Complement activation in circulation and central nervous system after Rituximab (Anti-CD20) treatment of B-Cell lymphoma

Rituximab (IDEC-C2B8, Mabthera (R), Rituxan (R)), a chimeric monoclonal antibody against the B-cell specific CD20-antigen, has been demonstrated to be effective in the treatment of non-Hodgkin's B-cell lymphoma (B-NHL). Previous in vitro studies have shown that direct complement-dependent cytotoxicity (CDC), ADCC and apoptosis are important in the rituximab-induced killing of lymphoma cells. It is, however, unknown whether rituximab penetrates the blood-brain barrier. Therefore, we studied rituximab levels and complement (C) activation in blood and cerebrospinal fluid (CSF) following intravenous rituximab therapy in a patient with relapsing non-Hodgkin's lymphoma with central nervous system (CNS) involvement. Longitudinal samples from blood and CSF were taken at 13 time-points during the treatment period. The results show that the C cascade becomes activated in blood during the First mAb infusion (C3a-desArg concentration rose from 55 to 138 mug/ml during the first 2 hours). After the first infusion the proportions of lymphocytes positive for the CD19- and CD20-antigens in the peripheral blood were reduced from 41 % and 35 %, respectively, to a level of 2 % (for both). In CSF the rituximab concentration increased after successive infusions, but remained below 0.55 mug/ml (compared to a C-max of 400 mug/ml in peripheral blood), Although a minor and delayed C activation response was seen in the CSF the treatment did not clear CD20-positive cells away from the CNS. Thus, it appears that an intact blood-brain barrier restricts the entry of rituximab into the CNS. Possible options to circumvent this would be dose escalation or intrathecal rituximab treatment.