Curative strategies for HIV will need to eliminate the replication competent latent reservoir. Immune Checkpoint molecules (ICP) are promising therapeutic targets for the elimination of the HIV latent reservoir, as CD4 T cells expressing ICP have been shown to preferentially harbor latent, replication-competent HIV. T cells expressing ICP are also considered as being exhausted. T follicular helper cell subset of CD4 T cells are critical for B cell differentiation for which induction of IL-21 is favorable while IL-2 is inhibitory. 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.
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); 2) co-expression of PD1 with ICP (TIGIT, LAG3, TIM3 and CTLA4); 3) 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.
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). 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 compared to low HIV DNA (table 1). PD1+ CD4 T cells (unstimulated) also showed correlations with ENV antigen activated circulating T follicular helper cells (Tfh) expressing CD40L (r=-0.41, p<0.05) with selective induction of IL2 (r=0.47, p<0.05) suggesting that PD-1 expression on CD4 can be associated with dysfunctional T:B cells interaction in response to HIV antigens.
This study confirms that vertically HIV infected children and young adults under long-term viral control maintain the association between expression of PD1 on CD4 T cells and size of viral reservoirs and also implicates the size of the viral reservoir in altered Tfh functionality.