Radiation Induced Changes CD20 Surface Levels Determine Therapeutics Response of Anti-CD20 Monoclonal Antibodies

Over the past 30 years, anti-CD20 mAbs induced depletion of Burkitt’s lymphoma still remains incurable due to low levels of CD20 surface expression. Therefore selectively control CD20 expression may beneficial to improve therapeutic response of anti-CD20 mAbs. The CD20 is transmembrane glycoproteins which are exclusively expressed on transformed B cells. During present investigation the sensitivity of human Burkitt’s lymphoma cells to rituximab (Rtx) was assessed on cells expressing different levels of CD20 on surface. This report provide evidence that irradiation just prior to immunotherapy may provide new treatment options even in aggressive B cell tumors.
Over three decades, antibody cancer therapeutics approach have been established and used clinically in an effort to appreciate the potential of targeted therapy. However, disease still remains incurable because of the acquired resistance in B-cell lymphomas following exposure to anti-CD20 mAbs may also be associated with reduced surface levels of CD20 and induce modest levels of cell death [1-5].
CD20 a non-glycosylated transmembrane protein, exclusively expressed on B cells. It appears during the pre-B cell stage, however absent during the earlier or later stages of B cell differentiation such as antibody secreting plasma cells [6, 7]. Therefore, CD20 has received extensive evaluation as an ideal target for immunotherapy and radio-immunotherapy, in part because of its ubiquitous expression, stable localization within the cell membrane of target cells (transformed B cells). Various monoclonal antibodies (mAbs) have been raised against CD20, which exerts various effects upon ligation such as complement-dependent cytotoxicity (CDC), antibody-dependent cellular phagocytosis (ADCP), antibody-dependent cellular cytotoxicity (ADCC) and can directly induce programmed cell death (PCD) [8-11]. A range of signaling events are induced following ligation of CD20 with mAbs. The earlier report suggests that the chimeric anti-CD20 mAb (Rtx) and cross-linking Fab’2 fragment, on B-cell chronic lymphocytic leukaemia cells (B-CLL) induce apoptosis through p38 MAP-kinase activation [12]. Radiation-induced changes in CD20 expression on B cells were evidenced first time in 1997 by Philippe et. al. [13]. Later on, Kunala et al have studied in more detail on various B lymphoblastoid cells types viz.Raji, Ramos, IM9 [14] and recently Gupta et al have investigated that low dose IR exposure to cells alters intracellular redox status, which determines expression of CD20 on malignant B cells [15]. The combination of ionizing radiation (IR) exposure and anti-CD20 mAbs in relation to therapeutic efficacy at surface levels of CD20 is poorly understood. Therefore, the ability to selectively control CD20 expression may be of great importance in enhancing therapeutic value and in optimizing anti-CD20 immunotherapy and radio-immunotherapy the modulation in CD20 expression may provide more binding sites for anti-CD20 mAbs and may play a major role in therapeutic response.
Improvement of antibody mediated cellular cytotoxicity or programmed cell death by modulation of CD20 surface level would also be an ideal approach. Since, ionizing radiation increases the surface levels of CD20 in treatment of Burkitt’s lymphoma. We have under taken present investigation to response of anti-CD20 mAb (Rtx) and their relation with CD20 cell surface expression in vitro. We additionally expanded our investigation on mode of cell death in vitro following treatment of cells with Rtx association with CD20 surface levels. In current investigation, our data strongly suggests that sub-lethal dose of γ-radiation induced CD20 surface levels beneficial for improvement of anti-CD20 response in vitro. Based on these findings we hypothesized that irradiation just prior to immunotherapy may provide new treatment options even in aggressive B cell tumors.