Chemoenzymatic Synthesis of Nanobody-Peptide Conjugates Capable of Harnessing HBV Vaccine-Induced Antibodies for Cancer Immunotherapy

Redirecting endogenous antibodies toward tumor cells through rationally designed antibody-recruiting molecules (ARMs) has emerged as a promising strategy in cancer immunotherapy. However, current ARMs face inherent limitations, as they primarily depend on hapten-specific antibodies, which exhibit heterogeneity across populations and exist at suboptimal physiological concentrations. In this study, we explored the feasibility of leveraging Hepatitis B virus (HBV) vaccine-induced anti-HBV surface antigen (HBsAg) antibodies for cancer therapy. We developed a series of nanobody-peptide conjugates comprising an EGFR-targeting nanobody covalently linked to the LOOP2 peptide─an immunodominant epitope of HBsAg, through varying-length PEG spacers. The results demonstrated that these conjugates were capable of recruiting vaccine-induced anti-HBsAg antibodies onto the cancer cell surface and evoking potent antibody-dependent cell-mediated phagocytosis (ADCP) and complement-dependent cytotoxicity (CDC) for cell elimination. Interestingly, structure-activity relationship studies revealed that the PEG spacer had a minimal impact on ADCP efficacy, while it significantly affected CDC function. This proof-of-concept study establishes a novel paradigm for ARM-based therapeutics that leverages population-wide immunity from routine vaccination programs, thereby circumventing key limitations associated with the hapten-dependent system.