The structure of the humanised A33 Fab C226S variant, an immunotherapy candidate for colorectal cancer

Colorectal cancer (CRC) causes the second highest cancer-related deaths worldwide. The human A33 antigen is a validated immunotherapy target, which is homogeneously expressed in 95% cases of primary and metastatic colorectal cancers. In this article, we report the structure of a humanised antigen-binding fragment A33 (A33 Fab), a therapeutic antibody candidate, in two different crystal forms. Insights into the structural features of A33 Fab are provided with a focus on the ‘grafted’ complementarity-determining regions (CDRs) and the switch linker between the variable and the constant regions. Synopsis The crystal structure of humanised A33 Fab, targeting colorectal cancer related antigen, was determined in two different space groups.