Application of in Vitro T Cell Assay Using Human Leukocyte Antigen-Typed Healthy Donors for the Assessment of Drug Immunogenicity.

It is unclear whether priming of naïve T cells to drugs is detectable in healthy human donors expressing different human leukocyte antigen (HLA) alleles. Thus, we examined T cell priming with drugs associated with HLA risk alleles and control compounds in 14 HLA-typed donors. Nitroso sulfamethoxazole and piperacillin activated T cells from all donors, whereas responses to carbamazepine and oxypurinol were only seen in donors expressing HLA-B*15:02 and HLA-B*58:01, respectively. Weak flucloxacillin-specific T cell responses were detected in donors expressing HLA-B*57:01 and HLA-B*58:01. These data show that the priming of T cells with certain drugs is skewed toward donors expressing specific HLA alleles.

Oxypurinol directly and immediately activates the drug-specific T cells via the preferential use of HLA-B*58:01.

Allopurinol (ALP) hypersensitivity is a major cause of severe cutaneous adverse reactions and is strongly associated with the HLA-B*58:01 allele. However, it can occur in the absence of this allele with identical clinical manifestations. The immune mechanism of ALP-induced severe cutaneous adverse reactions is poorly understood, and the T cell-reactivity pattern in patients with or without the HLA-B*58:01 allele is not known. To understand the interactions among the drug, HLA, and TCR, we generated T cell lines that react to ALP or its metabolite oxypurinol (OXP) from HLA-B*58:01(+) and HLA-B*58:01(-) donors and assessed their reactivity. ALP/OXP-specific T cells reacted immediately to the addition of the drugs and bypassed intracellular Ag processing, which is consistent with the "pharmacological interaction with immune receptors" (p-i) concept. This direct activation occurred regardless of HLA-B*58:01 status. Although most OXP-specific T cells from HLA-B*58:01(+) donors were restricted by the HLA-B*58:01 molecule for drug recognition, ALP-specific T cells also were restricted to other MHC class I molecules. This can be explained by in silico docking data that suggest that OXP binds to the peptide-binding groove of HLA-B*58:01 with higher affinity. The ensuing T cell responses elicited by ALP or OXP were not limited to particular TCR Vß repertoires. We conclude that the drug-specific T cells are activated by OXP bound to HLA-B*58:01 through the p-i mechanism.

Allopurinol hypersensitivity is primarily mediated by dose-dependent oxypurinol-specific T cell response.

BACKGROUND: Allopurinol is a main cause of severe cutaneous adverse reactions (SCAR). How allopurinol induces hypersensitivity remains unknown. Pre-disposing factors are the presence of the HLA-B*58:01 allele, renal failure and possibly the dose taken. OBJECTIVE: Using an in vitro model, we sought to decipher the relationship among allopurinol metabolism, HLA-B*58:01 phenotype and drug concentrations in stimulating drug-specific T cells. METHODS: Lymphocyte transformation test (LTT) results of patients who had developed allopurinol hypersensitivity were analysed. We generated allopurinol or oxypurinol-specific T cell lines (ALP/OXP-TCLs) from allopurinol naïve HLA-B*58:01(+) and HLA-B*58:01(-) individuals using various drug concentrations. Their reactivity patterns were analysed by flow cytometry and (51) Cr release assay. RESULTS: Allopurinol allergic patients are primarily sensitized to oxypurinol in a dose-dependent manner. TCL induction data show that both the presence of HLA-B*58:01 allele and high concentration of drug are important for the generation of drug-specific T cells. The predominance of oxypurinol-specific lymphocyte response in allopurinol allergic patients can be explained by the rapid conversion of allopurinol to oxypurinol in vivo rather than to its intrinsic immunogenicity. OXP-TCLs do not recognize allopurinol and vice versa. Finally, functional avidity of ALP/OXP-TCL is dependent on both the induction dose and HLA-B*58:01 status. CONCLUSIONS AND CLINICAL RELEVANCE: This study establishes the important synergistic role of drug concentration and HLA-B*58:01 allele in the allopurinol or oxypurinol-specific T cell responses. Despite the prevailing dogma that Type B adverse drug reactions are dose independent, allopurinol hypersensitivity is primarily driven by oxypurinol-specific T cell response in a dose-dependent manner, particular in the presence of HLA-B*58:01 allele.

Some adverse reactions to allopurinol may be mediated by lymphocyte reactivity to oxypurinol.

Six of 9 patients with previously documented adverse reactions to allopurinol exhibited transformation of their peripheral blood lymphocytes when these were exposed in vitro to the allopurinol metabolite, oxypurinol. In 2 of these subjects, intradermal skin challenge was positive at 48 hours with either allopurinol or oxypurinol. The evidence presented suggests that some adverse reactions to allopurinol represent delayed-type hypersensitivity to oxypurinol.

Allergic reaction to allopurinol with cross-reactivity to oxypurinol.

A 25-year-old white man with gout and nephropathy and with a previous reaction to allopurinol was given a trial dose of oxypurinol. He developed malaise, a generalized erythematous reaction with edema, pruritus, and emesis; this was clinically identical to the reaction he experienced with allopurinol. When the patient's lymphocytes were exposed in vitro to oxypurinol and allopurinol, increased DNA synthesis was observed, suggesting an immunologic basis for the reaction. This patient indicates that clinical cross reactivity to allopurinol and oxypurinol does occur and may be of an immunologic basis. There is a need for additional xanthine oxidase inhibitors for such patients.