Gut Homing CD4+ and CD8+ T-Cell Frequencies in HIV Infected Individuals on Antiretroviral Treatment

Altered mucosal immunity in HIV-positive colon adenoma: decreased CD4+ T cell infiltration is correlated with nadir but not current CD4+ T cell blood counts

BACKGROUND

People living with HIV (PLWH) face greater risks of developing non-AIDS-defining cancers (NADCs) than the general population; however, the underlying mechanisms remain elusive. The tumor microenvironment plays a significant role in the carcinogenesis of colorectal cancer (CRC), an NADC. We studied this carcinogenesis in PLWH by determining inflammatory phenotypes and assessing PD-1/PD-L1 expression in premalignant CRC stages of colon adenomas in HIV-positive and HIV-negative patients.

METHODS

We obtained polyp specimens from 22 HIV-positive and 61 HIV-negative participants treated with colonoscopy and polyp excision. We analyzed adenomas from 33 HIV-positive and 99 HIV-negative patients by immunohistochemistry using anti-CD4, anti-CD8, anti-FoxP3, and anti-CD163 antibodies. Additionally, we analyzed the expression levels of immune checkpoint proteins. We also evaluated the correlation between cell infiltration and blood cell counts.

RESULTS

HIV-positive participants had fewer infiltrating CD4⁺ T cells than HIV-negative participants (p = 0.0016). However, no statistical differences were observed in infiltrating CD8⁺ and FoxP3⁺ T cells and CD163⁺ macrophages. Moreover, epithelial cells did not express PD-1 or PD-L1. Notably, CD4⁺ T cell infiltration correlated with nadir blood CD4⁺ T cell counts (p <  0.05) but not with current blood CD4⁺ T cell counts.

CONCLUSION

Immune surveillance dysfunction owing to decreased CD4⁺ T cell infiltration in colon adenomas might be involved in colon carcinogenesis in HIV-positive individuals. Collectively, since the nadir blood CD4⁺ T cell count is strongly correlated with CD4⁺ T cell infiltration, it could facilitate efficient follow-up and enable treatment strategies for HIV-positive patients with colon adenomas.

Differential localization and limited cytotoxic potential of duodenal CD8+ T cells

The duodenum is a major site of HIV persistence during suppressive antiretroviral therapy despite harboring abundant tissue-resident memory (Trm) CD8⁺ T cells. The role of duodenal Trm CD8⁺ T cells in viral control is still not well defined. We examined the spatial localization, phenotype, and function of CD8⁺ T cells in the human duodenal tissue from people living with HIV (PLHIV) and healthy controls. We found that Trm (CD69⁺CD103^hi) cells were the predominant CD8⁺ T cell population in the duodenum. Immunofluorescence imaging of the duodenal tissue revealed that CD103⁺CD8⁺ T cells were localized in the intraepithelial region, while CD103^–CD8⁺ T cells and CD4⁺ T cells were mostly localized in the lamina propria (LP). Furthermore, HIV-specific CD8⁺ T cells were enriched in the CD69⁺CD103^–/lo population. However, the duodenal HIV-specific CD8⁺ Trm cells rarely expressed canonical molecules for potent cytolytic function (perforin and granzyme B) but were more polyfunctional than those from peripheral blood. Taken together, our results show that duodenal CD8⁺ Trm cells possess limited perforin-mediated cytolytic potential and are spatially separated from HIV-susceptible LP CD4⁺ T cells. This could contribute to HIV persistence in the duodenum and provides critical information for the design of cure therapies.

Associations between recent thymic emigrants and CD4+ T-cell recovery after short-term antiretroviral therapy initiation

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Objective:

Around 20–30% of HIV-infected individuals (HIV+) on successful antiretroviral therapy (ART) fail to normalize their CD4⁺ T-cell counts. Various factors could contribute to the lack of immune reconstitution, one of them being thymic insufficiency. We aimed to explore associations between recent thymic emigrants (RTEs) and CD4⁺ T-cell recovery.

Design:

ART-naive HIV+ individuals who started ART with advanced AIDS were selected. Good versus poor immune reconstitution was defined by CD4⁺ gains above or below 100 CD4⁺ T cells/μl. The follow-up period was 6 months.

Methods:

Peripheral blood mononuclear cells were isolated and flow cytometry was used to characterize RTEs as the fraction of naive CD4⁺ T cells expressing CD31⁺, the platelet endothelial cell adhesion molecule. Markers of cellular activation, senescence, exhaustion and cycling were also assessed.

Results:

After 6 months on ART, HIV+ individuals with good immune reconstitution had higher absolute numbers of RTEs, compared with those with poor immune reconstitution, and these strongly correlated with CD4⁺ gains in those individuals with good immune reconstitution but not with poor immune reconstitution. We also found that CD8⁺ T-cell immune activation decreased as early as 2 months post-ART initiation in individuals with good immune reconstitution, but only at month 6 post-ART in individuals with poor immune reconstitution. Levels of immune activation were inversely correlated with the absolute numbers of RTEs in both groups, but more strongly so in individuals with poor immune reconstitution.

Conclusion:

We show that RTEs are linked to CD4⁺ T-cell recovery and that the degree of immune reconstitution is not directly linked to persistent immune activation.

Plasma levels of soluble membrane attack complex are elevated despite viral suppression in HIV patients with poor immune reconstitution

The complement system is now a therapeutic target for the management of serious and life-threatening conditions such as paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, glomerulonephritis and other diseases caused by complement deficiencies or genetic variants. As complement therapeutics expand into more clinical conditions, monitoring complement activation is increasingly important, as is the baseline levels of complement activation fragments in blood or other body fluid levels. Although baseline complement levels have been reported in the literature, the majority of these data were generated using non-standard assays and with variable sample handling, potentially skewing results. In this study, we examined the plasma and serum levels of the soluble membrane attack complex of complement (sMAC). sMAC is formed in the fluid phase when complement is activated through the terminal pathway. It binds the regulatory proteins vitronectin and/or clusterin and cannot insert into cell membranes, and can serve as a soluble diagnostic marker in infectious disease settings, as previously shown for intraventricular shunt infections. Here we show that in healthy adults, serum sMAC levels were significantly higher than those in plasma, that plasma sMAC levels were similar between in African Americans and Caucasians and that plasma sMAC levels increase with age. Plasma sMAC levels were significantly higher in virally suppressed people living with HIV (PLWH) compared to non-HIV infected healthy donors. More specifically, PLWH with CD4+ T cell counts below 200 had even greater sMAC levels, suggesting diagnostic value in monitoring sMAC levels in this group.

Mucosal cell populations may contribute to peripheral immune abnormalities in HIV-infected subjects introducing cART with moderate immune-suppression

HIV infection causes the progressive depletion of CD4+ T-lymphocytes and profound modifications of T-cell homeostasis, which persist despite virologically-suppressive treatment and have been linked to a worse clinical outcome. Enduring alterations of the gastrointestinal tract may represent the underlying pathogenic mechanisms of these phenomena. Twenty-six HIV-infected subjects were assessed over a 12-month period following the introduction of antiretroviral therapy. 18 uninfected individuals were enrolled as controls. Parameters of peripheral T-cell homeostasis (activation, maturation), gastrointestinal function (microbial translocation, gut inflammation, fecal microbiota composition) and mucosal immunity (CD4+CCR6+CD161+, CD4+CCR9+α4β7+, stem cell memory CD4+/CD8+ T-cells) were assessed. CD4+CCR6+CD161+ cells were depleted in HIV-infected untreated subjects and maintained significantly lower levels compared to controls, despite the introduction of effective antiviral treatment. The frequency of gut-homing CD4+CCR9+α4β7+ cells was also impaired in untreated infection and correlated with the HIV RNA load and CD4+HLADR+CD38+; during therapy, we observed a contraction of this pool in the peripheral blood and the loss of its correlation with antigenic exposure/immune activation. A partial correction of the balance between stem cell memory pools and T-cell homeostasis was registered following treatment. In HIV-infected subjects with moderate immune-suppression, antiretroviral therapy has a marginal impact on mucosal immune populations which feature distinctive kinetics in the periphery, possibly reflecting their diverse recruitment from the blood to the mucosa. The persistent defects in mucosal immunity may fuel peripheral T-cell abnormalities through diverse mechanisms, including the production of IL-17/IL-22, cellular permissiveness to infection and regulation of T-lymphocyte maturation.

Mechanisms regulating expansion of CD8+ T cells during HIV-1 infection

Abnormal immune activation and expansion of CD8+ T cells, especially of memory and effector phenotypes, take place during HIV-1 infection, and these abnormal features persist during administration of antiretroviral therapy (ART) to infected patients. The molecular mechanisms for CD8+ T-cell expansion remain poorly characterized. In this article, we review the literature addressing features of CD8+ T-cell immune pathology and present an integrated view on the mechanisms leading to abnormal CD8+ T-cell expansion during HIV-1 infection. The expression of molecules important for directing the homing of CD8+ T cells between the circulation and lymphoid tissues, in particular CCR5 and CXCR3, is increased in CD8+ T cells in circulation and in inflamed tissues during HIV-1 infection; these disturbances in the homing capacity of CD8+ T cells have been linked to increased CD8+ T-cell proliferation. The production of IL-15, a cytokine responsible for physiological proliferation of CD8+ T cells, is increased in lymphoid tissues during HIV-1 infection as result of microbial translocation and severe inflammation. IL-15, and additional inflammatory cytokines, may lead to deregulated proliferation of CD8+ T cells and explain the accumulation of CD8+ T cells in circulation. The decreased capacity of CD8+ T cells to localize to gut-associated lymphoid tissue also contributes to the accumulation of these cells in blood. Control of inflammation, through ART administration during primary HIV-1 infection or therapies aimed at controlling inflammation during HIV-1 infection, is pivotal to prevent abnormal expansion of CD8+ T cells during HIV-1 infection.

The Human Penis Is a Genuine Immunological Effector Site

The human penis is a main portal of entry for numerous pathogens, and vaccines able to control resulting infections locally are highly desirable. However, in contrast to the gastrointestinal or vaginal mucosa, the penile immune system and mechanisms inducing a penile immune response remain elusive. In this descriptive study, using multiparametric flow cytometry and immunohistochemistry, we characterized mucosal immune cells such as B, T, and natural killer (NK) cells from the urethra, fossa, and glans of human adult penile tissues. We show that memory B lymphocytes and CD138⁺ plasma cells are detected in all penile compartments. CD4⁺ and CD8⁺ T lymphocytes reside in the epithelium and lamina propria of the penile regions and have mostly a resting memory phenotype. All penile regions contain CD56^dim NK cells surface expressing the natural cytotoxicity receptor NKp44 and the antibody-dependent cell cytotoxicity receptor CD16. These cells are also able to spontaneously secrete pro- and anti-inflammatory cytokines, such as IL-17 and IL-22. Finally, CCR10 is the main homing receptor detected in these penile cells although, together with CCR3, CCR6, and CCR9, their expression level differs between penile compartments. Unlike antigen-presenting cells which type differ between penile regions as we reported earlier, urethral, fossa, and glans content in immune B, T, and NK cells is comparable. However, median values per each analysis suggest that the glans, containing higher number and more activated NK cells together with higher number of terminally differentiate effector CD8⁺ T cells, is a superior effector site than the urethra and the fossa. Thus, the human penis is an immunologically active tissue containing the cellular machinery required to induce and produce a specific and effective response against mucosal pathogens. It can therefore be considered as a classic mucosal effector site, a feature that must be taken into account for the elaboration of efficient strategies, including vaccines, against sexually transmitted infections.