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Keywords:

  • allopurinol;
  • avidity;
  • dose;
  • drug hypersensitivity;
  • HLA;
  • HLA-B*58:01;
  • oxypurinol;
  • severe cutaneous adverse reaction;
  • T cells

Abstract

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 51Cr 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.