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.

Intravaginal practices (IVP) are common among African women and are associated with HIV acquisition. A behavioral intervention to reduce IVP is a potential new HIV risk-reduction strategy. Fifty-eight HIV-1-uninfected Kenyan women reporting IVP and 42 women who denied IVP were followed for 3 months. Women using IVP attended a skill-building, theory-based group intervention occurring weekly for 3 weeks to encourage IVP cessation. Vaginal swabs at each visit were used to detect yeast, to detect bacterial vaginosis, and to characterize the vaginal microbiota. Intravaginal insertion of soapy water (59%) and lemon juice (45%) was most common among 58 IVP women. The group-counseling intervention led to a decrease in IVP from 95% (54/58) at baseline to 0% (0/39) at month 3 ( p = 0.001). After 3 months of cessation, there was a reduction in yeast on vaginal wet preparation (22% to 7%, p = 0.011). Women in the IVP group were more likely to have a Lactobacillus iners-dominated vaginal microbiota at baseline compared to controls [odds ratio (OR), 6.4, p = 0.006] without significant change in the microbiota after IVP cessation. The group counseling intervention was effective in reducing IVP for 3 months. Reducing IVP may be important in itself, as well as to support effective use of vaginal microbicides, to prevent HIV acquisition.

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.

BackgroundHIV disease progresses more rapidly in children than adults with mortality rates exceeding 50% by 2 years of age without antiretroviral therapy (ART) in sub-Saharan Africa. Recent World Health Organization (WHO) guidelines recommend universal treatment for all living persons with HIV, yet there is limited supporting evidence in pediatric populations. The objective of this study was to determine whether CD4 cell counts reflect immunological markers associated with disease progression in ART naïve perinatally-infected HIV+ children and adolescents and their response to ART.MethodsPBMC and plasma samples were collected from 71 HIV negative and 132 HIV+ children (65 ART naïve and 67 on ART) between ages 1–19 years from Mombasa, Kenya. Untreated HIV+ subjects were sub-categorized by high or low CD4 T cell counts. Immune activation markers CD38, HLA-DR and Ki67 were analyzed by flow cytometry. Plasma soluble CD14 (sCD14) was quantified by ELISA.ResultsHIV-infected children and adolescents with preserved CD4 cell counts had depleted CD4 percentages and CD4:CD8 ratios, and high immune activation levels. ART initiation rapidly and persistently reversed T cell activation, but failed to normalize CD4:CD8 ratios and plasma sCD14 levels.ConclusionsDiminished CD4 percentages and CD4:CD8 ratios along with profound immune activation occur independent of CD4 cell count thresholds in ART naïve HIV+ children and adolescents. Immediate ART initiation, as recommended in the most recent WHO guidelines may protect them from pathologic sequelae associated with persistent inflammation.

This study highlights differences in PD-1+ CD4 T-cell memory phenotype and response to blockade between HIV-infected children and adults, with implications for potential immune checkpoint therapies.