Development and in vitro characterization of a bispecific TCR-like antibody targeting the PRAME301–309/HLA-A*24:02 complex for cancer immunotherapy

T cell receptor (TCR)-like antibodies recognize intracellular antigenic peptides presented by major histocompatibility complex (MHC) class I molecules. HLA-A*02:01 (HLA-A2) is the most frequent MHC class I allele worldwide, and most TCR-like antibodies have been designed to target peptides presented by HLA-A2. However, their therapeutic applicability may be limited by allele-restricted peptide presentation and the extensive polymorphism of MHC class I molecules. In this study, we developed a TCR-like antibody specific for the preferentially expressed antigen in melanoma (PRAME) peptide presented by HLA-A*24:02 (HLA-A24), the second most frequent MHC class I allele worldwide and the most common in East Asian populations. PRAME is a cancer-testis antigen expressed in various cancers but absent from normal adult tissues except the testes, making it an attractive target for TCR-like antibodies. An anti-PRAME 301–309 /HLA-A24 TCR-like scFv 2F7 was identified by phage display and reformatted into a bispecific T-cell–engaging antibody. In vitro studies using human peripheral blood mononuclear cells (PBMCs) and cancer cell lines demonstrated that the 2F7 bispecific TCR-like antibody (bsTLA) specifically bound to the PRAME 301–309 /HLA-A24 complex and redirected PBMC-derived T cells to kill target cells presenting this peptide-HLA complex.