Background First-line anti-tuberculosis drugs (FLTD) are the commonest cause of severe immune-mediated adverse drug reactions, including SJS/TEN and DRESS in PLHV. The mechanisms of these life-threatening reactions are poorly understood, making diagnosis and treatment challenging in patients who can ill-afford suboptimal treatment.

Methods We aimed to identify genetic markers for FLTD-induced SJS/TEN and DRESS through HLA, ERAP and KIR typing, and used an integrated single-cell approach involving: i) CyTOF2 (n=8), and ii) ScRNA-seq (n=3) to characterise peripheral blood immune cells activated by offending drug.

Results Rifampicin (RIF)-associated DRESS was commonest. IFN-gamma ELISPOT, optimised for FLTDs, was most sensitive (75%) for RIF-DRESS. RIF-DRESS/SJS/TEN(ELISPOT+) cases were associated with HLA-B*44:03, and single-cell work was restricted to these cases and matched controls. HIV-related chronic immune activation drove expansion of exhausted (CD57+PD-1+TIGIT+) CD8+ T cells in cases and controls. However, a subpopulation of these CD8+ T cells in cases expressed co-stimulation (CD28+CD27+) markers. We confirmed these with ScRNA-seq, as KLRG1lowCX3CR1high CD8+ T-cells with RIF-specific proliferative and cytotoxic capabilities (IFNGhiTNFhiGNLYhiGZMBhiPerforinhi). The V-J junction and CDR3αβ analysis showed a unique TCR repertoire for each case, with predominantly CD8+ oligoclonality. GLIPH2 analysis of TCRβ sequences found eight common T-cell groups across the three cases. Differential gene expression identified the SQVP TCR-motif as having RIF-induced proliferative and cytotoxic profiles. Regulatory T-cells (CD127lowCD25hiCCR4hi) were higher in controls and produced more TGF-beta.

Conclusion This study is the first detailed immunophenotyping work of RIF-DRESS in PLHV; including optimised ELISPOT to identify IFN-gamma T-cells to FLTD, with a strong association between HLA-B*44:03 and RIF-DRESS. We propose that, despite expanded, exhausted CD8+ T-cell populations characteristic of HIV-related advanced immunosuppression, RIF-DRESS patients have drug-specific cytotoxic CD8+ T cells, potentially sharing low-frequency TCR-motifs like SQVP. Increased functional regulatory T-cells may contribute to maintaining tolerance in HLAB*44:03+ controls. Future site-of-disease and in-vitro work is required to better define proposed pathogenic T-cell populations.