Background: Susceptibility to a clinically significant drug hypersensitivity syndrome associated with abacavir use has a significant genetic component. We have shown that the presence of HLA-B*5701 strongly predicts abacavir (ABC) hypersensitivity, particularly in combination with other allelic markers specific to the 57.1 ancestral haplotype, and identified a potential susceptibility locus within a 300-kb region between MEGT1 and C4A6 loci in the central MHC. Here we used fine recombinant haplotype mapping to identity the susceptibility loci.
Methods: We studied 248 consecutive ABC-exposed individuals, representing full ascertainment of ABC use in the Western Australian HIV Cohort study. Hypersensitivity was definite in 18 cases (7.3%); 230 tolerant controls were identified, utilizing an updated clinical classification that included corroborative epicutaneous skin patch test. Patients were typed for genetic markers using standard molecular techniques. Intracellular measurement of TNF (3-color flow cytometry) and intracellular localization of Hsp70 and HLA-B57 (confocal microscopy) were undertaken on abacavir exposed ex vivo polymorphic blood mononuclear cell (PBMC) cultures.
Results: Recombinant mapping in patients with allelic markers of the 57.1 ancestral haplotype suggest a susceptibility locus within the Hsp70 gene cluster. HLA-B*5701 was present in 94.4% of hypersensitive cases and 1.7% of controls (OR 960, p <0.00001). A haplotypic non-synonymous polymorphism of Hsp70-Hom (HspA1L, M493T) was found in combination with HLA-B*5701 in 94.4% of hypersensitive cases and 0.4% of controls (OR 3893, p <0.00001). The Hsp70-Hom M493T allele was present in 22% of controls (OR 60, p <0.00001), suggesting that the combination of HLA-B*5701 and Hsp70-Hom M493T conferred susceptibility. Individuals hypersensitive to ABC exhibited a significantly higher proportion of monocytes expressing TNF in response to ex vivo ABC stimulation, which was abrogated, on depletion of CD8+ T cells from whole blood. Increased intracellular expression of Hsp70 and HLA-B57 molecules in abacavir exposed ex vivo cultured PBMCs was observed in hypersensitive patients compared with controls. Hsp70 and HLA-B57 molecules co-localized within discrete vesicles.
Conclusions: These data indicate that the presence of HLA-B*5701 and Hsp70-Hom M493T are predisposing factors in the development of hypersensitivity to ABC, and implicates them in the generation of a Class I-restricted pathogenic immune response
