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

Area of Science:

• Immunology
• Oncology
• Biotechnology

Background:

• Cancer cells overexpress complement-regulatory proteins (CRPs) like CD46, CD55, and CD59, enabling immune evasion.
• CRPs inhibit therapeutic antibody efficacy by blocking complement-mediated cell lysis.
• Systemic inhibition of CRPs is challenging due to their widespread functions.

Purpose of the Study:

• To develop a bispecific antibody targeting both CD20 and CD59 on cancer cells.
• To enhance antibody-mediated complement-dependent cytotoxicity (CDC) against cancer cells.
• To overcome resistance mechanisms mediated by CRPs.

Main Methods:

• Selected CD59-specific Fc fragments with novel antigen-binding sites (Fcabs) using yeast display.
• Engineered rituximab, an anti-CD20 antibody, by incorporating an anti-CD59 Fcab to create a bispecific antibody.
• Assessed the bispecific antibody's CDC activity on Raji cells (expressing CD20 and CD59) using a lactate dehydrogenase-release assay.

Main Results:

• The bispecific antibody demonstrated significantly enhanced CDC against CD20 and CD59 expressing Raji cells compared to controls.
• The enhanced CDC was specific, with no effect observed on cells with low CD20 expression or CD20-negative cells.
• The engineered antibody induced potent specific cytotoxicity at lower concentrations, reducing complement component exhaustion.

Conclusions:

• Bispecific antibodies combining anti-CD20 and anti-CD59 offer a promising strategy to overcome CRP-mediated immune evasion in cancer.
• This approach enhances targeted cancer cell killing through potent and specific CDC.
• These molecules represent potential next-generation therapeutics for lymphoid malignancies, offering improved efficacy and reduced side effects.