Ublituximab, a Novel, Glycoengineered Anti-CD20 Monoclonal Antibody (mAb), Demonstrates Enhanced Antibody-Dependent Cellular Cytotoxicity (ADCC) Relative to Other Anti-CD20 mAbs
Deren Huang1, Enrique Alvarez2, Hari Miskin3, Lily Lee3, John Foley4
1Mount Carmel Neurology, 2University of Colorado, 3TG Therapeutics, 4Rocky Mountain MS Clinic
Objective:
In vitro functional characterization of ublituximab relative to other anti-CD20 mAbs.
Background:
Anti-CD20–mediated B-cell depletion is induced by several mechanisms, including ADCC and complement-dependent cytotoxicity. ADCC is independent of the complement system and is mediated by interactions between the Fc region of anti-CD20 mAbs and the Fcγ receptor (FcγR) on effector cells (eg, natural killer cells), which initiate a series of signaling pathways leading to B-cell depletion. Polymorphisms of the FcγR at amino acid 158 (F/V) can lead to impaired binding to immunoglobulin G and reduce effector-cell engagement. Ublituximab is a novel, chimeric, type 1 mAb targeting a unique epitope of CD20 on B cells. Ublituximab is glycoengineered to exclude certain sugar molecules on its Fc region, conferring greater affinity to FcγRs leading to enhanced ADCC.
Design/Methods:
CD20 binding, FcγRIIIa-receptor binding, and ADCC for ublituximab versus other commercially available CD20 therapies (ocrelizumab, ofatumumab, and rituximab) were evaluated in in vitro studies. CD20 binding was evaluated using a CD20-expressing cell line (Jeko-1) and a MesoScale Discovery electrochemiluminescence assay. FcγR affinity was evaluated using surface plasmon resonance. ADCC activity was evaluated using CD20-expressing Raji cells plus KILR (CD16+) effector cells and diluted human serum samples in a luminescent cytotoxicity assay.
Results:
All evaluated mAbs had comparable CD20-binding affinity (EC50 [μg/mL): ublituximab, 0.063; ocrelizumab, 0.111; ofatumumab, 0.092; and rituximab, 0.133. Ublituximab had the highest binding affinity (KD [nM]) for FcγRIIIa 158V (64.1 versus 1025.8 [ocrelizumab], 1641.4 [ofatumumab], and 1199.8 [rituximab]) and FcγRIIIa 158F (680.3 versus 6762.9 [ocrelizumab], 14,815.2 [ofatumumab], and 6960.9 [rituximab]) as well as the highest ADCC activity (EC50 [pg/mL]): 2.4 versus 60.8 (ocrelizumab), 74.1 (ofatumumab), and 5457.0 (rituximab).
Conclusions:
Findings from in vitro studies demonstrated that ublituximab has higher FcγR binding and ADCC activity as a result of its glycoengineered Fc region compared with other commercially available anti-CD20 mAbs.