Bispecific mAb2 Antibodies Targeting CD59 Enhance the Complement-Dependent Cytotoxicity Mediated by Rituximab

Abstract

Inhibition of complement activation via the overexpression of complement-regulatory proteins (CRPs), most notably CD46, CD55 and CD59, is an efficient mechanism of disguise of cancer cells from a host immune system. This phenomenon extends to counteract the potency of therapeutic antibodies that could lyse target cells by eliciting complement cascade. The manifold functions and ubiquitous expression of CRPs preclude their systemic specific inhibition. We selected CD59-specific Fc fragments with a novel antigen binding site (Fcabs) from yeast display libraries using recombinant antigens expressed in bacterial or mammalian cells. To produce a bispecific antibody, we endowed rituximab, a clinically applied anti-CD20 antibody, used for therapy of various lymphoid malignancies, with an anti-CD59 Fcab. This bispecific antibody was able to induce more potent complement-dependent cytotoxicity for CD20 and CD59 expressing Raji cell line measured with lactate dehydrogenase-release assay, but had no effect on the cells with lower levels of the primary CD20 antigen or CD20-negative cells. Such molecules are promising candidates for future therapeutic development as they elicit a higher specific cytotoxicity at a lower concentration and hence cause a lower exhaustion of complement components.

Unveiling CD59-Antibody Interactions to Design Paratope-Mimicking Peptides for Complement Modulation

“…Moreover, it is a distinctive feature of severe SARS-CoV-2 infection [31][32][33]. Repressing the terminal lysis capacity of the complement system through the involvement of the inhibiting RCA protein CD59 is characteristic of cancer resistance and of the action of infectious pathogens, which tend to hijack the complement system regulators to defend from its aggression [10][11][12][13][14]. For instance, CD59 is incorporated in the viral capside, such as HIV and vaccinia, in an effort to avoid complement-mediated lysis [16].…”

“…It has been shown that neoplastic cells overexpress both CD59 and CD55 to resist complement-mediated cytolysis (CMC) [9]. Consistently, the use of bispecific antibodies targeting these RCAs and the targets of conventional cancer immunotherapy regimens, such as trastuzumab (anti-HER2) and rituximab (anti-CD20), enhance the complement-dependent cytotoxicity (CDC) against breast cancer and non-Hodgkin's leukemia cells, respectively [10][11][12][13][14]. Importantly, HIV-1 virions are vulnerable to complement-mediated lysis (virolysis).…”