PDCD1 and B-cell chronic lymphocytic leukemia: Our study further showed that the highest levels of PD-1, PD-L1, and CTLA-4 on CD4+, CD8+, and CD19 + lymphocytes were found in the SID EBV + and CLL EBV + groups, indicating advanced immunosuppression resulting from EBV reactivation (Fig. 5).