ABSTRACT: HIV-1 infection of resting memory CD4+ T cells forms a barrier to curing HIV-1. Identification of immune biomarkers that correlate with HIV-1 reservoir size could aid with assessing efficacy of HIV-1 eradication strategies, especially in pediatric infections where blood sampling is limited. In adults, the immune exhaustion marker PD-1 on central memory CD4+ T cells (Tcm) correlates with HIV-1 reservoir size. Immune correlates of HIV-1 reservoir size are less defined in perinatal infection. Using multi-parameter flow cytometry, we examined immune activation (CD69, CD25, HLA-DR), and exhaustion (PD-1, TIGIT, LAG-3 and TIM-3) markers on CD4+ T cell subsets (naïve (Tn), central memory (Tcm), and a combination (Ttem) of transitional (Ttm) and effector memory (Tem) in 10 children living with HIV-1 (median age 15.9 years; median duration of virologic suppression 7.0 years), in whom HIV-1 reservoir size was determined with both the Intact Proviral HIV-1 DNA assay (IPDA) and the Tat/Rev limiting dilution assay (TILDA). Total HIV-1 DNA in CD4+ T cells was also measured. Correlations between immune activation, and exhaustion markers on T cell subsets with the various markers of proviral reservoir size, and baseline CD4+ T cell transcriptomes were examined. The median total HIV-1 DNA concentration was 211.9 copies per million CD4+ T cells, with a median intact proviral load in individuals with HIV-1 subtype B of 8.0 copies per million CD4+ T cells. Levels of HLA-DR and TIGIT on Ttem were strongly correlated with total HIV-1 DNA (r=0.758, p=0.015) and (r=0.721, p=0.023), respectively, but not with intact proviral load or inducible reservoir size. HIV-1 DNA load was also positively correlated with transcriptional clusters associated with HLA-DR. In contrast, PD-1 expression on Tcm was inversely correlated with both total HIV-1 DNA (r=-0.67, p=0.039) and HLA-DR in Ttem (r=-0.89, p=0.060). Gene expression profiles for HLA-DR and PD-1 were also inversely correlated. In conclusion, with virologically suppressed perinatal HIV-1 infection, HLA-DR and TIGIT on Ttem CD4+ T cells correlate with total HIV-1 DNA, and may serve as immune biomarkers for transcriptionally active proviruses, including defectives persisting on ART.
