Rituximab Infusion Promotes Rapid Complement Depletion and Acute CD20 Loss in Chronic Lymphocytic Leukemia

Abstract

Complement plays an important role in the immunotherapeutic action of the anti-CD20 mAb rituximab, and therefore we investigated whether complement might be the limiting factor in rituximab therapy. Our in vitro studies indicate that at high cell densities, binding of rituximab to human CD20+ cells leads to loss of complement activity and consumption of component C2. Infusion of rituximab in chronic lymphocytic leukemia patients also depletes complement; sera of treated patients have reduced capacity to C3b opsonize and kill CD20+ cells unless supplemented with normal serum or component C2. Initiation of rituximab infusion in chronic lymphocytic leukemia patients leads to rapid clearance of CD20+ cells. However, substantial numbers of B cells, with significantly reduced levels of CD20, return to the bloodstream immediately after rituximab infusion. In addition, a mAb specific for the Fc region of rituximab does not bind to these recirculating cells, suggesting that the rituximab-opsonized cells were temporarily sequestered by the mononuclear phagocytic system, and then released back into the circulation after the rituximab-CD20 complexes were removed by phagocytic cells. Western blots provide additional evidence for this escape mechanism that appears to occur as a consequence of CD20 loss. Treatment paradigms to prevent this escape, such as use of engineered or alternative anti-CD20 mAbs, may allow for more effective immunotherapy of chronic lymphocytic leukemia.

Rituximab therapy in malignant lymphoma

“…The role of complement-dependent cytotoxicity (CDC) is suggested by the consumption of complement observed after rituximab administration but in vitro CDC does not correlate with clinical response in lymphomas (Winkler et al, 1999;Weng and Levy, 2001). However, CDC seems to be the most important mechanism of cell lysis in chronic lymphocytic leukemia (CLL) patients (Kennedy et al, 2004). CDC is probably involved in the cytokine-release syndrome and its toxicity (Bienvenu et al, 2001).…”

CD40 stimulation sensitizes CLL cells to rituximab-induced cell death

“…This poor efficacy has been explained by low CD20 expression levels of CLL cells, 9,10 the presence of complement inactivating molecules (CD55, CD59) on CLL cells, 11 the presence of soluble CD20 (ref. 12), shaving and downmodulation of CD20 after rituximab treatment, 13,14 resistance to antibody dependent cellular cytotoxicity by natural killer cells in vitro 15 andFlast but not leastF the intrinsic anti-apoptotic profile of CLL cells. 16 In this study, we show that, in sharp contrast to the induction of resistance to cytotoxic drugs, CD40 stimulation of CLL cells considerably increases sensitivity to anti-CD20-mediated cell death.…”

The Shaving Reaction: Rituximab/CD20 Complexes Are Removed from Mantle Cell Lymphoma and Chronic Lymphocytic Leukemia Cells by THP-1 Monocytes

“…Extensive preclinical evidence showed that it is neither internalized nor shed when bound to B cells (9,27,33). We recently reported that during the standard infusion of RTX in patients with chronic lymphocytic leukemia (CLL), a large fraction of B cells was rapidly cleared from the circulation after only 30 mg of RTX was infused (34). However, immediately after the total dose of ϳ700 mg of RTX had been infused, when the concentration of RTX in the bloodstream was quite high (Ͼ100 g/ml), substantial B cell recrudescence was evident.…”