Drug-induced liver injury (DILI) frequently has a delayed onset with several human leukocyte antigen (HLA) genotypes affecting susceptibility, indicating a potential role for the adaptive immune system in the disease. The aim of this study was to investigate whether drug-responsive T lymphocytes are detectable in patients who developed DILI with the combination, antimicrobial amoxicillin-clavulanate. Lymphocytes from 6 of 7 patients were found to proliferate and/or secrete interferon-gamma (IFN-c) when cultured with amoxicillin and/or clavulanic acid. Amoxicillin (n 5 105) and clavulanic acid (n 5 16) responsive CD4 1 and CD8 1 T-cell clones expressing CCR, chemokine (C-C motif ) receptor 4, CCR9, and chemokine (C-X-C motif ) receptor 3 were generated from patients with and without HLA risk alleles; no cross-reactivity was observed between the two drug antigens. Amoxicillin clones were found to secrete a heterogeneous panel of mediators, including IFN-c, interleukin-22 and cytolytic molecules. In contrast, cytokine secretion by the clavulanic acid clones was more restricted. CD4 1 and CD8 1 clones were major histocompatability complex class II and I restricted, respectively, with the drug antigen being presented to CD4 1 clones in the context of HLA-DR molecules. Several pieces of evidence indicate that the clones were activated by a hapten mechanism: First, professional antigen-presenting cells (APCs) were required for optimal activation; second, pulsing APCs for 4-16 hours activated the clones; and third, inhibition of processing abrogated the proliferative response and cytokine release. Conclusion: Both amoxicillin-and clavulanic acid-specific T cells participate in the liver injury that develops in certain patients exposed to amoxicillin-clavulanate. (HEPATOLOGY 2015;62:887-899) D rug-induced liver injury (DILI) is a major concern for public health as well as for drug development given that it is a leading cause of drug withdrawal. A recent study evaluating the short-term outcomes of 660 patients with DILI found that nearly 1 in 10 die or undergo liver transplantation within 6 months of DILI onset, and nearly 1 in 5 of the remaining patients have evidence of persistent liver injury at 6 months. 1 Liver injury tends to have a delayed onset, occurring 5-90 days after initial drug exposure. Furthermore, strong associations between expression of specific major histocompatibility complex (MHC; or human

Amoxicillin-clavulanate (AC) is one of the most common causes of drug induced liver injury (DILI). The association between AC-DILI and HLA alleles and the detection of drug-specific T cells in patients with AC-DILI indicate that the adaptive immune system is involved in the disease pathogenesis. In this study, mass spectrometric methods were employed to characterize the antigen formed by AC in exposed patients and the antigenic determinants that stimulate T cells. Amoxicillin formed penicilloyl adducts with lysine residues on human serum albumin (HSA) in vitro, with K190 and K199 being the most reactive sites. Amoxicillin-modified K190 and K199 have also been detected in all patients, and more extensive modification was observed in patients exposed to higher doses of amoxicillin. In contrast, the binding of clavulanic acid to HSA was more complicated. Multiple adducts were identified at high concentrations in vitro, including those formed by direct binding of clavulanic acid to lysine residues, novel pyrazine adducts derived from binding to the degradation products of clavulanic acid, and a cross-linking adduct. Stable adducts derived from formylacetic acid were detected in all patients exposed to the drug. Importantly, analysis of hapten-protein adducts formed in the cell culture medium revealed that the highly drug-specific T-cell responses were likely driven by the markedly different haptenic structures formed by these two drugs. In this study, the unique haptenic structures on albumin in patients formed by amoxicillin and clavulanic acid have been characterized and shown to function as chemically distinct antigens which can stimulate separate, specific T-cell clones.

A number of serious adverse drug reactions are caused by T cells. An association with HLA alleles has been identified with certain reactions, which makes it difficult to develop standardized preclinical tests to predict chemical liability. We have recently developed a T cell priming assay using the drug metabolite nitroso sulfamethoxazole (SMX-NO). We now report on reproducibility of the assay, establishment of a biobank of PBMC from 1000 HLA-typed volunteers, and generation of antigen-specific responses to a panel of compounds. Forty T cell priming assays were performed with SMX-NO; 5 gave weak responses (1.5-1.9) and 34 showed good (SI 2.0-3.9) or strong responses (SI > 4.0) using readouts for proliferation and cytokine release. Thus, SMX-NO can be used as a model reagent for in vitro T cell activation. Good to strong responses were also generated to haptenic compounds (amoxicillin, piperacillin and Bandrowski's base) that are not associated with an HLA risk allele. Furthermore, responses were detected to carbamazepine (in HLA-B*15:02 donors), flucloxacillin (in 1 HLA-B*57:01 donor) and oxypurinol (in HLA-B*58:01 donors), which are associated with HLA-class I-restricted forms of hypersensitivity. In contrast, naïve T cell priming to ximelagatran, lumiracoxib, and lapatinib (HLA-class II-restricted forms of hypersensitivity) yielded negative results. Abacavir, which activates memory T cells in patients, did not activate naïve T cells from HLA-B*57:01 donors. This work shows that the priming assay can be used to assess primary T cell responses to drugs and to study mechanisms T cell priming for drugs that display HLA class I restriction. Additional studies are required to investigate HLA-class II-restricted reactions.

Idiosyncratic drug‐induced liver injury (DILI) is a rare, often difficult‐to‐predict adverse reaction with complex pathomechanisms. However, it is now evident that certain forms of DILI are immune‐mediated and may involve the activation of drug‐specific T cells. Exosomes are cell‐derived vesicles that carry RNA, lipids, and protein cargo from their cell of origin to distant cells, and they may play a role in immune activation. Herein, primary human hepatocytes were treated with drugs associated with a high incidence of DILI (flucloxacillin, amoxicillin, isoniazid, and nitroso‐sulfamethoxazole) to characterize the proteins packaged within exosomes that are subsequently transported to dendritic cells for processing. Exosomes measured between 50 and 100 nm and expressed enriched CD63. Liquid chromatography–tandem mass spectrometry (LC/MS‐MS) identified 2,109 proteins, with 608 proteins being quantified across all exosome samples. Data are available through ProteomeXchange with identifier PXD010760. Analysis of gene ontologies revealed that exosomes mirrored whole human liver tissue in terms of the families of proteins present, regardless of drug treatment. However, exosomes from nitroso‐sulfamethoxazole‐treated hepatocytes selectively packaged a specific subset of proteins. LC/MS‐MS also revealed the presence of hepatocyte‐derived exosomal proteins covalently modified with amoxicillin, flucloxacillin, and nitroso‐sulfamethoxazole. Uptake of exosomes by monocyte‐derived dendritic cells occurred silently, mainly through phagocytosis, and was inhibited by latrunculin A. An amoxicillin‐modified 9‐mer peptide derived from the exosomal transcription factor protein SRY (sex determining region Y)‐box 30 activated naïve T cells from human leukocyte antigen A*02:01–positive human donors. Conclusion: This study shows that exosomes have the potential to transmit drug‐specific hepatocyte‐derived signals to the immune system and provide a pathway for the induction of drug hapten‐specific T‐cell responses.

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