Abacavir reactive HLA-B*5701 restricted memory CD8+ T cells are present in abacavir unexposed donors

Background: Drug hypersensitivity syndromes have been attributed to naive T cell responses to neoantigen generated by the drug. However, the occurrence of patch test confirmed abacavir hypersensitivity syndrome (ABC HSR) within 2 days of first drug exposure, and consistent, robust expansion of ABC-responsive CD8+ T cells in HLA-B*5701+ ABC-unexposed healthy donor peripheral blood mononuclear cells (PBMC) suggest a cross-reacting preexisting HLA-B*5701 restricted memory CD8+ T cell response. Methods: Memory T cell responses to ABC were examined in 3 ABC-unexposed HLA-B*5701+ healthy donor PBMC exposed to C1R.B57 antigen–presenting cells, which had been cultured overnight ±10 μg/mL ABC and then washed, at a ratio of 10:1 PBMC:APC, in culture for 2 hours. Cells were labelled on ice with interferon-g (IFN-γ) capture reagent (Miltenyi Biotec), warmed and chased for a further 4 hours. IFN-γ+ T cells were detected by surface labelling for CD8, CD4, and IFN-γ-PE and either examined directly by flow cytometry or further concentrated using anti-PE magnetic beads followed by flow cytometry. Next, CD45RAmid-low, CD62Lhi-low CD4+, and CD8+ T cells or CD8+ T cells alone were obtained from three HLA-B*5701+ and 2 HLA-B*5701– donors, representing a sample of the donor’s memory T cells. Sorted memory T cells responded to CEF peptides by secreting IFN-γ in contrast to CD45RAhi, CD62Lhi sorted naive T cells from the same individuals; 5 to 8 x 104 memory CD4+ and CD8+ T cells or memory CD8+ T cells alone were co-cultured with irradiated, ±ABC-treated, C1R.B57 cells for 10 days before re-stimulation with ABC treated and washed C1R.B57 cells. Results: PBMC from HLA-B*5701+ ABC-naive donors were stimulated for 6 h by ABC-treated C1R.B57 antigen–presenting cells: 2/3 showed a clear ABC-specific CD8+ T cell response above control background. Sorted CD4+ and CD8+ memory T cells cultured in the presence of APC+ABC resulted in the detection of ABC-specific CD8+ T cells in all 3 HLA-B*5701+ donors, but not in 2 HLA-B*5701– donors. ABC-specific CD8+ T cells were also detected from similarly treated, sorted HLA-B*5701+ CD8+ memory T cells. Conclusions: ABC-reactive HLA-B*5701 restricted memory CD8+ T cells can be detected in ABC-unexposed individuals and can be further expanded ex vivo from the memory CD8+ T cell pool. This suggests that an HLA-B*5701-restricted, memory CD8+ T cell response to a prevalent pathogen cross reacts with the neoantigen generated by ABC.