Bispecific antibody targeting shared indel-derived neoantigen of APC.

T cells play a pivotal role in cancer immunotherapy by recognizing tumor-specific neoantigens presented on HLA molecules, which are specifically expressed on cancer cells. While neoantigens are generally unique to individual cancers, certain neoantigens, known as 'shared neoantigens' that are common in a subset of cancer patients, represent promising immunotherapeutic targets. We previously identified an immunogenic shared frameshift neoantigen, 1472SP2, derived from recurrent frameshift indel mutation cluster (APC-F2-1472*) in the APC gene and presented on HLA-A24:02. In this study, we attempted to identify an antibody targeting a complex formed by the APC 1472SP2 neoantigen and HLA-A24. Using the phage display library screening, we isolated single-chain variable fragments (scFvs) that specifically recognize the 1472SP2/HLA-A24 complex. We then designed a bispecific antibody (BsAb) that would connect T cells via an anti-CD3 scFv to the cancer-specific 1472SP2 presented on the HLA-A24 molecule. ELISA analysis revealed that BsAb specifically recognized both 1472SP2-HLA-A24 monomer and CD3 protein. When T cells were co-cultured with antigen-presenting cells expressing HLA-A24:02, IFN-γ release and cytotoxicity were observed only in the presence of 1472SP2-BsAb, indicating that the 1472SP2-BsAb effectively activated T cells to lyse target cells presenting this neoantigen. This approach implies an off-the-shelf, cancer selective approach to target cancers expressing shared neoantigens for patients who are difficult to treat with conventional therapies.