Utility of patch testing in patients with hypersensitivity syndromes associated with abacavir

Delayed Skin Testing for Systemic Medications: Helpful or Not?

Cutaneous adverse drug reactions collectively are delayed drug reactions such as morbilliform drug eruption and severe cutaneous adverse reactions (SCARs). Morbilliform drug eruption may wane over time, be the result of drug viral interactions, and be amenable to slow reintroduction or rechallenge, whereas SCARs are HLA class I restricted, T-cell-mediated reactions that demonstrate durable immunity and warrant lifelong avoidance. SCARs such as drug reaction with eosinophilia and systemic symptoms, Stevens-Johnson syndrome and toxic epidermal necrolysis, acute generalized exanthematous pustulosis, and generalized bullous fixed drug eruption often occur in the setting of multiple drugs dosed together. Collectively, they lead to significant morbidity, mortality, and drug safety concerns that could severely limit future treatment options. Currently, no single or combination of diagnostic tests for SCARs such as ex vivo or in vitro testing, in vivo (skin) testing, or other adjunctive tests such as HLA typing have 100% negative predictive value. In this "Controversies in Allergy Review" article, we review the current literature on delayed skin testing (patch and delayed prick/intradermal test) and critically assess the evidence base of its utility across different drugs and clinical phenotypes of delayed hypersensitivity reactions.

Utility and Safety of Skin Tests in Drug Reaction With Eosinophilia and Systemic Symptoms (DRESS): A Systematic Review

BACKGROUND

Determination of culprit drug in drug reaction with eosinophilia and systemic symptoms (DRESS) is crucial. Skin tests have been used, although it remains unclear how sensitive these are.

OBJECTIVE

To determine the value of skin tests in the assessment of drug causality in DRESS.

METHODS

A systematic literature search was conducted for publications from 1996 onward of skin tests (skin prick test = SPT, patch test = PT, intradermal test = IDT) performed in clearly defined DRESS cases. Outcomes of testing, drug culpability assessments, and challenge test data were extracted.

RESULTS

A total of 17 articles met inclusion criteria. In 290 patients with DRESS, patch testing was most frequent (PT = 97.2% [n = 282], IDT = 12.4% [n = 36], SPT = 3.1% [n = 9]). Positive results were noted in 58.4% (n = 160 of 282) of PTs, 66.5% of IDTs, and 25% of SPTs. When confidence of drug causality was high (n = 73 of 194), testing did not correlate well with clinical suspicion: PTs, 37.6%; IDTs, 36.5%. Direct comparison of skin testing with provocation testing (n = 12) showed 83.3% correlation. Positive IDT results were reported in 8 negative PT cases.

CONCLUSIONS

Skin tests, particularly PTs and IDTs, have been reported as tools for diagnosis of causal drugs in DRESS. Heterogeneity in methodology, results analysis, and reporting of cohorts make meta-analysis to determine sensitivity and specificity of published literature impossible and highlight weaknesses in the field. We propose that international collaboration is essential to harmonize the methodology and reporting measures from hypersensitivity testing studies in larger cohorts.

Delabeling Delayed Drug Hypersensitivity: How Far Can You Safely Go?

Delayed immune-mediated adverse drug reactions (IM-ADRs) are defined as reactions occurring more than 6 hours after dosing. They include heterogeneous clinical phenotypes that are typically T-cell-mediated reactions with distinct mechanisms across a wide spectrum of severity from benign exanthems through to life-threatening cutaneous or organ-specific diseases. For mild reactions such as benign exanthem, considerations for delabeling are similar to immediate reactions and may include a graded or single-dose drug challenge with or without preceding skin or patch testing. Evaluation of challenging cases such as the patient who is on multiple drugs at the time a severe delayed IM-ADR occurs should prioritize clinical ascertainment of the most likely phenotype and implicated drug(s). Although not widely available and validated, procedures such as patch testing, delayed intradermal skin testing, and laboratory-based functional drug assays or genetic (human leukocyte antigen) testing may provide valuable information to further help risk stratify patients and identify the likely implicated and/or cross-reactive drug(s). The decision to use a drug challenge as a diagnostic or delabeling tool in a patient with a severe delayed IM-ADR should weigh the risk-benefit ratio, balancing the severity and priority for the treatment of the underlying, and the availability of alternative efficacious and safe treatments.

An Updated Review of the Diagnostic Methods in Delayed Drug Hypersensitivity

Delayed drug hypersensitivity reactions are clinically diverse reactions that vary from isolated benign skin conditions that remit quickly with no or symptomatic treatment, drug discontinuation or even continued drug treatment, to the other extreme of severe cutaneous adverse reactions (SCARs) that are associated with presumed life-long memory T-cell responses, significant acute and long-term morbidity and mortality. Diagnostic "in clinic" approaches to delayed hypersensitivity reactions have included patch testing (PT), delayed intradermal testing (IDT) and drug challenges for milder reactions. Patch and IDT are, in general, performed no sooner than 4-6 weeks after resolution of the acute reaction at the maximum non-irritating concentrations. Functional in vitro and ex vivo assays have largely remained the province of research laboratories and include lymphocyte transformation test (LTT) and cytokine release enzyme linked ImmunoSpot (ELISpot) assay, an emerging diagnostic tool which uses cytokine release, typically IFN-γ, after the patient's peripheral blood mononuclear cells are stimulated with the suspected drug(s). Genetic markers such as human leukocyte antigen have shown recent promise for both pre-prescription screening as well as pre-emptive and diagnostic testing strategies.

Role of in vivo and in vitro Tests in the Diagnosis of Severe Cutaneous Adverse Reactions (SCAR) to Drug

Severe cutaneous adverse reactions (SCAR) are life-threatening conditions including acute generalized exanthematous pustulosis (AGEP), Stevens-Johnson Syndrome (SJS), toxic epidermal necrolysis (TEN) and drug reaction with eosinophilia and systemic symptoms (DRESS). Diagnosis of causative underlying drug hypersensitivity (DH) is mandatory due to the high morbidity and mortality upon re-exposure with the incriminated drug. If an underlying DH is suspected, in vivo test, including patch tests (PTs), delayed-reading intradermal tests (IDTs) and in vitro tests can be performed in selected patients for which the suspected culprit drug is mandatory, or in order to find a safe alternative treatment. Positivity of in vivo and in vitro tests in SCAR to drug varies depending on the type of reaction and the incriminated drugs. Due to the severe nature of these reactions, drug provocation test (DPT) is highly contraindicated in patients who experienced SCAR. Thus, sensitivity is based on positive test results in patients with a suggestive clinical history. Patch tests still remain the first-line diagnostic tests in the majority of patients with SCAR, followed, in case of negative results, by delayed-reading IDTs, with the exception of patients with bullous diseases where IDTs are still contra-indicated. In vitro tests have shown promising results in the diagnosis of SCAR to drug. Positivity is particularly high when the lymphocyte transformation test (LTT) is combined with cytokines and cytotoxic markers measurement (cyto-LTT), but this still has to be confirmed with larger studies. Due to the rarity of SCAR, large multi-center collaborative studies are needed to better study the sensitivity and specificity of in vivo and in vitro tests.

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.

Drug Reaction with Eosinophilia and Systemic Symptoms (DReSS): How Far Have We Come?

Drug reaction with eosinophilia and systemic symptoms (DReSS), also known as drug-induced hypersensitivity syndrome (DiHS), is an uncommon severe adverse reaction to medications. It is important to recognize it as it is potentially fatal and can cause significant morbidity. From the first reports of drug reactions related to certain anticonvulsants characterized by fever, liver enzyme elevation, and skin changes, our continuously growing understanding of this entity has allowed us to describe its physiopathology and clinical features even further. The relationship of genetic factors, viral activation, and specific drug exposure is now known to play a role in this disease. There is still not a widely accepted marker for DReSS/DiHS, but the spectrum of clinical and laboratory features has now been better outlined. The mainstay of treatment is the use of systemic corticosteroids, but other options such as intravenous immunoglobulin, cyclosporine, mycophenolate mofetil, rituximab, and cyclophosphamide have been described. We present a comprehensive review of the literature on DReSS/DiHS, focusing on its history, etiopathogenesis, diagnosis, therapeutic approach, and outcome.

Controversies in drug allergy: Testing for delayed reactions

Controversies exist with regard to in vivo approaches to delayed immunologically mediated adverse drug reactions, such as exanthem (maculopapular eruption), drug reaction with eosinophilia and systemic symptoms, acute generalized exanthematous pustulosis, Stevens-Johnson syndrome/toxic epidermal necrolysis, and fixed drug eruptions. In particular, widespread differences exist between regions and practice on the availability and use of intradermal and patch testing, the standard drug concentrations used, the use of additional drugs in intradermal and patch testing to help determine cross-reactivity, the timing of testing in relation to the occurrence of the adverse drug reaction, the use of testing in specific phenotypes, and the use of oral challenge in conjunction with delayed intradermal and patch testing to ascertain drug tolerance. It was noted that there have been advances in the science of delayed T cell-mediated reactions that have shed light on immunopathogenesis and provided a mechanism of preprescription screening in the case of HLA-B*57:01 and abacavir hypersensitivity and HLA-B*15:02 and carbamazepine Stevens-Johnson syndrome/toxic epidermal necrolysis in Southeast Asian subjects. Future directions should include the collaboration of large international networks to develop and standardize in vivo diagnostic approaches, such as skin testing and patch testing, combined with ex vivo and in vitro laboratory approaches.

A transgenic mouse model for HLA-B*57:01-linked abacavir drug tolerance and reactivity

Adverse drug reactions (ADRs) are a major obstacle to drug development, and some of these, including hypersensitivity reactions to the HIV reverse transcriptase inhibitor abacavir (ABC), are associated with HLA alleles, particularly HLA-B*57:01. However, not all HLA-B*57:01+ patients develop ADRs, suggesting that in addition to the HLA genetic risk, other factors may influence the outcome of the response to the drug. To study HLA-linked ADRs in vivo, we generated HLA-B*57:01-Tg mice and show that, although ABC activated Tg mouse CD8+ T cells in vitro in a HLA-B*57:01-dependent manner, the drug was tolerated in vivo. In immunocompetent Tg animals, ABC induced CD8+ T cells with an anergy-like phenotype that did not lead to ADRs. In contrast, in vivo depletion of CD4+ T cells prior to ABC administration enhanced DC maturation to induce systemic ABC-reactive CD8+ T cells with an effector-like and skin-homing phenotype along with CD8+ infiltration and inflammation in drug-sensitized skin. B7 costimulatory molecule blockade prevented CD8+ T cell activation. These Tg mice provide a model for ABC tolerance and for the generation of HLA-B*57:01-restricted, ABC-reactive CD8+ T cells dependent on both HLA genetic risk and immunoregulatory host factors.

HLAs: Key regulators of T-cell-mediated drug hypersensitivity

Adverse drug reactions (ADR) can be broadly categorised as either on-target or off-target. On-target ADRs arise as a direct consequence of the pharmacological properties of the drug and are therefore predictable and dose-dependent. On-target ADRs comprise the majority (>80%) of ADRs, relate to the drug's interaction with its known pharmacological target and are a result of a complex interplay of genetic and ecologic factors. In contrast, off-target ADRs, including immune-mediated ADRs (IM-ADRs), are due to unintended pharmacological interactions such as inadvertent ligation of host cell receptors or non-pharmacological interactions mediated through an adaptive immune response. IM-ADRs can be classified according to the primary immune cell involved and include B-cell-mediated (Gell-Coombs type I-III reactions) and T-cell-mediated (Gell-Coombs type IV or delayed hypersensitivity) reactions. IM-ADRs mediated by T cells are associated with phenotypically distinct clinical diagnoses and can vary from a mild delayed rash to a life-threatening cutaneous, systemic or organ disease, such as Stephen Johnson syndrome/toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms and drug-induced liver disease. T-cell-mediated ADRs are strongly linked to the carriage of particular HLA risk alleles which are in the case of abacavir hypersensitivity and HLA-B*57:01 has led to translation into the clinic as a routine screening test. In this review, we will discuss the immunogenetics and pathogenesis of IM-ADRs and how HLA associations inform both pre-drug screening strategies and mechanistic understanding.

The 3 Cs of Antibiotic Allergy-Classification, Cross-Reactivity, and Collaboration

Antibiotic allergy labeling is highly prevalent and negatively impacts patient outcomes and antibiotic appropriateness. Reducing the prevalence and burden of antibiotic allergies requires the engagement of key stakeholders such as allergists, immunologists, pharmacists, and infectious diseases physicians. To help address this burden of antibiotic allergy overlabeling, we review 3 key antibiotic allergy domains: (1) antibiotic allergy classification, (2) antibiotic cross-reactivity, and (3) multidisciplinary collaboration. We review the available evidence and research gaps of currently used adverse drug reaction classification systems, antibiotic allergy cross-reactivity, and current and future models of antibiotic allergy care.

The Combined Utility of Ex Vivo IFN-γ Release Enzyme-Linked ImmunoSpot Assay and In Vivo Skin Testing in Patients with Antibiotic-Associated Severe Cutaneous Adverse Reactions

BACKGROUND

For severe cutaneous adverse reactions (SCARs) associated with multiple antibiotics dosed concurrently, clinical causality is challenging and diagnostic approaches are limited, leading to constricted future antibiotic choices.

OBJECTIVE

To examine the combined utility of in vivo and ex vivo diagnostic approaches at assigning drug causality in a cohort of patients with antibiotic-associated (AA)-SCARs.

METHODS

Patients with AA-SCARs were prospectively recruited between April 2015 and February 2017. In vivo testing (patch testing or delayed intradermal testing) was performed to the implicated antibiotic(s) at the highest nonirritating concentration and read at 24 hours through 1 week. Ex vivo testing used patient peripheral blood mononuclear cells (PBMCs) stimulated with a range of pharmacologically relevant concentrations of implicated antibiotics to measure dose-dependent IFN-γ release from CD4+ and CD8+ T cells via an enzyme-linked immunoSpot assay.

RESULTS

In 19 patients with AA-SCARs, combined in vivo and ex vivo testing assigned antibiotic causality in 15 (79%) patients. Ten patients (53%) with AA-SCARs were positive on IFN-γ release enzyme-linked immunoSpot assay, with an overall reported sensitivity of 52% (95% CI, 29-76) and specificity of 100% (95% CI, 79-100), with improved sensitivity noted in acute (within 1 day to 6 weeks after SCAR onset) testing (75%) and in patients with higher phenotypic scores (59%). There was increased use of narrow-spectrum beta-lactams and antibiotics from within the implicated class following testing in patients with a positive ex vivo or in vivo test result.

CONCLUSIONS

We demonstrate the potential utility of combined in vivo and ex vivo testing in patients with AA-SCARs to assign drug causality with high specificity.

Severe Delayed Cutaneous and Systemic Reactions to Drugs: A Global Perspective on the Science and Art of Current Practice

Most immune-mediated adverse drug reactions (IM-ADRs) involve the skin, and many have additional systemic features. Severe cutaneous adverse drug reactions (SCARs) are an uncommon, potentially life-threatening, and challenging subgroup of IM-ADRs with diverse clinical phenotypes, mechanisms, and offending drugs. T-cell-mediated immunopathology is central to these severe delayed reactions, but effector cells and cytokines differ by clinical phenotype. Strong HLA-gene associations have been elucidated for specific drug-SCAR IM-ADRs such as Stevens-Johnson syndrome/toxic epidermal necrolysis, although the mechanisms by which carriage of a specific HLA allele is necessary but not sufficient for the development of many IM-ADRs is still being defined. SCAR management is complicated by substantial short- and long-term morbidity/mortality and the potential need to treat ongoing comorbid disease with related medications. Multidisciplinary specialist teams at experienced units should care for patients. In the setting of SCAR, patient outcomes as well as preventive, diagnostic, treatment, and management approaches are often not generalizable, but rather context specific, driven by population HLA-genetics, the pharmacology and genetic risk factors of the implicated drug, severity of underlying comorbid disease necessitating ongoing treatments, and cost considerations. In this review, we update the basic and clinical science of SCAR diagnosis and management.

Pharmacogenomics of off-target adverse drug reactions

Off-target adverse drug reactions (ADRs) are associated with significant morbidity and costs to the healthcare system, and their occurrence is not predictable based on the known pharmacological action of the drug's therapeutic effect. Off-target ADRs may or may not be associated with immunological memory, although they can manifest with a variety of shared clinical features, including maculopapular exanthema, severe cutaneous adverse reactions (SCARs), angioedema, pruritus and bronchospasm. Discovery of specific genes associated with a particular ADR phenotype is a foundational component of clinical translation into screening programmes for their prevention. In this review, genetic associations of off-target drug-induced ADRs that have a clinical phenotype suggestive of an immunologically mediated process and their mechanisms are highlighted. A significant proportion of these reactions lack immunological memory and current data are informative for these ADRs with regard to disease pathophysiology, therapeutic targets and biomarkers which may identify patients at greatest risk. Although many serious delayed immune-mediated (IM)-ADRs show strong human leukocyte antigen associations, only a small subset have successfully been implemented in screening programmes. More recently, other factors, such as drug metabolism, have been shown to contribute to the risk of the IM-ADR. In the future, pharmacogenomic targets and an understanding of how they interact with drugs to cause ADRs will be applied to drug design and preclinical testing, and this will allow selection of optimal therapy to improve patient safety.

Pharmacogenomics in the age of personalized medicine

The aim of personalized medicine is to offer the right treatment to the right person at the right dose, thus maximizing efficacy and minimizing toxicity for each individual patient. Pharmacogenomic approaches attempt to refine the aim of personalized medicine by utilizing an individual's germline and somatic DNA signatures to guide treatment. In this review, we highlight the current use of pharmacogenomic based biomarker information in drug labeling. We also present several case studies on the implementation of pharmacogenomic strategies in drug discovery and development. Lastly, we comment on current challenges to implementing pharmacogenomic based testing in the clinic.

Prevalence of abacavir-associated hypersensitivity syndrome and HLA-B*5701 allele in a Portuguese HIV-positive population

Background

Human Immunodeficiency Virus (HIV)-positive patients treated with the antiretroviral drug abacavir (ABC) may develop a potentially fatal ABC-associated hypersensitivity syndrome (ABC-HS), typically characterized by fever, malaise, rash, vomiting/diarrhoea and/or dyspnoea/cough. ABC-HS has been strongly associated with HLA-B*57:01 carriage and screening for this allele is recommended.

Objective

To determine the prevalence of HLA-B*57:01 and to characterize suspected ABC-HS in the adult HIV population from our hospital during a 7-year period.

Methods

Clinical data on patients under ABC treatment from January 2006 to December 2012 were analyzed to search for symptoms of ABC-HS. Reactions of suspected ABC-HS were characterized. HLA-B*57:01 and patch tests (1% and 10% ABC in petrolatum) with readings at 48 h were performed in those without previous testing. From January 2008 routine HLA-B*57:01 screening was implemented.

Results

From January 2006 to December 2007, 186 patients began treatment with ABC (data from 163 were available): 7 (4%) patients stopped ABC for suspected ABC-HS (71% males, median age 45 years) and the median time for onset of the reaction after starting ABC was 7 days. Four of the 7 patients had the HLA-B*57:01 allele and 2 of these 4 had positive patch tests. After HLA-B*57:01 screening implementation (January 2008), 573 patients were evaluated and 35 (6.1%) were HLA-B*57:01 positive; no suspected ABC-HS were observed since then.

Conclusion

Four patients with suspected ABC-HS (of 6 screened) were HLA-B*57:01 positive. No ABC-HS occurred since January 2008, after HLA-B*57:01 screening was implemented.

Old dog begging for new tricks: current practices and future directions in the diagnosis of delayed antimicrobial hypersensitivity

PURPOSE OF REVIEW

Antimicrobials are a leading cause of severe T cell-mediated adverse drug reactions (ADRs). The purpose of this review is to address the current understanding of antimicrobial cross-reactivity and the ready availability of and evidence for in-vitro, in-vivo, and ex-vivo diagnostics for T cell-mediated ADRs.

RECENT FINDINGS

Recent literature has evaluated the efficacy of traditional antibiotic allergy management, including patch testing, skin prick testing, intradermal testing, and oral challenge. Although patch and intradermal testing are specific for the diagnosis of immune-mediated ADRs, they suffer from drug-specific limitations in sensitivity. The use of ex-vivo diagnostics, especially enzyme-linked immunospot, has been highlighted as a promising new approach to assigning causality. Knowledge of true rates of antimicrobial cross-reactivity aids empirical antibiotic choice in the setting of previous immune-mediated ADRs.

SUMMARY

In an era of increasing antimicrobial resistance and use of broad-spectrum antimicrobial therapy, ensuring patients are assigned the correct 'allergy label' is essential. Re-exposure to implicated antimicrobials, especially in the setting of severe adverse cutaneous reaction, is associated with significant morbidity and mortality. The process through which an antibiotic label gets assigned, acted on and maintained is still imprecise. Predicting T cell-mediated ADRs via personalized approaches, including human leukocyte antigen-typing, may pave future pathways to safer antimicrobial prescribing guidelines.

New genetic findings lead the way to a better understanding of fundamental mechanisms of drug hypersensitivity

Drug hypersensitivity reactions are an important clinical problem for both health care and industry. Recent advances in genetics have identified a number of HLA alleles associated with a range of these adverse reactions predominantly affecting the skin but also other organs, such as the liver. The associations between abacavir hypersensitivity and HLA-B*57:01 and carbamazepine-induced Stevens-Johnson syndrome and HLA-B*15:02 have been implemented in clinical practice. There are many different mechanisms proposed in the pathogenesis of drug hypersensitivity reactions, including the hapten hypothesis, direct binding to T-cell receptors (the pharmacologic interaction hypothesis), and peptide-binding displacement. A problem with all the hypotheses is that they are largely based on in vitro findings, with little direct in vivo evidence. Although most studies have focused on individual mechanisms, it is perhaps more important to consider them all as being complementary, potentially occurring at the same time with the same drug in the same patient. This might at least partly account for the heterogeneity of the immune response seen in different patients. There is a need to develop novel methodologies to evaluate how the in vitro mechanisms relate to the in vivo situation and how the highly consistent genetic findings with different HLA alleles can be more consistently used for both prediction and prevention of these serious adverse reactions.

Evolving models of the immunopathogenesis of T cell-mediated drug allergy: The role of host, pathogens, and drug response

Immune-mediated (IM) adverse drug reactions (ADRs) are an underrecognized source of preventable morbidity, mortality, and cost. Increasingly, genetic variation in the HLA loci is associated with risk of severe reactions, highlighting the importance of T-cell immune responses in the mechanisms of both B cell-mediated and primary T cell-mediated IM-ADRs. In this review we summarize the role of host genetics, microbes, and drugs in IM-ADR development; expand on the existing models of IM-ADR pathogenesis to address multiple unexplained observations; discuss the implications of this work in clinical practice today; and describe future applications for preclinical drug toxicity screening, drug design, and development.

Antiviral drug allergy

Antiviral drugs used to treat HIV and hepatitis C are common causes of delayed drug hypersensitivities for which many of the more severe reactions have been recently shown to be immunogenetically mediated such as abacavir hypersensitivity where HLA-B(∗)57:01 is now used routinely as a screening test to exclude patients carrying this allele from abacavir prescription. Most antiviral drug allergies consist of mild to moderate delayed rash without other serious features (eg, fever, mucosal involvement, blistering rash, organ impairment. In these cases treatment can be continued with careful observation and symptomatic management and the discontinuation rate is low.

Abacavir-reactive memory T cells are present in drug naïve individuals

Background

Fifty-five percent of individuals with HLA-B*57:01 exposed to the antiretroviral drug abacavir develop a hypersensitivity reaction (HSR) that has been attributed to naïve T-cell responses to neo-antigen generated by the drug. Immunologically confirmed abacavir HSR can manifest clinically in less than 48 hours following first exposure suggesting that, at least in some cases, abacavir HSR is due to re-stimulation of a pre-existing memory T-cell population rather than priming of a high frequency naïve T-cell population.

Methods

To determine whether a pre-existing abacavir reactive memory T-cell population contributes to early abacavir HSR symptoms, we studied the abacavir specific naïve or memory T-cell response using HLA-B*57:01 positive HSR patients or healthy controls using ELISpot assay, intra-cellular cytokine staining and tetramer labelling.

Results

Abacavir reactive CD8+ T-cell responses were detected in vitro in one hundred percent of abacavir unexposed HLA-B*57:01 positive healthy donors. Abacavir-specific CD8+ T cells from such donors can be expanded from sorted memory, and sorted naïve, CD8+ T cells without need for autologous CD4+ T cells.

Conclusions

We propose that these pre-existing abacavir-reactive memory CD8+ T-cell responses must have been primed by earlier exposure to another foreign antigen and that these T cells cross-react with an abacavir-HLA-B*57:01-endogenous peptide ligand complex, in keeping with the model of heterologous immunity proposed in transplant rejection.

HLA associations and clinical implications in T-cell mediated drug hypersensitivity reactions: an updated review

T-cell mediated drug hypersensitivity reactions may range from mild rash to severe fatal reactions. Among them, drug reaction with eosinophilia and systemic symptoms (DRESS) or drug-induced hypersensitivity syndrome (DIHS), Stevens-Johnson syndrome/ toxic epidermal necrolysis (SJS/TEN), are some of the most life-threatening severe cutaneous adverse reactions (SCARs). Recent advances in pharmacogenetic studies show strong genetic associations between human leukocyte antigen (HLA) alleles and susceptibility to drug hypersensitivity. This review summarizes the literature on recent progresses in pharmacogenetic studies and clinical application of pharmacogenetic screening based on associations between SCARs and specific HLA alleles to avoid serious conditions associated with drug hypersensitivity.

Antimicrobial stewardship's new weapon? A review of antibiotic allergy and pathways to 'de-labeling'

PURPOSE OF REVIEW

The continued emergence of multiresistant pathogens and widespread antimicrobial use has led to a greater emphasis on antimicrobial stewardship programs. Concurrently, an increased awareness of the rising number of antibiotic allergy labels and impact on antimicrobial use has surfaced. The integration of antibiotic allergy de-labeling and antimicrobial stewardship programs may be a pathway worthy of further focus and investigation.

RECENT FINDINGS

Recent literature has evaluated the efficacy of antibiotic allergy management (historical de-labeling, in-vitro testing, skin prick testing, intradermal testing, and oral challenges) and impact of antibiotic allergy labels on patient outcome. The importance of true and perceived antibiotic allergy cross-reactivity in the setting of β-lactam allergies has been highlighted. The impact of dedicated antibiotic allergy de-labeling clinics, inpatient antibiotic allergy testing, and integrated antimicrobial stewardship programs has been recently appraised.

SUMMARY

More recent literature supports that appropriate antibiotic allergy in-vitro and in-vivo testing and subsequent antibiotic allergy de-labeling, particularly in regard to β-lactams, can decrease broad-spectrum antibiotic use, costs, patient length of stay, and mortality. Integration of antibiotic allergy management into the decision support systems of inpatient and outpatient antimicrobial stewardship programs represents an important opportunity to further improve measured outcomes from antibiotic utilization.

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.

Genotyping for severe drug hypersensitivity

Over the past decade, there have been significant advances in our understanding of the immunopathogenesis and pharmacogenomics of severe immunologically-mediated adverse drug reactions. Such T-cell-mediated adverse drug reactions such as Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN), drug-induced liver disease (DILI) and other drug hypersensitivity syndromes have more recently been shown to be mediated through interactions with various class I and II HLA alleles. Key examples have included the associations of HLA-B*15:02 and carbamazepine induced SJS/TEN in Southeast Asian populations and HLA-B*57:01 and abacavir hypersensitivity. HLA-B*57:01 screening to prevent abacavir hypersensitivity exemplifies a successful translational roadmap from pharmacogenomic discovery through to widespread clinical implementation. Ultimately, our increased understanding of the interaction between drugs and the MHC could be used to inform drug design and drive pre-clinical toxicity programs to improve drug safety.

Fixed dose combination abacavir/lamivudine in the treatment of HIV-1 infection

The fixed dose combination of abacavir with lamivudine represents a new treatment option for patients infected with HIV. Fixed dose combination abacavir/lamivudine has the convenience of one pill and once-daily dosing. It achieves comparable suppression of plasma HIV RNA with the pill's individual components dosed twice daily and with thymidine analogs combined with lamivudine. The combination is well tolerated, with the potential advantages of less lipoatrophy and fewer metabolic perturbations. However, the abacavir component may cause hypersensitivity reactions, which are reported in up to 8% of patients, and are potentially life threatening. Fixed dose combination abacavir/lamivudine should be considered as a viable treatment option for HIV-infected patients, particularly for those who have otherwise limited nucleoside reverse transcriptase inhibitor choices.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Skin test concentrations for systemically administered drugs -- an ENDA/EAACI Drug Allergy Interest Group position paper

Skin tests are of paramount importance for the evaluation of drug hypersensitivity reactions. Drug skin tests are often not carried out because of lack of concise information on specific test concentrations. The diagnosis of drug allergy is often based on history alone, which is an unreliable indicator of true hypersensitivity.To promote and standardize reproducible skin testing with safe and nonirritant drug concentrations in the clinical practice, the European Network and European Academy of Allergy and Clinical Immunology (EAACI) Interest Group on Drug Allergy has performed a literature search on skin test drug concentration in MEDLINE and EMBASE, reviewed and evaluated the literature in five languages using the GRADE system for quality of evidence and strength of recommendation. Where the literature is poor, we have taken into consideration the collective experience of the group.We recommend drug concentration for skin testing aiming to achieve a specificity of at least 95%. It has been possible to recommend specific drug concentration for betalactam antibiotics, perioperative drugs, heparins, platinum salts and radiocontrast media. For many other drugs, there is insufficient evidence to recommend appropriate drug concentration. There is urgent need for multicentre studies designed to establish and validate drug skin test concentration using standard protocols. For most drugs, sensitivity of skin testing is higher in immediate hypersensitivity compared to nonimmediate hypersensitivity.

HLA and pharmacogenetics of drug hypersensitivity

Immunologically mediated drug reactions have been traditionally classified as unpredictable based on the fact that they cannot be predicted strictly on the pharmacological action of the drug. Such adverse drug reactions are associated with considerable morbidity and include severe cutaneous adverse reactions such as Stevens-Johnson syndrome/toxic epidermal necrolysis and the drug hypersensitivity syndromes (drug reaction with eosinophilia and systemic symptoms/drug-induced hypersensitivity syndrome). Over the last decade there have been many associations between these syndromes and Class I and II HLA alleles of the MHC, which have enriched and driven our knowledge of their immunopathogenesis. Significant translation has also occurred in the case of HLA-B*5701 screening being used to exclude at risk patients from abacavir and prevent abacavir hypersensitivity. The ultimate translation of the knowledge of how drugs interact with HLA would be applicable to preclinical drug screening programs to improve the safety and cost-effectiveness of drug design and development.

Human leukocyte antigen-associated drug hypersensitivity

A growing number of associations between adverse drug reactions and alleles of the human leukocyte antigen (HLA) genes are now known. Although several models have been proposed to explain these associations, an underlying molecular basis has only recently been described. The associations between HLA-B*57:01 and abacavir hypersensitivity syndrome, and HLA-B*15:02 and carbamazepine-induced bullous skin disease have provided new insights into the mechanism associated with hypersensitivity reactions to these drugs. Here we discuss recent evidence that small molecules can interact with specific HLA to distort self-peptide presentation leading to autoimmune-like drug hypersensitivities that potentially provide clues to the mechanisms underlying other immunopathologies.

The pharmacogenetics of antiretroviral therapy

PURPOSE OF REVIEW

Although the past 20 years have seen many advances in HIV pharmacotherapy, host variability has only been more recently recognized as an important driver of both treatment response and toxicity. This review will focus on the importance of variability in drug metabolizing enzymes and the potential research and clinical applications of these findings in HIV care.

RECENT FINDINGS

The treatment of HIV is complex and involves chronic treatment with multiple drugs and drug classes. Recent research has been important in uncovering genetic differences in drug metabolizing and drug transporter genes, which underpin dose-dependent toxicity and efficacy, but also in genes defining differences in immune response and human leukocyte antigen genes, which restrict processes that are less dependent on the drug dose.

SUMMARY

The advancement of pharmacogenetics will continue to further our knowledge of disease-drug interactions and pathogenesis. Ultimately, the goals of pharmacogenetics and pharmacogenomics in HIV medicine will be the development of the right drugs for the right patient or population. The strong association between HLA-B5701 and abacavir hypersensitivity reaction shows promise for a genetic screening test to be feasibly incorporated into clinical practice. The clinical applicability of many findings demonstrating associations between single nucleotide polymorphisms, particularly in drug metabolism and transporter genes and drug efficacy and toxicity, are currently uncertain.