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Tissue-resident memory T cells (TRM) were first described in 2009. While initially the major focus was on CD8 + TRM, there has recently been increased interest in defining the phenotype and the role of CD4 + TRM in diseases. Circulating CD4 + T cells seed CD4 + TRM, but there also appears to be an equilibrium between CD4 + TRM and blood CD4 + T cells. CD4 + TRM are more mobile than CD8 + TRM, usually localized deeper within the dermis/lamina propria and yet may exhibit synergy with CD8 + TRM in disease control. This has been demonstrated in herpes simplex infections in mice. In human recurrent herpes infections, both CD4 + and CD8 + TRM persisting between lesions may control asymptomatic shedding through interferon-gamma secretion, although this has been more clearly shown for CD8 + T cells. The exact role of the CD4 + /CD8 + TRM axis in the trigeminal ganglia and/or cornea in controlling recurrent herpetic keratitis is unknown. In HIV, CD4 + TRM have now been shown to be a major target for productive and latent infection in the cervix. In HSV and HIV co-infections, CD4 + TRM persisting in the dermis support HIV replication. Further understanding of the role of CD4 + TRM and their induction by vaccines may help control sexual transmission by both viruses.

Problem: The effects of HIV on the gastrointestinal tract (GIT), including CD4 depletion, epithelial disruption, and collagen deposition, are well documented and only partially reversed by combination antiretroviral therapy (cART). However, the effects of HIV on the female reproductive tract (FRT) are poorly understood, and most studies have focused on ectocervix and vagina without assessing the upper tract. Here, we investigated CD4 + T-cell frequency, phenotype, and HIV-specific T-cell responses in the endocervix and endometrium of HIV-infected women, comparing these tissues to the GIT., Method of Study: Mucosal samples and blood were obtained from 18 women: four who were HIV-positive and not on cART for at least 3 years prior to sampling, including two natural controllers (viral load [VL] undetectable and CD4 >350); nine women on cART with low to undetectable VL; and five HIV-uninfected women. Mucosal samples included terminal ileum, sigmoid colon, endocervical cytobrush, endocervical curettage, and endometrial biopsy. T-cell frequency, phenotypes, and HIV-specific T-cell responses were analyzed by multiparameter flow cytometry., Results: T-cell activation, measured by CD38/HLA-DR co-expression, remained significantly elevated in endometrium following cART, but was lower in gastrointestinal tissues. HIV-specific CD8 + T-cell responses were detected in ileum, colon, and endometrial tissues of women both on and off cART, and were of higher magnitude on those not on cART., Conclusion: Our findings reveal differences in CD4 + T-cell frequencies, immune activation, and HIV-specific T-cell responses between the gastrointestinal and reproductive tracts, and highlight differences between HIV controllers and women on cART., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Purpose of Review: This review summarizes our current understanding of HIV-1-specific T-cell responses in mucosal tissues, emphasizing recent work and specifically highlighting papers published over the past 18 months., Recent Findings: Recent work has improved the standardization of tissue sampling approaches and provided new insights on the abundance, phenotype and distribution of HIV-1-specific T-cell populations in mucosal tissues. In addition, it has recently been established that some lymphocytes exist in tissues as "permanent resident" memory cells that differ from their counterparts in blood., Summary: HIV-1-specific T-cell responses have been extensively characterized; however, the vast majority of reports have focused on T-cells isolated from peripheral blood. Mucosal tissues of the genitourinary and gastrointestinal tracts serve as the primary sites of HIV-1 transmission, and provide "front line" barrier defenses against HIV-1 and other pathogens. In addition, the gastrointestinal tract remains a significant viral reservoir throughout the chronic phase of infection. Tissue-based immune responses may be critical in fighting infection, and understanding these defenses may lead to improved vaccines and immunotherapeutic strategies.

Depot-medroxyprogesterone acetate is a commonly used injectable contraceptive that has been associated with an increased risk of HIV acquisition. This study compares effects of depot-medroxyprogesterone acetate on immune parameters from several upper reproductive tract compartments relevant to HIV-1 susceptibility in repetitive samples from 15 depot-medroxyprogesterone acetate users and 27 women not on hormonal contraceptives. Compared with samples from unexposed women in the mid-luteal phase, depot-medroxyprogesterone acetate use was associated with: increased endocervical concentrations of MCP1 and IFNalpha2; decreased endocervical concentrations of IL1beta and IL6; increased proportions of endometrial CD4+ and CD8+ cells expressing the activation marker HLADR; increased density of endometrial macrophages; and decreased density of endometrial regulatory T cells. Unlike previous reports with samples from the vagina, we did not observe increased expression of the HIV co-receptor CCR5 on CD4+ T cells in the endocervix or endometrium. Our results indicate important differences in anatomic compartments regarding mechanisms by which depot-medroxyprogesterone acetate could be associated with increased risk of HIV acquisition, including increased recruitment of macrophages to the endometrium, decreased levels of pro-inflammatory cytokines in the endocervix possibly leading to enhanced susceptibility to viral infection, and activation of endometrial T cells.

Problem: The goal of this study was to investigate the phenotype and functional responsiveness of CD4(+) and CD8(+) T-cells in the upper reproductive tract of healthy premenopausal women. The lower reproductive tract is frequently studied as a site of sexually transmitted infections; however, the upper reproductive tract may also be a portal of entry and dissemination for pathogens, including HIV-1., Method of Study: Endometrial biopsy, endocervical curettage, cytobrush, and blood were collected during mid-luteal phase from 23 healthy women. T-cells were isolated and analyzed by flow cytometry., Results: As compared with their counterparts in blood, endometrial and endocervical T-cells had enhanced CCR5 expression, and were enriched for activated, effector memory cells. Endometrial T-cells were more responsive to polyclonal stimuli, producing a broad range of cytokines and chemokines., Conclusion: These findings underscore the responsiveness of endometrial T-cells to stimulation, and reveal their activated phenotype. These findings also suggest susceptibility of the upper reproductive tract to HIV-1 infection., (© 2013 John Wiley & Sons Ltd.)

The CCR5 inhibitor maraviroc has been hypothesized to decrease T-cell activation in HIV-infected individuals, but its independent immunologic effects have not been established in a placebo-controlled trial. We randomized 45 HIV-infected subjects with CD4 counts <350 cells per mm(3) and plasma HIV RNA levels <48 copies per mL on antiretroviral therapy (ART) to add maraviroc vs placebo to their regimen for 24 weeks followed by 12 weeks on ART alone. Compared with placebo-treated subjects, maraviroc-treated subjects unexpectedly experienced a greater median increase in % CD38+HLA-DR+ peripheral blood CD8+ T cells at week 24 (+2.2% vs -0.7%, P = .014), and less of a decline in activated CD4+ T cells (P < .001). The % CD38+HLA-DR+ CD4+ and CD8+ T cells increased nearly twofold in rectal tissue (both P < .001), and plasma CC chemokine receptor type 5 (CCR5) ligand (macrophage-inflammatory protein 1β) levels increased 2.4-fold during maraviroc intensification (P < .001). During maraviroc intensification, plasma lipopolysaccharide declined, whereas sCD14 levels and neutrophils tended to increase in blood and rectal tissue. Although the mechanisms explaining these findings remain unclear, CCR5 ligand-mediated activation of T cells, macrophages, and neutrophils via alternative chemokine receptors should be explored. These results may have relevance for trials of maraviroc for HIV preexposure prophylaxis and graft-versus-host disease. This trial was registered at www.clinicaltrials.gov as #NCT00735072.

Objective: The objective of this study was to assess the effects of HAART initiation on CD4(+) T-cell repopulation and T-cell immune activation in rectal and duodenal mucosa., Design: The effects of HAART on the gastrointestinal tract remain controversial, and studies have reached different conclusions regarding its effectiveness at restoring mucosal CD4(+) T cells depending upon time of initiation, duration of treatment and gastrointestinal tract region studied., Methods: We obtained blood, rectal biopsies and duodenal biopsies from 14 chronically infected individuals at baseline and at 4-9 months post-HAART initiation. We examined CD4(+) T-cell frequencies in blood, rectum and duodenum at both time points, and performed a detailed assessment of CD4(+) T-cell phenotype, immune activation marker expression and HIV-specific CD8(+) T-cell responses in blood and rectal mucosa., Results: CD4(+) T-cell percentages increased significantly in blood, rectal and duodenal mucosa after 4-9 months of HAART (P = 0.02, 0.0005, 0.0002), but remained lower than in uninfected controls. HIV-specific CD8(+) T-cell responses in blood and rectal mucosa declined following HAART initiation (P = 0.0015, 0.021). CD8(+) T-cell coexpression of CD38 and HLA-DR in blood and mucosa, as well as plasma sCD14, declined significantly. CD28 expression on blood and mucosal CD8(+) T cells increased, whereas programmed death receptor-1 expression on blood HIV-specific CD4(+) and CD8(+) T cells decreased., Conclusion: Within the first months of HAART, limited CD4(+) T-cell reconstitution occurs in small and large intestinal mucosa. Nevertheless, decreased immune activation and increased CD28 expression suggest rapid immunological benefits of HAART despite incomplete CD4(+) T-cell reconstitution.

Background: Some human immunodeficiency virus (HIV)-infected individuals are not able to achieve a normal CD4(+) T cell count despite prolonged, treatment-mediated viral suppression. We conducted an intensification study to assess whether residual viral replication contributes to replenishment of the latent reservoir and whether mucosal HIV-specific T cell responses limit the reservoir size., Methods: Thirty treated subjects with CD4(+) T cell counts of <350 cells/mm(3) despite viral suppression for ≥ 1 year were randomized to add raltegravir (400 mg twice daily) or matching placebo for 24 weeks. The primary end points were the proportion of subjects with undetectable plasma viremia (determined using an ultrasensitive assay with a lower limit of detection of <.3 copy/mL) and a change in the percentage of CD38(+)HLA-DR(+)CD8(+) T cells in peripheral blood mononuclear cells (PBMCs)., Results: The proportion of subjects with undetectable plasma viremia did not differ between the 2 groups (P = .42). Raltegravir intensification did not have a significant effect on immune activation or HIV-specific responses in PBMCs or gut-associated lymphoid tissue., Conclusions: Low-level viremia is not likely to be a significant cause of suboptimal CD4(+) T cell gains during HIV treatment., Clinical Trials Registration: NCT00631449.

A small percentage of human immunodeficiency virus (HIV)-infected individuals, termed elite controllers, are able to spontaneously control HIV replication in blood. As the gastrointestinal mucosa is an important site of HIV transmission and replication as well as CD4+ T-cell depletion, it is important to understand the nature of the immune responses occurring in this compartment. Although the role of the HIV-specific CD8+ T-cell responses in mucosal tissues has been described, few studies have investigated the role of mucosal HIV-specific CD4+ T cells. In this study, we assessed HIV-specific CD4+ T-cell responses in the rectal mucosa of 28 "controllers" (viral load [VL] of <2,000 copies/ml), 14 "noncontrollers" (VL of >10,000 copies/ml), and 10 individuals on highly active antiretroviral therapy (HAART) (VL of <75 copies/ml). Controllers had higher-magnitude Gag-specific mucosal CD4+ T-cell responses than individuals on HAART (P<0.05), as measured by their ability to produce gamma interferon (IFN-γ), interleukin-2 (IL-2), tumor necrosis factor alpha (TNF-α), and macrophage inflammatory protein 1β (MIP-1β). The frequency of polyfunctional mucosal CD4+ T cells was also higher in controllers than in noncontrollers or individuals on HAART (P<0.05). Controllers with the strongest HIV-specific CD4+ T-cell responses possessed class II HLA alleles, HLA-DRB1*13 and/or HLA-DQB1*06, previously associated with a nonprogression phenotype. Strikingly, individuals with both HLA-DRB1*13 and HLA-DQB1*06 had highly polyfunctional mucosal CD4+ T cells compared to individuals with HLA-DQB1*06 alone or other class II alleles. The frequency of polyfunctional CD4+ T cells in rectal mucosa positively correlated with the magnitude of the mucosal CD8+ T-cell response (Spearman's r=0.43, P=0.005), suggesting that increased CD4+ T-cell "help" may be important in maintaining strong CD8+ T-cell responses in the gut of HIV controllers.

The importance of the enzyme-linked immunosorbent spot (ELISPOT) assay as a tool for studying immune responses in vitro is becoming increasingly apparent. However, there remains a need for enhanced sensitivity for the detection of low frequency antigen-specific T cell responses. We reasoned that the addition of a combination of the cytokines interleukin (IL)-7 and IL-15 would selectively increase interferon-gamma (IFN-gamma) production from antigen-stimulated CD4+ and CD8+ effector memory T cells. Freshly isolated or cryopreserved peripheral blood mononuclear cells (PBMC) from four healthy donors were analysed by ELISPOT for the frequency of purified protein derivative (PPD)-specific CD4+ T cells or cytomegalovirus (CMV) peptide-specific CD8+ T cells. Addition of IL-7 and IL-15 increased the number of PPD-specific CD4+ T cells up to 2.4-fold in fresh PBMC and up to 18-fold in cryopreserved PBMC. The cytokines also increased the number of CMV peptide-specific CD8+ T cells in fresh PBMC up to 7.5-fold. No additional increases were seen when antibodies to co-stimulatory molecules CD28 and CD49d were applied together with the cytokine combination. These data demonstrate that the sensitivity of the ELISPOT assay may be significantly augmented by addition of the cytokines IL-7 and IL-15 to antigen-stimulated cells. This method will be particularly useful for the assessment of antigen-stimulated cytokine production by T cells in cryopreserved biological specimens.

Acute HIV-1 infection depletes CD4(+) T cells in gut-associated lymphoid tissue (GALT). The failure of containment of local viral replication, and consequent CD4(+) T cell depletion, might be due to delayed mobilization of effector CD8(+) T cells or absence of functioning HIV-1-specific CD8(+) T cell effectors within GALT. No studies have addressed human intestinal HIV-1-specific CD8(+) T cell functions. We sought to determine whether functional HIV-1-specific CTL were present in GALT and whether the repertoire differed from HIV-1-specific CTL isolated from peripheral blood mononuclear cells. From three HIV-1-infected subjects, we isolated HIV-1-specific CD8(+) T cells expressing the mucosal lymphocyte integrin CD103 from GALT. These antigen-specific effector cells could be expanded in vitro and lysed target cells in an MHC class I-restricted manner. HIV-1-specific CTL could be isolated from both duodenal and rectal GALT sites, indicating that CD8(+) effectors were widespread through GALT tissue. The breadth and antigenic specificities of GALT CTL appeared to differ from those in peripheral blood in some cases. In summary, we found HIV-1-specific CD8(+) effector T cells in GALT, despite HIV-1-induced CD4(+) T cell lymphopenia. This suggests that HIV-1-specific CTL in gut tissue can be maintained with limited CD4(+) T cell help., (Copyright 2000 Academic Press.)