Correlation of clinical response to rituximab with depletion of CD19+CD27+ memory B cells. Clinical response to rituximab correlates with depletion of CD19+CD27+ memory B cells in peripheral blood (PB) and in the bone marrow (BM) of rheumatoid arthritis (RA) patients. PB CD19+CD27+ cells increased by 29 ± 16% in nonresponders (NR) (n = 5), compared with a reduction by 26 ± 10% in responders (R) (P = 0.023) (n = 4). Similarly, BM CD19+CD27+ cells increased by 31 ± 13% in NR (n = 4), whereas they decreased by 26 ± 13% in R (n = 2). *P < 0.05 for paired analysis between baseline and 3 months.