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

Prospective epidemiological study of the prevalence of human leukocyte antigen (HLA)-B*5701 in HIV-1-infected UK subjects

OBJECTIVES

Human leukocyte antigen (HLA)-B(*)5701 is strongly associated with developing a hypersensitivity reaction to abacavir (ABC) in White and Hispanic subjects. Across the UK, limited data exist on HLA-B(*)5701 prevalence in HIV-1-infected subjects. We determined HLA-B(*)5701 prevalence in the general HIV-1-infected population and in specific ethnic groups, particularly Black Africans who, in general, exhibit greater genetic diversity. We also compared HLA-B(*)5701 results obtained from local laboratories with those from a central provider.

DESIGN AND METHODS

Multi-centre, observational study. All HIV-1-infected adult individuals receiving care at participating centres were eligible, irrespective of treatment status or prior exposure to ABC. Subjects provided samples for HLA-B(*)5701 assessment by both local (blood) and central laboratories (buccal swabs). HLA-B(*)5701 prevalence was adjusted to represent the ethnic group composition of the general UK population, and by main ethnic group. RESULTS; From eight UK centres, 1494 subjects [618 (41%) White, 770 (52%) Black] were recruited. Eighty-nine per cent of Black subjects reported an immediate country of origin in Africa. Overall adjusted HLA-B(*)5701 prevalence was 4.55% [95% confidence interval (CI) 3.49% to 5.60%]. Among White subjects, prevalence was 7.93% (CI 5.80% to 10.06%). Among Black subjects, only two (both Ugandan) were HLA-B(*)5701 positive giving a rate of 0.26% (CI 0.07% to 0.94%).

CONCLUSIONS

HLA-B(*)5701 prevalence was similar to previously reported rates in White HIV-infected subjects but considerably lower than that reported in Black HIV-1-infected subjects, as a result of the large proportion of Black African subjects.

Successful translation of pharmacogenetics into the clinic: the abacavir example

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.

Personalizing antiretroviral therapy: is it a reality?

The concept of personalizing antiretroviral therapy is not novel, since the complexity of the HIV patient and their therapy has always demanded consideration of the patient's 'pharmacoecology', taking into account factors such as adherence, drug-drug and food-drug interactions, underlying disease and host states, such as organ dysfunction and pregnancy. Recent advances in science have taken this one step further with the technology now available to use both a candidate and whole-genome approach to explore the genetics of host-virus interactions, as well as the pharmacogenetics of the toxicity and efficacy of antiretroviral therapy. The genetics of host-virus interactions have improved our understanding of the pathogenesis of HIV which will aid in the research and development of an HIV vaccine. Most published HIV pharmacogenetic studies have utilized a candidate gene approach. Although these types of studies have provided insight into the pathogenesis and pharmacogenetics of drug disposition, drug interactions, drug efficacy and toxicity and host-virus interactions, very few will lend themselves to a widespread clinical application. The application of HLA-B*5701 screening to prevent abacavir hypersensitivity acts as an important example of the successful widespread implementation of a pharmacogenetic test into the clinic and defines the key steps necessary for the clinical application of pharmacogenetic tests in general.

HIV as a chronic disease

The 25th anniversary of the first reports of a catastrophic illness later classified as AIDS and the 10th anniversary of highly active antiretroviral therapy (HAART) both occurred in 2006. Where available, HAART has revolutionised the treatment of HIV. This success has brought challenges--the unknown long-term history of treated HIV infection, the development of toxicity and drug resistance, and the ageing HIV-infected patient. Despite these advances, the number of HIV cases continues to rise in vulnerable populations in under-resourced areas of the world. These anniversaries allow us to appreciate the milestones achieved thus far and those yet to be achieved. Only a collaborative global effort will stop the epidemic from overwhelming efforts to contain it.

Abacavir-induced reaction with fever and severe skin rash in a patient tested human leukocyte antigen-B*5701 negative

The most serious adverse event caused by abacavir is the hypersensitivity reaction, which is usually associated with the presence of the human leukocyte antigen (HLA) subtype B*5701, as shown in recent studies. We describe the case of a 41-year-old Caucasian female patient, who tested HLA-B*5701 negative and developed fever and severe skin rash 10 weeks after the start of abacavir therapy. Similar reports suggest that not all severe abacavir-induced adverse events occur as a result of classic hypersensitivity reactions, and can present also in HLA-B*5701-negative patients.

The impact of pharmacogenetics on HIV therapy

The use of highly active antiretroviral therapy in the treatment of HIV infection has resulted in significant reductions in mortality and morbidity worldwide. However, there is considerable interindividual variability in patient outcomes in terms of drug disposition, drug efficacy and adverse events. The basis of these differences is multifactorial, but host genetics are believed to play a significant part. To date, most attempts to explain this variability have focused on isolated single nucleotide polymorphisms. The most exciting development to date is the discovery of human leukocyte antigen subtype B*5701 (HLA B*5701) as a strong predictor of the abacavir hypersensitivity reaction. There is a gradual move away from single candidate gene analyses towards a high throughput whole genome approach. These studies must be performed on well characterized cohorts and reported associations must be validated in independent, ethnically diverse populations.

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.

Should HLA-B*5701 screening be performed in every ethnic group before starting abacavir?

Human leukocyte antigen allele (HLA)-B*5701 is associated with abacavir hypersensitivity. However, the carriage rate of HLA-B*5701 has rarely been studied in Asians. In 534 Korean patients with human immunodeficiency virus infection, HLA-B*5701 status was determined by polymerase chain reaction with HLA-B*5701-specific primers. No patients had the HLA-B*5701 allele (95% confidence interval, 0%-0.7%). This explains the paucity of immunologically confirmed cases of abacavir hypersensitivity in Koreans.

[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.

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.

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.