The predominant drug-specific T-cell population may switch from cytotoxic T cells to regulatory T cells during the course of anticonvulsant-induced hypersensitivity

Abstract Background Delayed hypersensitivity is responsible for severe cutaneous adverse drug reactions (cADRs), especially in Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis, and drug-induced hypersensitivity syndrome (DIHS) (also known as drug rash with eosinophilia and systemic symptoms [DRESS] syndrome). The drug-induced lymphocyte stimulation test (DLST), or lymphocyte transformation test (LTT), is used to identify the culprit drug in severe cADR cases. Objective The aim of this study was to examine the immune reactions in cADR patients through the identification of the drug-specific proliferating cells by flow cytometric DLST (FCM-DLST). Methods The peripheral blood mononuclear cells of 16 anticonvulsant-induced cADR patients were investigated by conventional DLST and a FCM-DLST protocol in which CFSE dilution and BrdU incorporation were combined. FCM-DLST allowed for the identification of the drug-specific proliferating cells in six cases. Three of these cases were DIHS cases, whereas there was one case of SJS, one case of maculopapular rash (MP), and one case of erythema multiforme (EM) among the six cases. Results In FCM-DLST, drug-specific proliferating T cells were detected as CFSElow BrdUhigh cells. These cells corresponded to the cells incorporating3 H-thymidine in conventional DLST. Although CD4+ T-cell proliferation dominated the observed proliferation in most of the cases (in the recovery stage of the three DIHS cases, the MP case, and the EM case), drug-specific CD8+ cytotoxic T lymphocytes (CTLs) were detected, especially in the acute stages of the SJS case and one of the DIHS cases. There was a dramatic switch in the predominant drug-specific proliferating T-cell population in the course of one of the cases of DIHS in which CD8+ CTLs were predominant initially, whereas CD4+ T cells were predominant later. Moreover, drug-specific CD4+ CD25+ Foxp3+ regulatory T cells (Tregs) proliferated during the recovery stage in one DIHS case. Conclusions FCM-DLST revealed that the cell proliferation detected by conventional DLST is a heterogeneous proliferation of both CD8+ CTLs and CD4+ T cells that likely includes Tregs. However, the number of cADR cases in this study was limited, which limits the conclusions that can be drawn from it.