A Novel Concept of Phased Desensitization Using Bortezomib and Rituximab for Highly HLA-Sensitized Kidney Transplantation: 866

Introduction: Donor specific alloantibody producing plasma cells (DSA-PCs) appear resistant to conventional immunosuppressive agents. The recent studies demonstrated the impact of pretransplant desensitization with the proteasome inhibitor bortezomib on DSA-PCs in sensitized renal allograft candidates. However, other studies have showed that one cycle of bortezomib alone does not decrease DSA levels in sensitized kidney transplant recipients. We developed a concept of phased desensitization with rituximab and bortezomib, and applied it in to a highly sensitized kidney transplant candidate. Methods: We assessed the activity of bortezomib against various B cell subpopulations and plasma cells and suppressive effect of that to produce anti-blood group antibodies (Abs) DSA in mice. To elicit Abs against allopeptide (DSA), B6 mice were immunized with thymocytes from Balb/c mice. After the immunization, the mice received intravenous injections of bortezomib (0.75 mg/kg body weight) 3 times a week for 1 week. On the basis of the results, we have established a novel concept of desensitization for a sensitized patient. Results: Bortezomib led to a significant reduction in the subpopulations of CD21-/IgMhigh plasmablasts, and CD138+/CD25-/IgG κ-light chain+ plasma cells in the spleen of Balb/c mice, but not in that of CD21+/IgMhigh marginal-zone B cells and the CD21low/IgMlow follicular B cells. Flow cytometry analyses revealed that bortezomib did not reduce the B cells with receptors for either A-carbohydrates. Thus, bortezomib reduced not only IgG producing plasma cells but also IgM producing cells, although their precursor memory B cells were resistant to this reagent. Taken together with a known fact that rituximab is able to deplete memory B cells, we have proposed a concept of phased desensitization using bortezomib and rituximab, and applied it in to a highly sensitized kidney transplant patient. A 56-year-old man with renal graft failure was referred to our hospital. His first renal graft from his brother remained functioning for 16 years but was lost due to chronic rejection. This allograft loss resulted in sensitization of the recipient against HLA antigens. Unfortunately, his wife who volunteered as a second donor shared the same A2 antigen with the first donor, which might be a target of the preformed anti-HLA Abs. Single antigen flow-based DSA testing revealed 11 anti-HLA class I Abs including anti-donor HLA A2 Ab. He received a desensitization regimen consisting of a single dose of rituximab (375 mg/m2) combined with double-filtration plasmapheresis (DFPP) followed by low doses of intravenous immuno-globulin (DFPP/IVIG treatment). Tacrolimus and mycophenolate mofetil were started 2 weeks before the DFPP/IVIG treatment. Despite 3 DFPP/IVIG sessions, the crossmatch remained positive. Thereafter, he was treated with one cycle of bortezomib (1.3mg/m2 × 4 doses). After 3 DFPP/IVIG sessions, the crossmatch turned negative and renal transplantation was successfully performed. The induction quadruple immunosuppression protocol comprised tacrolimus, mycophenolate mofetil and methylprednisolone. After the transplantation, neither Ab-mediated rejection nor severe acute cellular rejection was encountered in this patient. Conclusions: The current study suggests that phased desensitization with rituximab and bortezomib may be needed for highly HLA-sensitized kidney transplant candidates.