Effect of mycophenolic acid and bortezomib on purified human B cells: an in vitro study of long-term functionally stable MICA-sensitized renal recipients.

OBJECTIVES We sought to develop a B-cell in vitro culture system and test B cells isolated from sensitized kidney recipients and healthy controls, and assess the effectiveness of proteasome inhibitors and mycophenolic acid on antibody secretion and cell apoptosis. MATERIALS AND METHODS CD19(+) B cells and CD19(+)CD27(+) memory B-cell subsets were detected from peripheral blood mononuclear cells obtained from 6 MICA-sensitized kidney recipients and 6 healthy controls. Peripheral blood B cells were isolated and cultured with CpG2006, PMA, MICA antigen, B-cell activating factor, CD40 ligand (CD40L), human recombinant IL-2 (rhuIL-2), rhuIL-10, rhuIL-4, and rhuIL-21. After culturing for 7 days, we tested several variables of B-cell activity including differentiation, apoptosis, and IgM production. We also assessed the effects of 2 immunosuppressive drugs (mycophenolic acid and bortezomib) on antibody secretion and cellular apoptosis. RESULTS Kidney recipients had a lower ratio of CD19+ B cells in peripheral blood mononuclear cells than did healthy controls. However, the percentage of CD19(+)CD27(+) B cells was higher in kidney recipients than in healthy controls. In the cell stimulation culture system, the ratio of CD19(+) B cells, CD19(+)CD27(+) B cells, and CD19(+)CD138(+) B cells increased after culturing for 7 days compared with unstimulated controls. In addition, the percentage of apoptotic B cells decreased, and antibody production increased in sensitized transplant patients and healthy controls. Treatment with bortezomib or mycophenolic acid induced B-cell apoptosis and inhibited secretion of antibodies. CONCLUSIONS This study describes establishment of a B-cell in vitro culture system, showing that B cells may be stimulated to secrete antibodies. The study also provides an assay for studying B cells in vitro. This study provides information suggesting that bortezomib and mycophenolic acid can inhibit B-cell antibody secretion.