Anti-PD-L1 Augmentation of IFN-γ ELISpot Improves Detection of Culprit Drugs in Nonimmediate Drug Hypersensitivity: A Cohort Study.

BACKGROUND

The IFN-γ enzyme-linked immunospot (ELISpot) assay identifies culprit drugs in nonimmediate drug hypersensitivity reactions (DHRs), but sensitivity is reduced in certain clinical contexts, particularly with systemic corticosteroid use.

OBJECTIVE

To evaluate whether anti-programmed death-ligand 1 (anti-PD-L1) supplementation increases detectable drug-specific T-cell responses in patients at a higher risk of false-negative conventional ELISpot results.

METHODS

In this retrospective cohort study, 223 patients (450 drug-level tests) with severe cutaneous adverse reactions and other nonimmediate DHRs underwent paired ELISpot testing under conventional and anti-PD-L1-supplemented conditions. Anti-PD-L1 was applied selectively to patients with corticosteroid use, remote reaction history, or drug reaction with eosinophilia and systemic symptoms (DRESS) phenotype. Positivity was defined as ≥20 spot-forming units (SFU) per 106 peripheral blood mononuclear cells. Paired positivity was compared by McNemar's test and SFU magnitude by the Wilcoxon signed-rank test, with prespecified subgroup analyses by corticosteroid exposure, phenotype, and drug class.

RESULTS

Anti-PD-L1 supplementation increased ELISpot positivity from 14.4% (65 of 450) to 35.3% (159 of 450), an absolute increase of 20.9% (94 additional positive tests; P < .001). Conventional positivity was numerically lower in corticosteroid-treated patients (11.6% vs 18.5%, P = .059), whereas anti-PD-L1-modified positivity was similar between groups (35.4% vs 34.7%, P = .950). Augmented responses were consistent across all phenotypes and correlated with established causality scores. Among 114 patients tested against more than 1 distinct drug, positivity remained predominantly limited to a single drug per patient under both testing conditions.

CONCLUSIONS

Anti-PD-L1 supplementation substantially increased detectable ELISpot reactivity. Although conventional positivity was numerically lower in corticosteroid-treated patients, positivity was similar between groups after anti-PD-L1 supplementation. Although single-drug positivity predominated, some patients showed reactivity to 2 or more drugs under anti-PD-L1-supplemented conditions. Prospective multicenter validation is warranted.