Adverse drug reactions (ADRs) are a major obstacle to drug development, and some of these, including hypersensitivity reactions to the HIV reverse transcriptase inhibitor abacavir (ABC), are associated with HLA alleles, particularly HLA-B*57:01. However, not all HLA-B*57:01⁺ patients develop ADRs, suggesting that in addition to the HLA genetic risk, other factors may influence the outcome of the response to the drug. To study HLA-linked ADRs in vivo, we generated HLA-B*57:01–Tg mice and show that, although ABC activated Tg mouse CD8⁺ T cells in vitro in a HLA-B*57:01–dependent manner, the drug was tolerated in vivo. In immunocompetent Tg animals, ABC induced CD8⁺ T cells with an anergy-like phenotype that did not lead to ADRs. In contrast, in vivo depletion of CD4⁺ T cells prior to ABC administration enhanced DC maturation to induce systemic ABC-reactive CD8⁺ T cells with an effector-like and skin-homing phenotype along with CD8⁺ infiltration and inflammation in drug-sensitized skin. B7 costimulatory molecule blockade prevented CD8⁺ T cell activation. These Tg mice provide a model for ABC tolerance and for the generation of HLA-B*57:01–restricted, ABC-reactive CD8⁺ T cells dependent on both HLA genetic risk and immunoregulatory host factors.