Single cell approaches to define the pathogenic immune cells that mediate drug hypersensitivity

Rationale Striking class I HLA risk associations and CD8+ T cell dependency have been described for both Stevens-Johnson Syndrome/toxic epidermal necrolysis (SJS/TEN) and abacavir hypersensitivity (AHS). However, distinct clinical phenotypes and positive predictive values (55% for HLA-B*57:01 restricted AHS and <8% for all HLA risk alleles and SJS/TEN) highlight key mechanistic differences. Methods Single cell technologies including T-cell receptor αβ sequencing, multi-parameter flow cytometry, full transcriptome RNA-seq, and mass cytometry were used to define the clonality and molecular signatures of pathogenic drug-specific T cells from paired PBMC, blister fluid, and acute, recovery, and patch test positive skin in SJS/TEN and AHS (n=25). Results Dominant CD8+ T-cell clonotypes of effector memory phenotype (CCR7-) with variable expression of skin homing/residence markers (CLA, CD103) were seen in SJS/TEN skin and blister fluid and were present at much lower frequency in both acute and drug-stimulated recovery peripheral blood. A public TCR was dominant in blister fluid of HLA-B*15:02 restricted carbamazepine-SJS/TEN. For allopurinol SJS/TEN, a dominant clonotype was identified in HLA-B*58:01+ blister fluid and a novel HLA class I restriction was identified with striking T-cell clonality (>97%) in blister fluid and skin. In contrast, for AHS, abacavir responsive CD8+ T cells with shared TCR clonotypes were isolated from the peripheral blood and positive patch tests that were polyclonal. Conclusions Single cell approaches that define the signatures of drug-specific T cells in the skin and peripheral blood highlight mechanistic differences between HLA class I restricted drug hypersensitivity syndromes and will help drive the development of targeted therapeutics and screening approaches.