Transgenic murine models for the study of drug hypersensitivity reactions linked to HLA-I molecules.

Purpose of review: Immune-mediated drug hypersensitivity reactions (DHRs) can be life-threatening and an impediment to drug development. Mechanism of disease studies are difficult to perform in humans. Here we review human leukocyte antigens class I (HLA-I) transgenic murine models and highlight how these systems have helped to elucidate drug-specific and host immune factors that initiate, propagate and control severe drug toxicities to skin and liver.

Recent findings: HLA transgenic mice have been developed and used to study immune-mediated drug reactions in vitro and in vivo . CD8+ T cells from HLA-B∗57:01-expressing mice respond strongly to abacavir (ABC) in vitro but have self-limited responses to drug exposure in vivo . Immune tolerance can be overcome by depleting regulatory T cells (Treg) allowing antigen-presenting dendritic cells to express CD80/86 costimulatory molecules and signal through CD28 on the CD8+ T cell. Depletion of Treg also removes competition for interleukin 2 (IL-2) to allow T cell expansion and differentiation. Fine tuning of responses depends on inhibitory checkpoint molecules such as PD-1. Improved mouse models express only HLA in the absence of PD-1. These models show enhanced liver injury to flucloxacillin (FLX) which depends on drug priming, CD4+ T cell depletion, and lack of PD-1 expression. Drug-specific HLA-restricted cytotoxic CD8+ T cells can infiltrate the liver but are suppressed by Kupffer and liver sinusoidal endothelial cells.

Summary: HLA-I transgenic mouse models are now available to study ABC, FLX and carbamazepine-induced adverse reactions. In vivo studies range from characterizing drug-antigen presentation, T cell activation, immune-regulatory molecules and cell-cell interaction pathways that are specifically involved in causing or controlling unwanted DHRs.