PD-1+ CD4 T cells are associated with HIV reservoir size and impaired function of T follicular helper cells in children and young adults on long-term viral control

Background: Curative strategies for HIV will need to eliminate the replication competent latent reservoir. CD4 T cells expressing Immune Checkpoint molecules (ICP) have been shown to preferentially harbor latent, replication-competent HIV. T follicular helper (Tfh) cell subset of CD4 T cells are critical for B cell differentiation. Here a cohort of HIV vertically infected children and young adults under durable viral control (PHIV) were investigated for CD4 ICP, immune activation (IA) markers and function in relation to HIV reservoir size.

Methods: 40 PHIV (4-19yrs age) who started ART <2 years of life and had undetectable viremia (<50 HIV copies/ml) for the past 5 years, were enrolled in 7 European research centers. HIV-DNA copies per million peripheral blood mononuclear cells (PBMC) were measured by real-time PCR. Flow cytometry was used to investigate CD4 T cells for 1) co-expression of PD1 with IA (ICOS, CD38, Ki67 and HLA-DR) or ICP (TIGIT, LAG3, TIM3 and CTLA4) and 2) intracellular cytokine production (IL2, IFNg, TNFα, IL21) after stimulation with ENV peptides. Pearson correlations and 2 group comparisons were performed using the Mann-Whitney T Test. P value<0.05 was considered significant.

Results: Total PD1+ CD4 T cells positively correlated with HIV-DNA (r=0.46) as did CD4 T cells co-expressing PD1 with other ICP or IA (table 1 below). We then divided our cohort based on HIV-DNA distribution into those with high (4th quartile) and low (1st quartile) HIV-DNA. We found that PD1+ CD4 T cells co-expressing IA or ICP were higher in participants with high HIV-DNA (table 1). PD1+ CD4 T cells also showed negative correlation with ENV antigen activated Tfh expressing CD40L (r=-0.41, p<0.05) with selective induction of IL2 (r=0.47, p<0.05), a cytokine that is inhibitory for Tfh.

Conclusions: This study suggests that PD-1 expression on CD4 T cells is associated with dysfunctional T:B cell interaction in response to HIV antigens, and supports the association of PD1 expression on CD4 T cells with size of viral reservoirs in vertically HIV infected children and young adults under long-term viral control.