CD19 and B-cell chronic lymphocytic leukemia: To assess the impact of immune dysregulation and EBV reactivation on immunosuppression in patients with CLL and SID, we analyzed the expression of immune checkpoints and their ligands on the surface of CD4 + T cells, CD8 + T cells, and CD19 + B cells, as well as the levels of their soluble forms in serum in the individual study groups (Fig. 5A-S).