Chemical Synthesis of Antibody-Hapten Conjugates Capable of Recruiting the Endogenous Antibody to Magnify the Fc Effector Immunity of Antibody for Cancer Immunotherapy.

Monoclonal antibodies (mAbs) with enhanced effector functions in cancer immunotherapy, such as complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC), could improve the clinical performance. Here, we develop an mAb-hapten conjugate strategy to augment the mAb effector functions with the engagement of endogenous antibodies. An "off-the-shelf" mAb, rituximab, is site-specifically conjugated with the rhamnose (Rha) hapten to generate rituximab-Rha conjugates. The octopus-like conjugates could recruit -Rha antibodies onto the cancer cell surface and further form an immune complex that is able to provide multivalent Fc domains to interact with immune cells or complement protein C1q, leading to magnified ADCC and CDC simultaneously. One optimal conjugate with PEG2 as a linker exhibits the most potent cancer cell killing activity and significant antitumor efficacy in a xenograft model. This is a general and cost-effective approach to generate mAb with improved effector functions that may have broad applications.