Involvement of T cells in drug-induced allergies

New Insights into Drug Reaction with Eosinophilia and Systemic Symptoms Pathophysiology

Drug reaction with eosinophilia and systemic symptoms (DRESS), also known as drug-induced hypersensitivity syndrome, is a severe type of cutaneous drug-induced eruption. DRESS may be a difficult disease to diagnose since the symptoms mimic those of cutaneous and systemic infectious pathologies and can appear up to 3 months after the initial culprit drug exposure. The symptoms of DRESS syndrome include rash development after a minimum of 3 weeks after the onset of a new medication, associated with facial edema, lymphadenopathy, and fever. Biological findings include liver abnormalities, leukocytosis, eosinophilia, atypical lymphocytosis, and reactivation of certain human herpes viruses. In DRESS, liver, kidneys, and lungs are frequently involved in disease evolution. Patients with serious systemic involvement are treated with oral corticosteroids, and full recovery is achieved in the majority of cases. DRESS is a rare disease, and little is known about factors that predict its occurrence. The key features of this reaction are eosinophil involvement, the role of the culprit drug, and virus reactivation that trigger an inappropriate systemic immune response in DRESS patients. Interestingly, it was evidenced that at-risk individuals within a genetically restricted population shared a particular HLA loci. In this respect, a limited number of well-known drugs were able to induce DRESS. This review describes the up-to-date advances in our understanding of the pathogenesis of DRESS.

The association between oxcarbazepine-induced maculopapular eruption and HLA-B alleles in a northern Han Chinese population

Background

We investigated the association between oxcarbazepine (OXC)-induced maculopapular eruption (MPE) and HLA-B alleles in a northern Han Chinese population, and conducted an analysis of clinical risk factors for OXC-MPE.

Methods

Forty-two northern Han Chinese patients who had been treated with OXC in Changchun, China were genotyped. Among them were 14 cases with OXC-induced MPE; the remaining 28 were OXC-tolerant. The HLA-B allele frequencies of the normal control group were found in the Allele Frequency Net Database. Polymerase chain reaction-sequence specific primer( PCR-SSP )was used for HLA-B*1502 testing and direct sequencing for four-digit genotype determination.

Results

Four-digit allele sequencing showed that there was no statistically significant difference in the frequency of the HLA-B*1502 allele between the OXC-MPE and OXC-tolerant controls (3.6% versus 7.5%, OR = 0.38, 95% CI = 0.04–3.40, P = 0.65), as well as between OXC-MPE and normal controls (3.6% versus 2.4%, OR = 1.54, 95% CI = 0.20–11.73, P = 0.49). However, a significant difference in the frequency of HLA-B*3802 alleles was found between the MPE group and normal controls (10.7% versus 1.9%, OR = 6.329, 95% CI = 1.783-22.460, P = 0.018). There was no significant difference in terms of age, gender, or final OXC dose between the OXC-MPE and OXC-tolerant groups.

Conclusions

There was no significant association between OXC-MPE and HLA-B*1502 in the northern Han Chinese population in our study. Instead, HLA-B*3802 was found to be a potential risk factor for OXC-MPE.

Genome-wide association study identifies HLA-A*3101 allele as a genetic risk factor for carbamazepine-induced cutaneous adverse drug reactions in Japanese population

An anticonvulsant, carbamazepine (CBZ), is known to show incidences of cutaneous adverse drug reactions (cADRs) including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN) and drug-induced hypersensitivity syndrome (DIHS). To identify a gene(s) susceptible to CBZ-induced cADRs, we conducted a genome-wide association study (GWAS) in 53 subjects with the CBZ-induced cADRs, including SJS, TEN and DIHS, and 882 subjects of a general population in Japan. Among the single nucleotide polymorphisms (SNPs) analyzed in the GWAS, 12 SNPs showed significant association with CBZ-induced cADRs, and rs1633021 showed the smallest P-value for association with CBZ-induced cADRs (P = 1.18 × 10⁻¹³). These SNPs were located within a 430 kb linkage disequilibrium block on chromosome 6p21.33, including the HLA-A locus. Thus, we genotyped the individual HLA-A alleles in 61 cases and 376 patients who showed no cADRs by administration of CBZ (CBZ-tolerant controls) and found that HLA-A*3101 was present in 60.7% (37/61) of the patients with CBZ-induced cADRs, but in only 12.5% (47/376) of the CBZ-tolerant controls (odds ratio = 10.8, 95% confidence interval 5.9-19.6, P = 3.64 × 10⁻¹⁵), implying that this allele has the 60.7% sensitivity and 87.5% specificity when we apply HLA-A*3101 as a risk predictor for CBZ-induced cADRs. Although DIHS is clinically distinguished from SJS and TEN, our data presented here have indicated that they share a common genetic factor as well as a common pathophysiological mechanism. Our findings should provide useful information for making a decision of individualized medication of anticonvulsants.

Processing-dependent and -independent pathways for recognition of iodinated contrast media by specific human T cells

BACKGROUND

One to three percent of patients exposed to intravenously injected iodinated contrast media (CM) develop delayed hypersensitivity reactions. Positive patch test reactions, immunohistological findings, and CM-specific proliferation of T cells in vitro suggest a pathogenetic role for T cells. We have previously demonstrated that CM-specific T cell clones (TCCs) show a broad range of cross-reactivity to different CM. However, the mechanism of specific CM recognition by T cell receptors (TCRs) has not been analysed so far.

OBJECTIVE

To determine how T cells specifically recognize CM.

METHODS

CM-specific TCCs were generated from human blood of three CM-allergic patients and a specific TCR was transfected into a mouse T cell hybridoma. Functional analysis such as proliferation assays, IL-2 secretion assays, and calcium influx experiments were performed using irradiated, glutaraldehyde-fixed, CM-pre-incubated, human leucocyte antigen (HLA)-DR-matched or -mismatched antigen-presenting cells (APCs), and HLA-blocking antibodies.

RESULTS

We identified two mechanisms of T cell stimulation: some TCCs and the transfectant reacted to CM independent of uptake by APCs because proliferation/IL-2 secretion occurred in the presence of glutaraldehyde-fixed APCs, and intracellular calcium increased within seconds after drug addition. Other TCCs required functional APCs, compatible with uptake and presentation of CM on MHC-class II molecules, as implied by three findings: (1) glutaraldehyde fixation of APCs abrogated presentation; (2) CM could not be washed away from CM-pre-incubated APCs; and (3) the optimal pulsing time was 10-20 h. Because allogeneic, MHC-matched, CM-pulsed APCs could induce proliferative responses as well, the ability of CM uptake and presentation is not unique to APCs from patients with CM-induced delayed hypersensitivity.

CONCLUSION

Our data suggest that CM may be stimulatory for T cells either by direct binding to the MHC-TCR complex or by binding after uptake and processing by APCs. This questions the assumed inert nature of CM.

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

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

Role of Metabolism in Drug-Induced Idiosyncratic Hepatotoxicity

Rare adverse reactions to drugs that are of unknown etiology, or idiosyncratic reactions, can produce severe medical complications or even death in patients. Current hypotheses suggest that metabolic activation of a drug to a reactive intermediate is a necessary, yet insufficient, step in the generation of an idiosyncratic reaction. We review evidence for this hypothesis with drugs that are associated with hepatotoxicity, one of the most common types of idiosyncratic reactions in humans. We identified 21 drugs that have either been withdrawn from the U.S. market due to hepatotoxicity or have a black box warning for hepatotoxicity. Evidence for the formation of reactive metabolites was found for 5 out of 6 drugs that were withdrawn, and 8 out of 15 drugs that have black box warnings. For the other drugs, either evidence was not available or suitable studies have not been carried out. We also review evidence for reactive intermediate formation from a number of additional drugs that have been associated with idiosyncratic hepatotoxicity but do not have black box warnings. Finally, we consider the potential role that high dosages may play in these adverse reactions.

Cytokine Profiling in Abacavir Hypersensitivity Patients

Background

Abacavir hypersensitivity in genetically susceptible individuals implicates an abacavir-specific T-cell response to either the parent drug or a metabolite generated in vivo. We have analysed the cytokine profile in antigen-presenting cells and the T-lymphocytes that are involved in the pathological immune response to abacavir.

Methods

In this study, we compared abacavir-specific cytokine responses in cultured peripheral blood mononuclear cells (PBMCs) from HIV-infected abacavir hypersensitive, tolerant and naive individuals. Cells were cultured in the presence or absence of abacavir. Cytokine expression was determined by microarray analysis, enzyme-linked immunosorbent assays and flow cytometry.

Results

We demonstrated using in vitro models of immune activation that the production of interferon-γwas specifically induced by abacavir treatment in PBMCs obtained from hypersensitive patients carrying the HLA-B*5701 allele (median 123.86 compared with -30.83 for tolerant controls, P=0.001).

Conclusion

These results provide further insight into the immunological and metabolic basis of abacavir hypersensitivity syndrome. In vitro assays could assist in the identification of susceptible loci by providing a surrogate marker for the hypersensitivity reaction. Such a marker could be studied in unexposed individuals to shed further light on the immunopathogenesis of the abacavir hypersensitivity syndrome.

Predicting and diagnosing abacavir and nevirapine drug hypersensitivity: from bedside to bench and back again

There is a growing discussion surrounding the issue of personalized approaches to drug prescription based on an individual's genetic makeup. This field of investigation has focused primarily on identifying genetic factors that influence drug metabolism and cellular disposition, thereby contributing to dose-dependent toxicities and/or variable drug efficacy. However, pharmacogenetic approaches have also proved valuable in predicting drug hypersensitivity reactions in selected patient populations, including HIV-infected patients receiving long-term antiretroviral therapy. In this instance, susceptibility has been strongly linked to genetic loci involved in antigen recognition and presentation to the immune system--most notably within the major histocompatibility complex (MHC) region--consistent with the notion that hypersensitivity reactions represent drug-specific immune responses that are largely dose independent. Here the authors describe their experiences with the development of pharmacogenetic approaches to hypersensitivity reactions associated with abacavir and nevirapine, two commonly prescribed antiretroviral drugs. It is demonstrated that prospective screening tests to identify and exclude individuals with a certain genetic makeup may be largely successful in decreasing or eliminating incidence of these adverse drug reactions in certain populations. This review also explores the broader implications of these findings.

Clinical Pharmacology

The dose of a drug is a major determinant of its safety, and establishing a safe dose of a novel drug is a prime objective during clinical development. The design of pre-marketing clinical trials precludes the representation of important subpopulations such as children, the elderly and people with co-morbidities. Therefore, postmarketing surveillance (PMS) activities are required to monitor the safety profile of drugs in real clinical practice. Furthermore, individual variations in pharmacogenetic profiles, the immune system, drug metabolic pathways and drug-drug interactions are also important factors in the occurrence of adverse drug reactions. Thus, the safety of a drug is a major clinical consideration before and after it is marketed. A multidisciplinary approach is required to enhance the safety profile of drugs at all stages of development, including PMS activities. Clinical pharmacology encompasses a range of disciplines and forms the backbone of drug safety consideration during clinical drug development. In this review we give an overview of the clinical drug development process and consider its limitations. We present a discussion of several aspects of clinical pharmacology and their application to enhancing drug safety. Pharmacokinetic-pharmacodynamic modelling provides a method of predicting a clinically safe dose; consideration of drug pharmacokinetics in special populations may enhance safe therapeutics in a wider spectrum of patients, while pharmacogenetics provides the possibility of genotype-specific therapeutics. Pharmacovigilance activities are also discussed. Given the complex nature and unpredictability of type B reactions, PMS activities are crucial in managing the risks drugs pose to the general population. The various aspects of clinical pharmacology discussed make a strong case for this field as the backbone of optimising and promoting safe development and use of drugs.

Degeneracy and additional alloreactivity of drug-specific human alpha beta(+) T cell clones

It has been well established that T cells can recognize small mol. wt compounds such as drugs. Results from previous studies revealing a high heterogeneity and cross-reactivity of drug-specific T cell clones (TCC) in individual patients prompted us to analyze the degeneracy of drug-reactive TCR in detail. Hence, we analyzed the MHC restriction pattern of a panel of 100 drug-specific TCC isolated from different drug-allergic donors. We found that 28 of the tested clones showed an MHC allele-unrestricted drug recognition. Most of these clones were at the same time highly drug specific, i.e. they could only be stimulated by the original drug and not by any drug derivatives. In contrast, TCC with the ability to interact with different drug derivatives displayed a clearly MHC allele-restricted drug recognition. Therefore, we concluded that the TCR of these clones is mainly interacting with side chains of the appropriate drug molecules and hence able to tolerate alterations in the MHC molecule. Moreover, we tested all clones for additional alloreactivity and found that 27 clones could be stimulated by a self-MHC--peptide--drug complex as well as by a non-self-MHC--peptide complex. This cross-reactivity with allogeneic MHC molecules was substantially higher in drug-specific TCC compared to tetanus toxoid-specific clones from the same donors. This suggests that from the point of view of drug-specific TCR, non-self-MHC--peptide complexes have a higher incidence to mimic the 'original' self-MHC--peptide-drug complex and this may occur for TCR recognizing self-MHC--pathogen-derived peptide complexes. Finally, the biological functions of bispecific TCC were not influenced by the nature of the stimulating ligand. Both drug as well as allogeneic stimulation led to similar reaction patterns in the analyzed TCC.

Metabolic activation in drug allergies

Drug allergies are a major problem in the clinic and during drug development. At the present time, it is not possible to predict the potential of a new chemical entity to produce an allergic reaction (hypersensitivity) in patients in preclinical development. Such adverse reactions, because of their idiosyncratic nature, only become apparent once the drug has been licensed. Our present chemical understanding of drug hypersensitivity is based on the hapten hypothesis, in which covalent binding of the drug (metabolite) plays a central role in drug immunogenicity and antigenicity. If this theory is correct, then it should be possible to develop in vitro systems to assess the potential of drugs to bind to critical proteins, either directly or indirectly after metabolic activation to protein-reactive metabolites (bioactivation) and initiate hypersensitivity. The purpose of this review is to assess critically the evidence to support the hapten mechanism, and also to consider alternative mechanisms by which drugs cause idiosyncratic toxicity.

Recognition of local anesthetics by alphabeta+ T cells

Patients with drug allergy show a specific immune response to drugs. Chemically nonreactive drugs like, for example, local anesthetics are directly recognized by alphabeta+ T cells in an HLA-DR restricted way, as neither drug metabolism nor protein processing is required for T cell stimulation. In this study we identified some of the structural requirements that determine cross-reactivity of T cells to local anesthetics, with the aim to improve the molecular basis for the selection of alternatives in individuals sensitized to a certain local anesthetic and to better understand presentation and T cell recognition of these drugs. Fifty-five clones (52 lidocaine specific, three mepivacaine specific from two allergic donors) were analyzed. Stimulatory compounds induced a down-regulation of the T cell receptor, demonstrating that these non-peptide antigens are recognized by the T cell receptor itself. A consistent cross-reactivity between lidocaine and mepivacaine was found, as all except one lidocaine specific clone proliferated to both drugs tested. Sixteen chemically related local anesthetics (including ester local anesthetics, OH- and desalkylated metabolites) were used to identify structural requirements for T cell recognition. Each of the four clones examined in detail was uniquely sensitive to changes in the structures of the local anesthetic: clone SFT24, i.e., did not recognize any of the tested OH- or desalkylated metabolites, while the clone OFB2 proliferated to all OH-metabolites and other differently modified molecules. The broadly reactive clone OFB2 allowed us to propose a model, suggesting that the structure of the amine side chain of local anesthetics is essential for recognition by the T cell receptor.

Molecular mechanisms of CD8+ T cell-mediated delayed hypersensitivity: implications for allergies, asthma, and autoimmunity

Delayed-type hypersensitivity (DTH) is defined as the recruitment of T cells into tissues to be activated by antigen-presenting cells to produce cytokines that mediate local inflammation. CD8+ T cells are now known to mediate DTH responses in allergic contact dermatitis, drug eruptions, asthma, and autoimmune diseases. This inflammatory effector capability of CD8+ cytotoxic T cells was previously poorly recognized, but there is now considerable evidence that these diseases may be mediated by CD8+ DTH. The difference between CD8+ T cells and CD4+ T cells mediating DTH relates to the molecular mechanisms by which antigens are processed and presented to the T cells. Antigens external to the cell are phagocytosed and processed for presentation on MHC class II molecules (eg, HLA-DR) to CD4+ T cells. In contrast, internal cytoplasmic antigens are processed by the endogenous pathway for presentation on MHC class I molecules (eg, HLA-A, -B, and -C) to CD8+ T cells. External allergens can also enter the endogenous pathway to be presented to CD8+ T cells. These include many contact sensitizers, chemical and protein respiratory allergens, viral antigens, metabolic products of drugs, and autoantigens. The resulting CD8+ T-cell response explains the role of CD8+ T-cell DTH mechanisms in allergic contact dermatitis, asthma, drug eruptions, and autoimmune diseases.