HLA‐A*02:01 Presents Penicillin‐Modified Cysteinylated Peptides for T Cell Recognition

Background A subset of patients experience immune‐mediated hypersensitivity reactions towards β‐lactam antibiotics, with drug‐specific T cells implicated as one of the causative factors. The principal mechanism is thought to involve chemical haptenation of self‐peptides, resulting in novel peptide drug‐adducts that may trigger T cell recognition. Understanding the interactions between the β‐lactam drug, the T cell receptor (TCR) and the peptide/human leukocyte antigen (pHLA) complex is critical to gain further mechanistic insights into these hypersensitivity reactions. This study aimed to 1) explore the array of haptenated ligands presented by HLA‐A*02:01, 2) evaluate the repertoire of T cells involved in penicillin‐induced reactions in a hypersensitive patient and 3) determine if a dominant penicillin‐specific TCR clonotype recognises haptenated HLA peptides. Method An immunopeptidomics approach was applied to identify benzylpenicillin (BP)‐modified peptide ligands within the HLA‐A*02:01 ligandome. The drug‐reactive TCR repertoire was analysed by single‐cell sequencing of CD8 + T cells expanded in the presence of BP, and the dominant TCR assayed for reactivity in a reporter cell line. Result We report that BP modifies cysteine in preference to lysine residues within the HLA‐A*02:01 immunopeptidome. This modification occurs via cysteine‐drug conjugate formation, in conjunction with disulphide‐mediated peptide modification, which has not previously been considered in the context of drug hypersensitivities. Furthermore, we demonstrate that a BP‐specific TCR expanded from a patient reacts towards a reduction‐sensitive epitope, consistent with a BP‐cysteine adduct disulphide linked to a cysteine residue within the T cell epitope. Conclusion Our study provides evidence that cysteine‐penicillin adducts can be accommodated by HLA ligands with the potential to induce T cell‐mediated allergic reactions.