Impaired generation and function of EBV-specific CD8⁺ T cells in CD27-deficient individuals. (A-B) PBMCs from healthy HLA-mismatched, HLA-matched (n = 4-8), and CD27-deficient patients (n = 4-7) were stained with specific EBV- or CMV-peptide-MHC class I tetramers, mAbs to CD4, CD8, CCR7, CD45RA, CD57, CD95, PD-1, 2B4, and NKG2D. EBV-specific and CMV-specific CD8⁺ T cells quantified in HLA-mismatched or -matched controls and CD27-deficient patients, presented for all individuals as well as based on the specific HLA alleles (HLA-A*0201, HLA-A*2402, or HLA B*0702). Statistics were performed using ANOVA; *P < .05. (C) Distribution of EBV-specific CD8⁺ T cells in the naive, T_CM, T_EM, and T_EMRA CD8⁺ T-cell populations in HLA-matched controls and CD27-deficient patients. (D) Expression of 2B4 and NKG2D on EBV-specific CD8⁺ T cells from healthy control and CD27-deficient patients. (E) Relative expression of 2B4 and NKG2D on EBV- and CMV-specific CD8⁺ T cells from CD27-deficient patients determined by calculating fold change relative to virus-specific CD8⁺ T cells from HLA-matched donors. (F) PBMCs were stained ex vivo with EBV-specific HLA tetramer, and mAbs to CD8, granzyme B, and perforin. Expression of granzyme B or perforin in EBV-specific CD8⁺ T cells from CD27-deficient patients was determined relative to that in EBV-specific CD8⁺ T cells from healthy donors.