PDL241 treatment of RA synovial fibroblast-PBMC co-cultures leads to reduction on plasmablasts with no effect on B cells. (A) B cells differentiated into CD19+CD27hiCD38hiCD319+ plasmablasts after co-culture with RA-synovial fibroblasts. PBMC from normal donors were cultured with RA synovial fibroblasts. At day 0 and day 7, cells in the culture were analyzed by flow cytometry. After co-culture for seven days, differentiated plasmablast cells (CD19+CD27hiCD38hi) (gate 1) could be detected and were found to be CD319 positive (solid line) as compared to isotype control staining (dotted line); in contrast, memory (CD19+CD27+) (gate 2) and naïve B cells (CD19+CD27−) (gate 3) did not express CD319. (B) Removal of CD319+ plasmablast cells by PDL241 in RA synovial fibroblast-PBMC co-cultures. Addition of PDL241 to cultures specifically depleted CD19+CD27hiCD38hi plasmablasts, as compared to rituximab, which depleted only B cells. A FcR-binding deficient mutant of PDL241 (241-G2M3) had no effect on plasmablast cell numbers. The number in the gated population was calculated based on 10,000 events recoded. A representative experiment of n = 4 is shown. PBMC, peripheral blood mononuclear cells; RA, rheumatoic arthritis.