Toxic epidermal necrolysis (TEN) is a very rare but extremely severe drug reaction characterized by widespread apoptosis of epidermis with extensive blisters. We previously found drug-specific cytotoxic CD8 T lymphocytes in the blisters of a single patient.

To confirm the role of drug specific cytotoxic lymphocytes in a larger series, to test the cytotoxicity on keratinocytes, and to look for cross-reactivity between chemically related drugs.

The phenotype of lymphocytes present in the blister fluids of 6 patients with TEN was analyzed by flow cytometry. Cytotoxic functions were tested by chromium release assay on a variety of target cells (autologous or MHC class I–matched EBV-transformed lymphocytes, autologous keratinocytes) after nonspecific (CD3 monoclonal antibody) or specific (suspected and potentially cross-reactive drugs) activation.

Blister lymphocytes were CD8⁺HLA-DR⁺CLA⁺CD56⁺. In all 6 cases, they were cytotoxic after nonspecific activation. A drug-specific cytotoxicity was observed in 4 cases (3 related to cotrimoxazole and 1 to carbamazepine) toward lymphocytes. Blister cells also killed IFN-γ–activated autologous keratinocytes in the presence of drug in the 2 patients tested. Blister cells showed a strong immunoreactivity for granzyme B, and cytotoxicity was abolished by EGTA, but not by anti-Fas/CD95, suggesting perforin/granzyme–mediated killing.

By using several sulfonamides for testing the specificity of the drug T-cell receptor interaction, we observed cross-reactivity only between 4 structurally closely related medications.

These results strongly suggest that drug-specific, MHC class I–restricted, perforin/granzyme–mediated cytotoxicity probably has a primary role in TEN.