Comparison of relative amounts of immature CD19⁺CD21⁻ B lymphocytes between ECP responders and ECP nonresponders. (A) Low percentages of immature CD19⁺CD21⁻ B cells before therapy correlate significantly with complete resolution of chronic graft-versus-host disease to extracorporeal photopheresis (ECP). Patients were divided into 3 groups, complete responders (CR, n = 6), partial responders (PR, n = 6), and nonresponders (NR, n = 7) 6 months after start of ECP. Immature CD19⁺CD21⁻ B cells assessed before start of ECP are shown in box plot format. Numbers indicate mean percentages (bold horizontal lines). Comparison of groups was performed using unpaired Student t test. (B) Complete ECP responders have significantly lower percentages of immature CD19⁺CD21⁻ B cells 6, 12, and 21 months after start of ECP therapy compared with ECP nonresponders. Patients with complete response (CR; black bars), partial response (PR; white bars) and no response (NR; gray bars) to ECP are shown. Results are shown in box plot format. The bold horizontal line indicates the mean percentages. Comparison of groups was performed using unpaired Student t test.