Direct interaction between HLA-B and carbamazepine activates T cells in patients with Stevens-Johnson syndrome

Background: Increasing studies have revealed that HLA alleles are the major genetic determinants of drug hypersensitivity; however, the underlying molecular mechanism remains unclear. Objective: We adopted the HLA-B1502 genetic predisposition to carbamazepine (CBZ)-induced Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) as a model to study the pathologic role of HLA in delayed-type drug hypersensitivity. Methods: We in vitro expanded CBZ-specific cytotoxic T lymphocytes (CTLs) from patients with CBZ-induced SJS/TEN and analyzed the interaction between HLA-B and CBZ analogs based on CTL response, surface plasmon resonance, peptide-binding assay, site-directed mutagenesis, and computer modeling. Results: The endogenous peptide-loaded HLA-B1502 molecule presented CBZ to CTLs without the involvement of intracellular drug metabolism or antigen processing. The HLA-B1502/peptide/ β₂-microglobulin protein complex showed binding affinity toward chemicals sharing 5-carboxamide on the tricyclic ring, as with CBZ. However, modifications of the ring structure of CBZ altered HLA-B1502 binding and CTL response. In addition to HLA-B1502, other HLA-B75 family members could also present CBZ to activate CTLs, whereas members of the HLA-B62 and HLA-B72 families could not. Three residues (Asn63, Ile95, and Leu156) in the peptide-binding groove of HLA-B1502 were involved in CBZ presentation and CTL activation. In particular, Asn63 shared by members of the B75 family was the key residue. Computer simulations revealed a preferred molecular conformation of the 5-carboxamide group of CBZ and the side chain of Arg62 on the B pocket of HLA-B1502. Conclusions: This study demonstrates a direct interaction of HLA with drugs, provides a detailed molecular mechanism of HLA-associated drug hypersensitivity, and has clinical correlations for CBZ-related drug-induced SJS/TEN.