Alterations in B-cell subset frequencies between no/low EBV and high EBV patients following allo-HSCT. (A) Representative staining of PBMCs to identify CD27⁻IgD⁺ naive, CD27⁺IgD⁻ isotype-switched memory, CD27⁺IgD⁺ nonswitched memory, and CD27⁻IgD⁻ B-cell populations in no/low EBV and high EBVallo-HSCT recipients, and in a healthy control. The no/low EBV patient was bled 98 days posttransplant when the EBV load was undetectable in whole blood. The high EBV patient was bled at 101 days posttransplant during high-level DNAemia (1.54 × 10⁶ EBV copies per mL blood). (B) Enumeration of CD27⁻IgD⁺ naive B cells expressed as a percentage of CD45⁺ lymphocytes (left panel) or absolute numbers (right panel) in allo-HSCT patients and healthy controls. (C) Enumeration of CD27⁺IgD⁻ memory B cells expressed as a percentage of CD45⁺ lymphocytes (left panel) or absolute numbers (right panel) in allo-HSCT patients and healthy controls. In panels B and C, the solid horizontal lines represent the median values for each group. Both the percentage (P < .0001) and number (P < .0001) of memory B cells were significantly higher in the high EBV group compared with the no/low EBV group. (D) Enumeration of CD19⁺CD27⁺IgD⁻ memory B cells in PBMC samples prereactivation and at the point of high-level EBV DNAemia. There was a significant increase in both the proportion (P < .004) and absolute number (P < .002) of memory B cells during high-level EBV reactivation.