Effects of the Anti-CD20 Antibody Rituximab on B Cells in Human Secondary Lymphoid Organs

Abstract

Introduction: A single dose of the anti-CD20 monoclonal antibody rituximab (RTX) induces a nearly complete B-cell depletion in peripheral blood. However, there remains a residual B-cell population in secondary lymphoid organs, such as spleen and lymph nodes. An intriguing question that remains to be answered is whether these remaining B cells are modified due to binding by RTX. Methods: To mimic the in vivo situation, where B cells are exposed to RTX but only partially depleted, spleen cells obtained from organ donors were incubated in vitro with RTX and a low concentration of complement. The distribution of B-cell subsets was analyzed after 3 days of culture in the presence or absence of CpG-B. Results: Incomplete B-cell depletion followed by culture in the absence of CpG-B resulted in a IgD+CD27- (naïve): IgD-CD27+ (switched memory) B-cell ratio that was comparable to the non-depleted condition. However, after culture in the presence of CpG-B, the B cells that survived the depletion procedure showed a reduced naïve: switched memory ratio. In contrast to the total splenic B-cell population, the depletion surviving B cells did not contain IL-10 producing cells after culture with CpG-B. Moreover, B cells were also characterized ex vivo in peripheral blood and lymph nodes obtained during renal transplant surgery from patients (n=4) who had received RTX 4 weeks before transplantation. As described in literature, a complete depletion of B cells in the peripheral blood was obtained after a single dose of RTX, however in the lymph nodes the frequency of B cells was comparable to that of untreated control patients. Remarkably, the remaining lymph node B cells from RTX-treated patients showed a lower percentage of IgD+CD27- and a higher percentage of IgD-CD27+ B cells compared to lymph node B cells of untreated patients. Conclusion: Exposure of both spleen and lymph node B cells to RTX results in a shift of B cells from a naïve to a switched memory phenotype.