Low IRF4 expression by HIV-specific CD8⁺T cells was independent of PD-1 signals. (A) PD-1 and CD69 expression by IRF4⁺CD137⁺CD8⁺ T cells in unstimulated, CEF-stimulated, or HIV-stimulated PBMCs. A representative of 7 samples (left panel). PD-1 MFI by CEF- and HIV-specific CD8⁺ T cells (middle panels). Gated on IRF4⁺CD137⁺CD8⁺ T cells (n = 7). One donor showed high PD-1 by HIV-specific CD8⁺ T cells (black symbols). (B) PBMCs from HIV⁺ subjects were treated for 30 minutes with anti–PD-L1 antibody and stimulated with HIV peptides for 18 hours. IRF4/CD137 expression with or without pretreatment with anti–PD-L1. Gated on CD8⁺ T cells. A representative result from 5 experiments is shown. (C) MFI of IRF4 in HIV-specific CD8⁺ T cells treated or not with anti–PD-L1. Gated on IRF4⁺CD137⁺CD8⁺ T cells (n = 5). One donor showed high PD-1 by HIV-specific CD8⁺ T cells (black symbols). NS, not significant (paired Student t test).