Background
Immune checkpoint blockade (ICB) partially reverses the dysfunctional state of antigen-specific T cell in chronic infections. However, its impact on the diverse subsets of CD4+ T cells in humans is largely unknown.
Methods
We examined immune checkpoint (IC) expression and function in HIV-specific CD4+ T cells of viremic individuals (≥5000 vRNA cp/ml, n = 17) prior to ART and persons with spontaneous (n = 11) or therapy-induced (n = 16) viral suppression (<40 cp/ml). We investigated IC patterns associated with exhaustion-related transcription factors and chemokine receptors using activation-induced marker assays. We determined effector functions representative of TFH, TH1, and TH17/TH22 using RNA flow cytometric fluorescence in situ hybridization (FISH). We compared increase in cytokine expression upon ICB across functions and patient status. Findings: Expression of dysfunction-related molecules, such as transcription factors and ICs PD-1, TIGIT, and CD200, followed a hierarchy associated with infection status and effector profile. In vitro responsiveness to PD-L1 blockade varied with defined functions rather than IC levels: frequencies of cells with TH1- and TH17/TH22-, but not TFH-related functions, increased. Cells co-expressing TH1 and TFH functions showed response to ICB, suggesting that the cell's state rather than function dictates responsiveness to PD-L1 blockade. Response to PD-L1 blockade was strongest in viremic participants and reduced after ART initiation. Interpretation: Our data highlight a polarization-specific regulation of IC expression and differing sensitivities of antigen-specific T helper subsets to PD-1-mediated inhibition. This heterogeneity may direct and constrain ICB efficacy in restoring CD4+ T cell function in HIV infection and other diseases. Funding: NIH, CIHR, CFI, FRQS.