Selected Murine Residues Endow Human TCR with Enhanced Tumor Recognition

TCR-gene transfer can mediate tumor regression in terminally ill melanoma patients. However, the formation of mix dimers between endogenous and transduced TCR chains may result in the surface dilution of the introduced TCR, which translates in poorer cellular avidity. Recently, we reported that murinization of human TCRs (i.e., the replacement of human C regions by murine ones) can improve TCR function. However, because xenogenic sequences may trigger immunogenicity, we sought to identify the essential murine residues that mediate this enhanced functional effect. We constructed murine/human chimeras of alpha- and beta-chains and assessed for their surface expression and function. We identified an evolutionary-unique lysine residue in Cbeta, central to murine TCR function. The mapping of Calpha revealed that a few short stretches of amino acids play a role in enhancing TCR function, one of the most important ones being the SDVP sequence. This information led us to design improved and minimally murinized human TCR C regions that mediate increased tumor recognition. This also enabled us to suggest a structural model that could explain the role of the aforementioned residues in promoting the preferential pairing and stability of murinized TCRs. Overall, these findings could have implications for the treatment of malignant diseases using TCR-gene transfer.