Pharmacodynamics of Rituximab in Kidney Allotransplantation

The anti‐CD20 antibody rituximab has recently gained interest as a B‐cell depleting agent in renal transplantation. However, little is known about the pharmacodynamics of rituximab in renal transplant recipients. We have therefore studied the effect of single‐dose rituximab in combination with conventional triple immunosuppressive therapy on the B‐cell population in peripheral blood as well as in tissues. A total of 49 renal transplant recipients received single‐dose rituximab, as induction therapy (n = 36) or as anti‐rejection therapy (n = 13). We counted B cells in peripheral blood and performed immunohistochemical staining on lymph nodes and kidney transplant tissue samples to assess the prevalence of B cells. In all but 6 patients (88%) complete depletion of B cells in peripheral blood was achieved. In adults, 15 months after treatment the CD19+ and CD20+ cell counts were still below 5 cells/μL in the majority of patients (78%). The immunohistochemical staining showed a complete elimination of B cells in kidney tissue and a reduction of B cells in lymph nodes. In conclusion, single‐dose rituximab in kidney transplant recipients evokes a long‐term elimination of B cells in peripheral blood as well as within the kidney transplant. The effect seems to extend beyond the expected 3–12 months observed in lymphoma patients. This study of 49 kidney transplant recipients receiving a single dose of rituximab therapy demonstrated that 88% showed complete depletion of B cells in peripheral blood with persisting low CD19+ cells at 15 months in most patients, and elimination of B cells from kidney tissue.