Hypersensitivity reactions to carbamazepine: characterization of the specificity, phenotype, and cytokine profile of drug-specific T cell clones

Selective HLA Class II Allele-Restricted Activation of Atabecestat Metabolite-Specific Human T-Cells

Elevations in hepatic enzymes were detected in several trial patients exposed to the Alzheimer's drug atabecestat, which resulted in termination of the drug development program. Characterization of hepatic T-lymphocyte infiltrates and diaminothiazine (DIAT) metabolite-responsive, human leukocyte antigen (HLA)-DR-restricted, CD4+ T-lymphocytes in the blood of patients confirmed an immune pathogenesis. Patients with immune-mediated liver injury expressed a restricted panel of HLA-DRB1 alleles including HLA-DRB1*12:01, HLA-DRB1*13:02, and HLA-DRB1*15:01. Thus, the objectives of this study were to (i) generate DIAT-responsive T-cell clones from HLA-genotyped drug-naive donors, (ii) characterize pathways of DIAT-specific T-cell activation, and (iii) assess HLA allele restriction of the DIAT-specific T-cell response. Sixteen drug-naive donors expressing the HLA-DR molecules outlined above were recruited, and T-cell clones were generated. Cellular phenotype, function, and HLA-allele restriction were assessed using culture assays. Peptides displayed by HLA class II molecules in the presence and absence of atabecestat were analyzed by mass spectrometry. Several DIAT-responsive CD4+ clones, displaying no reactivity toward the parent drug, were successfully generated from donors expressing HLA-DRB1*12:01, HLA-DRB1*13:02, and HLA-DRB1*15:01 but not from other donors expressing other HLA-DRB1 alleles. T-cell clones were activated following direct binding of DIAT to HLA-DR proteins expressed on the surface of antigen presenting cells. DIAT binding did not alter the HLA-DRB1 peptide binding repertoire, indicative of a binding interaction with the HLA-associated peptide rather than with the HLA protein itself. DIAT-specific T-cell responses displayed HLA-DRB1*12:01, HLA-DRB1*13:02, and HLA-DRB1*15:01 restriction. These data demonstrate that DIAT displays a degree of selectivity toward HLA protein and associated peptides, with expression of certain alleles increasing and that of others decreasing, the likelihood that a drug-specific T-cell response develops.

EAACI/ENDA position paper on drug provocation testing

In drug hypersensitivity, drug provocation testing (DPT), also called drug challenge, is the gold standard for investigation. In recent years, risk stratification has become an important tool for adjusting the diagnostic strategy to the perceived risk, whilst still maintaining a high level of safety for the patient. Skin tests are recommended before DPT but may be omitted in low-risk patients. The task force suggests a strict definition of such low-risk patients in children and adults. Based on experience and evidence from studies of allergy to beta-lactam antibiotics, an algorithm on how to adjust DPT to the risk, and when to omit skin tests before DPT, is presented. For other antibiotics, non-steroidal anti-inflammatory drugs and other drugs, skin tests are poorly validated and DPT is frequently necessary. We recommend performing DPT with chemotherapeutics and biologicals to avoid unnecessary desensitization procedures and DPT with skin tests negative contrast media. We suggest DPT with anesthetics only in highly specialized centers. Specifics of DPT to proton pump inhibitors, anticonvulsants and corticosteroids are discussed. This position paper provides general recommendations and guidance on optimizing use of DPT, whilst balancing benefits with patient safety and optimizing the use of the limited available resources.

Glycolysis: An early marker for vancomycin-specific T-cell activation

BACKGROUND

Vancomycin, a glycopeptide antibiotic used for Gram-positive bacterial infections, has been linked with drug reaction with eosinophilia and systemic symptoms (DRESS) in HLA-A*32:01-expressing individuals. This is associated with activation of T lymphocytes, for which glycolysis has been isolated as a fuel pathway following antigenic stimulation. However, the metabolic processes that underpin drug-reactive T-cell activation are currently undefined and may shed light on the energetic conditions needed for the elicitation of drug hypersensitivity or tolerogenic pathways. Here, we sought to characterise the immunological and metabolic pathways involved in drug-specific T-cell activation within the context of DRESS pathogenesis using vancomycin as model compound and drug-reactive T-cell clones (TCCs) generated from healthy donors and vancomycin-hypersensitive patients.

METHODS

CD4+ and CD8+ vancomycin-responsive TCCs were generated by serial dilution. The Seahorse XFe96 Analyzer was used to measure the extracellular acidification rate (ECAR) as an indicator of glycolytic function. Additionally, T-cell proliferation and cytokine release (IFN-γ) assay were utilised to correlate the bioenergetic characteristics of T-cell activation with in vitro assays.

RESULTS

Model T-cell stimulants induced non-specific T-cell activation, characterised by immediate augmentation of ECAR and rate of ATP production (JATPglyc). There was a dose-dependent and drug-specific glycolytic shift when vancomycin-reactive TCCs were exposed to the drug. Vancomycin-reactive TCCs did not exhibit T-cell cross-reactivity with structurally similar compounds within proliferative and cytokine readouts. However, cross-reactivity was observed when analysing energetic responses; TCCs with prior specificity for vancomycin were also found to exhibit glycolytic switching after exposure to teicoplanin. Glycolytic activation of TCC was HLA restricted, as exposure to HLA blockade attenuated the glycolytic induction.

CONCLUSION

These studies describe the glycolytic shift of CD4+ and CD8+ T cells following vancomycin exposure. Since similar glycolytic switching is observed with teicoplanin, which did not activate T cells, it is possible the master switch for T-cell activation is located upstream of metabolic signalling.

The allopurinol metabolite, oxypurinol, drives oligoclonal expansions of drug-reactive T cells in resolved hypersensitivity cases and drug-naïve healthy donors

Allopurinol (ALP) is a successful drug used in the treatment of gout. However, this drug has been implicated in hypersensitivity reactions that can cause severe to life-threatening reactions such as Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). Individuals who carry the human leukocyte antigen (HLA)-B*58:01 allotype are at higher risk of experiencing a hypersensitivity reaction (odds ratios ranging from 5.62 to 580.3 for mild to severe reactions, respectively). In addition to the parent drug, the metabolite oxypurinol (OXP) is implicated in triggering T cell-mediated immunopathology via a labile interaction with HLA-B*58:01. To date, there has been limited information regarding the T-cell receptor (TCR) repertoire usage of reactive T cells in patients with ALP-induced SJS or TEN and, in particular, there are no reports examining paired αβTCRs. Here, using in vitro drug-treated PBMCs isolated from both resolved ALP-induced SJS/TEN cases and drug-naïve healthy donors, we show that OXP is the driver of CD8+ T cell-mediated responses and that drug-exposed memory T cells can exhibit a proinflammatory immunophenotype similar to T cells described during active disease. Furthermore, this response supported the pharmacological interaction with immune receptors (p-i) concept by showcasing (i) the labile metabolite interaction with peptide/HLA complexes, (ii) immunogenic complex formation at the cell surface, and (iii) lack of requirement for antigen processing to elicit drug-induced T cell responsiveness. Examination of paired OXP-induced αβTCR repertoires highlighted an oligoclonal and private clonotypic profile in both resolved ALP-induced SJS/TEN cases and drug-naïve healthy donors.

Drug hypersensitivity and eosinophilia: The decisive role of p-i stimulation

Eosinophilia is a common finding in drug hypersensitivity reactions (DHR). Its cause is unclear, as neither antigen/allergen-driven inflammation nor clonal expansion is involved. Most delayed-DHRs are due to p-i (pharmacologic interaction of drugs with immune receptors). These are off-target activities of drugs with immune receptors that result in various types of T-cell stimulation, some of which involve excessive IL-5 production. Functional and phenotypic studies of T-cell clones and their TCR-transfected hybridoma cell lines revealed that some p-i-induced drug stimulations occur without CD4/ CD8 co-receptor engagement. The CD4/CD8 co-receptors link Lck (lymphocyte-specific protein tyrosine kinase) and LAT (linker for activation of T cells) to the TCR. Alteration of Lck or LAT can result in a TCR signalosome with enhanced IL-5 production. Thus, if a more affine TCR-[drug/peptide/HLA] interaction allows bypassing the CD4 co-receptor, a modified Lck/LAT activation may lead to a TCR signalosome with elevated IL-5 production. This "IL-5-TCR-signalosome" hypothesis could also explain eosinophilia in superantigen or allo-stimulation (graft-versus-host disease), in which evasion of CD4/CD8 co-receptors has also been described. It may open new therapeutic possibilities in certain eosinophilic diseases by directly targeting the IL-5-TCR signalosome.

Activation of Human CD8+ T Cells with Nitroso Dapsone-Modified HLA-B*13:01-Binding Peptides

Previous studies have shown that cysteine-reactive drug metabolites bind covalently with protein to activate patient T cells. However, the nature of the antigenic determinants that interact with HLA and whether T cell stimulatory peptides contain the bound drug metabolite has not been defined. Because susceptibility to dapsone hypersensitivity is associated with the expression of HLA-B*13:01, we have designed and synthesized nitroso dapsone-modified, HLA-B*13:01 binding peptides and explored their immunogenicity using T cells from hypersensitive human patients. Cysteine-containing 9-mer peptides with high binding affinity to HLA-B*13:01 were designed (AQDCEAAAL [Pep1], AQDACEAAL [Pep2], and AQDAEACAL [Pep3]), and the cysteine residue was modified with nitroso dapsone. CD8+ T cell clones were generated and characterized in terms of phenotype, function, and cross-reactivity. Autologous APCs and C1R cells expressing HLA-B*13:01 were used to determine HLA restriction. Mass spectrometry confirmed that nitroso dapsone-peptides were modified at the appropriate site and were free of soluble dapsone and nitroso dapsone. APC HLA-B*13:01-restricted nitroso dapsone-modified Pep1- (n = 124) and Pep3-responsive (n = 48) CD8+ clones were generated. Clones proliferated and secreted effector molecules with graded concentrations of nitroso dapsone-modified Pep1 or Pep3. They also displayed reactivity against soluble nitroso dapsone, which forms adducts in situ, but not with the unmodified peptide or dapsone. Cross-reactivity was observed between nitroso dapsone-modified peptides with cysteine residues in different positions in the peptide sequence. These data characterize a drug metabolite hapten CD8+ T cell response in an HLA risk allele-restricted form of drug hypersensitivity and provide a framework for structural analysis of hapten HLA binding interactions.

Pathology of T-cell-mediated drug hypersensitivity reactions and impact of tolerance mechanisms on patient susceptibility

PURPOSE OF REVIEW

T-cell-mediated drug hypersensitivity is responsible for significant morbidity and mortality, and represents a substantial clinical concern. The purpose of this article is to focus on T-cell reactions and discuss recent advances in disease pathogenesis by exploring the impact of tolerance mechanisms in determining susceptibility in genetically predisposed patients.

RECENT FINDINGS

Certain drugs preferentially activate pathogenic T cells that have defined pathways of effector function. Thus, a critical question is what extenuating factors influence the direction of immune activation. A large effort has been given towards identifying phenotypic (e.g., infection) or genotypic (e.g., human leukocyte antigen) associations which predispose individuals to drug hypersensitivity. However, many individuals expressing known risk factors safely tolerate drug administration. Thus, mechanistic insight is needed to determine what confers this tolerance. Herein, we discuss recent clinical/mechanistic findings which indicate that the direction in which the immune system is driven relies upon a complex interplay between co-stimulatory/co-regulatory pathways which themselves depend upon environmental inputs from the innate immune system.

SUMMARY

It is becoming increasingly apparent that tolerance mechanisms impact on susceptibility to drug hypersensitivity. As the field moves forward it will be interesting to discover whether active tolerance is the primary response to drug exposure, with genetic factors such as HLA acting as a sliding scale, influencing the degree of regulation required to prevent clinical reactions in patients.

Advances in the Pathomechanisms of Delayed Drug Hypersensitivity

Delayed drug hypersensitivity continues to contribute to major clinical problems worldwide. The clinical presentations of delayed drug hypersensitivity are diverse, ranging from mild skin rashes to life-threatening systemic reactions. The pathomechanism of delayed drug hypersensitivity involves human leukocyte antigens (HLA) presentation of drugs/metabolites to T cell receptors (TCR), resulting in T-cell activation. The pathogenesis of delayed drug hypersensitivity also has reactivation of the virus, and activation of many immune mediators. In this review, we discuss the immune pathogenesis, molecular interactions of HLA/drugs/TCR, and downstream signaling of cytotoxic proteins/cytokines/chemokines, as well as disease prevention and management for delayed drug hypersensitivity.

HLA Allele-Restricted Immune-Mediated Adverse Drug Reactions: Framework for Genetic Prediction

Human leukocyte antigen (HLA) is a hallmark genetic marker for the prediction of certain immune-mediated adverse drug reactions (ADRs). Numerous basic and clinical research studies have provided the evidence base to push forward the clinical implementation of HLA testing for the prevention of such ADRs in susceptible patients. This review explores current translational progress in using HLA as a key susceptibility factor for immune ADRs and highlights gaps in our knowledge. Furthermore, relevant findings of HLA-mediated drug-specific T cell activation are covered, focusing on cellular approaches to link genetic associations to drug-HLA binding as a complementary approach to understand disease pathogenesis. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Dendritic cells inclusion and cell-subset assessment improve flow-cytometry-based proliferation test in non-immediate drug hypersensitivity reactions

BACKGROUND

Lymphocyte transformation test (LTT) has been widely used to evaluate non-immediate drug hypersensitivity reactions (NIDHRs). However, the lack of standardization and the low sensitivity have limited its routine diagnostic use. The drug presentation by dendritic cells (DCs) and the assessment of proliferation on effector cells have shown promising results. Flow-cytometry-based methods can help apply these improvements. We aimed to assess the added value of using drug-primed-DCs and the determination of the proliferative response of different lymphocyte subpopulations in NIDHRs.

METHODS

Patients with confirmed NIDHR were evaluated by both conventional (C-LTT) and with drug-primed-DCs LTT (dDC-LTT)analysing the proliferative response in T cells and other effector cell subpopulations by using the fluorescent molecule, carboxyfluorescein diacetate succinimidyl ester (CFSE).

RESULTS

The C-LTT showed a significantly lower sensitivity (29.4%) compared with dDC-LTT (61.8%), which was confirmed analysing each particular clinical entity: SJS-TEN (62.5% vs 87.5%), MPE (15% vs 47.4%) and AGEP (33% vs 80%). When including the effector cell subpopulations involved in each clinical entity, CD3⁺ +CD4⁺ T_h 1 or CD3⁺ +NK cells in SJS-TEN, CD3⁺ +CD4⁺ T_h 1+NK cells in MPE and CD3⁺ +NK cells in AGEP, we could significantly increase the sensitivity of the in vitro test to 100%, 68.4% and 100%, respectively, with an overall sensitivity of 87% and 85% of specificity in NIDHR.

CONCLUSIONS

The use of a flow-cytometry-based test, DCs as drug presenting cells, and focusing on effector cell subpopulations for each clinical entity significantly improved the drug-specific proliferative response in NIDHRs with a unique cellular in vitro test.

Lymphocyte transformation test and cytokine detection assays: Determination of read out parameters for delayed-type drug hypersensitivity reactions

Drug hypersensitivity reactions (DHRs) occur in certain people and are often not predictable. DHRs can be classified as immediate and delayed reactions regarding to onset of clinical manifestations. Both reactions are considered to be an important public health problem because they can lead to life-threatening conditions; however, this review article will focus on delayed DHRs. The most important points for diagnosis of delayed DHRs are the recognition of drug hypersensitivity characteristics and culprit drug identification. While it is usually difficult to identify a culprit drug; clinical evaluation using the causality assessment method, a non-invasive process, can identify the culprit drug without the need for intensive investigation. Delayed DHRs can cause life-threatening conditions; therefore, in vivo skin tests, as well as drug provocation tests, have to be cautiously performed by a drug allergist and have not been recommended in uncontrolled conditions. ENDA/EAACI has recommended that in vitro tests (if available) be performed prior to any in vivo tests. Therefore, in vitro diagnostic tests can be alternative methods to identify a culprit drug for delayed DHR diagnosis as there is no or very low risk for patients under investigation. There are many testing approaches to identify causative agents for delayed DHRs such as: the lymphocyte transformation test (LTT), cytokine/mediator detection assays (i.e. ELISA and flow cytometry-based bead assays), multiplex bead-based immunoassay and ELISpot. The LTT is the most standardized method whereas it has been available in medical schools affiliated with university hospitals. Other in vitro tests, like cytokine detection assays, have also been used, even though they are still being evaluated. They could supplement LTT results that would provide drug allergist's with documentary evidence and prevent risk to patients by avoiding in vivo or drug provocation testing. Hence, the in vitro tests have been promising tests contributing to the management of the delayed DHR work-up process in clinical practice.

Characterization of T-Cell Responses to SMX and SMX-NO in Co-Trimoxazole Hypersensitivity Patients Expressing HLA-B*13:01

HLA-B*13:01-positive patients in Thailand can develop frequent co-trimoxazole hypersensitivity reactions. This study aimed to characterize drug-specific T cells from three co-trimoxazole hypersensitive patients presenting with either Stevens-Johnson syndrome or drug reaction with eosinophilia and systemic symptoms. Two of the patients carried the HLA allele of interest, namely HLA-B*13:01. Sulfamethoxazole and nitroso sulfamethoxazole specific T cell clones were generated from T cell lines of co-trimoxazole hypersensitive HLA-B*13:01-positive patients. Clones were characterized for antigen specificity and cross-reactivity with structurally related compounds by measuring proliferation and cytokine release. Surface marker expression was characterized via flow cytometry. Mechanistic studies were conducted to assess pathways of T cell activation in response to antigen stimulation. Peripheral blood mononuclear cells from all patients were stimulated to proliferate and secrete IFN-γ with nitroso sulfamethoxazole. All sulfamethoxazole and nitroso sulfamethoxazole specific T cell clones expressed the CD4+ phenotype and strongly secreted IL-13 as well as IFN-γ, granzyme B and IL-22. No secretion of IL-17 was observed. A number of nitroso sulfamethoxazole-specific clones cross-reacted with nitroso dapsone but not sulfamethoxazole whereas sulfamethoxazole specific clones cross-reacted with nitroso sulfamethoxazole only. The nitroso sulfamethoxazole specific clones were activated in both antigen processing-dependent and -independent manner, while sulfamethoxazole activated T cell responses via direct HLA binding. Furthermore, activation of nitroso sulfamethoxazole-specific, but not sulfamethoxazole-specific, clones was blocked with glutathione. Sulfamethoxazole and nitroso sulfamethoxazole specific T cell clones from hypersensitive patients were CD4+ which suggests that HLA-B*13:01 is not directly involved in the iatrogenic disease observed in co-trimoxazole hypersensitivity patients.

Genomic Risk Factors Driving Immune-Mediated Delayed Drug Hypersensitivity Reactions

Adverse drug reactions (ADRs) remain associated with significant mortality. Delayed hypersensitivity reactions (DHRs) that occur greater than 6 h following drug administration are T-cell mediated with many severe DHRs now associated with human leukocyte antigen (HLA) risk alleles, opening pathways for clinical prediction and prevention. However, incomplete negative predictive value (NPV), low positive predictive value (PPV), and a large number needed to test (NNT) to prevent one case have practically prevented large-scale and cost-effective screening implementation. Additional factors outside of HLA contributing to risk of severe T-cell-mediated DHRs include variation in drug metabolism, T-cell receptor (TCR) specificity, and, most recently, HLA-presented immunopeptidome-processing efficiencies via endoplasmic reticulum aminopeptidase (ERAP). Active research continues toward identification of other highly polymorphic factors likely to impose risk. These include those previously associated with T-cell-mediated HLA-associated infectious or auto-immune disease such as Killer cell immunoglobulin-like receptors (KIR), epistatically linked with HLA class I to regulate NK- and T-cell-mediated cytotoxic degranulation, and co-inhibitory signaling pathways for which therapeutic blockade in cancer immunotherapy is now associated with an increased incidence of DHRs. As such, the field now recognizes that susceptibility is not simply a static product of genetics but that individuals may experience dynamic risk, skewed toward immune activation through therapeutic interventions and epigenetic modifications driven by ecological exposures. This review provides an updated overview of current and proposed genetic factors thought to predispose risk for severe T-cell-mediated DHRs.

Carbamazepine Induces Focused T Cell Responses in Resolved Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis Cases But Does Not Perturb the Immunopeptidome for T Cell Recognition

Antiseizure medications (ASMs) are frequently implicated in T cell-mediated drug hypersensitivity reactions and cause skin tropic pathologies that range in severity from mild rashes to life-threatening systemic syndromes. During the acute stages of the more severe manifestations of these reactions, drug responsive proinflammatory CD8⁺ T cells display classical features of Th1 cytokine production (e.g. IFNγ) and cytolysis (e.g. granzyme B, perforin). These T cells may be found locally at the site of pathology (e.g. blister cells/fluid), as well as systemically (e.g. blood, organs). What is less understood are the long-lived immunological effects of the memory T cell pool following T cell-mediated drug hypersensitivity reactions. In this study, we examine the ASM carbamazepine (CBZ) and the CBZ-reactive memory T cell pool in patients who have a history of either Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN) from 3-to-20 years following their initial adverse reaction. We show that in vitro drug restimulation of CBZ-reactive CD8⁺ T cells results in a proinflammatory profile and produces a mainly focused, yet private, T cell receptor (TCR) usage amongst human leukocyte antigen (HLA)-B*15:02-positive SJS or TEN patients. Additionally, we show that expression of these CBZ-reactive TCRs in a reporter cell line, lacking endogenous αβTCR, recapitulates the features of TCR activation reported for ASM-treated T cell lines/clones, providing a useful tool for further functional validations. Finally, we conduct a comprehensive evaluation of the HLA-B*15:02 immunopeptidome following ASM (or a metabolite) treatment of a HLA-B*15:02-positive B-lymphoblastoid cell line (C1R.B*15:02) and minor perturbation of the peptide repertoire. Collectively, this study shows that the CBZ-reactive T cells characterized require both the drug and HLA-B*15:02 for activation and that reactivation of memory T cells from blood results in a focused private TCR profile in patients with resolved disease.

Current Perspective Regarding the Immunopathogenesis of Drug-Induced Hypersensitivity Syndrome/Drug Reaction with Eosinophilia and Systemic Symptoms (DIHS/DRESS)

Drug-induced hypersensitivity syndrome/drug reaction with eosinophilia and systemic symptoms (DIHS/DRESS) is a severe type of adverse drug eruption associated with multiorgan involvement and the reactivation of human herpesvirus 6, which arises after prolonged exposure to certain drugs. Typically, two waves of disease activity occur during the course of DIHS/DRESS; however, some patients experience multiple waves of exacerbation and remission of the disease. Severe complications, some of which are related to cytomegalovirus reactivation, can be fatal. DIHS/DRESS is distinct from other drug reactions, as it involves herpes virus reactivation and can lead to the subsequent development of autoimmune diseases. The association between herpesviruses and DIHS/DRESS is now well established, and DIHS/DRESS is considered to arise as a result of complex interactions between several herpesviruses and comprehensive immune responses, including drug-specific immune responses and antiviral immune responses, each of which may be mediated by distinct types of immune cells. It appears that both CD4 and CD8 T cells are involved in the pathogenesis of DIHS/DRESS but play distinct roles. CD4 T cells mainly initiate drug allergies in response to drug antigens, and then herpesvirus-specific CD8 T cells that target virus-infected cells emerge, resulting in tissue damage. Regulatory T-cell dynamics are also suggested to contribute to the diverse symptoms of DIHS/DRESS. However, the pathomechanisms of this complex disease remain largely unknown. In particular, how viral infections contribute to the pathogenesis of DIHS/DRESS and why autoimmune sequelae arise in DIHS/DRESS are yet to be elucidated. This review describes the clinical features of DIHS/DRESS, including the associated complications and sequelae, and discusses recent advances in our understanding of the immunopathogenic mechanisms of DIHS/DRESS.

Liver transplantation after DRESS syndrome: A case report and review of the literature

This study reports a patient with DRESS syndrome, associated with liver failure, treated with orthotopic liver transplantation.

Drug-Induced liver Injury Associated with Severe Cutaneous Hypersensitivity Reactions: A Complex Entity in Need of a Multidisciplinary Approach

Idiosyncratic drug-induced liver injury (DILI) occasionally occurs in the setting of severe cutaneous adverse reactions (SCARs), including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN) and drug reaction with eosinophilia and systemic symptoms (DRESS). This strengthens the proposed immunologic mechanism associated with this adverse reaction. DRESS exhibits the most common association with DILI. SCARs have a wide spectrum of heterogeneous clinical presentations and severity, and genetic predisposition has been identified. In the context of SCARs, DILI present a different clinical picture, ranging from mild injury to acute liver failure. Elucidating the role of DILI in the clinical presentation and outcome of SCARs represents a challenge due to limited information from published studies and the lack of consensus on definitions. The cholestatic and mixed pattern of liver damage typically predominates in the case of DILI associated with SCARs, which is different from DILI without SCARs where hepatocellular is the most common injury pattern. Only a few drugs have been associated with both DILI and SCARs. Is this article, the criteria used for DILI recognition among SCARS have been revised and discussed, along with the drugs most commonly involved in these syndromes as well as the outcome, prognostic factors and the need for a multidisciplinary approach to improve the management of DILI in the context of SCARs.

Immune dysregulation increases the incidence of delayed-type drug hypersensitivity reactions

Delayed-type, T cell-mediated, drug hypersensitivity reactions are a serious unwanted manifestation of drug exposure that develops in a small percentage of the human population. Drugs and drug metabolites are known to interact directly and indirectly (through irreversible protein binding and processing to the derived adducts) with HLA proteins that present the drug-peptide complex to T cells. Multiple forms of drug hypersensitivity are strongly linked to expression of a single HLA allele, and there is increasing evidence that drugs and peptides interact selectively with the protein encoded by the HLA allele. Despite this, many individuals expressing HLA risk alleles do not develop hypersensitivity when exposed to culprit drugs suggesting a nonlinear, multifactorial relationship in which HLA risk alleles are one factor. This has prompted a search for additional susceptibility factors. Herein, we argue that immune regulatory pathways are one key determinant of susceptibility. As expression and activity of these pathways are influenced by disease, environmental and patient factors, it is currently impossible to predict whether drug exposure will result in a health benefit, hypersensitivity or both. Thus, a concerted effort is required to investigate how immune dysregulation influences susceptibility towards drug hypersensitivity.

Pharmacogenetics of carbamazepine

Carbamazepine (CMZ) is a drug from the group of anticonvulsants, similar in chemical structure to tricyclic antidepressants. CMZ is widely used for mental disorders and neurological diseases. The lecture discusses the safety of CMZ in respect to personalized medicine, while considering the pharmacogenetic profile of the patient.

The authors declare about the absence of conflict of interest with respect to this publication. All authors contributed equally to this article.

T-Cell Activation by Low Molecular Weight Drugs and Factors That Influence Susceptibility to Drug Hypersensitivity

Drug hypersensitivity reactions adversely affect treatment outcome, increase the length of patients' hospitalization, and limit the prescription options available to physicians. In addition, late stage drug attrition and the withdrawal of licensed drugs cost the pharmaceutical industry billions of dollars. This significantly increases the overall cost of drug development and by extension the price of licensed drugs. Drug hypersensitivity reactions are characterized by a delayed onset, and reactions tend to be more serious upon re-exposure. The role of drug-specific T-cells in the pathogenesis of drug hypersensitivity reactions and definition of the nature of the binding interaction of drugs with HLA and T-cell receptors continues to be the focus of intensive research, primarily because susceptibility is associated with expression of one or a small number of HLA alleles. This review critically examines the mechanisms of T-cell activation by drugs. Specific examples of drugs that activate T-cells via the hapten, the pharmacological interaction with immune receptors and the altered self-peptide repertoire pathways, are discussed. Furthermore, the impacts of drug metabolism, drug-protein adduct formation, and immune regulation on the development of drug antigen-responsive T-cells are highlighted. The knowledge gained from understanding the pathways of T-cell activation and susceptibility factors for drug hypersensitivity will provide the building blocks for the development of predictive in vitro assays that will prevent or help to minimize the incidence of these reactions in clinic.

An Update on the Immunological, Metabolic and Genetic Mechanisms in Drug Hypersensitivity Reactions

Drug hypersensitivity reactions (DHRs) represent a major burden on the healthcare system since their diagnostic and management are complex. As they can be influenced by individual genetic background, it is conceivable that the identification of variants in genes potentially involved could be used in genetic testing for the prevention of adverse effects during drug administration. Most genetic studies on severe DHRs have documented HLA alleles as risk factors and some mechanistic models support these associations, which try to shed light on the interaction between drugs and the immune system during lymphocyte presentation. In this sense, drugs are small molecules that behave as haptens, and currently three hypotheses try to explain how they interact with the immune system to induce DHRs: the hapten hypothesis, the direct pharmacological interaction of drugs with immune receptors hypothesis (p-i concept), and the altered self-peptide repertoire hypothesis. The interaction will depend on the nature of the drug and its reactivity, the metabolites generated and the specific HLA alleles. However, there is still a need of a better understanding of the different aspects related to the immunological mechanism, the drug determinants that are finally presented as well as the genetic factors for increasing the risk of suffering DHRs. Most available information on the predictive capacity of genetic testing refers to abacavir hypersensitivity and anticonvulsants-induced severe cutaneous reactions. Better understanding of the underlying mechanisms of DHRs will help us to identify the drugs likely to induce DHRs and to manage patients at risk.

Immune pathomechanism and classification of drug hypersensitivity

Drug hypersensitivity reactions (DHR) are based on distinct mechanisms and are clinically heterogeneous. Taking into account that also off-target activities of drugs may lead to stimulations of immune or inflammatory cells, three forms of DHR were discriminated: the allergic-immune mechanism relies on the covalent binding of drugs/chemicals to proteins, which thereby form new antigens, to which a humoural and/or cellular immune response can develop. In IgE-mediated drug allergies, a possible tolerance mechanism to the drug during sensitization and the need of a covalent hapten-carrier link for initiation, but not for elicitation of IgE-mediated reactions is discussed. The p-i ("pharmacological interaction with immune receptor") concept represents an off-target activity of drugs with immune receptors (HLA or TCR), which can result in unorthodox, alloimmune-like stimulations of T cells. Some of these p-i stimulations occur only in carriers of certain HLA alleles and can result in clinically severe reactions. The third form of DHR ("pseudo-allergy") is represented by drug interactions with receptors or enzymes of inflammatory cells, which may lead to their direct activation or enhanced levels of inflammatory products. Specific IgE or T cells are not involved. This classification is based on the action of drugs and is clinically useful, as it can explain differences in sensitizations, unusual clinical symptoms, dependence on drug concentrations, predictability and immunological and pharmacological cross-reactivities in DHR.

HLA-associated antiepileptic drug-induced cutaneous adverse reactions

Adverse drug reactions (ADRs) are a common cause of hospital admissions (up to 19%), with the majority of cases due to off-target predictable drug effects (type A reactions). However, idiosyncratic drug-induced immune activated (type B) reactions contribute to a range of hypersensitivity reactions, with T-cell-mediated type IV hypersensitivity reactions mainly manifesting as cutaneous ADRs (cADRs). Aromatic antiepileptic drugs (AEDs), used in the treatment of epilepsy as well as bipolar disorder or neuropathic pain, have been implicated as culprit drugs in a spectrum of pathologies ranging from mild maculopapular exanthema (MPE) to severe and life-threatening conditions including drug reaction with eosinophilia and systemic symptoms (DRESS), Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). These AED-induced cADRs are unpredictable based on pharmacological and clinical factors alone, thereby prompting investigations into genomic contributors mediating risk of pathology. The most strongly associated risk genes identified are from the human leukocyte antigen (HLA) class I alleles, which play a critical role in adaptive immunity by flagging either infected or aberrant cells for recognition by surveying T-cells. In the setting of drug hypersensitivity, the immunogenicity of HLA molecules and their peptide cargo can be modulated by interactions with small drug molecules that drive inappropriate T-cell responses. This review discusses the current understanding of HLA class I molecules in modifying risk of AED-induced cADRs.

T Cell Assessment in Allergic Drug Reactions during the Acute Phase According to the Time of Occurrence

Allergic drug reactions can be classified as immediate, accelerated or delayed. This classification usually correlates with the mechanism involved: immediate reactions are IgE mediated and delayed reactions are T cell dependent. We analyzed lymphocyte involvement in patients with these reactions by determining cell subpopulations, activation state and skin homing receptor expression (CLA) in blood and skin. Patients with immediate, accelerated and delayed reactions were evaluated during the acute phase and after resolution. Controls taking drugs were included. Phenotypic immunofluorescence analysis was done by flow cytometry in peripheral blood, and by immunohistochemistry in skin for delayed reactions. Forty-six patients were included, 17 with immediate reactions, 10 accelerated and 19 delayed. At the acute phase CLA was significantly increased in delayed reactions and HLA-DR in all three types of reaction. In the severest delayed reactions, Steven-Johnson/Lyell syndromes, the CD4 subsets were increased in peripheral blood and skin compared to maculopapular exanthemas and urticaria and HLA-DR when compared with urticaria. In maculopapular exanthemas CLA was significantly increased in peripheral blood and skin compared to urticaria and the severe reactions. We found that T-cells are implicated, besides delayed reactions, in immediate and accelerated reactions. In delayed reactions there is a parallelism between results found in skin and peripheral blood with a higher participation of CD4+ cells the more severe the reaction.

Carbamazepine-Mediated Adverse Drug Reactions: CBZ-10,11-epoxide but Not Carbamazepine Induces the Alteration of Peptides Presented by HLA-B∗15:02

Among patients treated with the anticonvulsive and psychotropic drug carbamazepine (CBZ), approximately 10% develop severe and life-threatening adverse drug reactions. These immunological conditions are resolved upon withdrawal of the medicament, suggesting that the drug does not manifest in the body in long term. The HLA allele B∗15:02 has been described to be a genomic biomarker for CBZ-mediated immune reactions. It is not well understood if the immune reactions are triggered by the original drug or by its metabolite carbamazepine-10,11-epoxide (EPX) and how the interaction between the drug and the distinct HLA molecule occurs. Genetically engineered human B-lymphoblastoid cells expressing soluble HLA-B∗15:02 molecules were treated with the drug or its metabolite. Functional pHLA complexes were purified; peptides were eluted and sequenced. Applying mass spectrometric analysis, CBZ and EPX were monitored by analyzing the heavy chain and peptide fractions separately for the presence of the drug. This method enabled the detection of the drug in a biological situation post-pHLA assembly. Both drugs were bound to the HLA-B∗15:02 heavy chain; however, solely EPX altered the peptide-binding motif of B∗15:02-restricted peptides. This observation could be explained through structural insight; EPX binds to the peptide-binding region and alters the biochemical features of the F pocket and thus the peptide motif. Understanding the nature of immunogenic interactions between CBZ and EPX with the HLA immune complex will guide towards effective and safe medications.

Association between HLA alleles and lamotrigine-induced cutaneous adverse drug reactions in Asian populations: A meta-analysis

PURPOSE

The aim of this study was to assess the association between human leukocyte antigen (HLA) variants and lamotrigine (LTG)-induced cutaneous adverse drug reactions (cARDs).

METHODS

A comprehensive literature search was conducted on the relationship of HLA alleles with LTG-induced cADRs in Asian populations, through PubMed, Embase, and Cochrane Library. The last search was in February 2018. The pooled odds ratio (OR) with 95% confidence interval (95% CI) was used to access the strength of the association between an HLA allele and LTG-induced cADRs.

RESULTS

A total of 11 studies met the inclusion criteria and were enrolled in our meta- analysis, which were based on Chinese, Korean, and Thai populations. Among these populations, we observed that HLA-B*1502 is a risk allele for LTG-induced Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) in Chinese populations (pooled OR 2.4, 95% CI: 1.20-4.78, P = 0.01), HLA-A*2402 was found to be a significant risk allele for both SJS/TEN (pooled OR 3.50, 95% CI: 1.61-7.59, P = 0.002) and maculopapular eruption (MPE) (pooled OR 2.14, 95% CI: 1.10-4.16, P = 0.03), and HLA-B*3303 was considered to be a protective marker for MPE in Chinese and Korean populations (pooled OR 0.2, 95% CI 0.06-0.64, P = 0.007).

CONCLUSIONS

In Asian populations, HLA-B*1502 is a risk factor for LTG-induced bullous lesions such as SJS/TEN in Chinese populations, and HLA-A*2402 is associated with the susceptibility to either SJS/TEN or MPE. HLA-A*3303 is a protective allele against LTG-induced MPE in Chinese and Korean populations.

Clinical Pharmacogenetics Implementation Consortium Guideline for HLA Genotype and Use of Carbamazepine and Oxcarbazepine: 2017 Update

The variant allele HLA-B*15:02 is strongly associated with greater risk of Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) in patients treated with carbamazepine or oxcarbazepine. The variant allele HLA-A*31:01 is associated with greater risk of maculopapular exanthema, drug reaction with eosinophilia and systemic symptoms, and SJS/TEN in patients treated with carbamazepine. We summarize evidence from the published literature supporting these associations and provide recommendations for carbamazepine and oxcarbazepine use based on HLA genotypes.

Immune responses induced by diclofenac or carbamazepine in an oral exposure model using TNP-Ficoll as reporter antigen

Immune-mediated drug hypersensitivity reactions (IDHR) may result from immuno-sensitization to a drug-induced neo-antigen. They rarely occur in patients and are usually not predicted preclinically using standard toxicity studies. To assess the potential of a drug to induce T-cell sensitization, trinitrophenyl (TNP)-Ficoll was used here as a bystander antigen in animal experiments. TNP-Ficoll will only elicit TNP-specific IgG antibodies in the presence of non-cognate T-cell help. Therefore, the presence of TNP-specific IgG antibodies after co-injection of drug and TNP-Ficoll was indicative of T-cell sensitization potential. This TNP-Ficoll-approach was used here to characterize T-cell help induced by oral exposure to diclofenac (DF) or carbamazepine (CMZ). DF or CMZ was administered orally to BALB/c mice and after 3 w, the mice were challenged in a hind paw with TNP-Ficoll and a dose of the drug that by itself does only elicit a sub-optimal popliteal lymph node assay (PLNA) response. T-cell-dependent responses were then evaluated in paw-draining popliteal lymph nodes (PLN). Also, shortly after oral exposure, mesenteric lymph nodes (MLN) were excised for evaluation of local responses. Both drugs were able to increase PLN cellularity and TNP-specific IgG₁ production after challenge. Both DF and CMZ stimulated CD4⁺and CD8⁺ T-cells and caused shifts of the subsets toward an effector phenotype. DF, but not CMZ, appeared to stimulate interferon (IFN)-γ production. Remarkably, depletion of CD8⁺, but not CD4⁺, T-cells reduced TNP-specific IgG₁ production, and was more pronounced in CMZ- than in DF-exposed animals. Local responses in the MLN caused by DF or CMZ also showed shifts of CD4⁺and CD8⁺-cells toward a memory phenotype. Together, the data indicate that oral exposure to CMZ and DF differentially induced neo-antigen-specific T-cell reactions in the PLNA.

The Effect of Inhibitory Signals on the Priming of Drug Hapten-Specific T Cells That Express Distinct Vβ Receptors

Drug hypersensitivity involves the activation of T cells in an HLA allele-restricted manner. Because the majority of individuals who carry HLA risk alleles do not develop hypersensitivity, other parameters must control development of the drug-specific T cell response. Thus, we have used a T cell-priming assay and nitroso sulfamethoxazole (SMX-NO) as a model Ag to investigate the activation of specific TCR Vβ subtypes, the impact of programmed death -1 (PD-1), CTL-associated protein 4 (CTLA4), and T cell Ig and mucin domain protein-3 (TIM-3) coinhibitory signaling on activation of naive and memory T cells, and the ability of regulatory T cells (Tregs) to prevent responses. An expansion of the TCR repertoire was observed for nine Vβ subtypes, whereas spectratyping revealed that SMX-NO-specific T cell responses are controlled by public TCRs present in all individuals alongside private TCR repertoires specific to each individual. We proceeded to evaluate the extent to which the activation of these TCR Vβ-restricted Ag-specific T cell responses is governed by regulatory signals. Blockade of PD-L1/CTLA4 signaling dampened activation of SMX-NO-specific naive and memory T cells, whereas blockade of TIM-3 produced no effect. Programmed death-1, CTLA4, and TIM-3 displayed discrete expression profiles during drug-induced T cell activation, and expression of each receptor was enhanced on dividing T cells. Because these receptors are also expressed on Tregs, Treg-mediated suppression of SMX-NO-induced T cell activation was investigated. Tregs significantly dampened the priming of T cells. In conclusion, our findings demonstrate that distinct TCR Vβ subtypes, dysregulation of coinhibitory signaling pathways, and dysfunctional Tregs may influence predisposition to hypersensitivity.

Multiple Drug Hypersensitivity

Multiple drug hypersensitivity (MDH) is a syndrome that develops as a consequence of massive T-cell stimulations and is characterized by long-lasting drug hypersensitivity reactions (DHR) to different drugs. The initial symptoms are mostly severe exanthems or drug rash with eosinophilia and systemic symptoms (DRESS). Subsequent symptoms due to another drug often appear in the following weeks, overlapping with the first DHR, or months to years later after resolution of the initial presentation. The second DHR includes exanthema, erythroderma, DRESS, Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN), hepatitis, and agranulocytosis. The eliciting drugs can be identified by positive skin or in vitro tests. The drugs involved in starting the MDH are the same as for DRESS, and they are usually given in rather high doses. Fixed drug combination therapies like sulfamethoxazole/trimethoprim or piperacillin/tazobactam are frequently involved in MDH, and 30-40% of patients with severe DHR to combination therapy show T-cell reactions to both components. The drug-induced T-cell stimulation appears to be due to the p-i mechanism. Importantly, a permanent T-cell activation characterized by PD-1+/CD38+ expression on CD4+/CD25low T cells can be found in the circulation of patients with MDH for many years. In conclusion, MDH is a drug-elicited syndrome characterized by a long-lasting hyperresponsiveness to multiple, structurally unrelated drugs with clinically diverse symptoms.

Classification of Drug Hypersensitivity into Allergic, p-i, and Pseudo-Allergic Forms

Drug hypersensitivity reactions (DHR) are clinically and functionally heterogeneous. Different subclassifications based on timing of symptom appearance or type of immune mechanism have been proposed. Here, we show that the mode of action of drugs leading to immune/inflammatory cell stimulation is a further decisive factor in understanding and managing DHR. Three mechanisms can be delineated: (a) some drugs have or gain the ability to bind covalently to proteins, form new antigens, and thus elicit immune reactions to hapten-carrier complexes (allergic/immune reaction); (b) a substantial part of immune-mediated DHR is due to a typical off-target activity of drugs on immune receptors like HLA and TCR (pharmacological interaction with immune receptors, p-i reactions); such p-i reactions are linked to severe DHR; and (c) symptoms of DHR can also appear if the drug stimulates or inhibits receptors or enzymes of inflammatory cells (pseudo-allergy). These three distinct ways of stimulations of immune or inflammatory cells differ substantially in clinical manifestations, time of appearance, dose dependence, predictability, and cross-reactivity, and thus need to be differentiated.

Evaluation of Lymphocyte Transformation Test Results in Patients with Delayed Hypersensitivity Reactions following the Use of Anticonvulsant Drugs

BACKGROUND/AIM

Administration of the anticonvulsant drugs phenobarbital, phenytoin, carbamazepine and lamotrigine can be associated with severe hypersensitivity reactions. The lymphocyte transformation test (LTT) is a method to determine which drug has caused the hypersensitivity reaction. This study was done to evaluate the results of LTT in patients with delayed hypersensitivity reactions following the administration of anticonvulsants.

METHODS

Twenty-four patients with hypersensitivity reactions, e.g. drug-induced hypersensitivity syndrome/drug rash and eosinophilia with systemic symptoms (DIHS/DRESS), Stevens-Johnson syndrome (SJS) and toxic epidermal necrosis (TEN), following the administration of anticonvulsant drugs, and 24 patients who had used anticonvulsant drugs but did not have hypersensitivity reactions (the control group) were included in this study. Peripheral blood mononuclear cells were isolated. The cells were stimulated with the drugs, phytohemagglutinin as a mitogen and Candida as an antigen (positive controls). Lymphocyte proliferation was measured using the BrdU proliferation assay kit (Roche, Germany). The stimulation index was calculated as the mean ratio of the OD of stimulated cells divided by the OD of unstimulated cells. The results in the case and control groups were compared.

RESULTS

Of 24 patients in the test group, 14 (58.3%) had positive LTT results and 10 (41.7%) had negative results. Among patients in the control group, 1 (4.2%) had a positive LTT result and 23 (95.8%) had negative results. Among the patients who had received carbamazepine and phenytoin, there was a significant difference between the results of LTT in the case and control groups (p = 0.002 and p = 0.028, respectively). Although patients receiving lamotrigine and phenobarbital had more positive LTT results in the case group than in the control group, these differences were not statistically significant. The sensitivity, specificity, positive predictive value and negative predictive value of LTT were 58.4, 95.8, 93.3 and 69.9%, respectively.

CONCLUSIONS

Considering the significant difference in LTT results between the case and control groups in patients receiving carbamazepine and phenytoin, and not observing such a difference in patients receiving phenobarbital and lamotrigine, LTT results are more valuable for the diagnosis of hypersensitivity reactions following the administration of carbamazepine and phenytoin. The LTT has good specificity but low sensitivity for the diagnosis of drug hypersensitivity reactions.

Severe cutaneous adverse drug reactions

The clinical manifestations of drug eruptions can range from mild maculopapular exanthema to severe cutaneous adverse drug reactions (SCAR), including drug-induced hypersensitivity syndrome/drug reaction with eosinophilia and systemic symptoms, Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) which are rare but occasionally fatal. Some pathogens may induce skin reactions mimicking SCAR. There are several models to explain the interaction of human leukocyte antigen (HLA), drug and T-cell receptor (TCR): (i) the "hapten/prohapten" theory; (ii) the "p-i concept"; (iii) the "altered peptide repertoire"; and (iv) the "altered TCR repertoire". The checkpoints of molecular mechanisms of SCAR include specific drug antigens interacting with the specific HLA loci (e.g. HLA-B*15:02 for carbamazepine-induced SJS/TEN and HLA-B*58:01 for allopurinol-induced SCAR), involvement of specific TCR, induction of T-cell-mediated responses (e.g. granulysin, Fas ligand, perforin/granzyme B and T-helper 1/2-associated cytokines) and cell death mechanism (e.g. miR-18a-5p-induced apoptosis; annexin A1 and formyl peptide receptor 1-induced necroptosis in keratinocytes). In addition to immune mechanism, metabolism has been found to play a role in the pathogenesis of SCAR, such as recent findings of strong association of CYP2C9*3 with phenytoin-induced SCAR and impaired renal function with allopurinol SCAR. With a better understanding of the mechanisms, effective therapeutics and prevention for SCAR can be improved.

Oral exposure to immunostimulating drugs results in early changes in innate immune parameters in the spleen

The development of immune-dependent drug hypersensitivity reactions (IDHR) is likely to involve activation of the innate immune system to stimulate neo-antigen specific T-cells. Previously it has been shown that, upon oral exposure to several drugs with immune-adjuvant capacity, mice developed T-cell-dependent responses to TNP-OVA. These results were indicative of the adjuvant potential of these drugs. The present study set out to evaluate the nature of this adjuvant potential by focusing on early immune changes in the spleen, by testing several drugs in the same experimental model. Mice were exposed to one or multiple oral doses of previously-tested drugs: the non-steroidal-anti-inflammatory drug (NSAID) diclofenac (DF), the analgesic acetaminophen (APAP), the anti-epileptic drug carbamazepine (CMZ) or the antibiotic ofloxacin (OFLX). Within 24 h after the final dosing, early innate and also adaptive immune parameters in the spleen were examined. In addition, liver tissue was also evaluated for damage. Exposure to APAP resulted in severe liver damage, increased levels of serum alanine aminotransferase (ALT) and local MIP-2 expression. DF exposure did not cause visible liver damage, but did increase liver weight. DF also elicited clear effects on splenic innate and adaptive immune cells, i.e. increased levels of NK cells and memory T-cells. Furthermore, an increase in plasma MIP-2 levels combined with an influx of neutrophils into the spleen was observed. OFLX and CMZ exposure resulted in increased liver weights, MIP-2 expression and up-regulation of co-stimulatory molecules on antigen-presenting cells (APC). The data suggested that multiple immune parameters were altered upon exposure to drugs known to elicit immunosensitization and that broad evaluation of immune changes in straightforward short-term animal models is needed to determine whether a drug may harbor the hazard to induce IDHR. The oral exposure approach as used here may be applied in the future as an immunotoxicological research tool in this type of evaluation.

Use of the Biopharmaceutics Drug Disposition Classification System (BDDCS) to Help Predict the Occurrence of Idiosyncratic Cutaneous Adverse Drug Reactions Associated with Antiepileptic Drug Usage

Cutaneous adverse reactions (CARs) from antiepileptic drugs (AEDs) are common, ranging from mild to life-threatening, including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). The identification of subjects carrying the HLA-B*15:02, an inherited allelic variant of the HLA-B gene, and the avoidance of carbamazepine (CBZ) therapy in these subjects are strongly associated with a decrease in the incidence of carbamazepine-induced SJS/TEN. In spite of the strong genetic associations, the initiation of hypersensitivity for AEDs is still not very well characterized. Predicting the potential for other AEDs to cause adverse reactions will be undoubtedly beneficial to avoid CARs, which is the focus of this report. Here, we explore the use of the Biopharmaceutics Drug Disposition Classification System (BDDCS) to distinguish AEDs associated with and without CARs by examining the binding relationship of AEDs to HLA-B*15:02 and data from extensive reviews of medical records. We also evaluate the lack of benefit from a Hong Kong population policy on the effects of screening for HLA-B*15:02 and previous incorrect structure-activity hypotheses. Our analysis concludes that BDDCS class 2 AEDs are more prone to cause adverse cutaneous reactions than certain BDDCS class 1 AEDs and that BDDCS Class 3 drugs have the lowest levels of cutaneous adverse reactions. We propose that BDDCS Class 3 AEDs should be preferentially used for patients with Asian backgrounds (i.e., Han Chinese, Thai, and Malaysian populations) if possible and in patients predisposed to skin rashes.

The Absence of CYP3A5*3 Is a Protective Factor to Anticonvulsants Hypersensitivity Reactions: A Case-Control Study in Brazilian Subjects

Although aromatic anticonvulsants are usually well tolerated, they can cause cutaneous adverse drug reactions in up to 10% of patients. The clinical manifestations of the antiepileptics-induced hypersensitivity reactions (AHR) vary from mild skin rashes to severe cutaneous drug adverse reactions which are related to high mortality and significant morbidity. Genetic polymorphisms in cytochrome P450 genes are associated with altered enzymatic activity and may contribute to the risk of AHR. Here we present a case-control study in which we genotyped SNPs of CYP2C19, 2C9 and 3A5 of 55 individuals with varying severities of AHR, 83 tolerant, and 366 healthy control subjects from São Paulo, Brazil. Clinical characterization was based on standardized scoring systems and drug patch test. All in vivo investigation followed the ENDA (European Network of Drug Allergy) recommendations. Genotype was determined by real time PCR using peripheral blood DNA as a template. Of all 504 subjects, 65% were females, 45% self-identified as Afro-American, 38% as Caucasian and 17% as having non-African mixed ascendancy. Amongst 55 subjects with AHR, 44 had severe cutaneous drug adverse reactions. Of the 46 drug patch tests performed, 29 (63%) were positive. We found a strong association between the absence of CYP3A5*3 and tolerant subjects when compared to AHR (p = 0.0002, OR = 5.28 [CI95% 2.09–14.84]). None of our groups presented positive association with CYP2C19 and 2C9 polymorphisms, however, both SNPs contributed to separation of cases and tolerants in a Classification and Regression Tree. Our findings indicate that drug metabolism genes can contribute in the tolerability of antiepileptics. CYP3A5*3 is the most prevalent CYP3A5 allele associated with reduced enzymatic function. The current study provides evidence that normal CYP3A5 activity might be a protective factor to aromatic antiepileptics-induced hypersensitivity reactions in Brazilian subjects.

Recent advances of pharmacogenomics in severe cutaneous adverse reactions: immune and nonimmune mechanisms

Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug reaction with eosinophilia and systemic symptoms (DRESS) are severe cutaneous adverse reactions (SCAR) which are majorly caused by drugs. Though the incidence rate is low, SCAR sometimes can be life-threatening and leads to lifelong sequelae. Many pharmacogenomic associations in immune and nonimmune related genes with the development of SCAR have been discovered recently and the pharmacogenetic tests have been applied to prevent specific drug-induced SCAR. In this review, we discuss the recent advances of pharmacogenomics in SCAR.

In vitro diagnosis of delayed-type drug hypersensitivity: mechanistic aspects and unmet needs

Several laboratories use the lymphocyte transformation test for the diagnosis of delayed-type drug hypersensitivity reactions. Recently, the availability of multiple readouts has improved our ability to diagnose reactions. It is important to note that most published studies characterizing the usefulness of diagnostic tests utilize blood samples from well-defined test and control patient groups. The purpose of this article is to briefly summarize the cellular and chemical basis of delayed-type drug hypersensitivity reactions and to review in vitro assays that are available for drug hypersensitivity diagnosis.

The importance of hapten-protein complex formation in the development of drug allergy

PURPOSE OF REVIEW

Drug allergy is an adverse drug reaction that is immune-mediated. Immune activation can occur when drugs or haptens bind covalently to proteins and then act as antigens. The purpose of this review is to summarize the recent data on the formation of hapten-protein complexes and to assess the importance of these complexes in the generation of drug allergy.

RECENT FINDINGS

The formation of hapten-protein complexes by drugs and their reactive metabolites has largely been investigated using model proteins such as human serum albumin. Precise identification of the structure of the hapten and the resulting modified residue(s) in the protein has been undertaken for a small number of drugs, such as p-phenylenediamine, nevirapine, carbamazepine, β-lactams and abacavir. Some progress has also been made in identifying hapten-protein complexes in the serum of patients with allergy.

SUMMARY

Drug-specific T cells have been isolated from different patients with allergy. Formation of hapten-protein complexes, their processing and antigen presentation have been implicated in the development of drug allergy to p-phenylenediamine, sulfonamides and β-lactams. However, evidence also supports the pi mechanism of immune activation wherein drugs interact directly with immune receptors. Thus, multiple mechanisms of immune activation may occur for the same drug.