Predisposition to abacavir hypersensitivity conferred by HLA-B*5701 and a haplotypic Hsp70-Hom variant

[Role of tenofovir in HIV and hepatitis C virus coinfection]

Chronic hepatitis C virus (HCV) infection is common in HIV-infected individuals, especially if the route of infection is intravenous (e.g. intravenous drug use or blood transfusion). Prognosis is poorer in patients with HCV and HIV coinfection than in those with HCV monoinfection, mainly due to the immunodepression caused by HIV infection and probably also to a direct effect of HIV on the liver. Moreover, although antiretroviral therapy can cause liver damage, there is little doubt about the net benefits obtained with triple therapy in coinfected individuals, since suppression of HIV replication and immune recovery help to halt liver damage. However, not all antiretroviral agents are equal and those with the lowest hepatotoxicity and best metabolic profile should be used in coinfected patients, since hepatic steatosis accelerates progression of hepatic fibrosis and insulin resistance hampers the success of treatment with interferon and ribavirin. Tenofovir is currently one of the safest nucleos(t)ide analogues, due to its low hepatotoxicity and its lack of negative interference on treatment of HCV infection.

Immunogenetics of drug-induced skin blistering disorders. Part II: Synthesis

The overall immunopathogenesis relevant to a large series of disorders caused by a drug or its associated hyperimmune condition is discussed based upon examining the genetics of severe drug-induced bullous skin problems (sporadic idiosyncratic adverse events including Stevens–Johnson syndrome and Toxic epidermal necrolysis). New results from an exemplar study on shared precipitating and perpetuating inner causes with other related disease phenotypes including aphtous stomatitis, Behçets, erythema multiforme, Hashimoto’s thyroiditis, pemphigus, periodic fevers, Sweet’s syndrome and drug-induced multisystem hypersensitivity are presented. A call for a collaborative, wider demographic profiling and deeper immunotyping in suggested future work is made.

HLA-B*3505 allele is a strong predictor for nevirapine-induced skin adverse drug reactions in HIV-infected Thai patients

OBJECTIVE

Investigation of a possible involvement of differences in human leukocyte antigens (HLA) in the risk of nevirapine (NVP)-induced skin rash among HIV-infected patients.

METHODS

A step-wise case-control association study was conducted. The first set of samples consisted of 80 samples from patients with NVP-induced skin rash and 80 samples from NVP-tolerant patients. These patients were genotyped for the HLA-A, HLA-B, HLA-C, HLA-DRB1, HLA-DQB1, and HLA-DPB1 by a sequence-based HLA typing method. Subsequently, we verified HLA alleles that showed a possible association in the first screening using an additional set of samples consisting of 67 cases with NVP-induced skin rash and 105 controls.

RESULTS

An HLA-B*3505 allele revealed a significant association with NVP-induced skin rash in the first and second screenings. In the combined data set, the HLA-B*3505 allele was observed in 17.5% of the patients with NVP-induced skin rash compared with only 1.1% observed in NVP-tolerant patients [odds ratio (OR)=18.96; 95% confidence interval (CI)=4.87-73.44, Pc=4.6x10] and 0.7% in general Thai population (OR=29.87; 95% CI=5.04-175.86, Pc=2.6x10). The logistic regression analysis also indicated HLA-B*3505 to be significantly associated with skin rash with OR of 49.15 (95% CI=6.45-374.41, P=0.00017).

CONCLUSION

A strong association between the HLA-B*3505 and NVP-induced skin rash provides a novel insight into the pathogenesis of drug-induced rash in the HIV-infected population. On account of its high specificity (98.9%) in identifying NVP-induced rash, it is possible to utilize the HLA-B*3505 as a marker to avoid a subset of NVP-induced rash, at least in Thai population.

Variations in HSP70 genes associated with noise-induced hearing loss in two independent populations

Noise-induced hearing loss (NIHL) is one of the most important occupational health hazards. Millions of people worldwide are exposed daily to harmful levels of noise. NIHL is a complex disease resulting from an interaction between genetic and environmental factors. Although the environmental risk factors have been studied extensively, little is known about the genetic factors. Heat-shock proteins (HSPs) are induced after exposure to severe noise. When first induced by exposure to moderate sound levels, they can protect the ear from damage from excessive noise exposure. This protection is highly variable between individuals. An association of HSP70 genes with NIHL has been described by Yang et al (2006) in a Chinese sample set of noise-exposed workers. In this study, three polymorphisms (rs1043618, rs1061581 and rs2227956) in HSP70-1, HSP70-2 and HSP70-hom, respectively, were genotyped in 206 Swedish and 238 Polish DNA samples of noise-exposed subjects and analyzed. One SNP, rs2227956 in HSP70-hom, resulted in a significant association with NIHL in both sample sets. In addition, rs1043618 and rs1061581 were significant in the Swedish sample set. Analysis of the haplotypes composed of the three SNPs revealed significant associations between NIHL and haplotype GAC in both sample sets and with haplotype CGT in the Swedish sample set. In conclusion, this study replicated the association of HSP70 genes with NIHL in a second and third independent noise-exposed sample set, hereby adding to the evidence that HSP70 genes may be NIHL susceptibility genes.

[HLA-B*5701 and abacavir hypersensitivity reaction]

A potentially life-threatening hypersensitive reaction occurs in association with initiation of HIV nucleoside analogue abacavir therapy in 4 to 8% of patients. Preliminary studies appear to confirm the role of the immune system in abacavir hypersensitivity. The reaction is possibly the result of presentation of drug peptides onto HLA, that may induce a pathogenic T-cell response. Hypersensitivity reaction to abacavir is strongly associated with the presence of the HLA-B*5701 allele and prospective HLA-B*5701 genetic screening has now been instituted in clinical practice to reduce the risk of hypersensitivity reaction.

Current trends in screening across ethnicities for hypersensitivity to abacavir

Abacavir is a potent nucleoside analog reverse transcriptase inhibitor approved for the treatment of HIV infection. Approximately 5-8% of Caucasian patients receiving abacavir develop a hypersensitivity reaction, characterized by rash, fever and, occasionally, multisystemic involvement. Rechallenge with the drug can be fatal. The discovery of the mechanisms involved in this hypersensitivity reaction and the identification of tools for its prediction are the subject of this review. The most relevant finding is the recognition of a strong association between one specific haplotype at the HLA complex type I, HLA-B*5701, and the abacavir hypersensitivity reaction. The heterogeneity in the prevalence of HLA-B*5701 across distinct ethnicities accounts for differences in the risk of abacavir hypersensitivity reactions in distinct populations.

Are mutations in HIV type-1 reverse transcriptase 245 codon predictive of abacavir hypersensitivity reaction?

Background

HLA-B*5701 is strongly related to abacavir hypersensitivity reactions (HSRs). Polymorphisms at position 245 of HIV type-1 (HIV-1) reverse transcriptase (RT) show an association with HLA-B*5701 suggesting that viral genotyping performed for antiretroviral drug resistance testing could reduce human leukocyte antigen (HLA) screening necessity to prevent abacavir HSR.

Methods

To further test the validity of 245 codon analysis results for predicting HSR, we analysed 1,179 sequences from 752 HIV-1-infected patients.

Results

Mutant amino acid residues in RT 245 were found in 30.6% of sequences. Among 239 patients with multiple longitudinal genotypes, 245 residues varied in 37 (15.5%) from wild type to mutant and/or vice versa. All these changes appeared during antiretroviral treatment. A total of 15 out of 229 (6.5%) abacavir-treated patients developed a clinically confirmed HSR: all carried B subtypes. There was no significant difference in the prevalence of 245 mutants between abacavir-treated patients with HSR (27%) and those without (29%), even after limiting the analysis to subtype B carriers.

Conclusions

The significant intraindividual variability of 245 residues and the lack of their association with clinically confirmed HSR argue against their use as viral genetic markers to exclude patients at risk for HSR.

Developing the evidence base for applying pharmacogenomics: proceeds from DIA Workshop IV – Breakout Session 1

The 4th Drug Information Association Workshop in a series of workshops on Pharmacogenomics: ‘Biomarkers and Pharmacogenomics in Drug Development and Regulatory Decision Making’ took place on December 10–12, 2007 in Bethesda, MD, USA. A number of breakout sessions were conducted to focus on different aspects of the development of biomarkers. Breakout Session 1 considered the evidence base for the development of pharmacogenomic markers from both safety and efficacy perspectives, with a view to understanding the challenges in the design of appropriate clinical studies during drug development. Case studies based on data generated during all stages of drug development were used to stimulate discussion and refine considerations for what constitutes a sufficient evidence base to support the effective use of novel, pharmacogenomic biomarkers. The discussions were open and lively, and some broad principles were drawn from the discussion. In this article, we summarize the case studies presented and develop key discussion points that arose out of the meeting. These case studies help to illustrate the current state of the art in the application of pharmacogenomics in drug development and the challenges being faced in the development of pharmacogenomics from interesting, exploratory associations into predictive biomarkers with clinical utility. We hope that this will serve as a stimulus to consideration of the critical issues facing the implementation of pharmacogenomics into drug development.

[Pharmacogenetics of antiretroviral therapy 2008: toward personalized treatment?]

The degree of immune restoration in HIV-1-infected patients receiving the same antiretroviral regimen and achieving sustained virologic suppression is highly variable. Equally, not all persons receiving antiretroviral drugs experience adverse effects. Consequently, there seems to be wide interindividual variability in treatment response and toxicity due to antiretroviral therapy. Recent advances in pharmacogenetics and pharmacogenomics have identified several host genetic determinants that modulate treatment response and toxicity with these drugs. These findings contribute to the belief that personalized design of antiretroviral drug regimens, according to the host genetic background, may be feasible in the near future.

[Applicability of pharmacogenetic studies in daily clinical practice]

In the last few years, research in pharmacogenetics and pharmacogenomics has identified distinct variants or markers that can help to define the benefits and risk of patients requiring antiretroviral treatment. The beneficial effect of the deletion 32 allele of the CCR5 coreceptor on the natural history of HIV infection and, to a certain extent, on treatment response is well known. The bases of immune reconstitution after initiation of antiretroviral therapy, although the subject of intense study, are probably multifactorial and polygenetic and consequently conclusions with clear applicability to clinical practice are currently lacking. Among the risks, no significant progress has been made in lipodystrophy. The origin of dyslipidemia associated with antiretroviral treatment and the excess cardiovascular risk conferred by some antiretroviral drugs is probably polygenetic and, at present, poorly defined. The genetic bases of efavirenz-induced neurological toxicity and of hyperbilirubinemia secondary to atazanavir are fairly well known, although their application in daily clinical practice has not been adequately assessed. Some aspects that help to understand the molecular bases of hypersensitivity reaction to nevirapine and of nevirapine-induced hepatotoxicity have been described but are not applicable in most cases and consequently further studies are required. Some data correlate tenofovir-induced renal toxicity with genetic variations in some transport proteins. The most significant advance for clinical practice is the correlation between the presence of the HLA-B*5701 allele and hypersensitivity reaction to abacavir. In particular, one clinical trial with a large number of patients from distinct ethnic groups found that the probability of not developing hypersensitivity reaction (immunologically confirmed) was 100% if the patient was HLA-B*5701-negative. These data suggest the need to implement this test in daily clinical practice.

[HLA-B*5701 and hypersensitivity reactions to abacavir. Study methods and clinical relevance]

Hypersensitivity reactions to abacavir occur in 5-8% of patients starting treatment with this drug and limits future treatment. Some host genetic factors, especially the HLA-B*5701 allele, have been identified as risk factors for hypersensitivity reaction in Caucasians. Consequently, the possibility of routine implementation of a genetic test to rule out the presence of this allele has been proposed to achieve a personalized therapeutic profile. The present article discusses all the information related to hypersensitivity to abacavir and its genetic and immunological markers, as well as the distinct techniques for HLA-B*5701 allele detection. The various studies performed to date in distinct population are also discussed.

Refining Abacavir Hypersensitivity Diagnoses using a Structured Clinical Assessment and Genetic Testing in the Swiss HIV Cohort Study

Background

We aimed to assess the value of a structured clinical assessment and genetic testing for refining the diagnosis of abacavir hypersensitivity reactions (ABC-HSRs) in a routine clinical setting.

Methods

We performed a diagnostic reassessment using a structured patient chart review in individuals who had stopped ABC because of suspected HSR. Two HIV physicians blinded to the human leukocyte antigen (HLA) typing results independently classified these individuals on a scale between 3 (ABC-HSR highly likely) and -3 (ABC-HSR highly unlikely). Scoring was based on symptoms, onset of symptoms and comedication use. Patients were classified as clinically likely (mean score ≥2), uncertain (mean score ≥-1 and ≤1) and unlikely (mean score ≤-2). HLA typing was performed using sequence-based methods.

Results

From 131 reassessed individuals, 27 (21%) were classified as likely, 43 (33%) as unlikely and 61 (47%) as uncertain ABC-HSR. Of the 131 individuals with suspected ABC-HSR, 31% were HLA-B*5701-positive compared with 1% of 140 ABC-tolerant controls ( P<0.001). HLA-B*5701 carriage rate was higher in individuals with likely ABC-HSR compared with those with uncertain or unlikely ABC-HSR (78%, 30% and 5%, respectively, P<0.001). Only six (7%) HLA-B*5701-negative individuals were classified as likely HSR after reassessment.

Conclusions

HLA-B*5701 carriage is highly predictive of clinically diagnosed ABC-HSR. The high proportion of HLA-B*5701-negative individuals with minor symptoms among individuals with suspected HSR indicates overdiagnosis of ABC-HSR in the era preceding genetic screening. A structured clinical assessment and genetic testing could reduce the rate of inappropriate ABC discontinuation and identify individuals at high risk for ABC-HSR.

HLA-B locus in Japanese patients with anti-epileptics and allopurinol-related Stevens–Johnson syndrome and toxic epidermal necrolysis

Introduction: Stevens–Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are rare but life-threatening severe cutaneous adverse reactions. Recently, strong associations of HLA-B*1502 and HLA-B*5801 with carbamazepine- and allopurinol-induced severe cutaneous adverse reactions were found in Han Chinese patients, respectively, but ethnic differences in the associations have been reported. The objective of this study is to clarify the involvement of HLA-B*1502 and HLA-B*5801 in Japanese SJS/TEN patients. Methods: HLA-B genotyping was performed on 58 Japanese SJS/TEN patients between July 2006 and April 2008 from multicenters in Japan. Results: There were no HLA-B*1502 carriers among 58 SJS/TEN patients. This patient group included seven carbamazepine-related and 11 aromatic anti-epileptic agent-related SJS/TEN patients. In addition, there were five HLA-B*5801 carriers, which included four allopurinol-related SJS/TEN patients. Conclusion: While HLA-B*1502 is unlikely to be associated with carbamazepine-related or aromatic anti-epileptic agent-related SJS/TEN, HLA-B*5801 was significantly associated with allopurinol-related SJS/TEN in Japanese.

Designing pharmacogenetic projects in industry: practical design perspectives from the Industry Pharmacogenomics Working Group

Pharmacogenetic association studies have the potential to identify variations in DNA sequence which impact drug response. Identifying these DNA variants can help to explain interindividual variability in drug response; this is the first step in personalizing dosing and treatment regimes to a patient's needs. There are many intricacies in the design and analysis of pharmacogenetic association studies, including having adequate power, selecting proper endpoints, detecting and correcting the effects of population stratification, modeling genetic and nongenetic covariates accurately, and validating the results. At this point there are no formal guidelines on the design and analysis of pharmacogenetic studies. The Industry Pharmacogenomics Working Group has initiated discussions regarding potential guidelines for pharmacogenetic study design and analyses (http://i-pwg.org) and the results from these discussions are presented in this paper.

First large, multicenter, open-label study utilizing HLA-B*5701 screening for abacavir hypersensitivity in North America

A hypersensitivity reaction is associated with abacavir in approximately 2-8% of exposed patients. The frequency of the HLA-B*5701 allele varies across racial groups and significantly correlates with risk of hypersensitivity. Studies in Europe and Western Australia demonstrated that prospective screening can significantly reduce the rate of hypersensitivity by avoiding the use of abacavir in patients carrying the HLA-B*5701 allele. Prospective HLA-B*5701 screening in a large, racially diverse North American population resulted in less than 1% of individuals diagnosed with a suspected abacavir hypersensitivity reaction (ABC HSR) and no positive skin patch test through 30 weeks among HLA-B*5701-negative individuals.

Human leukocyte antigen class I-restricted activation of CD8+ T cells provides the immunogenetic basis of a systemic drug hypersensitivity

The basis for strong immunogenetic associations between particular human leukocyte antigen (HLA) class I allotypes and inflammatory conditions like Behçet's disease (HLA-B51) and ankylosing spondylitis (HLA-B27) remain mysterious. Recently, however, even stronger HLA associations are reported in drug hypersensitivities to the reverse-transcriptase inhibitor abacavir (HLA-B57), the gout prophylactic allopurinol (HLA-B58), and the antiepileptic carbamazepine (HLA-B*1502), providing a defined disease trigger and suggesting a general mechanism for these associations. We show that systemic reactions to abacavir were driven by drug-specific activation of cytokine-producing, cytotoxic CD8+ T cells. Recognition of abacavir required the transporter associated with antigen presentation and tapasin, was fixation sensitive, and was uniquely restricted by HLA-B*5701 and not closely related HLA allotypes with polymorphisms in the antigen-binding cleft. Hence, the strong association of HLA-B*5701 with abacavir hypersensitivity reflects specificity through creation of a unique ligand as well as HLA-restricted antigen presentation, suggesting a basis for the strong HLA class I-association with certain inflammatory disorders.

Host genetic influences on highly active antiretroviral therapy efficacy and AIDS-free survival

We studied the influence of AIDS restriction genes (ARGs) CCR5-Delta32, CCR2-64I, SDF1-3'A, IL10-5'A, CX3CR1-V249I, CX3CR1-T280M, and MDR1-C3435T and haplotypes of the CCR5 P1 promoter and RANTES variants -403A, In1.1C, 3'222C, and -28G among HIV-1 infected patients on highly active antiretroviral therapy (HAART) in the Multicenter AIDS Cohort Study (MACS) and the Multicenter Hemophilia Cohort Study (MHCS). Our results indicate that several ARGs also influence therapy efficacy (ie, the success in viral suppression) and subsequent progression to AIDS while on HAART. CCR5-Delta32 decreased time to viral suppression (<200 HIV RNA copies/mL, relative hazard [RH]=1.40; P=0.008) and was protective against AIDS (RH=0.11; P=or<0.0001), whereas the CCR5 P1 haplotype was associated with delayed viral suppression (RNA<50 copies/mL, odds ratio [OR]=0.65; P=0.03) and accelerated time to AIDS (RH=2.68; P=0.02). SDF1-3'A reduced viral suppression (OR=0.61; P=0.02) and accelerated AIDS (RH=3.18; P=0.009). Accelerated AIDS progression was also observed with the RANTES haplotype carrying RANTES-IN1.1C and RANTES-3'222C (P=0.005 to 0.007). In contrast, the RANTES haplotype H1, which lacks suspected deleterious single-nucleotide polymorphisms, was protective against AIDS. CX3CR1-V249I seemed to accelerate viral suppression (RNA<50 copies/mL, OR=1.27; P=0.01). ARG influence after HAART suggests residual HIV-1 replication, and spread continues even in patients successfully suppressing detectable viral RNA.

Advances in pharmacogenomics of antiretrovirals: an update

Recent developments in the pharmacogenomics of antiretroviral drugs provide new prospects for predicting the efficacy of treatment and potential adverse effects. HIV/AIDS is a serious but treatable infectious disease, yet current treatment is limited by high rates of adverse drug reactions and development of resistance due to suboptimal drug concentrations in a significant proportion of patients. Antiretroviral therapy is especially suitable for pharmacogenomic investigation as both drug exposure and treatment response can be quantified and certain adverse effects can be assessed with validated measures. Additionally, there is increasing knowledge of the pharmacokinetics and dynamics of antiretroviral drugs, and some candidate genes implicated in the metabolism, transport and adverse effects have been identified. However, recent studies of the association of particular genes and their genetic variants with HIV management and adverse drug reactions have not provided unifying conclusions. This article reviews the most recently published work and summarizes the state of research in this area. Future directions for research and the application of this technology to the clinical practice of individualizing treatment for HIV management are discussed.

High sensitivity of human leukocyte antigen-b*5701 as a marker for immunologically confirmed abacavir hypersensitivity in white and black patients

BACKGROUND

Although the human leukocyte antigen (HLA)-B*5701 is highly associated with a hypersensitivity reaction (HSR) to abacavir (ABC), variable sensitivities have been reported when clinical data alone have been used to define an ABC HSR. This study evaluated the sensitivity of detection of the HLA-B*5701 allele as a marker of ABC HSRs in both white and black patients, using skin patch testing to supplement clinical diagnosis.

METHODS

White and black patients, identified through chart review, were classified as having received a diagnosis of an ABC HSR based on clinical findings only (a clinically suspected ABC HSR) or based on clinical findings and a positive skin patch test result (an immunologically confirmed [IC] ABC HSR). Control subjects were racially matched subjects who tolerated ABC for >/=12 weeks without experiencing an ABC HSR. Patients and control subjects were tested for the presence of HLA-B*5701. Sensitivity, specificity, and odds ratios for the detection of HLA-B*5701 as a marker for an ABC HSR were calculated for white and black participants.

RESULTS

Forty-two (32.3%) of 130 white patients and 5 (7.2%) of 69 black patients who met the criteria for clinically suspected HSRs had IC HSRs. All 42 white patients with IC HSRs were HLA-B*5701 positive (sensitivity, 100%; odds ratio, 1945; 95% confidence interval, 110-34,352). Among all white patients with clinically suspected HSRs, sensitivity was 44% (57 of 130 patients tested positive for HLA-B*5701); specificity among white control subjects was 96%. Five of 5 black patients with IC HSRs were HLA-B*5701 positive (sensitivity, 100%; odds ratio, 900; 95% confidence interval, 38-21,045). Among black patients with clinically suspected HSRs, the sensitivity was 14% (10 of 69 tested positive for HLA-B*5701); specificity among black control subjects was 99%.

CONCLUSIONS

Although IC ABC HSRs are uncommon in black persons, the 100% sensitivity of HLA-B*5701 as a marker for IC ABC HSRs in both US white and black patients suggests similar implications of the association between HLA-B*5701 positivity and risk of ABC HSRs in both races.

Pharmacogenetics and the potential for the individualization of antiretroviral therapy

PURPOSE OF REVIEW

Genetic associations highlighting differences in the response to HIV infection and treatment have significantly furthered our understanding of the pathogenesis, pharmacokinetics and pharmacodynamics of antiretroviral drug action and toxicities and HIV disease itself. This review focuses on the current knowledge of associations between polymorphisms and treatment outcomes in HIV with particular emphasis on clinically relevant relationships likely to lead to the individualization of antiretroviral therapy.

RECENT FINDINGS

Our understanding of the immunogenetic basis of drug toxicity has been furthered by human leucocyte antigen associations with hypersensitivities for the antiretroviral drugs abacavir and nevirapine. For abacavir in particular, the use of HLA-B*5701 as a screening test appears to be generalizable across racially diverse populations and has been supported by both observational, and blinded randomized controlled trials.

SUMMARY

Differences in HIV acquisition and progression as well as antiretroviral efficacy and toxicity will continue to provide the basis for research to define the genetic basis of such diversity. Despite the plethora of research in this area, numerous barriers exist to the successful operationalization of genetic testing to the clinic. HLA-B*5701 screening to prevent abacavir hypersensitivity is currently the most relevant to clinical practice and highlights that the promise of cost-effective testing can be facilitated by robust laboratory methodology and quality assurance programs that can be applied to diverse treatment settings.

Pharmacogenetics of hypersensitivity to abacavir: from PGx hypothesis to confirmation to clinical utility

The hypersensitivity (HSR) to abacavir (ABC) pharmacogenetics (PGx) program represents the progression from an exploratory discovery to a validated biomarker. Within the program, two retrospective PGx studies were conducted to identify HIV-1 patients at increased risk for ABC HSR, a treatment-limiting and potentially life-threatening adverse event. A strong statistical association between the major histocompatibility complex allele, HLA-B*5701, and clinically diagnosed ABC HSR was identified but varied between racial populations. Subsequently, ABC skin patch testing was introduced as a research tool to supplement clinical case ascertainment. In a randomized, prospective study evaluating the clinical utility of HLA-B*5701 screening, avoidance of ABC in HLA-B*5701-positive patients significantly reduced clinically diagnosed ABC HSR and eliminated patch test-positive ABC HSR. Finally, a retrospective PGx study supports the generalizability of the association across races. Prospective HLA-B*5701 screening should greatly reduce the incidence of ABC HSR by identifying patients at high risk for ABC HSR before they are treated.

Abacavir hypersensitivity reaction: an update

OBJECTIVE

To review the clinical features, risk factors, diagnosis, and management of abacavir hypersensitivity reaction (HSR).

DATA SOURCES

A MEDLINE (1950-October 2007) and EMBASE (1980-October 2007) search using key words abacavir, HIV, human immunodeficiency virus, hypersensitivity reaction, HLA-B(*)5701, and patch tests was conducted. Conference abstracts and article bibliographies were reviewed to identify relevant studies.

STUDY SELECTION AND DATA EXTRACTION

Studies that investigated the clinical and immunogenetic risk factors for abacavir hypersensitivity and the benefit of genetic screening, as well as articles that focused on the clinical presentation, assessment, and management of abacavir HSR, were considered for this review.

DATA SYNTHESIS

Abacavir hypersensitivity is an immune-mediated reaction that typically occurs within the first 6 weeks of therapy. Signs and symptoms of abacavir HSR are nonspecific, which makes the diagnosis challenging, particularly in medically complex patients. Patch testing may improve the diagnosis and confirmation of abacavir HSR, but it remains experimental. Clinical management is aimed at supportive therapy and discontinuation of abacavir. Rechallenge with abacavir is contraindicated due to the risk of precipitating a life-threatening reaction. Appropriate patient education and a clear communication plan are essential for the safe use of this medication. Identification of patients at risk of developing abacavir hypersensitivity through routine genetic screening for human leukocyte antigen (HLA) HLA-B(*)5701 represents a significant advance in the field of pharmacogenomics, with an apparent 100% negative predictive value when used to screen for abacavir HSR. Preliminary data suggest that pharmacogenetic testing for HLA-B(*)5701 is cost effective. However, until routine testing is available, pharmacovigilance is necessary for the safe and effective use of abacavir.

CONCLUSIONS

Serious adverse events associated with the use of abacavir can be avoided by appropriate recognition and management of the HSR. Screening patients for HLA-B(*)5701 prior to initiation of abacavir represents a tool to further decrease the risk of HSRs as well as unnecessary discontinuation of this drug.

HLA-DRB1*01 associated with cutaneous hypersensitivity induced by nevirapine and efavirenz

HLA typing, demographic and immunological risk factors for nevirapine and efavirenz reactions were studied in a French cohort of HIV patients. Cases with isolated rash were significantly associated with HLA-DRB101 allele. No liver toxicity was observed and no association was detected with the percentage of CD4 T-cells. This study suggests that HLA-DRB101 allele plays an important role in susceptibility to cutaneous reactions associated with nevirapine and efavirenz in HIV patients.

HLA-B*5701 screening for hypersensitivity to abacavir

BACKGROUND

Hypersensitivity reaction to abacavir is strongly associated with the presence of the HLA-B*5701 allele. This study was designed to establish the effectiveness of prospective HLA-B*5701 screening to prevent the hypersensitivity reaction to abacavir.

METHODS

This double-blind, prospective, randomized study involved 1956 patients from 19 countries, who were infected with human immunodeficiency virus type 1 and who had not previously received abacavir. We randomly assigned patients to undergo prospective HLA-B*5701 screening, with exclusion of HLA-B*5701-positive patients from abacavir treatment (prospective-screening group), or to undergo a standard-of-care approach of abacavir use without prospective HLA-B*5701 screening (control group). All patients who started abacavir were observed for 6 weeks. To immunologically confirm, and enhance the specificity of, the clinical diagnosis of hypersensitivity reaction to abacavir, we performed epicutaneous patch testing with the use of abacavir.

RESULTS

The prevalence of HLA-B*5701 was 5.6% (109 of 1956 patients). Of the patients receiving abacavir, 72% were men, 84% were white, and 18% had not previously received antiretroviral therapy. Screening eliminated immunologically confirmed hypersensitivity reaction (0% in the prospective-screening group vs. 2.7% in the control group, P<0.001), with a negative predictive value of 100% and a positive predictive value of 47.9%. Hypersensitivity reaction was clinically diagnosed in 93 patients, with a significantly lower incidence in the prospective-screening group (3.4%) than in the control group (7.8%) (P<0.001).

CONCLUSIONS

HLA-B*5701 screening reduced the risk of hypersensitivity reaction to abacavir. In predominantly white populations, similar to the one in this study, 94% of patients do not carry the HLA-B*5701 allele and are at low risk for hypersensitivity reaction to abacavir. Our results show that a pharmacogenetic test can be used to prevent a specific toxic effect of a drug. (ClinicalTrials.gov number, NCT00340080.)

Pharmacogenetic information derived from analysis of HLA alleles

A large amount of pharmacogenetic information has, in particular, accumulated on the association between human leukocyte antigen (HLA) alleles and hypersensitivity to certain drugs. Prospective HLA typing has dramatically reduced the risk of abacavir hypersensitivity because of its strong association with HLA-B*5701. Significant predisposition to nevirapine hypersensitivity has been reported in Caucasian Australians harboring HLA-DRB1*0101 with high CD4+ T-cell counts, and Sardinians and Japanese harboring HLA-Cw8. A strong association between carbamazepine hypersensitivity and HLA-B*1502 has been reported in Han Chinese. Most Han Chinese individuals with allopurinol-induced severe cutaneous adverse reactions are positive for HLA-B*5801. HLA typing can stratify risk of hypersensitivity to certain drugs and allow personalized treatment, although the patients should be monitored closely even if they are negative for HLA alleles associated with hypersensitivity.

Cytokine Profiling in Abacavir Hypersensitivity Patients

Background

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.

Methods

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.

Results

We demonstrated using in vitro models of immune activation that the production of interferon-γwas 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).

Conclusion

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.

Case–control study of the association between select HLA genes and anti-erythropoietin antibody-positive pure red-cell aplasia

Aims: Antibody (Ab)-positive pure red-cell aplasia (PRCA) is a very rare but serious adverse event associated with recombinant human erythropoietin treatment (4.1 reports per 100,000 patient-years) in which patients produce antibodies to recombinant and endogenous erythropoietin, halting red blood cell production. In a previous case series, four Thai subjects with chronic kidney disease and Ab-positive PRCA were reported to have the HLA-DRB1*9 allele. To confirm a possible association of HLA-DRB1*9 and Ab-positive PRCA, we performed a pharmacogenomic analysis using subjects from an earlier case–control study of risk factors associated with Ab-positive PRCA, which had been performed using subjects from Europe or Canada. The primary goal of the analysis was to test the association between HLA-DRB1*9 and Ab-positive PRCA. A secondary goal was to perform an exploratory analysis in order to identify additional HLA alleles potentially associated with Ab-positive PRCA. Patients & Methods: Subjects were taken from a case–control study of Ab-positive PRCA in chronic kidney disease patients treated in Europe or Canada. Ab-positive PRCA cases (n = 24) were matched to controls (n = 81) by timing of treatment exposure and, when possible, by location. Results: The allele frequency of HLA-DRB1*9 was 12.5% in cases vs 1.2% in controls (p = 0.002). The frequency of the HLA-DRB1*9/other genotype was 25.0% in cases vs 2.5% in controls (p = 0.004; OR: 10.8 [95% CI: 2.2–53.7]). Within the exploratory analysis, six additional HLA alleles (HLA-A*25, HLA-B*53, HLA-C*12, HLA-DQB1*3, HLA-DQB1*6 and HLA-DRB1*4) were also found to be associated with Ab-positive PRCA. Conclusion: This study confirmed that HLA-DRB1*9 occurs at a significantly higher frequency in Ab-positive PRCA cases than in controls; however, within this sample set, carrying the *9 allele was neither necessary nor sufficient to cause Ab-positive PRCA.

Association between heat-shock protein 70 gene polymorphisms and DNA damage in peripheral blood lymphocytes among coke-oven workers

Hsp70 has been shown to act as a chaperone and be associated with cytoprotection against DNA damage caused by environmental stresses. However, it is unknown whether genetic variation in HSP70 plays a role in stress tolerance and cytoprotection against DNA damage. We determined the frequencies of three polymorphisms, HSP70-1 G190C, HSP70-2 G1267A, and HSP70-hom T2437C from 251 steel-plant workers exposed to coke-oven emission and 130 controls. We estimated the association between the HSP70variants/haplotypes and the levels of DNA damage in their peripheral blood lymphocytes detected by single-cell gel electrophoresis assay. Our results showed that overall coke-oven workers had higher levels of the Olive tail moment (Olive TM) (1.27+/-1.12) than that of the controls (0.56+/-0.99, P<0.001). Coke-oven workers with the HSP70-1 C/C genotype had higher levels of Olive TM (2.19+/-0.65), compared with HSP70-1 G/C and G/G carriers (Olive TM=1.34+/-1.09 and 1.14+/-1.08, respectively, P=0.022 and 0.003, respectively). However, the HSP70-2 G1267A and HSP70-hom T2437C polymorphisms were not associated with the levels of Olive TM (P=0.929 and 0.795, respectively). Haplotype analysis showed that carriers of TCG/TCG haplotype pairs had the highest levels of Olive TM among both the exposed subjects (2.04+/-0.59) and the controls (0.81+/-0.59). Our results suggest that the individuals with the homozygous HSP70-1 C/C genotype among the coke-oven workers may be susceptible to DNA damage.

Adverse drug reactions and pharmacogenomics: recent advances

The concept of pharmacogenomics, the study of how variation in the human genome affects response to drugs, attracts attention from clinicians and the pharmaceutical industry alike. The aim is to distinguish, using appropriate genetic tests, individuals who may be harmed by certain drugs from those who may benefit from them. Adverse drug reactions cause significant morbidity and mortality and incur a large cost to healthcare systems. Pharmacogenomics may help in the prediction and prevention of adverse reactions to drugs. While some recent studies (e.g., abacavir hypersensitivity) have shown strong associations with single genetic factors, whether these represent the exceptions rather than the rule is unclear. Further studies on adverse drug reaction pharmacogenetics are needed – these should be adequately powered and utilize the most appropriate study design that allows for an evaluation of both genetic and environmental factors. For pharmacogenetic testing to become acceptable in clinical practice, it is important that such studies are also able to provide evidence of clinical validity and clinical utility.

Idiosyncratic drug reactions: past, present, and future

Although the major working hypothesis for the mechanism of idiosyncratic drug reactions (IDRs), the hapten hypothesis, has not changed since 1987, several hypotheses have been added, for example, the danger hypothesis and the pharmaceutical interaction hypothesis. Genetic studies have found that several IDRs are linked to specific HLA genes, providing additional evidence that they are immune-mediated. Evidence that most IDRs are caused by reactive metabolites has led pharmaceutical companies to avoid drug candidates that form significant amounts of reactive metabolites; however, at least one IDR, ximelagatran-induced liver toxicity, does not appear to be caused by a reactive metabolite. It is possible that there are biomarkers such as those related to cell stress that would predict that a drug candidate would cause a significant incidence of IDRs; however, there has been no systematic study of the changes in gene expression induced by drugs known to cause IDRs. A major impediment to the study of the mechanisms of IDRs is the paucity of valid animal models, and if we had a better mechanistic understanding, it should be easier to develop such models. There is growing evidence that these adverse reactions are more varied and complex than previously recognized, and it is unlikely that a quick fix will be achieved. However, IDRs are an important cause of patient morbidity and mortality and markedly increase the uncertainty of drug development; therefore, continued basic research in this area is essential.

Prospective HLA-B*5701 screening and abacavir hypersensitivity: a single centre experience

Suspected hypersensitivity is the main reason for the early discontinuation of abacavir. After the observation that the risk of hypersensitivity correlated with ethnicity, the presence of the HLA allele B5701 was found to be the strongest retrospective predictor of hypersensitivity. Two prospective cohorts have since demonstrated a significant reduction in abacavir hypersensitivity rates with the use of prospective human leukocyte antigen screening. We describe our experience of prospective HLA-B5701 testing and the impact on rates of abacavir hypersensitivity.