HIV-Exposed Uninfected Infants Have Increased Regulatory T Cells That Correlate With Decreased T Cell Function

Abstract

Background: HIV-exposed uninfected infants (HEU) are at higher risk of severe infections, hospitalizations and death compared with HIV-unexposed uninfected infants (HUU), but the immune deficit underlying it is not known. To address this gap, we investigated T cell functionality and its relationship to phenotypic profiles of T cells and antigen presenting cells (APC) in HEU and HUU. Methods: Blood mononuclear cells from 55 HEU and 16 HUU were stimulated with Staphylococcal Enterotoxin B (SEB) or mock for 72 h, and tested by flow cytometry for proliferation and expression of Th1, Th2, and regulatory (Treg) markers. In parallel, cells were phenotypically assessed for differentiation profiles of Treg, conventional T cell (Tconv) and APC in unstimulated cells. Results: HEU had lower CD4+ functional responses to SEB/mock and similar CD8+ responses compared with HUU. In the phenotypic T cell panel, HEU showed higher proportions of CD4+ and CD8+ Treg expressing IL10, FOXP3, and CD25; higher effector Tconv and Treg; and lower naïve and CD4+TGFβ+ Treg compared with HUU. In the phenotypic APC panel, HEU showed higher proportions of CD1c+ cDC2, CD123+ pDC, CD16+ inflammatory monocytes and cDC and higher expression of CD103 on CD1c-CD123-CD16-cDC1 compared with HUU. Regression analyses adjusted for HIV exposure and multiple comparisons showed that higher CD8+IL10+ and CD8+FOXP3+ Treg in unstimulated cells were associated with lower CD8+ T cell functional responses to SEB/mock. Functionality was not affected by Tconv differentiation, but higher APC activation in aggregate was associated with higher CD8+IL10+ Treg responses to SEB. Conclusions: T cell functionality was decreased in HEU compared with HUU. High CD8+ Treg proportions were the most important predictors of decreased T cell functionality in HEU and HUU.

Keywords: HIV-exposed uninfected infants; T cell differentiation; T cell function; antigen presenting cells; regulatory T cells.

Figure 1

HEU and HUU functional CD4+ T cell responses. Data were derived from PBMC of 22 HEU and 17 HUU after stimulation with SEB and mock. Results were expressed as the ratio between SEB and mock stimulation. (A) shows the PCA distribution of the results. (B) shows results of the regression analysis.

Figure 2

Heatmap representation of functional T cell response correlations. Data were derived from PBMC of 22 HEU and 17 HUU after stimulation with SEB and mock. Analytes are shown on the graph axes. The correlation factor scale is shown on the side of each heatmap. The data represented in panels (A–D) are labeled in each of the corresponding panels.

Figure 3

Forest plot representation of significant effects of Treg on functional T cell outcomes in HEU and HUU. Data were derived from 6 HEU and 16HUU. Filled circles and horizontal lines indicate mean and 95% CI of the effect of each Treg population on the functional outcome indicated on the abscissa (Treg : functional outcome). No effect is indicated by the dotted vertical line. The effect represents the decrease of the functional outcome with each unit increase in the Treg population. For example, for each 1% increase in CD8+FOXP3 Treg, there is a 40% decrease in the CD8+TGFβ T cells; and for each 1% increase in CD8+IL10+ Treg there is a 95% decrease in the CD8+IFNγ+ T cells.