Decoupling peptide binding from T cell receptor recognition with engineered chimeric MHC-I molecules

Abstract

Abstract Human leucocyte antigens (HLAs) display a repertoire of epitopic peptides on the cell surface for T cell recognition. Amino acid polymorphisms in the peptide-binding groove of different HLA allotypes result in distinct antigenic repertoires, providing a basis for adaptive immunity to emerging pathogens at the population level. T cell receptors (TCRs) recognize pHLA antigens through interactions with both peptide and heavy chain residues. In this work, we use structural data from peptide:MHC-I and pMHC:TCR structures to identify residues important for peptide and/or TCR binding, and we outline a fixed-backbone computational design approach for engineering synthetic molecules that combine peptide binding and TCR recognition surfaces from existing HLA allotypes. X-ray crystallography demonstrates that chimeric molecules bridging divergent HLA alleles can bind selected peptide antigens in a specified backbone conformation. Moreover, in vitro tetramer staining and biophysical binding experiments using chimeric pMHC-I molecules presenting established antigens further demonstrate the requirement of TCR recognition on interactions with HLA framework residues, as opposed to interactions with peptide-centric Chimeric Antigen Receptors (CARs). Our results underscore a novel, structure-guided platform for developing synthetic HLA molecules displaying tumor-associated antigens with modified TCR interaction surfaces, which could further serve as platforms to elicit alloreactive T cell responses against self-antigens that are overexpressed in cancer. Finally, we gain a deeper understanding of the evolution and functional divergence of the different HLA allotypes by demonstrating an example of convergent evolution. Supported by grants from NIAID (5R01AI143997), NIGMS (5R35GM125034), and NIDDK (5U01DK112217)