Th17 T cells and immature dendritic cells are the preferential initial targets after rectal challenge with an SIV-based replication-defective dual-reporter vector

Temporal and spatial characterization of HIV/SIV infection at anorectal mucosa using rhesus macaque rectal challenge model

The study described herein is a continuation of our work in which we developed a methodology to identify small foci of transduced cells following rectal challenge of rhesus macaques with a non-replicative luciferase reporter virus. In the current study, the wild-type virus was added to the inoculation mix and twelve rhesus macaques were necropsied 2-4 days after the rectal challenge to study the changes in infected cell phenotype as the infection progressed. Relying on luciferase reporter we noted that both anus and rectum tissues are susceptible to the virus as early as 48h after the challenge. Small regions of the tissue containing luciferase-positive foci were further analyzed microscopically and were found to also contain cells infected by wild-type virus. Phenotypic analysis of the Env and Gag positive cells in these tissues revealed the virus can infect diverse cell populations, including but not limited to Th17 T cells, non Th17 T cells, immature dendritic cells, and myeloid-like cells. The proportions of the infected cell types, however, did not vary much during the first four days of infection when anus and rectum tissues were examined together. Nonetheless, when the same data was analyzed on a tissue-specific basis, we found significant changes in infected cell phenotypes over the course of infection. For anal tissue, a statistically significant increase in infection was observed for Th17 T cells and myeloid-like cells, while in the rectum, the non-Th17 T cells showed the biggest temporal increase, also of statistical significance.

The initial interplay between HIV and mucosal innate immunity

Human Immunodeficiency Virus (HIV) is still one of the major global health issues, and despite significant efforts that have been put into studying the pathogenesis of HIV infection, several aspects need to be clarified, including how innate immunity acts in different anatomical compartments. Given the nature of HIV as a sexually transmitted disease, one of the aspects that demands particular attention is the mucosal innate immune response. Given this scenario, we focused our attention on the interplay between HIV and mucosal innate response: the different mucosae act as a physical barrier, whose integrity can be compromised by the infection, and the virus-cell interaction induces the innate immune response. In addition, we explored the role of the mucosal microbiota in facilitating or preventing HIV infection and highlighted how its changes could influence the development of several opportunistic infections. Although recent progress, a proper characterization of mucosal innate immune response and microbiota is still missing, and further studies are needed to understand how they can be helpful for the formulation of an effective vaccine.

How Does Voluntary Medical Male Circumcision Reduce HIV Risk?

PURPOSE OF REVIEW

Voluntary medical male circumcision (VMMC) is a surgical procedure that reduces HIV acquisition risk by almost two-thirds. However, global implementation is lagging, in part due to VMMC hesitancy. A better understanding of the mechanism(s) by which this procedure protects against HIV may increase acceptance of VMMC as an HIV risk reduction approach among health care providers and their clients.

RECENT FINDINGS

HIV acquisition in the uncircumcised penis occurs preferentially across the inner foreskin tissues, due to increased susceptibility that is linked to elevated inflammatory cytokine levels in the sub-preputial space and an increased tissue density of HIV-susceptible CD4 + T cells. Inflammation can be caused by sexually transmitted infections, but is more commonly induced by specific anaerobic components of the penile microbiome. Circumcision protects by both directly removing the susceptible tissues of the inner foreskin, and by inducing a less inflammatory residual penile microbiome. VMMC reduces HIV susceptibility by removing susceptible penile tissues, and also through impacts on the penile immune and microbial milieu. Understanding these mechanisms may not only increase VMMC acceptability and reinvigorate global VMMC programs, but may also lead to non-surgical HIV prevention approaches focused on penile immunology and/or microbiota.

The rectal mucosal immune environment and HIV susceptibility among young men who have sex with men

Young men who have sex with men (YMSM) represent a particularly high-risk group for HIV acquisition in the US, despite similarly reported rates of sexual activity as older, adult MSM (AMSM). Increased rates of HIV infection among YMSM compared to AMSM could be partially attributable to differences within the rectal mucosal (RM) immune environment associated with earlier sexual debut and less lifetime exposure to receptive anal intercourse. Using an ex vivo explant HIV challenge model, we found that rectal tissues from YMSM supported higher levels of p24 at peak viral replication timepoints compared to AMSM. Among YMSM, the RM was characterized by increased CD4+ T cell proliferation, as well as lower frequencies of tissue resident CD8+ T cells and pro-inflammatory cytokine producing CD4+ and CD8+ T cells. In addition, the microbiome composition of YMSM was enriched for anaerobic taxa that have previously been associated with HIV acquisition risk, including Prevotella, Peptostreptococcus, and Peptoniphilus. These distinct immunologic and microbiome characteristics were found to be associated with higher HIV replication following ex vivo challenge of rectal explants, suggesting the RM microenvironment of YMSM may be uniquely conducive to HIV infection.

An in situ analysis pipeline for initial host-pathogen interactions reveals signatures of human colorectal HIV transmission

The initial immune response to HIV determines transmission. However, due to technical limitations we still do not have a comparative map of early mucosal transmission events. By combining RNAscope, cyclic immunofluorescence, and image analysis tools, we quantify HIV transmission signatures in intact human colorectal explants within 2 h of topical exposure. We map HIV enrichment to mucosal dendritic cells (DCs) and submucosal macrophages, but not CD4⁺ T cells, the primary targets of downstream infection. HIV⁺ DCs accumulate near and within lymphoid aggregates, which act as early sanctuaries of high viral titers while facilitating HIV passage to the submucosa. Finally, HIV entry induces recruitment and clustering of target cells, facilitating DC- and macrophage-mediated HIV transfer and enhanced infection of CD4⁺ T cells. These data demonstrate a rapid response to HIV structured to maximize the likelihood of mucosal infection and provide a framework for in situ studies of host-pathogen interactions and immune-mediated pathologies.

Immune parameters of HIV susceptibility in the female genital tract before and after penile-vaginal sex

Background

In women, most HIV infections are acquired through penile-vaginal sex. Inflammation in the female genital tract (FGT) increases the risk of HIV acquisition and transmission, likely through recruitment of HIV target cells and disruption of epithelial barrier integrity. Although sex may have important immune and epithelial effects, the impact of receptive penile-vaginal sex on the immune correlates of HIV susceptibility in the female genital tract is not well described.

Methods

STI-free heterosexual couples were recruited to the Sex, Couples and Science (SECS) Study, with the serial collection of cervical secretions (CVS), endocervical cytobrushes, blood and semen before and up to 72 h after either condomless (n = 29) or condom-protected (n = 8) penile-vaginal sex. Immune cells were characterized by flow cytometry, and immune factors including cytokines and soluble E-cadherin (sE-cad; a marker of epithelial disruption) were quantified by multiplex immunoassay. Co-primary endpoints were defined as levels of IP-10 and IL-1α, cytokines previously associated with increased HIV susceptibility.

Results

Here we show that cervicovaginal levels of vaginal IP-10, sE-cad and several other cytokines increase rapidly after sex, regardless of condom use. The proportion of endocervical HIV target cells, including Th17 cells, activated T cells, and activated or mature dendritic cells (DCs) also increase, particularly after condomless sex. Although most of these immune changes resolve within 72 h, increases in activated cervical CD4 + T cells and Tcm persist beyond this time.

Conclusions

Penile-vaginal sex induces multiple genital immune changes that may enhance HIV susceptibility during the 72 h post-sex window that is critical for virus acquisition. This has important implications for the mucosal immunopathogenesis of HIV transmission.

Women who acquire HIV most commonly do so during penile-vaginal sex. Although the risk of HIV acquisition is higher when there is pre-existing inflammation in the female genital tract, the impact of receptive penile-vaginal sex itself on immune markers of HIV susceptibility in the genital tract has not been widely studied. We recruited heterosexual couples, without HIV or sexually-transmitted infections, and studied the impact of a single episode of penile-vaginal sex on immune cells and proteins in the female genital tract. We found that some markers within the cervix and vagina increased immediately after sex, then returned to normal. We noticed differences in these changes depending on whether the sex was condom-protected and whether the male partner was circumcised. Our findings might help us to understand how sex impacts the immune system and how this might contribute to HIV acquisition.

Mohammadi et al. evaluate immune markers and cell types associated with HIV susceptibility in the female genital tract before and after penile-vaginal sex. The authors report that these immune parameters increase rapidly and transiently after sex, with condom use affecting some of the changes observed.

Condomless receptive anal intercourse is associated with markers of mucosal inflammation in a cohort of men who have sex with men in Atlanta, Georgia

Introduction

We previously showed that the rectal mucosal immune environment among men who have sex with men (MSM) engaging in condomless receptive anal intercourse (CRAI) is immunologically distinct from that of men who do not engage in anal intercourse (AI). Here, we further examined these differences with quantitative immunohistochemistry to better understand the geographic distribution of immune markers of interest.

Methods

We enrolled a cohort of MSM engaging in CRAI (n = 41) and men who do not engage in AI (n = 21) between October 2013 and April 2015. Participants were healthy, HIV‐negative men aged 18–45 from the metro Atlanta area. We performed rectal mucosal sampling via rigid sigmoidoscopy during two study visits separated by a median of nine weeks and timed with sexual activity for MSM engaging in CRAI. We used standardized, automated immunohistochemistry and quantitative image analysis to investigate the rectal mucosal distribution of neutrophils (MPO), IL‐17‐producing cells (IL‐17) and T_regs (FOXP3) in the lamina propria, and cellular proliferation (Ki67) and adherens junction protein (E‐cadherin) in the epithelium. We examined associations between biomarker expression and the rectal mucosal microbiota composition by 16s rRNA sequencing.

Results

Relative to the colonic crypt base, IL‐17, FOXP3, and MPO expression increased towards the rectal lumen, while Ki67 decreased and E‐cadherin was more uniformly distributed. Throughout the rectal mucosa distribution examined, MSM engaging in CRAI had higher mean lamina propria MPO expression (p = 0.04) and epithelial Ki67 (p = 0.04) compared to controls. There were no significant differences in IL‐17, FOXP3 or E‐cadherin expression. We found no significant associations of the five biomarkers with the global rectal microbiota composition or the individual taxa examined.

Conclusions

Understanding the mucosal distribution of inflammatory mediators can enhance our knowledge of the earliest events in HIV transmission. Neutrophil enrichment and crypt epithelial cell proliferation likely represent sub‐clinical inflammation in response to CRAI in the rectal mucosa of MSM, which could increase the risk for HIV acquisition. However, the contributory role of the microbiota in mucosal inflammation among MSM remains unclear. HIV prevention may be enhanced by interventions that reduce inflammation or capitalize on the presence of specific inflammatory mechanisms during HIV exposure.