The molecules that define human regulatory T cells (Tregs) phenotypically and functionally remain to be fully characterized. We recently showed that activated human Tregs express mRNA for a transmembrane protein called glycoprotein A repetitions predominant (GARP, or LRRC32). Here, using a GARP-specific mAb, we demonstrate that expression of GARP on activated Tregs correlates with their suppressive capacity.

Background Identification of the Th17 T cell subset as important mediators of host defense and pathology, prompted us to determine their susceptibility to HIV infection. Methods and Results We found that a sizeable portion of Th17 cells express HIV co-receptor CCR5 and produce very low levels of CCR5 ligands MIP-1α and MIP-1β. Accordingly, CCR5+ Th17 cells were efficiently infected with CCR5-tropic HIV and were depleted during viral replication in vitro. Remarkably, HIV+ individuals under treatment showed significantly reduced Th17 cells compared to HIV− subjects, regardless of their viral loads or CD4 numbers, whereas treatment naïve subjects had normal levels. However, there was a preferential reduction in CCR5+ T cells that were also CCR6+, which is expressed on all Th17 cells, as compared to CCR6−CCR5+ cells, in both treated and untreated HIV+ subjects. This observation suggests preferential targeting of CCR6+CCR5+ Th17 cells by CCR5-tropic viruses in vivo. Th17 cell levels also inversely correlated with activated CD4+ T cells in HIV+ individuals under treatment. Conclusion Our findings suggest a complex perturbation of Th17 subsets during the course of HIV-disease potentially through both direct viral infection and virus indirect mechanisms such as immune activation.

Chronic immune activation is a hallmark of HIV infection, yet the underlying triggers of immune activation remain unclear. Persistent antigenic stimulation during HIV infection may also lead to immune exhaustion, a phenomenon in which effector T cells become dysfunctional and lose effector functions and proliferative capacity. Several markers of immune exhaustion, such as PD-1, LAG-3, Tim-3, and CTLA-4, which are also negative regulators of immune activation, are preferentially upregulated on T cells during HIV infection. It is not yet clear whether accumulation of T cells expressing activation inhibitory molecules is a consequence of general immune or chronic HIV-specific immune activation. Importantly, however, in vitro blockade of PD-1 and Tim-3 restores HIV-specific T-cell responses, indicating potential for immunotherapies. In this review we discuss the evolution of our understanding of immune exhaustion during HIV infection, highlighting novel markers and potential therapeutic targets.

A subset of human regulatory T cells (Tregs) secretes IL-17 and thus resembles Th17 effector cells. How IL-17+Treg cells differentiate from naïve precursors remains unclear. Here, we show that IL-17-producing T-cells can differentiate from CCR6+ naïve T cell precursors in the presence of IL-2, IL-1β, TGF-β, and IL-23. CCR6+ naïve T cells are present in adult peripheral and umbilical cord blood and in both conventional T naïve (TN) and FOXP3+ naïve Treg (TNreg) subsets. IL-17+ cells derived from CCR6+ TNreg cells (referred to as IL-17+Treg) express FOXP3, but not HELIOS, another Treg-associated transcription factor, and these cells display suppressor capacity and a surface phenotype resembling memory Tregs. Remarkably, the IL-17+Treg compartment was preferentially reduced relative to the canonical Th17 and Treg compartments in a subset of HIV+ subjects, suggesting a specific perturbation of this subset during the course of disease. Our findings that CCR6+ naïve precursors contain a predetermined reservoir to replenish IL-17-secreting cells, may have implications in balancing the Th17 and IL-17+Treg compartments that are perturbed during HIV infection and potentially in other inflammatory diseases.

Objectives: We sought to describe the presentation, course, and outcomes of hospitalized pediatric coronavirus disease 2019 patients, with detailed description of those requiring mechanical ventilation, and comparisons between critically ill and noncritical hospitalized pediatric patients. Design: Observational cohort study.

Objectives HIV and antiretroviral (ART) exposure in utero may have deleterious effects on the infant, but uncertainty still exists. The objective of this study was to evaluate aspects of mitochondrial DNA (mtDNA) content, mitochondrial function and oxidative stress simultaneously in placenta, umbilical cord blood and infant blood in HIV/ART-exposed infants compared with uninfected controls. Methods HIV-1-infected pregnant women and HIV-1-uninfected healthy pregnant controls were enrolled in the study prospectively. Placenta and umbilical cord blood were obtained at delivery and infant blood was obtained within 48 h of delivery. mtDNA content was determined for each specimen. Nuclear [subunit IV of cytochrome c-oxidase (COX IV)]- and mitochondrial (COX II)-encoded polypeptides of the oxidative phosphorylation enzyme cytochrome c-oxidase were quantified in cord and infant blood. Placental mitochondria malondialdehyde (MDA) concentrations were measured as a marker of oxidative stress. Results Twenty HIV-positive/HIV-exposed and 26 control mother–infant pairs were enrolled in the study. All HIV-infected women and their infants received ART. Placental MDA concentration and mtDNA content in placenta and cord blood were similar between groups. The cord blood COX II:IV ratio was lower in the HIV-positive group than in the controls, whereas the infant peripheral blood mtDNA content was higher in the HIV-exposed infants, but the infant peripheral blood COX II:IV ratio was similar. No infant had clinical evidence of mitochondrial disease or acquired HIV infection. In multivariable regression analyses, the significant findings in cord and infant blood were both most associated with HIV/ART exposure. Conclusions HIV-exposed infants showed reduced umbilical cord blood mitochondrial enzyme expression with increased infant peripheral blood mitochondrial DNA levels, the latter possibly reflecting a compensatory mechanism to overcome HIV/ART-associated mitochondrial toxicity.

Mucosal-associated invariant T cells (MAIT) are innate T cells restricted by major histocompatibility related molecule 1 (MR1) presenting riboflavin metabolite ligands derived from microbes. Specificity to riboflavin metabolites confers MAIT cells a broad array of host-protective activity against gram-negative and -positive bacteria, mycobacteria, and fungal pathogens. MAIT cells are present at low levels in the peripheral blood of neonates and gradually expand to relatively abundant levels during childhood. Despite no anti-viral activity, MAIT cells are depleted early and irreversibly in HIV infected adults. Such loss or impaired expansion of MAIT cells in HIV-positive children may render them more susceptible to common childhood illnesses and opportunistic infections. In this study we evaluated the frequency of MAIT cells in perinatally HIV-infected children, their response to antiretroviral treatment and their associations with HIV clinical status and related innate and adaptive immune cell subsets with potent antibacterial effector functions. We found HIV+ children between ages 3 to 18 years have significantly decreased CD8+ MAIT cell frequencies compared to uninfected healthy children. Remarkably, CD8 MAIT levels gradually increased with antiretroviral therapy, with greater recovery when treatment is initiated at a young age. Moreover, diminished CD8+ MAIT cell frequencies are associated with low CD4:CD8 ratios and elevated sCD14, suggesting a link with HIV disease progression. Last, CD8+ MAIT cell levels tightly correlate with other antibacterial and mucosa-protective immune subsets, namely, neutrophils, innate-like T cells, and Th17 and Th22 cells. Together these findings suggest that low frequencies of MAIT cells in HIV positive children are part of a concerted disruption to the innate and adaptive immune compartments specialized in sensing and responding to pathogenic or commensal bacteria.

Regulatory T cells (Tregs) are functionally suppressive CD4 T cells, critical for establishing peripheral tolerance and controlling inflammatory responses. Previous reports of Tregs during chronic HIV disease have conflicting results with higher or lower levels compared to controls. Identifying true Tregs with suppressive activity proves challenging during HIV infection, as traditional Treg markers, CD25 and FOXP3, may transiently up-regulate expression as a result of immune activation. Helios is an Ikaros family transcription factor that marks natural Tregs with suppressive activity and does not up-regulate expression after activation. Coexpression of FOXP3 and Helios has been suggested as a highly specific marker of “bona fide” Tregs. We evaluated Treg subsets by FOXP3 co-expressed with either CD25 or Helios and their association with HIV disease progression in perinatally-infected HIV positive children. Identifying Tregs by FOXP3 coexpression with Helios rather than CD25 revealed markedly higher Treg frequencies, particularly in HIV+ children. Regardless of ART, HIV infected children had a selective expansion of memory FOXP3+Helios+ Tregs. The rise in memory Tregs correlated with declining HIV clinical status, indicated by falling CD4 percentages and CD4:CD8 ratios and increasing HIV plasma viremia and immune activation. In addition, untreated HIV+ children exhibited an imbalance between the levels of Tregs and activated T cells. Finally, memory Tregs expressed immune activation markers CD38 and Ki67 and exhaustion marker, PD-1, that tightly correlated with a similar phenotype in memory CD4 T cells. Overall, HIV infected children had significant disruptions of memory Tregs that associated with advancing HIV disease.