Abacavir Hypersensitivity Syndrome Research Articles

Proteomic Profiling and T Cell Receptor Usage of Abacavir Susceptible Subjects

Type B adverse drug reactions (ADRs) represent a significant threat as their occurrence arises unpredictable and despite proper application of the drug. The severe immune reaction Abacavir Hypersensitivity Syndrome (AHS) that arises in HIV+ patients treated with the antiretroviral drug Abacavir (ABC) strongly correlates to the presence of the human leukocyte antigen (HLA) genotype HLA-B*57:01 and discriminates HLA-B*57:01+ HIV+ patients from ABC treatment. However, not all HLA-B*57:01+ HIV+ patients are affected by AHS, implying the involvement of further patient-specific factors in the development of AHS. The establishment of a reliable assay to classify HLA-B*57:01 carriers as ABC sensitive or ABC tolerant allowed to investigate the T cell receptor (TCR) Vβ chain repertoire of effector cells and revealed Vβ6 and Vβ24 as potential public TCRs in ABC sensitive HLA-B*57:01 carriers. Furthermore, distinct effects of ABC on the cellular proteome of ABC sensitive and tolerant volunteers were observed and suggest enhanced activation and maturation of dentritic cells (DC) in ABC sensitive volunteers. Analysis of ABC-naïve cellular proteomes identified the T cell immune regulator 1 (TCIRG1) as a potential prognostic biomarker for ABC susceptibility and the involvement of significantly upregulated proteins, particularly in peptide processing, antigen presentation, interferon (IFN), and cytokine regulation.

Non-IgE-Mediated Drug Hypersensitivity Reactions.

Non-IgE-mediated drug reactions have traditionally been poorly defined and studied, though they are the most common form of hypersensitivity. Their presentations are highly variable and can range in severity from mild, cutaneous-only reactions to severe systemic disease. The most notable advance in non-IgE-mediated hypersensitivity reactions is in diagnostics. HLA alleles have traditionally been used for identifying certain patients at risk for abacavir hypersensitivity syndrome, but more recent studies have shown several other HLA alleles associated with severe cutaneous adverse reactions with various medications. This article also highlights the use of delayed intradermal testing for radiocontrast media and patch testing for delayed antibiotic reactions. Drug reactions remain a major cause of morbidity and reason for treatment changes. Non-IgE-mediated reactions have had an increase in research interest over the past decade with an increased emphasis on better understanding the clinical presentation and underlying pathophysiology.

Kinetics of Abacavir-Induced Remodelling of the Major Histocompatibility Complex Class I Peptide Repertoire.

Abacavir hypersensitivity syndrome can occur in individuals expressing the HLA-B*57:01 major histocompatibility complex class I allotype when utilising the drug abacavir as a part of their anti-retroviral regimen. The drug is known to bind within the HLA-B*57:01 antigen binding cleft, leading to the selection of novel self-peptide ligands, thus provoking life-threatening immune responses. However, the sub-cellular location of abacavir binding and the mechanics of altered peptide selection are not well understood. Here, we probed the impact of abacavir on the assembly of HLA-B*57:01 peptide complexes. We show that whilst abacavir had minimal impact on the maturation or average stability of HLA-B*57:01 molecules, abacavir was able to differentially enhance the formation, selectively decrease the dissociation, and alter tapasin loading dependency of certain HLA-B*57:01-peptide complexes. Our data reveals a spectrum of abacavir mediated effects on the immunopeptidome which reconciles the heterogeneous functional T cell data reported in the literature.

Detection of Abacavir-Induced Structural Alterations in Human Leukocyte Antigen-B*57 : 01 Using Phage Display.

The interaction of human leukocyte antigen (HLA) with specific drugs is associated with delayed-type hypersensitivity reactions, which cause severe cutaneous toxicity. Such interactions induce structural alterations in HLA complexes via several different mechanisms such as the hapten theory, p-i concept, and altered peptide repertoire model, leading to the activation of cytotoxic T cells. To date, comprehensive detection of such structural alterations in preclinical studies has been difficult. Here, we evaluated structural alterations in HLA complexes focusing on the interaction between the HLA-B*57 : 01 allele and abacavir (an anti-human immunodeficiency virus drug), representing a model of abacavir hypersensitivity syndrome induced by changes in the peptide repertoire on the HLA molecule. We employed a phage display method using a commercially available antibody library to screen specific phage antibodies able to recognize HLA-B*57 : 01. The affinity of selected phage antibodies increased because of structural alterations in HLA-B*57 : 01 following exposure to abacavir, indicating that specific phage antibodies can identify drug-mediated structural changes in HLA complexes. We also identified an unreported structural change in HLA-B*57 : 01 using the phage display method, whereby abacavir increased the expression of peptide-deficient HLA-B*57 : 01 on the cell surface. These results suggest that phage display technology is a useful method for detecting structural changes in HLA complexes. This technology represents a potential novel strategy for predicting HLA-associated hypersensitivity reactions by drugs in pre-clinical studies.

New genetic predictors for abacavir tolerance in HLA-B*57:01 positive individuals

Abacavir hypersensitivity syndrome (ABC HSS) is strongly associated with carriage of human leukocyte antigen (HLA)-B*57:01, which has a 100% negative predictive value for the development of ABC HSS. However, 45% of individuals who carry HLA-B*57:01 can tolerate ABC. We investigated immune and non-immune related genes in ABC HSS (n = 95) and ABC tolerant (n = 43) HLA-B*57:01 + patients to determine other factors required for the development of ABC HSS. Assignment of phenotype showed that ABC HSS subjects were significantly less likely than tolerants to carry only ERAP1 hypoactive trimming allotypes (p = 0.02). An altered self-peptide repertoire model by which abacavir activates T cells is in keeping with observation that endoplasmic reticulum aminopeptidase 1 (ERAP1) allotypes that favour efficient peptide trimming are more common in ABC HSS patients compared to patients who tolerate ABC. Independently, non-specific immune activation via soluble cluster of differentiation antigen 14 (sCD14) may also influence susceptibility to ABC HSS.

HLA-associated drug hypersensitivity and the prediction of adverse drug reactions.

Adverse drug reactions are an important cause of morbidity and mortality and constitute the leading reason of drug withdrawal from the market. Besides classical reactions that are related to pharmacologic activity of the drug, some reactions are unpredictable, not dose dependent, and seem to occur in genetically predisposed individuals. The majority of this reaction is immunologically driven and they are referred to as hypersensitivity reactions. A growing number of studies provided evidences that specific HLA alleles increase the risk of developing hypersensitivity drug reactions. In this context, drug hypersensitivities that have more robust pharmacogenetic data include abacavir hypersensitivity syndrome and severe cutaneous adverse reactions induced by allopurinol and carbamazepine.

The role of HLA genes in pharmacogenomics: unravelling HLA associated adverse drug reactions.

Genetic polymorphism in the genes encoding the human leukocyte antigen (HLA) molecules enables presentation of a wide range peptide ligands thus maximising immune surveillance of pathogens. A consequence of the diversification of the HLA Ag-binding pocket is the enhanced opportunity for off-target binding of small drugs by HLA molecules, with subsequent immune reactivity. These potential off-target interactions are 'set up' to generate T cell-mediated adverse drug reactions even though the precise mechanisms of most HLA-drug interactions are still poorly understood. The association between abacavir hypersensitivity syndrome and HLA-B*57:01 is one exception that has been resolved at a molecular and mechanistic level. Here, we explore the road to understanding the interaction between abacavir and the HLA-B*57:01 molecule and review the current state of understanding of interactions between other drugs and HLA molecules implicated in adverse drug reactions, which appear to involve multiple mechanisms. The continued expansion of the pharmacopoeia generates an imperative to understand these interactions at the molecular level in order to prevent the continued burden on individuals and the health care system.

CD4+ T cells prevent abacavir hypersensitivity reactions in HLA-B*57:01 transgenic mice

Abstract Adverse drug reactions (ADR) are a major obstacle to drug development. Genome-wide association studies identified several human leukocyte antigens (HLA)-class I alleles as risk factors for ADR. The HLA-B*57:01 allele has been found to be associated with the development of abacavir (ABC) hypersensitivity syndrome (AHS) and with the induction of liver injury by the β-lactam antibiotic flucloxacillin. The nucleoside analog ABC, an inhibitor of the HIV reverse transcriptase, can induce severe multi-organ toxicity in >50% of HLA-B*57:01+ patients with HIV infection. In a previous study we showed that ABC induced binding to the HLA-B*57:01 of altered self-peptides containing predominantly isoleucine or leucine residues at the carboxyl terminus. Recognition of these self-peptides drives in vitro activation of cytotoxic CD8+ T cells. However, the early immune events/danger signals required to overcome the immune tolerance that otherwise suppress ADR are still unknown. In order to study HLA-linked drug hypersensitivity in vivo and to understand better drug immune tolerance, HLA-B transgenic mice were generated. Here, we show that ABC activates HLA-B*57:01 transgenic CD8+ T cells in vitro via CD8 and HLA. A systemic, but partial, early response to the drug is also observed in vivo, however, ABC fails to promote skin hypersensitivity in immunocompetent transgenic mice. Instead, depletion of CD4+ T cells breaks immune tolerance to ABC and promotes ADR in HLA-B*57:01 transgenic mice. Supported by the Intramural Research Program of the NIAID, NIH, and CDER, FDA.

Pharmacogenetics of hypersensitivity drug reactions

Adverse drug reactions are a significant cause of morbidity and mortality and represent a major burden on the healthcare system. Some of those reactions are immunologically mediated (hypersensitivity reactions) and can be clinically subdivided into two categories: immediate reactions (IgE-related) and delayed reactions (T-cell-mediated). Delayed hypersensitivity reactions include both systemic syndromes and organ-specific toxicities and can be triggered by a wide range of chemically diverse drugs. Recent studies have demonstrated a strong genetic association between human leukocyte antigen alleles and susceptibility to delayed drug hypersensitivity. Most notable examples include human leukocyte antigen (HLA)-B*57:01 allele and abacavir hypersensitivity syndrome or HLA-B*15:02 and HLA-B*58:01 alleles related to severe cutaneous reactions induced by carbamazepine and allopurinol, respectively. This review aims to explore our current understanding in the field of pharmacogenomics of HLA-associated drug hypersensitivities and its translation into clinical practice for predicting adverse drug reactions.

P080 HLA disease association assignment by multiplexed NGS assay

Strong association of HLA molecules with autoimmune and inflammatory diseases have been identified, strengthening the value of HLA genetic screening for diagnostic purposes. There’s a strong association between Ankylosing Spondylitis (AS) and HLA-B27. In ∼90% of European patients, B27 alleles strongly predispose for AS. In ∼90% of patients with Coeliac Disease, the HLA-DQ2.5 phenotype is expressed, encoding HLA-DQA1∗05:01 and DQB1∗02:01 alleles, with the remaining 10% mostly expressing the HLA-DQ8 molecule, encoding the DQA1∗03 variant and DQB1∗03:02 alleles. Also in the field of pharmacogenetics there’s a growing interest in the role of HLA. HLA-B∗57:01 screening to prevent Abacavir hypersensitivity syndrome is now a routine clinical use in the developed world. We developed a novel NGS-based genetic screening test that enables 2nd field resolution typings of HLA-B, DQA1, and DQB1 in a single tube. A multiplexed amplification assay was established that encompass HLA-B, HLA-DQA1 and HLA-DQB1 locus-specific amplification of exon 2 and 3 in a single tube. The assay was compatible with the multiplex PCR kit (Qiagen) and required a PCR enhancer (GenDx). Analytical performance studies were assessed including screening of a large gDNA reference panel (n = 96 samples) to verify robustness. Amplicons were pooled and processed into the NGSgo workflow for Illumina (GenDx) and analyzed by NGSengine software (GenDx). For all samples tested (n = 96) strong amplicons of the expected sizes were generated in a multiplexed PCR. NGS data showed high locus mappability (>94%), and full coverage of the amplicon with even distribution of reads, especially for HLA-B, and HLA-DQA1, having average read depths >1500. For all samples, HLA-B, HLA-DQB1 and HLA-DQA1 typings were obtained that are in concordance with the pre-types. The multiplexed assay showed to be robust and capable of detecting both alleles when present in a balanced manner. We developed a novel NGS-based genetic screening test that enables HLA-B, DQA1, and DQB1 typings in a single tube. The genetic screening test proved to be robust and useful for pharmacogenetic screening of HLA-B alleles and identification of autoimmune disease associated genetic susceptibilities like celiac disease. N. Westerink: Employee; Company/Organization; GenDx.I. van Rooy: Employee; Company/Organization; Gendx. M. Van Heck: Employee; Company/Organization; GenDx. C. Rebel: Employee; Company/Organization; GenDx. E. Rozemuller: Stock Shareholder; Company/Organization; GenDx. M. Penning: Employee; Company/Organization; GenDx.

Genetics of immune-mediated adverse drug reactions: a comprehensive and clinical review.

Adverse drug reactions (ADRs) are common and are a major problem in drug therapy. Patients experience unnecessary morbidity and mortality whilst many effective drugs are withdrawn because of ADRs in a minority of patients. Recent studies have demonstrated significant associations between human leukocyte antigens (HLA) and predisposition to ADRs such as drug-induced skin injury (DISI) and drug-induced liver injury (DILI). HLA-B*58:01 has been significantly associated with allopurinol-induced hypersensitivity. Associations between HLA and carbamazepine hypersensitivity reactions demonstrate both ethnicity and phenotype specificity; with HLA-B*15:02 associated with Stevens-Johnson syndrome and toxic epidermal necrolysis in South East Asian patients only whilst HLA-A*31:01 is associated with all phenotypes of hypersensitivity in multiple ethnicities. Studies of ximelagatran, an oral direct thrombin inhibitor withdrawn because of hepatotoxicity, found associations between HLA-DRB1*07:01 and HLA-DQA1*02:01 and ximelagatran DILI. Interestingly, HLA-B*57:01 is associated with both abacavir DISI and flucloxacillin DILI but the reasons for the different phenotype of ADR remains unknown. Pharmacogenetic screening for HLA-B*57:01 prior to abacavir therapy has significantly reduced the incidence of abacavir hypersensitivity syndrome in clinical practice. No other HLA associations have been translated into clinical practice because of multiple reasons including failure to replicate, inadequate sample sizes, and our lack of understanding of pathophysiology of ADRs. Here, we review genetic associations that have been reported with ADRs and discuss the challenges that scientists, clinicians, pharmaceutical industry and regulatory agencies face when attempting to translate these associations into clinically valid and cost-effective tests to reduce the burden of ADRs in future.

Fever, Rash, and Systemic Symptoms: Understanding the Role of Virus and HLA in Severe Cutaneous Drug Allergy

Drug hypersensitivity syndromes such as abacavir hypersensitivity and the severe cutaneous adverse drug reactions have been associated with significant short- and long-term morbidity and mortality. More recently, these immunologically mediated and previously unpredictable diseases have been shown to be associated with primarily class I but also class II HLA alleles. The case of the association of HLA-B*57:01 and abacavir hypersensitivity has created a translational roadmap for how this knowledge can be used in the clinic to prevent severe reactions. Although many hurdles exist to the widespread translation of such HLA screening approaches, our understanding of how drugs interact with the major histocompatibility complex has contributed to the discovery of new models that have provided considerable insights into the immunopathogenesis of severe cutaneous adverse drug reactions and other T-cell-mediated drug hypersensitivity syndromes. Future translation of this knowledge will facilitate the development of preclinical toxicity screening to significantly improve efficacy and safety of drug development and design.

84-P: HEAT SHOCK PROTEIN-70 Hom M493T GENOTYPING INCREASES THE PREDICTIVE POTENTIAL OF HLA-B∗5701 AS A PHARMACOGENETIC TEST FOR ABACAVIR HYPERSENSITIVITY

Abacavir is a reverse transcriptase inhibitor used to treat patients with HIV-1. Approximately 5-10% of patients treated with Abacavir develop a potentially fatal Abacavir hypersensitivity syndrome (AHS). In a cohort of 488 HIV-1 positive patients, our research group has earlier shown patients carrying HLA B∗57:01 allele are at high risk of developing AHS. However, among HLA-B∗57:01 positive patients, who were treated with Abacavir, 10% were tolerant to Abacavir while the remaining 90% developed AHS. This suggests that other immunogenetic factors in addition to the carriage of HLA-B∗57:01 may also be involved in the pathogenesis of AHS. One such immunogenetic factor is Hsp-70Hom chaperone involved in presentation of Abacavir hapten to T cells. In the present study, we aim to determine if genotyping HIV-1 positive patients for Hsp-70 Hom M 493 T and HLA-B∗5701 will be better predictive of AHS than genotyping HLA-B∗57:01 alone. All HLA-B∗57:01 positive patients (n=20) from the same cohort of 488 HIV-1 patients were genotyped for Hsp-70 Hom M 493 T (defined T/C substitution at 9564 position). Genotyping was achieved by sequencing codon 493 of the Hsp-70 Hom gene. Both HLA-B∗57:01 positive patients who were tolerant of Abacavir were not found to be carrying the ancestral Hsp-70 Hom T allele (genotyped as C/C at 9564C > T). However, all other HLA-B∗57:01 positive individuals who developed AHS had a C/T genotype at 9564C > T. A 100% sensitivity and specificity was observed when a combined pharmacogenetic test (HLA_B∗57:01 and Hsp-70 Hom M 493 T genotyping) was used for prediction of AHS. Absence of the T allele on the Hsp-70 Hom M 493 T gene protects those who are HLA-B∗57:01 positive from developing Abacavir hypersensitivity syndrome. Genotyping Hsp-70 Hom M 493 T together with HLA-B∗57:01 will significantly increase the predictive potential of the pharmacogenetic testing for ABH.

A false sense of non-self

A drug used for HIV treatment can alter the set of antigens that activates T cells of the immune system, thereby triggering life-threatening reactions against the body's own proteins. See Letter p.554 Immunologically based drug reactions, such as abacavir hypersensitivity syndrome (AHS) and carbamazepine-induced Steven–Johnson's syndrome (SJS), have been associated with specific human leukocyte antigen (HLA) alleles. Here the authors describe a mechanism through which these small-molecule drugs affect antigen presentation and consequently the T-cell response. By binding non-covalently to the antigen-binding cleft of HLAB*57:01, abacavir induces changes in the shape and chemistry of this site, and as a result alters the affinity of endogenous peptide to HLA. Ultimately, this leads to the systemic reaction manifesting as AHS. The generality of the mechanism is captured by showing that carbamazepine binds to the allotype HLA-B*15:02 and induces a similar response.

Immune self-reactivity triggered by drug-modified HLA-peptide repertoire

Human leukocyte antigens (HLAs) are highly polymorphic proteins that initiate immunity by presenting pathogen-derived peptides to T cells. HLA polymorphisms mostly map to the antigen-binding cleft, thereby diversifying the repertoire of self-derived and pathogen-derived peptide antigens selected by different HLA allotypes. A growing number of immunologically based drug reactions, including abacavir hypersensitivity syndrome (AHS) and carbamazepine-induced Stevens-Johnson syndrome (SJS), are associated with specific HLA alleles. However, little is known about the underlying mechanisms of these associations, including AHS, a prototypical HLA-associated drug reaction occurring exclusively in individuals with the common histocompatibility allele HLA-B*57:01, and with a relative risk of more than 1,000 (refs 6, 7). We show that unmodified abacavir binds non-covalently to HLA-B*57:01, lying across the bottom of the antigen-binding cleft and reaching into the F-pocket, where a carboxy-terminal tryptophan typically anchors peptides bound to HLA-B*57:01. Abacavir binds with exquisite specificity to HLA-B*57:01, changing the shape and chemistry of the antigen-binding cleft, thereby altering the repertoire of endogenous peptides that can bind HLA-B*57:01. In this way, abacavir guides the selection of new endogenous peptides, inducing a marked alteration in 'immunological self'. The resultant peptide-centric 'altered self' activates abacavir-specific T-cells, thereby driving polyclonal CD8 T-cell activation and a systemic reaction manifesting as AHS. We also show that carbamazepine, a widely used anti-epileptic drug associated with hypersensitivity reactions in HLA-B*15:02 individuals, binds to this allotype, producing alterations in the repertoire of presented self peptides. Our findings simultaneously highlight the importance of HLA polymorphism in the evolution of pharmacogenomics and provide a general mechanism for some of the growing number of HLA-linked hypersensitivities that involve small-molecule drugs.

Human leukocyte antigen (HLA) and pharmacogenetics: screening for HLA-B*57:01 among human immunodeficiency virus–positive patients from southern Alberta

The field of pharmacogenetics is witnessing a growing interest in the role of the human leukocyte antigen (HLA) in manifestation of adverse drug reactions (ADR). Here we report a retrospective analysis of the association of HLA-B*5701 with abacavir hypersensitivity syndrome (AHS) in a large Canadian cohort of 489 human immunodeficiency virus-1-positive patients exposed to abacavir. A total of 3.7% of abacavir-exposed patients had developed AHS. Using polymerase chain reaction sequence-specific primer-based genotyping, the HLA-B*5701 allele was observed in 20 patients (4.1%). Of the 20 HLA-B*5701(+) abacavir-treated patients, 18 (90%) had developed AHS. Carriage of the HLA-B*5701 allele indicated a strong association with abacavir hypersensitivity (p < 0.0001; odds ratio = 6,934; 95% confidence interval = 321-149,735). HLA-B*5701 genotyping demonstrated high sensitivity, specificity, and positive and negative predictive values. The data derived from the study highlight the importance of engaging histocompatibility and immunogenetics laboratories in taking a lead in mapping other less characterized HLA and immunogenetic markers associated with ADRs.

Pharmacogenetics of Drug Hypersensitivity

Drug hypersensitivity reactions and severe cutaneous adverse drug reactions, such as Stevens-Johnson syndrome and toxic epidermal necrolysis, are examples of serious adverse drug reactions mediated through a combination of metabolic and immunological mechanisms that could traditionally not have been predicted based on the pharmacological characteristics of the drug alone. The discovery of new associations between these syndromes and specific HLA has created the promise that risk for these reactions could be predicted through pharmacogenetic screening, thereby avoiding serious morbidity and mortality associated with these types of drug reactions. Despite this, several hurdles exist in the translation of these associations into pharmacogenetic tests that could be routinely used in the clinical setting. HLA-B*5701 screening to prevent abacavir hypersensitivity syndrome is an example of a test now in widespread routine clinical use in the developed world.

Abacavir/lamivudine combination in the treatment of HIV: a review

Abacavir has been at the center of research and clinical interest in the last two years. The frequency of the associated abacavir hypersensitivity syndrome has decreased substantially since the introduction of routine testing for the HLA-B*5701 allele; the activity of the drug in HIV-infected persons with HIV RNA values more than 100,000 copies/mL has been questioned; the possible increased risk of myocardial infarction after recent exposure to abacavir has been debated; and the drug has been moved from the "recommended" category to the "alternative" category in several guidelines. Still, the drug remains a useful agent in combination with other drugs, including lamivudine, for the treatment of HIV infection. This review will focus on the pharmacokinetics, activity, side effects, and resistance profile of both abacavir and lamivudine, including a thorough review of all of the recent studies relevant to both drugs.

Successful Translation of Pharmacogenetics into the Clinic

Abacavir hypersensitivity syndrome (AHS) is a potentially life-threatening illness occurring in 4-8% of those initiating the drug. Early studies identified a strong association between the MHC class I allele HLA-B*5701 and AHS. These studies suggested that HLA-B*5701 holds promise as a screening test to prevent AHS, but concern arose from HLA-B*5701-negative cases with a clinical diagnosis of AHS, and particularly from early reports of apparently low sensitivities of HLA-B*5701 for AHS in patients of non-White race. However, open screening studies suggested that HLA-B*5701 screening can largely eliminate AHS. Furthermore, skin-patch testing was used in later-generation studies to separate those patients with true immunologically mediated AHS from those with false-positive clinical diagnoses. Currently, high-level evidence suggests that HLA-B*5701 has a negative predictive value of 100% for patch-test-confirmed AHS, which is generalizable across White and Black populations. Current HIV treatment guidelines have been revised to reflect the recommendation that HLA-B*5701 screening be incorporated into routine care for patients who may require abacavir. New laboratory techniques such as PCR and flow cytometric methods, as well as an international quality assurance program, have evolved to ensure the availability of cost-effective screening methods whose consistency and standard can be maintained over time. An elegant body of basic science has evolved, which supports and complements the clinical research in suggesting that AHS is specifically and exquisitely restricted by HLA-B*5701 and mediated by CD8+ lymphocytes. Abrogating factors explaining why 45% of those carrying HLA-B*5701 can tolerate abacavir remain to be defined. The research approach applied to AHS has led to a genetic screening test being successfully implemented globally in primary HIV clinical practice. The abacavir 'example' can be applied to other drugs to facilitate the development and operationalization of genetic tests that may be useful to predict and prevent otherwise unpredictable drug reactions.

Cytokine Profiling in Abacavir Hypersensitivity Patients

Abacavir hypersensitivity in genetically susceptible individuals implicates an abacavir-specific T-cell response to either the parent drug or a metabolite generated in vivo. We have analysed the cytokine profile in antigen-presenting cells and the T-lymphocytes that are involved in the pathological immune response to abacavir. In this study, we compared abacavir-specific cytokine responses in cultured peripheral blood mononuclear cells (PBMCs) from HIV-infected abacavir hypersensitive, tolerant and naive individuals. Cells were cultured in the presence or absence of abacavir. Cytokine expression was determined by microarray analysis, enzyme-linked immunosorbent assays and flow cytometry. We demonstrated using in vitro models of immune activation that the production of interferon-gamma was specifically induced by abacavir treatment in PBMCs obtained from hypersensitive patients carrying the HLA-B*5701 allele (median 123.86 compared with -30.83 for tolerant controls, P=0.001). These results provide further insight into the immunological and metabolic basis of abacavir hypersensitivity syndrome. In vitro assays could assist in the identification of susceptible loci by providing a surrogate marker for the hypersensitivity reaction. Such a marker could be studied in unexposed individuals to shed further light on the immunopathogenesis of the abacavir hypersensitivity syndrome.