Resistance to complement activation, cell membrane hypersialylation and relapses in chronic lymphocytic leukemia patients treated with rituximab and chemotherapy

Abstract

The anti-CD20-specific monoclonal antibody rituximab (RTX), in combination with chemotherapy, is commonly used for primary treatment in chronic lymphocytic leukemia (CLL). However, relapses remain important and activation of the complement pathway is one of the mechanisms by which RTX generates the destruction of B cells directly by complement-dependent cytotoxicity (CDC), or indirectly by antibody-dependent cellular phagocytosis. In this study, the RTX capacity to induce CDC was established in 69 untreated CLL patients, this cohort including 34 patients tested before the initiation of RTX-chemotherapy. In vitro CDC-resistance to RTX predicts lower response rates to RTX-chemotherapy and shorter treatment free survival. Furthermore, the predictive value of CDC-resistance was independent from the clinical, cytogenetic and FcγR3A V158F polymorphism status. In contrast, CLL cell resistance to CDC predominates in IGHV unmutated patients and was related to an important α2-6 sialyl transferase activity, which in turn increases cell surface α2-6 hypersialylation. Suspected factors associated with resistance to CDC (CD20, CD55, CD59, factor H, GM1, and sphingomyelin) were not differentially expressed or recruited between the two CLL groups. Altogether, results provide evidence that testing RTX capacity to induce CDC in vitro represents an independent predictive factor of therapeutic effects of RTX, and that α2-6 hypersialylation in CLL cells controls RTX response through the control of the complement pathway. At a time when CLL therapy is moving towards chemo-free treatments, further experiments are required to determine whether performing an initial in vitro assay to appreciate CLL CDC resistance might be useful to select patients.

17p deletion strongly influences rituximab elimination in chronic lymphocytic leukemia

“…Moreover, in non-del(17p) CLL patients, the absence of an association between FCGR3A genotypes and pharmacokinetic parameters further reinforces complement instead of Fc gamma dependent mechanisms for RTX elimination in CLL. This assertion is supported by a recent report showing the potential implication of TP53 loss in complement activation control [12, 19, 20].…”

How Do mAbs Make Use of Complement to Kill Cancer Cells? The Role of Ca2+

“…It would seem important to identify and optimize the primary killing mechanism to allow for efficient use of key resources, which comprise C and mAbs. Moreover, although the targeted malignant cells will employ a variety of defenses to ward off mAb-mediated attack [23][24][25][26][27][28][29][30], it is reasonable to ask that if the cells can be killed by CDC, then is there a common and general killing pathway? We developed several "complementary" (excuse the pun!)…”

“…The modifications (e.g., E430G) promote much more effective and rapid binding of the classical pathway initiating factor, hexameric C1q, to the mAb-opsonized cells, and thereby increase the CDC potential of a wide range of mAbs. We also note that numerous other strategies are under investigation for increasing the ability of mAbs to promote CDC of tumor cells [26,27,41,[63][64][65][66][67][68][69][70][71][72]. It will be interesting to compare the efficacy of these strategies if they progress to clinical trials.…”

<p>Clinical efficacy and safety of rituximab in lupus nephritis</p>

“…Rituximab (RTX) is a chimeric antibody which binds specifically to the B-cell surface antigen CD20 9. CD20 protein is expressed on immature and mature B lymphocytes, but it is not found in early B-cell precursors or plasma cells 10. Targeting and transiently depleting B cells is an ideal therapeutic approach for LN.…”