Avidity optimization of a MAGE-A1-specific TCR with somatic hypermutation

Abstract

A T-cell receptor (TCR) with optimal avidity to a tumor antigen can be used to redirect T cells to eradicate cancer cells via adoptive cell transfer. Cancer testis antigens (CTAs) are attractive targets because they are expressed in the testis, which is immune-privileged, and in the tumor. However, CTAs are self-antigens and natural TCRs to CTAs have low affinity/avidity due to central tolerance. We previously described a method of directed evolution of TCR avidity using somatic hypermutation. In this study, we made several improvements to this method and enhanced the avidity of the hT27 TCR, which is specific for the cancer testis antigen HLA-A2-MAGE-A1278-286. We identified eight point mutations with varying degrees of improved avidity. Human T cells transduced with TCRs containing these mutations displayed enhanced tetramer binding, IFN-γ and IL2 production, and cytotoxicity. Most of the mutations have retained specificity, except for one mutant with extremely high avidity. We demonstrate that somatic hypermutation is capable of optimizing avidity of clinically relevant TCRs for immunotherapy.