Hsiue et al. identified an antibody fragment (H2) that binds to the p53R175H peptide–HLA complex with high affinity, but not to p53WT, and linked it to an anti-CD3e scFv (UCHT1) to form a single-chain diabody (H2-scDb). H2 was selective due to the extensive interactions of its complementarity-determining region (CDR) loops with mutant His175 and the adjacent Arg174 protruding out of the HLA helices; it did not bind to any of three homologous human peptides identified using ScanProsite. In vitro, H2-scDb recognized low levels of p53R175H/HLA-A*02:01 on cancer cells, activated T cells, and induced cancer cell lysis; in T cell-engrafted mice bearing multiple myeloma xenografts it reduced tumor growth.
Contributed by Shishir Pant
ABSTRACT: TP53 (tumor protein p53) is the most commonly mutated cancer driver gene, but drugs that target mutant tumor suppressor genes, such as TP53, are not yet available. Here, we describe the identification of an antibody highly specific to the most common TP53 mutation (R175H, in which arginine at position 175 is replaced with histidine) in complex with a common human leukocyte antigen-A (HLA-A) allele on the cell surface. We describe the structural basis of this specificity and its conversion into an immunotherapeutic agent: a bispecific single-chain diabody. Despite the extremely low p53 peptide-HLA complex density on the cancer cell surface, the bispecific antibody effectively activated T cells to lyse cancer cells that presented the neoantigen in vitro and in mice. This approach could in theory be used to target cancers containing mutations that are difficult to target in conventional ways.