Combined immune modulation reveals carbamazepine-associated CD8⁺ T cell-dependent skin inflammation in HLA-A*31:01...

Human leukocyte antigen (HLA) alleles are among the strongest genetic risk factors for idiosyncratic drug toxicity. HLA-A*31:01 is a risk factor for carbamazepine (CBZ)-induced delayed drug hypersensitivity, yet allele carriage alone is insufficient for disease development. CD8⁺ T cells are implicated in these reactions; however, their activation mechanism remains unclear. Using HLA-A*31:01 knock-in (A31-KI) mice, we investigated whether CBZ exposure elicited CD8⁺ T-cell responses in vivo. The mice received CBZ for 7 days by oral administration (300 mg/kg/day) and auricular application (25 mg/kg/day). CBZ alone did not induce clear CD8⁺ T-cell activation. Under CD4⁺ T-cell depletion, CBZ markedly increased programmed cell death protein 1 (PD-1) expression in CD44^highCD62L^low CD8⁺ T cells, suggesting PD-1-mediated restraint of CBZ-responsive activation. Subsequent PD-1 blockade enhanced CD8⁺ T-cell activation in auricular lymph nodes and induced skin inflammation with elevated serum thymus and activation-regulated chemokine; both were attenuated by CD8⁺ T-cell depletion. To clarify how CBZ activated CD8⁺ T cells, we performed ex vivo analyses using splenocytes. CBZ (50 µM) induced proliferation of CD44^highCD8⁺ T cells, whereas this response was absent in purified CD8⁺ T-cell cultures and reduced by HLA class I and costimulatory blockade, supporting an antigen-presenting cell-dependent mechanism. Collectively, CBZ can activate CD8⁺ T cells; however, this response is restrained and remains latent. When immune control is disrupted, particularly in an HLA-A*31:01-bearing host, the response can progress to a CD8⁺ T cell-dependent inflammatory phenotype. Thus, A31-KI mice provide an in vivo platform for understanding CBZ-associated idiosyncratic toxicity and pathogenesis.