complex and dynamic with most of the critical events (e.g., transmission, CD4(+) T-cell destruction) occurring in mucosal tissues. In addition, although the resulting disease can progress over years, it is clear that many critical events happen within the first few weeks of infection when most patients are unaware that they are infected. These events occur predominantly in tissues other than the peripheral blood, particularly the gastrointestinal tract, where massive depletion of CD4(+) T cells occurs long before adverse consequences of HIV infection are otherwise apparent. Profound insights into these early events have been gained through the use of nonhuman primate models, which offer the opportunity to examine the early stages of infection with the simian immunodeficiency virus (SIV), a close relative of HIV that induces an indistinguishable clinical picture from AIDS in Asian primate species, but importantly, fails to cause disease in its natural African hosts, such as sooty mangabeys and African green monkeys. This article draws from data derived from both human and nonhuman primate studies.

Targeting the vaginal mucosa with human papillomavirus pseudovirion vaccines delivering simian immunodeficiency virus DNA

The majority of HIV infections occur via mucosal transmission. Vaccines that induce memory T and B cells in the female genital tract may prevent the establishment and systemic dissemination of HIV. We tested the immunogenicity of a vaccine that uses human papillomavirus (HPV)-based gene transfer vectors, also called pseudovirions (PsVs), to deliver SIV genes to the vaginal epithelium. Our findings demonstrate that this vaccine platform induces gene expression in the genital tract in both cynomolgus and rhesus macaques. Intravaginal vaccination with HPV16, HPV45, and HPV58 PsVs delivering SIV Gag DNA induced Gag-specific Abs in serum and the vaginal tract, and T cell responses in blood, vaginal mucosa, and draining lymph nodes that rapidly expanded following intravaginal exposure to SIV(mac251.) HPV PsV-based vehicles are immunogenic, which warrant further testing as vaccine candidates for HIV and may provide a useful model to evaluate the benefits and risks of inducing high levels of SIV-specific immune responses at mucosal sites prior to SIV infection.

The gp41 epitope, QARVLAVERY, is highly conserved and a potent inducer of IgA that neutralizes HIV-1 and inhibits viral transcytosis

Mucosal surfaces are the predominant site of human immunodeficiency virus (HIV)-1 transmission. For prophylactic approaches to effectively prevent HIV infection and subsequent dissemination, the induction of mucosally relevant protective immunity will be critical. Here, we have characterized the antibody (Ab) response generated by a highly conserved gp41epitope, QARVLAVERY, in an optimized immunization model that elicits potent epitope-specific Abs in the serum, vaginal washes, and fecal secretions of immunized mice. Our results show that QARVLAVERY is indeed a potent inducer of IgA and importantly, QARVLAVERY-specific IgA was effective in neutralizing HIV and inhibiting viral transcytosis. Intriguingly, QARVLAVERY also generated an approximate 1:1 ratio of IgG:IgA in the serum of immunized mice, independent of the delivery regimen and produced early systemic IgA, even before IgG. In light of the significantly high IgA induction by QARVLAVERY and the functionality of epitope-specific Abs in the inhibition of HIV infection and transcytosis, QARVLAVERY is an attractive epitope to be considered in mucosal vaccination strategies against HIV.

Evaluation of CD103 (αEβ7) integrin expression by CD8 T cells in blood as a surrogate marker to predict cervical T cell responses in the female genital tract during HIV infection

Mucosal homing receptors expressed by blood T cells may be useful surrogates for measuring mucosal T cell immune responses at the site of HIV transmission. Here, we investigated whether HIV-specific responses by T cells expressing the mucosal integrin receptor CD103 in blood reliably predicted corresponding HIV-specific responses at the cervix. The frequency of CD8+ T cells expressing CD103 in blood correlated significantly with the number of CD103+CD8+ T cells from the cervix suggesting that CD103 was involved in trafficking of T cells from blood to the cervical mucosa. TGF-β concentrations in plasma were significantly associated with the frequency of CD103 expression by blood but not cervical CD8 T cells. The majority of Gag-responsive CD8 T cells were CD103+ in both blood and at the cervix. Despite this, the magnitude of Gag-specific IFN-γ responses by CD103+CD8+ T cells in blood did not predict similar Gag-specific responses at the cervix.

SIV-specific CD8+ T cells are enriched in female genital mucosa of rhesus macaques and express receptors for inflammatory chemokines

PROBLEM

Mucosal T lymphocyte responses in the female reproductive tract, the primary site of HIV transmission in women, may be critical for initial control of virus infection. In addition, characterization of genital immune responses to HIV will be important for the development of a vaccine capable of preventing infection by this route.

METHOD OF STUDY

We analyzed lymphocytes isolated from vagina and cervix of chronically SIV-infected macaques for the frequency of SIV Gag tetramer-binding cells and expression of chemokine receptors.

RESULTS

We found that the frequency of SIV-specific CD8+ T cell responses was 3- to 30-fold higher in genital tissues than in peripheral blood. SIV-specific CD8+ T cells in genital tissues expressed high levels of CXCR3 and CCR5, chemokine receptors normally expressed on memory T cells that home to inflamed tissues. Cells expressing CXCR3 colocalized with its chemokine ligand CXCL9 [monokine induced by interferon gamma, MIG] in the vaginal lamina propria.

CONCLUSION

These results indicate that the frequency of SIV-specific CD8+ T cells in the female genital mucosa is enriched compared with peripheral blood and provide initial information regarding the signals that direct recruitment of T cells to the female reproductive tract.

Robust genital gag-specific CD8+ T-cell responses in mice upon intramuscular immunization with simian adenoviral vectors expressing HIV-1-gag

Most studies on E1-deleted adenovirus (Ad) vectors as vaccine carriers for antigens of HIV-1 have focused on induction of central immune responses, although stimulation of mucosal immunity at the genital tract (GT), the primary port of entry of HIV-1, would also be highly desirable. In this study, different immunization protocols using chimpanzee-derived adenoviral (AdC) vectors expressing Gag of HIV-1 clade B given in heterologous prime-boost regimens were tested for induction of systemic and genital immune responses. Although i.n. immunization stimulated CD8(+) T-cell responses that could be detected in the GT, this route induced only marginal cellular responses in systemic tissues and furthermore numbers of Gag-specific CD8(+) T cells contracted sharply within a few weeks. On the contrary, i.m. immunization induced higher and more sustained frequencies of vaccine-induced cells which could be detected in the GT as well as systemic compartments. Antigen-specific CD8(+) T cells could be detected 1 year after immunization in all compartments analyzed. Genital memory cells secreted IFN-γ, expressed high levels of CD103 and their phenotypes were consistent with a state of activation. Taken together, the results presented here show that i.m. vaccination with chimpanzee-derived (simian) adenovirus vectors is a suitable strategy to induce a long-lived genital CD8(+) T-cell response.

HIV-1 sexual transmission: early events of HIV-1 infection of human cervico-vaginal tissue in an optimized ex vivo model

Infection and dissemination of human immunodeficiency virus (HIV)-1 through the female body after vaginal intercourse depends on the activation/differentiation status of mucosal CD4 T cells. In this study, we investigated this status and the susceptibility to HIV-1 infection of human cervico-vaginal tissue ex vivo. We found that virtually all T cells are of the effector memory phenotype with broad CC chemokine receptor 5 (CCR5) expression. As it does in vivo, human cervico-vaginal tissue ex vivo preferentially supports the productive infection of R5 HIV-1 rather than that of X4 HIV-1 in spite of the broad expression of CXC chemokine receptor 4 (CXCR4). X4 HIV-1 replicated only in the few tissues that were enriched in CD27(+)CD28(+) effector memory CD4 T cells. Productive infection of R5 HIV-1 occurred preferentially in activated CD38(+)CD4 T cells and was followed by a similar activation of HIV-1-uninfected (bystander) CD4 T cells that may amplify viral infection. These results provide new insights into the dependence of HIV-1 infection and dissemination on the activation/differentiation of cervico-vaginal lymphocytes.

Memory T cells in Rhesus macaques

The Rhesus macaque (Macaca mulatta) is one of the best studied species of Old World monkeys. DNA sequencing of the entire Rhesus macaque genome, completed in 2007, has demonstrated that humans and macaques share about 93% of their nucleotide sequence. Rhesus macaques have been widely used for medical research including drug testing, neurology, behavioral and cognitive science, reproduction, xenotransplantation and genetics. Because of the Rhesus macaque's sensitivity to bacteria, parasites and viruses that cause similar disease in humans, these animals represent an excellent model to study infectious diseases. The recent pandemic of HIV and the discovery of SIV, a lentivirus genetically related to HIV Type 1 that causes AIDS in Rhesus macaques, have prompted the development of reagents that can be used to study innate and adaptive immune responses in macaques at the single cell level. This review will focus on the distribution of memory cells in the different immunologic compartments of Rhesus macaques. In addition, the strategies available to manipulate memory cells in Rhesus macaques to understand their trafficking and function will be discussed. Emphasis is placed on studies of memory cells in macaques infected with SIV because many studies are available. Lastly, we highlight the usefulness of the Rhesus macaque model in studies related to the aging of the immune system.

Mucosal immunity to HIV: a review of recent literature

PURPOSE OF REVIEW

This review summarizes recent literature in the field of mucosal immunology as it applies to HIV transmission and pathogenesis.

RECENT FINDINGS

Pertinent recent findings include elucidation of the role of mucosal antigen-presenting cells and retinoic acid in imprinting a gut-homing phenotype on antigen-specific T and B cells, and the identification of Th17 and T regulatory cells as key modulators of the balance between tolerance and inflammation in mucosal tissues.

SUMMARY

Mucosal surfaces of the body serve as the major portal of entry for HIV. These tissues also house a majority of the body's lymphocytes, including the CD4 T-cells that are the major cellular target for HIV infection. Elucidating mucosal immune responses is critical to our understanding of the host-pathogen relationship for two reasons: first, mucosal barriers are defended by a range of innate and adaptive defenses that might be exploited to develop effective vaccines or microbicides; second, adaptive immune responses in mucosal lymphoid tissues might serve to limit viral replication, decreasing the host's viral burden as well as reducing the likelihood of sexual transmission to a naïve host.

The gastrointestinal tract and AIDS pathogenesis

Gastrointestinal disease has been recognized as a major manifestation of human immunodeficiency virus infection since the earliest recognition of acquired immunodeficiency syndrome (AIDS). Originally, these disease manifestations were considered to be sequelae of the immune destruction that characterizes AIDS rather than being central to the pathogenesis of AIDS. Over time, it has become clear that the mucosal immune system in general and the intestinal immune system in particular are central to the pathogenesis of AIDS, with most of the critical events (eg, transmission, viral amplification, CD4+ T-cell destruction) occurring in the gastrointestinal tract. Compared with peripheral blood, these tissues are not easily accessible for analysis and have only begun to be examined in detail recently. In addition, although the resulting disease can progress over years, many critical events happen within the first few weeks of infection, when most patients are unaware that they are infected. Moreover, breakdown of the mucosal barrier and resulting microbial translocation are believed to be major drivers of AIDS progression. In this review, we focus on the interaction between primate lentiviruses and the gastrointestinal tract and discuss how this interaction promotes the pathogenesis of AIDS and drives immune dysfunction and progression to AIDS. This article draws extensively on work done in the nonhuman primate model of AIDS to fill gaps in our understanding of AIDS in humans.

Developing an HIV cytotoxic T-lymphocyte vaccine: issues of CD8 T-cell quantity, quality and location

Issues of quantity, quality and location impact the ability of CD8 T cells to mediate protection from infection. These issues are considered in light of human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) vaccination. Methods are reviewed that result in 100- to 1000-fold higher frequencies of vaccine-specific memory CD8 T cells than that achieved by current HIV/SIV vaccine approaches. Data demonstrating that location within mucosal tissues has a direct impact on memory CD8 T-cell function are discussed. Arguments are made that establishing memory CD8 T cells within mucosal sites of transmission, a priori to natural infection, may be essential for conferring optimal and rapid protection. Lastly, it is proposed that heterologous prime-boost vaccination with recombinant live replicating vectors, which has the potential to induce tremendous numbers of cytolytic memory CD8 T cells within mucosal tissues, would provide a far more stringent test of the hypothesis that memory CD8 T cells could, in principal, form the basis for a preventative HIV vaccine.

Enhancement of human immunodeficiency virus (HIV)-specific CD8+ T cells in cerebrospinal fluid compared to those in blood among antiretroviral therapy-naive HIV-positive subjects

During untreated human immunodeficiency virus type 1 (HIV-1) infection, virus-specific CD8(+) T cells partially control HIV replication in peripheral lymphoid tissues, but host mechanisms of HIV control in the central nervous system (CNS) are incompletely understood. We characterized HIV-specific CD8(+) T cells in cerebrospinal fluid (CSF) and peripheral blood among seven HIV-positive antiretroviral therapy-naïve subjects. All had grossly normal brain magnetic resonance imaging and spectroscopy and normal neuropsychometric testing. Frequencies of epitope-specific CD8(+) T cells by direct tetramer staining were on average 2.4-fold higher in CSF than in blood (P = 0.0004), while HIV RNA concentrations were lower. Cells from CSF were readily expanded ex vivo and responded to a broader range of HIV-specific human leukocyte antigen class I restricted optimal peptides than did expanded cells from blood. HIV-specific CD8(+) T cells, in contrast to total CD8(+) T cells, in CSF and blood were at comparable maturation states, as assessed by CD45RO and CCR7 staining. The strong relationship between higher T-cell frequencies and lower levels of viral antigen in CSF could be the result of increased migration to and/or preferential expansion of HIV-specific T cells within the CNS. This suggests an important role for HIV-specific CD8(+) T cells in control of intrathecal viral replication.

Protection of macaques against vaginal SHIV challenge by systemic or mucosal and systemic vaccinations with HIV-envelope

BACKGROUND

Worldwide, the majority of human immunodeficiency virus (HIV) infections occur by heterosexual transmission. Thus, the development of a vaccine that can prevent intravaginal HIV infection is an important goal of AIDS vaccine research.

OBJECTIVES

To determine which single or combination of systemic and mucosal routes of immunizations of female rhesus macaques with an HIV-1 SF162 envelope protein vaccine induced protection against intravaginal challenge with SHIV.

DESIGN

Female rhesus macaques were immunized with an HIV-1 SF162 envelope protein vaccine administered systemically (intramuscularly), or mucosally (intranasally), or as a sequential combination of both routes. The macaques were then challenged intravaginally with SHIV SF162P4, expressing an envelope that is closely matched (homologous) to the vaccine.

RESULTS

Macaques receiving intramuscular immunizations, alone or in combination with intranasal immunizations, were protected from infection, with no detectable plasma viral RNA, provirus, or seroconversion to nonvaccine viral proteins, and better preservation of intestinal CD4+ T cells. Serum neutralizing antibodies against the challenge virus appeared to correlate with protection.

CONCLUSIONS

The results of this study demonstrate that, in the nonhuman primate model, it is possible for vaccine-elicited immune responses to prevent infection after intravaginal administration of virus.

Current concepts in AIDS pathogenesis: insights from the SIV/macaque model

The pathogenesis of AIDS has proven to be quite complex and dynamic, with most of the critical events (e.g., transmission, CD4(+) T cell destruction) occurring in tissues that are not easily accessible for analysis. In addition, although the disease can progress over years, many critical events happen within the first few weeks of infection, when most patients are unaware that they are infected. The nonhuman primate model of AIDS has been used extensively to fill these gaps in our understanding of AIDS pathogenesis.

Distribution of simian immunodeficiency virus target cells in vaginal tissues of normal rhesus macaques: implications for virus transmission

Most new cases of HIV-1 infection occur as the result of vaginal transmission. Identifying the phenotype and distribution of potential viral target cells in the vagina is important for understanding events in viral transmission and for developing effective prevention strategies. For example, compounds that prevent CD4 or CCR5 binding have been demonstrated recently to prevent vaginal transmission in rhesus macaques, but the expression and distribution of CCR5 has not been examined in the macaque vagina. The objective of this study was to examine the distribution and phenotype of cells and molecules in the vagina of rhesus macaques that may be involved in HIV transmission, including CCR5, CD3, CD4, CD8, CD1a, CD28, CD95, CD123 and HLA-DR. Normal juvenile and adult female rhesus macaques were examined by multicolor immunohistochemistry and flow cytometry. Although both CD4 and CCR5 were observed in the lamina propria, essentially no CD4 or CCR5 expression was detected within the squamous or keratinized layers of the vaginal epithelium. CCR5 expression was higher in the vaginal lamina propria of mature macaques compared to 1-3-year-old juveniles. The vast majority of CD4(+)CCR5(+) lymphocytes in the vagina had a central memory (CD95(+)CD28(+)) phenotype. Numerous CCR5-expressing dendritic cells (CD123(+)) or macrophages (CD68(+)) were observed in the lamina propria, but no CCR5, CD4 or DC-SIGN expression was detectable in the epithelium. Thus, the multiple layers of squamous epithelium normally covering the vaginal mucosa may provide an effective barrier against vaginal HIV-1 transmission. Microbicides that block CD4 or CCR5 expression may act within the deeper layers of the vaginal epithelium rather than on the epithelial surface.

CD8+ T-lymphocyte response to major immunodominant epitopes after vaginal exposure to simian immunodeficiency virus: too late and too little

In the acute stage of infection following sexual transmission of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV), virus-specific CD8+ T-lymphocyte responses partially control but do not eradicate infection from the lymphatic tissues (LTs) or prevent the particularly massive depletion of CD4+ T lymphocytes in gut-associated lymphatic tissue (GALT). We explored hypothetical explanations for this failure to clear infection and prevent CD4+ T-lymphocyte loss in the SIV/rhesus macaque model of intravaginal transmission. We examined the relationship between the timing and magnitude of the CD8+ T-lymphocyte response to immunodominant SIV epitopes and viral replication, and we show first that the failure to contain infection is not because the female reproductive tract is a poor inductive site. We documented robust responses in cervicovaginal tissues and uterus, but only several days after the peak of virus production. Second, while we also documented a modest response in the draining genital and peripheral lymph nodes, the response at these sites also lagged behind peak virus production in these LT compartments. Third, we found that the response in GALT was surprisingly low or undetectable, possibly contributing to the severe and sustained depletion of CD4+ T lymphocytes in the GALT. Thus, the virus-specific CD8+ T-lymphocyte response is "too late and too little" to clear infection and prevent CD4+ T-lymphocyte loss. However, the robust response in female reproductive tissues may be an encouraging sign that vaccines that rapidly induce high-frequency CD8+ T-lymphocyte responses might be able to prevent acquisition of HIV-1 infection by the most common route of transmission.

Homing in on the cellular immune response to HSV-2 in humans

PROBLEM

Genital herpes simplex infections are generally limited to epithelia and neurons. Vaccines have had activity in herpes simplex virus (HSV)-seronegative women only. Understanding how HSV-specific T cells traffic to infected sites may assist in vaccine design.

METHOD OF STUDY

Herpes simplex virus epitopes recognized by HSV-specific CD8 T cells were identified and used to make fluorescent human leukocyte antigen (HLA)-peptide tetramers. Molecules related to lymphocyte rolling adhesion were studied by flow cytometry and cell binding. HSV-specific CD4 T cells identified ex vivo by cytokine accumulation or activation marker expression, or detected in vitro by 5-(and-6)-carboxyfluorescein diacetate, succinimidyl ester (CFSE) dilution, were similarly investigated.

RESULTS

Herpes simplex virus-specific T cells are 10- to 100-fold more prevalent in lesional skin compared with blood and greatly enriched in lesions compared with normal skin. Diverse viral antigens are recognized by HSV-specific T cells. Functionally active E-selectin ligand, and cutaneous lymphocyte antigen (CLA), are expressed by circulating HSV-2-specific CD8 cells. CD4 cells display lower levels of CLA that are dramatically up-regulated upon re-stimulation with antigen.

CONCLUSIONS

Herpes simplex virus-2-specific CD8 and CD4 T cells differ in constitutive expression of skin homing molecules. Vaccines designed to induce proper homing are postulated to have increased efficacy.

Characterization of human immunodeficiency virus Gag-specific gamma interferon-expressing cells following protective mucosal immunization with alphavirus replicon particles

A safe, replication-defective viral vector that can induce mucosal and systemic immune responses and confer protection against many infectious pathogens, such as human immunodeficiency virus type 1 (HIV-1), may be an ideal vaccine platform. Accordingly, we have generated and tested alphavirus replicon particles encoding HIV-1 Gag from Sindbis virus (SIN-Gag) and Venezuelan equine encephalitis virus (VEE-Gag), as well as chimeras between the two (VEE/SIN-Gag). Following intramuscular (i.m.), intranasal (i.n.), or intravaginal (IVAG) immunization with VEE/SIN-Gag and an IVAG challenge with vaccinia virus encoding HIV Gag (VV-Gag), a larger number of Gag-specific CD8+ intracellular gamma interferon-expressing cells (iIFNEC) were detected in iliac lymph nodes (ILN), which drain the vaginal/uterine mucosa (VUM), than were observed after immunizations with SIN-Gag. Moreover, a single i.n. or IVAG immunization with VEE/SIN-Gag induced a larger number of cells expressing HIV Gag in ILN, and immunizations with VEE/SIN-Gag through any route induced better protective responses than immunizations with SIN-Gag. In VUM, a larger percentage of iIFNEC expressed alpha4beta7 or alpha(Ebeta)7 integrin than expressed CD62L integrin. However, in spleens (SP), a larger percentage of iIFNEC expressed alpha4beta7 or CD62L than expressed alpha(Ebeta)7. Moreover, a larger percentage of iIFNEC expressed the chemokine receptor CCR5 in VUM and ILN than in SP. These results demonstrate a better induction of cellular and protective responses following immunizations with VEE/SIN-Gag than that following immunizations with SIN-Gag and also indicate a differential expression of homing and chemokine receptors on iIFNEC in mucosal effector and inductive sites versus systemic lymphoid tissues.

Correlation between viral RNA levels but not immune responses in plasma and tissues of macaques with long-standing SIVmac251 infection

Plasma virus in human immunodeficiency virus type 1/simian immunodeficiency virus (HIV-1/SIV) infection most likely results from the combination of viruses produced in different tissues. As immunological pressure may be higher in effector sites than secondary lymphoid tissues, we investigated quantitative and qualitative changes in viral RNA in blood and tissues of 10 Mamu-A*01-positive SIV-infected macaques in parallel with the frequency of CD8+ T cells recognizing the dominant Gag181-189 CM9 epitope. The plasma virus level in these macaques directly correlated with the viral RNA levels in lymph nodes, spleen, lungs, colon, and jejunum. In contrast, the frequency of the Gag181-189 CM9 tetramer did not correlate with SIV RNA levels in any compartment. We investigated the presence of viral immune escape in RNA from several tissues. The complete substitution of wild-type genotype with viral immune-escape variant within the Gag181-189 CM9 epitope was associated with low tetramer response in all tissues and blood of two macaques. In one macaque, the replacement of wild type with an immune-escape mutant was asynchronous. While the mutant virus was prevalent in blood and effector tissues (lungs, jejunum, and colon), secondary lymphoid organs such as spleen and lymph nodes still retained 80% and 40%, respectively, of the wild-type virus. These results may imply that there are differences in the immunological pressure exerted by cytotoxic T lymphocytes (CTLs) in tissue compartments of SIVmac251-infected macaques.

Resistance to viral infection by intraepithelial lymphocytes in HIV-1 P18-I10-specific T-cell receptor transgenic mice

For the analysis of mucosal immunity to HIV-1, we have recently established a line of transgenic (Tg) mice expressing the TCRalpha and TCRbeta genes of the murine CTL clone RT1 specific for P18-I10 (RGPGRAFVTI), an immunodominant gp160 envelope-derived epitope of IIIB isolate, restricted by the H-2D(d) MHC-I molecule. Here we examine those cells bearing specific TCR among the intraepithelial lymphocytes (IELs), with flow cytometric analysis using H-2D(d)/P18-I10 tetramers. We observed three distinct CD3(+), tetramer positive populations among the IELs: extra-thymic CD8alphabeta(+), alphabetaTCR T-cells; CD8 alphaalpha+, gammadeltaTCR T-cells; and thymus-derived CD8alphabeta+, alphabetaTCR T-cells. Challenge of these Tg mice with P18-I10 encoded by a vaccinia virus vector, either intrarectally (i.r.) or intraperitoneally (i.p.), revealed that the intraepithelial compartment seems to be a major site for prevention of the spread of viral infection. Such immunity appears due to the thymus-derived, CD8alphabeta+ antigen-specific CTLs together with CD8alphaalpha+ gammadelta cells, which regulate virus spread. This model system for studying CTL based immunity at mucosal sites should prove helpful in developing rational approaches for HIV control.

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

The vaginal and rectal mucosae are the first line of cellular immune defense to sexually transmitted human immunodeficiency virus type 1 (HIV-1) entry. Thus, intraepithelial lymphocytes (IELs) may be important in the immune response to HIV infection. Here we investigated whether functional IELs in mucosal compartments could be visualized by direct staining with a tetrameric complex specific for the simian immunodeficiency virus (SIV) immunodominant Gag epitope in either separated IEL cells or tissues of macaques infected with SIVmac251. Of the 15 Mamu-A*01-positive macaques studied here, eight were chronically infected with either SIVmac251 or simian-human immunodeficiency virus (SHIV) KU2 and the remaining seven were exposed mucosally to SIVmac251 and sacrificed within 48 h to assess the local immune response. Gag-specific CD8+ T-cells were found in separated IELs from the rectum, colon, jejunum, and vagina of most infected animals. Direct staining of tetramers also revealed their presence in intact tissue. These Gag-specific IELs expressed the activation marker CD69 and produced IFN-gamma, suggesting an active immune response in this locale.

High frequency of virus-specific CD8+ T cells in the central nervous system of macaques chronically infected with simian immunodeficiency virus SIVmac251

Infection with human immunodeficiency virus or simian immunodeficiency virus (SIV) induces virus-specific CD8(+) T cells that traffic to lymphoid and nonlymphoid tissues. In this study, we used Gag-specific tetramer staining to investigate the frequency of CD8(+) T cells in peripheral blood and the central nervous system of Mamu-A*01-positive SIV-infected rhesus macaques. Most of these infected macaques were vaccinated prior to SIVmac251 exposure. The frequency of Gag(181-189) CM9 tetramer-positive cells was consistently higher in the cerebrospinal fluid and the brain than in the blood of all animals studied and did not correlate with either plasma viremia or CD4(+)-T-cell level. Little or no infection in the brain was documented for most animals by nucleic acid sequence-based amplification or in situ hybridization. These data suggest that this Gag-specific response may contribute to the containment of viral replication in this locale.

Quantitative ex vivo analysis of functional virus-specific CD8 T lymphocytes in the blood and genital tract of HIV-infected women

BACKGROUND

CD8 T lymphocytes are important in HIV-1 control and mediate virus-specific immunity in the blood and genital tract. The induction and monitoring of mucosal CD8 cell responses will be an important component of HIV-1 vaccine trials, but information regarding the frequency, phenotype and function of genital tract CD8 cell responses is lacking.

METHODS

Simultaneous blood and cervical cytobrush samples were obtained from 16 HIV-1-infected Kenyan sex workers. Epitope-specific CD8 T lymphocyte frequencies in the blood and genital tract were analysed after short-term peptide incubation and intracellular cytokine staining for interferon-gamma (IFN gamma).

RESULTS

Cervical sampling resulted in adequate cell numbers for analysis in 10/16 women. Background IFN gamma production was higher in CD3+/CD8+ lymphocytes from the genital tract than from blood (0.48% versus 0.1%; P < 0.01). Responses to staphylococcal enterotoxin B were detected in cervical CD8 lymphocytes from 10/10 women, at a similar frequency to blood (16.7% in cervix and 13.3% in blood; P = 0.4). HIV-1-specific responses were detected the cervix of 8/10 women, with a trend to higher response frequencies in the genital tract than blood (2.1% versus 0.8%; P = 0.09). Co-expression of integrin CD103 (alpha E beta 7), a mucosal marker, was used to confirm the mucosal origin of cervical responses.

CONCLUSIONS

Cytobrush sampling and intracellular cytokine staining is well suited to the analysis of cervical CD8 cell responses. The frequency of functional virus-specific CD3+/CD8+ T cells is similar in the genital tract and blood of HIV-1-infected women. The role of genital tract CD8 cell responses in HIV-1 control warrants further investigation.

Trafficking of human immunodeficiency virus type 1-specific CD8+ T cells to gut-associated lymphoid tissue during chronic infection

Gut-associated lymphoid tissue (GALT) is a significant but understudied lymphoid organ, harboring a majority of the body's total lymphocyte population. GALT is also an important portal of entry for human immunodeficiency virus (HIV), a major site of viral replication and CD4(+) T-cell depletion, and a frequent site of AIDS-related opportunistic infections and neoplasms. However, little is known about HIV-specific cell-mediated immune responses in GALT. Using lymphocytes isolated from rectal biopsies, we have determined the frequency and phenotype of HIV-specific CD8(+) T cells in human GALT. GALT CD8(+) T cells were predominantly CD45RO(+) and expressed CXCR4 and CCR5. In 10 clinically stable, chronically infected individuals, the frequency of HIV Gag (SL9)-specific CD8(+) T cells was increased in GALT relative to peripheral blood mononuclear cells by up to 4.6-fold, while that of cytomegalovirus (CMV)-specific CD8(+) T cells was significantly reduced (P = 0.012). Both HIV- and CMV-specific CD8(+) T cells in GALT expressed CCR5, but only HIV-specific CD8(+) T cells expressed alpha E beta 7 integrin, suggesting that mucosal priming may account for their retention in GALT. Chronically infected individuals exhibited striking depletion of GALT CD4(+) T cells expressing CXCR4, CCR5, and alpha E beta 7 integrin, but CD4(+)/CD8(+) T-cell ratios in blood and GALT were similar. The percentage of GALT CD8(+) T cells expressing alpha E beta 7 was significantly decreased in infected individuals, suggesting that HIV infection may perturb lymphocyte retention in GALT. These studies demonstrate the feasibility of using tetramers to assess HIV-specific T cells in GALT and reveal that GALT is the site of an active CD8(+) T-cell response during chronic infection.

Live, attenuated simian immunodeficiency virus SIVmac-M4, with point mutations in the Env transmembrane protein intracytoplasmic domain, provides partial protection from mucosal challenge with pathogenic SIVmac251

Attenuated molecular clones of simian immunodeficiency virus (SIVmac) are important tools for studying the correlates of protective immunity to lentivirus infection in nonhuman primates. The most highly attenuated SIVmac mutants fail to induce disease but also fail to induce immune responses capable of protecting macaques from challenge with pathogenic virus. We recently described a novel attenuated virus, SIVmac-M4, containing multiple mutations in the transmembrane protein (TM) intracytoplasmic domain. This domain has been implicated in viral assembly, infectivity, and cytopathogenicity. Whereas parental SIVmac239-Nef(+) induced persistent viremia and simian AIDS in rhesus macaques, SIVmac-M4 induced transient viremia in juvenile and neonatal macaques, with no disease for at least 1 year postinfection. In this vaccine study, 8 macaques that were infected as juveniles (n = 4) or neonates (n = 4) with SIVmac-M4 were challenged with pathogenic SIVmac251 administered through oral mucosa. At 1 year postchallenge, six of the eight macaques had low to undetectable plasma viremia levels. Assays of cell-mediated immune responses to SIVmac Gag, Pol, Env, and Nef revealed that all animals developed strong CD8(+) T-cell responses to Gag after challenge but not before. Unvaccinated control animals challenged with SIVmac251 developed persistent viremia, had significantly weaker SIV-specific T-cell responses, and developed AIDS-related symptoms. These findings demonstrate that SIVmac-M4, which contains a full-length Nef coding region and multiple point mutations in the TM, can provide substantial protection from mucosal challenge with pathogenic SIVmac251.

Both mucosal and systemic routes of immunization with the live, attenuated NYVAC/simian immunodeficiency virus SIV(gpe) recombinant vaccine result in gag-specific CD8(+) T-cell responses in mucosal tissues of macaques

As most human immunodeficiency virus (HIV) infection occurs via mucosal surfaces, an important goal of vaccination may be the induction of virus-specific immune responses at mucosal sites to contain viral infection early on. Here we designed a study in macaques carrying the major histocompatibility complex class I Mamu-A(*)01 molecule to assess the capacity of the highly attenuated poxvirus NYVAC/simian immunodeficiency virus (SIV) SIV(gpe) vaccine candidate administered by the intranasal, intramuscular, or intrarectal route to induce mucosal immunity. All macaques, including one naive macaque, were exposed to SIV(mac251) by the intrarectal route and sacrificed 48 h after infection. The kinetics of immune response at various time points following immunization with NYVAC/SIV(gpe) and the anamnestic response to SIV(mac251) at 48 h after challenge were assessed in blood, in serial rectal and vaginal biopsy samples, and in tissues at euthanasia with an SIV(mac) Gag-specific tetramer. In addition, at euthanasia, antigen-specific cells producing gamma interferon or tumor necrosis factor alpha from the jejunum lamina propria were quantified in all macaques. Surprisingly, antigen-specific CD8(+) T cells were found in the mucosal tissues of all immunized macaques regardless of whether the vaccine was administered by a mucosal route (intranasal or intrarectal) or systemically. In addition, following mucosal SIV(mac251) challenge, antigen-specific responses were mainly confined to mucosal tissues, again regardless of the route of immunization. We conclude that immunization with a live vector vaccine results in the appearance of CD8(+) T-cell responses at mucosal sites even when the vaccine is delivered by nonmucosal routes.

Beyond 51Cr release: New methods for assessing HIV-1-specific CD8+ T cell responses in peripheral blood and mucosal tissues

Much scientific effort has been directed towards elucidating the complexities of cell-mediated immune responses to HIV-1(reviewed in [1,2]). These studies have attempted to explain the immune system's ultimate failure to contain viral replication, leading to development of AIDS disease, and to identify immune responses that will be useful in developing immunomodulatory therapies and novel vaccine strategies. Although many of the complex interactions involved in AIDS pathogenesis remain unsolved, great progress has been made in characterizing the kinetics, specificity and functional dynamics of HIV-1-specific T cell responses. These investigations have come at a time when advances in virology, cellular immunology and molecular biology have converged to provide a variety of methodological approaches not available at the onset of the AIDS pandemic. Application of these tools to other infectious diseases and immunopathological conditions will provide a fertile area of research for future years. This review focuses on recent developments in the assessment of HIV-1-specific T cell responses in peripheral blood and tissues, with a particular emphasis on flow cytometry-based approaches.

Human immunodeficiency virus-specific CD8(+) T cells in human breast milk

Breast-feeding infants of human immunodeficiency virus (HIV)-infected women ingest large amounts of HIV, but most escape infection. While the factors affecting transmission risk are poorly understood, HIV-specific cytotoxic T-lymphocyte (CTL) responses play a critical role in controlling HIV levels in blood. We therefore investigated the ability of breast milk cells (BMC) from HIV-infected women from the United States and Zambia to respond to HIV-1 peptides in a gamma interferon enzyme-linked immunospot assay. All (n = 11) HIV-infected women had responses to pools of Gag peptide (range, 105 to 1,400 spot-forming cells/million; mean = 718), 8 of 11 reacted to Pol, 7 reacted to Nef, and 2 of 5 reacted to Env. Conversely, of four HIV-negative women, none responded to any of the tested HIV peptide pools. Depletion and tetramer staining studies demonstrated that CD8(+) T cells mediated these responses, and a chromium-release assay showed that these BMC were capable of lysing target cells in an HIV-specific manner. These data demonstrate the presence of HIV-specific major histocompatibility complex class I-restricted CD8(+) CTLs in breast milk. Their presence suggests a role in limiting transmission and provides a rationale for vaccine strategies to enhance these responses.