Abacavir induces loading of novel self-peptides into HLA-B*57

Abstract

Background Abacavir drug hypersensitivity in HIV-treated patients is associated with HLA-B*57:01 expression. To understand the immunochemistry of abacavir drug reactions, we investigated the effects of abacavir on HLA-B*57:01 epitope-binding in vitro and the quality and quantity of self-peptides presented by HLA-B*57:01 from abacavir-treated cells. Design and methods An HLA-B*57:01-specific epitope-binding assay was developed to test for effects of abacavir, didanosine or flucloxacillin on self-peptide binding. To examine whether abacavir alters the peptide repertoire in HLA-B*57:01, a B-cell line secreting soluble human leucocyte antigen (sHLA) was cultured in the presence or absence of abacavir, peptides were eluted from purified human leucocyte antigen (HLA), and the peptide epitopes comparatively mapped by mass spectroscopy to identify drug-unique peptides. Results Abacavir, but not didansosine or flucloxacillin, enhanced binding of the FITC-labeled self-peptide LF9 to HLA-B*57:01 in a dose-dependent manner. Endogenous peptides isolated from abacavir-treated HLA-B*57:01 B cells showed amino acid sequence differences compared with peptides from untreated cells. Novel drug-induced peptides lacked typical carboxyl (C) terminal amino acids characteristic of the HLA-B*57:01 peptide motif and instead contained predominantly isoleucine or leucine residues. Drug-induced peptides bind to soluble HLA-B*57:01 with high affinity that was not altered by abacavir addition. Conclusion Our results support a model of drug-induced autoimmunity in which abacavir alters the quantity and quality of self-peptide loading into HLA-B*57:01. Drug-induced loading of novel self-peptides into HLA, possibly by abacavir either altering the binding cleft or modifying the peptide-loading complex, generates an array of neo-antigen peptides that drive polyclonal T-cell autoimmune responses and multiorgan systemic toxicity.

Drug Hypersensitivity: How Drugs Stimulate T Cells via Pharmacological Interaction with Immune Receptors

“…Neither carbamazepine nor abacavir hypersensitivity peptides eluted from purified HLA molecules of drug-pulsed APC carried a covalently bound drug [27,28,29,30]. Indeed, a highly selective HLA allele association argues against the involvement of a hapten-driven T cell stimulation.…”

“…A breakthrough in understanding the link between DHR and HLA association was the crystallographic structure of the HLA-B*57:01 molecule with bound abacavir [29,30]. It showed that the drug binds below the peptide presented by the HLA-B*57:01 molecule, away from the site of peptide-TCR interaction [28,29].…”

“…It showed that the drug binds below the peptide presented by the HLA-B*57:01 molecule, away from the site of peptide-TCR interaction [28,29]. Analysis of peptides eluted from abacavir-treated HLA-B*57:01 + APC revealed that approximately 20% of the eluted peptides were absent in the pool of peptides eluted from abacavir-untreated HLA-B*57:01 molecules [28,29,30]. The data suggest that when abacavir is incubated with APC, it is taken up, enters the endoplasmic reticulum, and binds the still empty F-pocket of HLA-B*57:01 via noncovalent bonds (fig.…”

“…This has two consequences: (i) the abacavir binding alters the peptide-binding capacity of HLA-B*57:01. In addition and/or instead of usual peptides, altered peptides are selected for binding to {abacavir-HLA-B*57:01} [28,29,30]; (ii) moreover, the abacavir binding makes the {abacavir-HLA-B*57:01} complex look like a foreign (allo) HLA-protein. The {abacavir-peptHLA} complex is transported to the cell surface, where it elicits an auto- and predominantly an allo-like immune reaction [40].…”

Classification of Drug Hypersensitivity into Allergic, p-i, and Pseudo-Allergic Forms

“…• Many severe DHR were linked to the presence of a certain HLA allele due to direct drug binding to a critical region of the HLA protein and thus represent a typical “p-i HLA”-type reaction [25,27,28,29,32,33,34,35,36]. …”