Proliferation status of CD27⁺ B cells in high load allo-HSCT patients. (A) Representative staining of PBMCs from a high EBV patient and a healthy control donor to identify CD38^hi plasmablasts within the CD19⁺CD27⁺ memory B-cell population. (B) Proportion of CD19⁺CD27⁺ memory B cells exhibiting a CD38^hi plasmablastic phenotype in high EBV patients and healthy controls. The proportion of plasmablasts in the high EBV group was highly significantly increased (P < .0001) compared with the healthy controls. (C) Intracellular staining for Ki-67 expression. Naive and memory B cells, sorted by FACS, from a healthy individual and a representative EBV-transformed LCL (included as a positive control) were stained with an anti-Ki-67 antibody (shaded histogram) or isotype control antibody (open histogram) followed by flow cytometric analysis. (D) Ki-67 expression in naive and memory B cells sorted by FACS from 3 allo-HSCT patients with high-level EBV reactivation.