CD8+ dermal T cells from a sulphamethoxazole-induced bullous exanthem proliferate in response to drug-modified liver microsomes

Viral infections and drug hypersensitivity

Virus infections and T-cell-mediated drug hypersensitivity reactions (DHR) can influence each other. In most instances, systemic virus infections appear first. They may prime the reactivity to drugs in two ways: First, by virus-induced second signals: certain drugs like β-lactam antibiotics are haptens and covalently bind to various soluble and tissue proteins, thereby forming novel antigens. Under homeostatic conditions, these neo-antigens do not induce an immune reaction, probably because co-stimulation is missing. During a virus infection, the hapten-modified peptides are presented in an immune-stimulatory environment with co-stimulation. A drug-specific immune reaction may develop and manifest as exanthema. Second, by increased pharmacological interactions with immune receptors (p-i): drugs tend to bind to proteins and may even bind to immune receptors. Without viral infections, this low affine binding may be insufficient to elicit T-cell activation. During a viral infection, immune receptors are more abundantly expressed and allow more interactions to occur. This increases the overall avidity of p-i reactions and may even be sufficient for T-cell activation and symptoms. There is a situation where the virus-DHR sequence of events is inversed: in drug reaction with eosinophilia and systemic symptoms (DRESS), a severe DHR can precede reactivation and viremia of various herpes viruses. One could explain this phenomenon by the massive p-i mediated immune stimulation during acute DRESS, which coincidentally activates many herpes virus-specific T cells. Through p-i stimulation, they develop a cytotoxic activity by killing herpes peptide-expressing cells and releasing herpes viruses. These concepts could explain the often transient nature of DHR occurring during viral infections and the often asymptomatic herpes-virus viraemia after DRESS.

Synthetic antigenic determinants of clavulanic acid induce dendritic cell maturation and specific T cell proliferation in patients with immediate hypersensitivity reactions

BACKGROUND

Immediate drug hypersensitivity reactions (IDHRs) to clavulanic acid (CLV) have increased in the last decades due to a higher consumption alongside amoxicillin (AX). Due to its chemical instability, diagnostic procedures to evaluate IDHRs to CLV are difficult, and current in vitro assays do not have an optimal sensitivity. The inclusion of the specific metabolites after CLV degradation, which are efficiently recognised by the immune system, could help to improve sensitivity of in vitro tests.

METHODS

Recognition by dendritic cells (DCs) of CLV and the synthetic analogues of two of its hypothesised antigenic determinants (ADs) was evaluated by flow cytometry in 27 allergic patients (AP) and healthy controls (HC). Their ability to trigger the proliferation of T cells was also analysed by flow cytometry.

RESULTS

The inclusion of synthetic analogues of CLV ADs, significantly increased the expression of maturation markers on DCs from AP compared to HC. A different recognition pattern could be observed with each AD, and, therefore, the inclusion of both ADs achieves an improved sensitivity. The addition of synthetic ADs analogues increased the proliferative response of CD4⁺ Th2 compared to the addition of native CLV. The combination of results from both ADs increased the sensitivity of proliferative assays from 19% to 65% with a specificity higher than 90%.

CONCLUSIONS

Synthetic ADs from CLV are efficiently recognised by DCs with ability to activate CD4⁺ Th2 cells from AP. The combination of analogues from both ADs, significantly increased the sensitivity of DC maturation and T-cell proliferation compared to native CLV.

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.

In-Vitro Approaches to Predict and Study T-Cell Mediated Hypersensitivity to Drugs

Mitigating the risk of drug hypersensitivity reactions is an important facet of a given pharmaceutical, with poor performance in this area of safety often leading to warnings, restrictions and withdrawals. In the last 50 years, efforts to diagnose, manage, and circumvent these obscure, iatrogenic diseases have resulted in the development of assays at all stages of a drugs lifespan. Indeed, this begins with intelligent lead compound selection/design to minimize the existence of deleterious chemical reactivity through exclusion of ominous structural moieties. Preclinical studies then investigate how compounds interact with biological systems, with emphasis placed on modeling immunological/toxicological liabilities. During clinical use, competent and accurate diagnoses are sought to effectively manage patients with such ailments, and pharmacovigilance datasets can be used for stratification of patient populations in order to optimise safety profiles. Herein, an overview of some of the in-vitro approaches to predict intrinsic immunogenicity of drugs and diagnose culprit drugs in allergic patients after exposure is detailed, with current perspectives and opportunities provided.

Association of CD8(+) T lymphocyte repertoire spreading with the severity of DRESS syndrome

T-cell receptor (TCR)-mediated cross-recognition is a major mechanism in the pathogenesis of drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome. However, the characteristics of the TCR repertoire and the clinical significance of repertoire reformation throughout the course of DRESS are unknown. Here, we isolated CD4(+) and CD8(+) T-cells from peripheral blood of 8 DRESS patients at 10-day intervals and, sequenced CDR3-regions of the TCRB chain by high-throughput sequencing to analyze the dynamic reformation in the T-cell repertoire hierarchy. Compared with healthy donors, T-cell expanded in peripheral repertoires from DRESS patient. The extent of fluctuation of dominant CD8(+) T-cell clones, but not of CD4(+) counterparts, correlated positively with the clinical severity and helped classify the enrolled subjects into "fluctuant" and "flat" repertoire groups. The anti-herpesvirus response, which was measured using anti-EBV/HHV antibodies, and the proportion of the homologous CD8(+) EBV-specific clonotypes, in the "fluctuant" group was substantial higher than that in the "flat" group. Furthermore, autoimmune sequelae were observed in a cured "fluctuant" patient. Collectively, the clinical relevance of the fluctuant CD8(+) T-cell repertoires supports the notion that herpes virus-mediated continuously de novo priming of newly pathogenic CD8(+) T-cell clones is an alternate mechanism responsible for the pathogenicity of DRESS.

Immunologic evaluation of drug allergy

Hypersensitivity drug reactions (HDR) consist of an individual abnormal response with the involvement of the immunological system. In addition to specific immunological mechanisms where specific antibodies or sensitised T cells participate, release of inflammatory mediators by non-specific immunological recognition may also occur. Within this category are one of the most common groups of drugs, the non-steroidal anti-inflammatory drugs. In addition to chemical drugs new emerging ones with an increasing protagonism are biological agents like humanised antibodies and others. For IgE dependent reactions both in vivo and in vitro tests can be used for the immunological evaluation. Sensitivity of these is not optimal and very often a drug provocation test must be considered for knowing the mechanism involved and/or establishing the diagnosis. For non-immediate reactions also both in vivo and in vitro tests can be used. Sensitivity for in vivo tests is generally low and in vitro tests may be needed for the immunological evaluation. Immunohistochemical studies of the affected tissue enable a more precise classification of non-immediate reactions. The monitorization of the acute response of the reactions has given clues for understanding these reactions and has promising results for the future of the immunological evaluation of HDR.

Drug allergy: an updated practice parameter

Adverse drug reactions (ADRs) result in major health problems in the United States in both the inpatient and outpatient setting. ADRs are broadly categorized into predictable (type A and unpredictable (type B) reactions. Predictable reactions are usually dose dependent, are related to the known pharmacologic actions of the drug, and occur in otherwise healthy individuals, They are estimated to comprise approximately 80% of all ADRs. Unpredictable are generally dose independent, are unrelated to the pharmacologic actions of the drug, and occur only in susceptible individuals. Unpredictable reactions are subdivided into drug intolerance, drug idiosyncrasy, drug allergy, and pseudoallergic reactions. Both type A and B reactions may be influenced by genetic predisposition of the patient

CD8+ T cells mediate skin allergy to amoxicillin in a mouse model

BACKGROUND

Delayed allergic skin reactions to drugs are common iatrogenic diseases mediated by activation of specific T cells in the skin.

METHODS

To better understand the role of T cells in these diseases, we developed a mouse model of drug allergy induced by skin sensitization to amoxicillin (amox), a penicillin antibiotic frequently involved in delayed drug allergy.

RESULTS

Whereas wild-type mice could not be sensitized to amox, CD4+ T-cell-deficient mice developed an amox-specific allergic skin response, mediated by IFN-gamma-producing CD8+ T cells. Amox-specific CD8+ T cells, induced in lymphoid organs at a high frequency during sensitization, were recruited in the skin upon challenge. CD8+ T cells were effectors of the allergic skin reaction to amox as in vivo treatment with depleting anti-CD8 mAbs abrogated the skin inflammatory reaction and as purified CD8+ T cells could adoptively transfer the allergic response to naive recipients.

CONCLUSION

CD8+ T cells mediate penicillin skin allergy.

[Pharmacogenetics]

Allergic reactions to drugs belong to the group of B-reactions, which are characterized not only by the pharmacologic profile of the drug but also by individual risk factors. Pharmacogenetic approaches facilitate identifying these risk factors. The most important example for Caucasian patients is NIDR (non-immediate drug reaction) to abacavir. Chinese patients possess risk factors for NIDR to allopurinol and anticonvulsants and the HLA locus on chromosome 6. Another potentially important area is assessing risk factors to prevent allergic reactions to antibiotics, especially with regard to the effective treatment of MRSA.

Immune mediation of hypersensitivity adverse drug reactions: implications for therapy

Adverse drug reactions are among the top causes of death in the developed world, and among the spectrum of adverse drug reactions, drug hypersensitivity is a principal contributor to serious adverse drug events. The pathophysiology of drug hypersensitivity remains incompletely understood, but seems to involve the initial recognition of a drug or metabolite by the immune system followed by an immune response that determines the clinical manifestations. At present, there are two competing theories for how immune recognition occurs: the Hapten Hypothesis in which drug hapten-carrier association is the key driver for immune recognition and the Pharmacological Interference Concept that postulates direct recognition of drugs by low affinity association with the T cell receptor. The Danger Hypothesis provides a potentially important addition to the Hapten Hypothesis. Therapy for drug hypersensitivity has traditionally involved excellent supportive care. Although corticosteroids and intravenous immunoglobulin have both been used as immunomodulatory therapy, there is no robust evidence supporting the efficacy of their therapy for drug hypersensitivity. Recent advances in molecular biology and genomic pharmacology offer previously unappreciated opportunities to clarify the controversies surrounding drug hypersensitivity and to better diagnose, treat and, it is hoped, prevent drug hypersensitivity in the future.

Role of T cells in nonimmediate allergic drug reactions

PURPOSE OF REVIEW

This review presents the current knowledge of the role of T cells in drug allergy manifesting as exanthematous, pustular and bullous skin diseases, collectively referred to as nonimmediate allergic drug reactions.

RECENT FINDINGS

Both CD4+ and CD8+ T cells producing type 1 and type 2 cytokines and endowed with cytotoxic properties are involved in nonimmediate allergic drug reactions. Recent studies have confirmed that CD8+ T cells play a major role in the pathophysiology of nonimmediate allergic drug reactions, and have characterized new cytotoxic molecular pathways responsible for the severity of the bullous forms of nonimmediate allergic drug reactions.

SUMMARY

Nonimmediate allergic drug reactions are mediated by T cells and mostly affect the skin. Nonimmediate allergic drug reactions comprise several diseases ranging from the frequent and benign maculo-papular exanthema to the severe and rare toxic epidermal necrolysis. Progress in the knowledge of the pathophysiology of nonimmediate allergic drug reactions comes from a better understanding of the mechanisms of drug recognition by T cells and from a careful analysis of the phenotype and functions of CD4+ and CD8+ T cells infiltrating the skin lesions. Recent studies have confirmed that the different clinical forms of nonimmediate allergic drug reactions are associated with distinct types of T cell-mediated skin inflammation. However, CD8+ T cells appear as major effector T cells in most of the nonimmediate allergic drug reactions. Future studies to analyze the early cellular and molecular events leading to the development of the allergic skin reaction will be helpful in order to define diagnostic and therapeutic targets.

Reactive metabolites and agranulocytosis

Central to most hypotheses of the mechanism of idiosyncratic drug-induced blood dyscrasias is the involvement of reactive metabolites. In view of the reactive nature of the majority of such metabolites, it is likely that they are formed by, or in close proximity to the blood cells affected. The major oxidative system of neutrophils generates hypochlorous acid. We have demonstrated that the drugs associated with the highest incidence of agranulocytosis are oxidized to reactive metabolites by hypochlorous acid and/or activated neutrophils. There are many mechanisms by which such reactive metabolites could induce agranulocytosis. In the case of aminopyrine-induced agranulocytosis, most cases appear to involve drug-dependent anti-neutrophil antibodies, and these are likely to be induced by cell membrane antigens modified by the reactive metabolite of aminopyrine. The target of agranulocytosis associated with many other drugs is usually neutrophil precursors and may involve cytotoxicity or a cell-mediated immune reaction induced by a reactive metabolite. In the case of aplastic anaemia, there is evidence in some cases for involvement of cytotoxic T cells, which could either be induced by metabolites generated by neutrophils, or more likely, by reactive metabolites generated by stem cells.

Erythema multiforme and related disorders

Erythema multiforme (EM) and related disorders comprise a group of mucocutaneous disorders characterized by variable degrees of mucosal and cutaneous blistering and ulceration that occasionally can give rise to systemic upset and possibly compromise life. The clinical classification of these disorders has often been variable, thus making definitive diagnosis sometimes difficult. Despite being often caused by, or at least associated with, infection or drug therapy, the pathogenic mechanisms of these disorders remain unclear, and as a consequence, there are no evidence-based, reliably effective therapies. The present article reviews aspects of EM and related disorders of relevance to oral medicine clinical practice and highlights the associated potential etiologic agents, pathogenic mechanisms and therapies.

Generation and characterization of antigen-specific CD4+, CD8+, and CD4+CD8+ T-cell clones from patients with carbamazepine hypersensitivity

BACKGROUND

Hypersensitivity is a serious manifestation of anticonvulsant therapy characterized by infiltration of the epidermis and dermis by activated CD8(+) and CD4(+) T-cells, respectively. Attempts to characterize drug-specific CD8(+) T cells have been largely unsuccessful.

OBJECTIVES

The aim of these studies was to generate and characterize CD4(+), CD8(+), and CD4(+)CD8(+) T cells in patients with carbamazepine hypersensitivity.

METHODS

Carbamazepine-specific T-cell clones were generated from 5 patients by using modified cloning methodologies. Cell surface receptor phenotype, functionality, and mechanisms of antigen presentation were then compared.

RESULTS

Ninety CD4(+), 23 CD8(+), and 14 CD4(+)CD8(+) carbamazepine-specific T-cell clones were generated. CD4(+) T-cell clones proliferated vigorously with carbamazepine associated with MHC class II but exhibited little cytotoxic activity. In contrast, most CD8(+) T cells proliferated weakly but effectively killed target cells via an MHC class I or MHC class II restricted, perforin-dependent pathway. CD4(+)CD8(+) T cells displayed characteristics similar to those of CD4(+) T cells; however, drug stimulation was demonstrable in the absence of antigen-presenting cells. Carbamazepine was presented to CD4(+), CD8(+), and CD4(+)CD8(+) T cells in the absence of antigen processing. Drug stimulation resulted in the secretion of IFN-gamma and IL-5. A panel of CD11a(+)CD27(-) clones differentially expressed the receptors CXCR4, CCR4, CCR5, CCR8, CCR9, and CCR10.

CONCLUSION

Carbamazepine-specific CD4(+), CD8(+), and CD4(+)CD8(+) T cells exist in the peripheral circulation of hypersensitive patients, often many years after the resolution of clinical manifestations.

CLINICAL IMPLICATIONS

Carbamazepine-specific CD4(+), CD8(+), and CD4(+)CD8(+) T cells displaying different effector functions and homing characteristics persist in hypersensitive patients' blood for many years after resolution of clinical symptoms.

Concepts in molecular dermatotoxicology

In the recent years, molecular research has successfully elucidated some of the major mechanisms through which environmental noxae damage human skin. From this knowledge, novel concepts for skin protection have been developed. Here, we provide a brief overview of some of the most exciting and intriguing concepts in molecular dermatotoxicology.

Immune mechanisms in drug allergy

Clinicians had suspected for years that drug eruptions were probably mediated by immune mechanisms because their timing suggested sensitization and specific immunologic memory rather than direct toxicity. An immune response to medications was also demonstrated by positive skin tests and by several types of in vitro tests that evidenced immediate or delayed hypersensitivity. In the last decade several teams of researchers obtained in vitro drug-specific human T-cell clones, in a variety of clinical types of drug eruptions. These clones were produced from blood or skin mononuclear cells of patients with a history of drug reaction by stimulation in vitro with drug. They were either of CD4 or CD8 phenotypes. Drug specific clones were stimulated by the parent drug much more often than by reactive metabolites. That challenged the classical "hapten hypothesis" that the immune response was initiated by reactive metabolites combined to self proteins. The medication usually stimulated specific T-cells after non-covalent binding to major histocompatibility (MHC) molecules on antigen presenting cells. In toxic epidermal necrolysis, T-lymphocytes present at the site of lesions, exhibited a drug specific cytotoxicity against autologous target cells, or allogeneic cells that shared the same HLA than autologous cells. This MHC class I restriction and mediation of death by perforin/granzyme release, is the classical behavior of cytotoxic T lymphocytes, like those operating in the reject of a transplanted organ. MHC restriction could explain the key role of HLA genes as predisposing factors to severe drug reactions. A strong association between HLA and hypersensitivity to abacavir, SJS or TEN to carbamazepine or allopurinol has been recently demonstrated. Resemblance to graft rejection points to the possible therapeution value of immuno suppressive agents. Most drug eruptions appear to result from T-cell mediated delayed hypersensitivity. The secondary activation of different cascades of cytokines, may contribute to the heterogeneity of clinical presentations.

Diagnosis of drug hypersensitivity: lymphocyte transformation test and cytokines

For all types of allergic reactions including immediate type of reactions, types II and III reactions as well as delayed-type reactions the recognition of the antigen by specifically sensitized T-lymphocytes is a prerequisite. Evidences for the key role of T-lymphocytes in the pathophysiology of allergic drug reactions are positive patch test reactions and the LTT. The proliferative response that can be measured by means of the incorporation of 3H-thymidine during DNA synthesis can be expressed as stimulation index (SI) which is the relation between the cell proliferation with antigen compared without antigen. In addition drug-specific activation of PBMC consistently resulted in IL-5 expression and secretion. The sensitivity of the LTT for the detection of drug sensitization could be improved up to 92% by the measurement of released interleukin-5. The expression and secretion of other cytokines such as IFN-gamma and IL-10 was less consistently and had a diagnostic sensitivity of 36 and 50%, respectively. Microarrays are a promising new technical platform to look for better markers which can be used as a read out in the LTT and other similar assays and to study pharmacological interactions between drugs including cytokines such as interferons and the immune system.

The lymphocyte transformation test in the diagnosis of drug hypersensitivity

Diagnosis of drug hypersensitivity is difficult, as an enormous amount of different drugs can elicit various immune-mediated diseases with distinct pathomechanism. The lymphocyte transformation test (LTT) measures the proliferation of T cells to a drug in vitro--from which one concludes to a previous in vivo reaction due to a sensitization. This concept of the LTT has been confirmed by the generation of drug-specific T-cell clones and the finding that drugs can directly interact with the T-cell receptor, without previous metabolism or need to bind to proteins. In this review, technical aspects and usefulness of this test for the diagnosis of drug hypersensitivity are discussed. The main advantage of this test is its applicability with many different drugs in different immune reactions, as drug-specific T cell are almost always involved in drug hypersensitivity reactions. Its main disadvantages are that an in vitro proliferation of T cells to a drug is difficult to transfer to the clinical situation and that the test per se is rather cumbersome and technically demanding. In addition, its sensitivity is limited (for beta-lactam allergy it is in the range of 60-70%), - although at least in our hands - it is higher than of other tests for drug hypersensitivity diagnosis. Consequently, drug hypersensitivity diagnosis needs to rely on a combination of history and different tests, as none of the single tests available has per se a sufficiently good sensitivity. Within this setting, the LTT has proven to be a useful test for the diagnosis of drug hypersensitivity reactions and helped to better understand these reactions. Further work on the simplification of this test and systematic evaluation of its sensitivity and specificity in some main groups of drugs are necessary to make this test more widely available.

Drug hypersensitivity reactions in skin: understanding mechanisms and the development of diagnostic and predictive tests

Cutaneous manifestations of drug hypersensitivity can be serious and potentially life threatening and may prevent effective drug therapy. T cells play an important role in the pathology of drug hypersensitivity reactions. Classical studies suggest that T-cell activation requires drug bioactivation, covalent binding to protein and antigen processing to stimulate an immune response. Recent studies have shown that drugs can also be presented to T cells in the absence of antigen processing and drug metabolism. In this article, sulfamethoxazole is used as a paradigm to describe the chemical mechanisms involved in the initiation and maintenance of an aberrant drug antigen specific T-cell response. Presentation of the same drug to different individuals can cause a variety of skin diseases. Such reactions have been classified according to the phenotype and functionality of the T-cell response. This review summarises the different forms of cutaneous hypersensitivity reactions and describes how T-cell clones generated from hypersensitive patients have been used to study the cellular mechanisms of anticonvulsant hypersensitivity. Potential uses of in vitro cell culture assays for patient diagnosis and drug evaluation are also discussed.

Gene polymorphisms within the immune system that may underlie drug allergy

Drug allergy encompasses a broad spectrum of different diseases. It occurs in some individuals, whereas it does not occur in many others. This suggests, among others, the involvement of hereditary factors, and thus of gene polymorphisms. Since drug metabolising enzymes as well as the immune system itself may be responsible for drug allergy, gene polymorphisms are relevant in both systems. While already some information exists on gene polymorphisms of drug metabolising enzymes that result in drug allergy, little information is available on gene polymorphisms within the immune system that result in such allergy. This review sets out to provide an avenue for future research aimed at discovering such polymorphisms. To this end, immune mechanisms that underlie drug allergy will be discussed. A pivotal mechanism underlying several types of drug allergy, immediate-type (type I) hypersensitivity, is also a hallmark of asthma, and therefore drug allergy and asthma share a range of candidate genes. Research on asthma has come relatively far in establishing associations of disease with polymorphisms in these genes. Therefore, these polymorphisms and their associations with asthma will be discussed. These studies on asthma provide us with lessons on how to conduct such studies on drug allergy.

Immunoregulation of hapten and drug induced immune reactions

PURPOSE OF REVIEW

Unbalanced immune responses to haptens lead to a variety of diseases, including allergic contact dermatitis to skin sensitizers and drug induced immune reactions. The occurrence, magnitude and persistence of immune responses are modulated by specialized T cell subsets with regulatory function. The purpose of this brief review is to summarize the recent data on the role of regulatory T cells in the control of hapten mediated diseases.

RECENT FINDINGS

Several subsets of regulatory T cells, including T regulatory cell 1-like lymphocytes, and cutaneous lymphocyte associated antigen+ CD4+CD25+ regulatory T cells have been isolated from the skin at sites of hapten challenge. Both cell types suppress specific T cell responses to cutaneous sensitizers, such as nickel.

SUMMARY

Although data concerning the regulation of drug hypersensitivity are lacking, several reports indicate the role of regulatory T cell subsets in allergic contact dermatitis to haptens. The understanding of their role in hapten diseases and the requirement for their in-vivo and in-vitro expansion appears as a critical step for the development of specific desensitization protocols.

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

Administration of carbamazepine (CBZ) causes hypersensitivity reactions clinically characterized by skin involvement, eosinophilia, and systemic symptoms. These reactions have an immune etiology; however, the role of T cells is not well defined. The aim of this study was to characterize the specificity, phenotype, and cytokine profile of CBZ-specific T cells derived from hypersensitive individuals. Proliferation of blood lymphocytes was measured using the lymphocyte transformation test. CBZ-specific T cell clones were generated by serial dilution and characterized in terms of their cluster of differentiation and T cell receptor V beta phenotype. Proliferation, cytotoxicity, and cytokine secretion were measured by [(3)H]thymidine incorporation, (51)Cr release, and enzyme-linked immunosorbent assay, respectively. HLA blocking antibodies were used to study the involvement of antigen-presenting cells. The specificity of the drug T cell receptor interaction was studied using CBZ metabolites and other structurally related compounds. Lymphocytes from hypersensitive patients (stimulation index: 32.1 +/- 24.2 [10 microg ml(-1)]) but not control patients (stimulation index: 1.2 +/- 0.4 [10 microg ml(-1)]) proliferated upon stimulation with CBZ. Of 44 CBZ-specific T cell clones generated, 10 were selected for further analysis. All 10 clones were either CD4+ or CD4+/CD8+, expressed the alpha beta T cell receptor, secreted IFN-gamma, and were cytotoxic. T-cell recognition of CBZ was dependent on the presence of HLA class II (DR/DQ)-matched antigen-presenting cells. The T cell receptor of certain clones could accommodate some CBZ metabolites, but no cross-reactivity was seen with other anticonvulsants or structural analogs. These studies characterize drug-specific T cells in CBZ-hypersensitive patients that are phenotypically different from T cells involved in other serious cutaneous adverse drug reactions.

Immunopharmacology of hypersensitivity reactions to drugs

Drug hypersensitivity reactions are characterized by their unpredictability, lack of simple dose-dependency, host sensitivity, and potentially serious clinical outcome. They occur in a small proportion of patients, and usually the predisposing factors are unknown, although there is increasing evidence for genetic predisposition and disease being significant risk factors. The current understanding of the chemical basis of immune-mediated reactions is based on the hapten hypothesis, which requires drug bioactivation, covalent binding to proteins, followed by uptake, antigen processing, and a polyclonal immune response. The recently proposed "danger hypothesis" can be considered to be an essential addition to the hapten hypothesis. According to the danger hypothesis, the immune response to a drug-derived antigen requires the presence of co-stimulatory signals and cytokines, which propagate and determine the type of immune response. The "danger signal" might result from chemical, physical, or viral stress.

The danger hypothesis--potential role in idiosyncratic drug reactions

Idiosyncratic or type B reactions are characterised by their unpredictability and lack of simple dose-dependency. They occur in a small proportion of patients, and usually the predisposing factors are unknown. A proportion of, but not all, idiosyncratic reactions are immune-mediated. Our understanding of immune-mediated reactions is based on the hapten hypothesis, which requires drug bioactivation, covalent binding to proteins, followed by uptake, antigen processing and a polyclonal immune response. The recently proposed 'danger hypothesis' can be considered to be additive to the hapten hypothesis. The hypothesis states that the immune system only responds when it detects danger. If no danger is detected, tolerance results. Thus, stimulation of an immune response to a drug-protein conjugate (signal 1) requires the presence of co-stimulatory signals and cytokines (signals 2 and 3), which propagate and determine the type of immune response. The nature of the danger signal is poorly defined, and has been proposed to include different forms of stress including chemical, physical and viral. Indeed, there are several examples where the frequency of drug hypersensitivity is increased in the presence of a viral infection, most notably in HIV disease. Nevertheless, this clinical evidence has to be regarded as being circumstantial and more direct experimental evidence is required to understand the role of 'danger' in the overall pathogenesis of drug hypersensitivity reactions.

Covalent binding of the nitroso metabolite of sulfamethoxazole leads to toxicity and major histocompatibility complex-restricted antigen presentation

Treatment with sulfamethoxazole (SMX) can lead to hypersensitivity reactions. T cells from hypersensitive patients recognize either the parent drug and/or the reactive nitroso (SMX-NO) metabolite. In this study, using a novel in vitro rat splenocyte assay, we have investigated the toxicological and immunological consequences of cell surface haptenation by SMX-NO. SMX-NO was found to be unstable in solution; spontaneous transformation yielded appreciable amounts of SMX-hydroxylamine, nitro-SMX, and the previously unknown azoxy and azo dimers within 15 min. Irreversible binding of SMX-NO to cellular protein was demonstrated by flow cytometry, with haptenation being greater on the surface of antigen-presenting cells than on T cells. The consequences of irreversible binding of SMX-NO were examined in two ways. First, haptenation above a threshold level led to a proportionate increase in cell death (both apoptosis and necrosis). Indeed, the cells that became haptenated were the same as those that underwent necrotic cell death. Second, sensitized splenocytes proliferated in the presence of major histocompatibility complex (MHC)-restricted antigen derived from both viable and dead cells haptenated with low and high levels of SMX-NO, respectively. However, direct modification of MHC by SMX-NO was not the mechanism of antigen presentation. The antigenic threshold of SMX-NO for T-cell proliferation and toxicity was estimated to be between 0.5 and 1 microM and 5 to 10 microM, respectively. The potential of SMX-NO to generate a potent antigen and cause cytotoxicity may in combination provide the signals necessary to induce a hypersensitivity reaction to SMX.

Mechanistic perspectives on sulfonamide-induced cutaneous drug reactions

PURPOSE OF REVIEW

Idiosyncratic drug reactions continue to limit the therapeutic utility of sulfonamide drugs because of their associated morbidity and mortality. Cutaneous reactions are the predominant reasons for withdrawal of such drugs from use in patients. As a consequence of the recognized metabolic and immunologic capability of the skin, an understanding of the pathogenic role of this tissue in the development of sulfonamide-induced cutaneous drug reactions may provide insight into the mechanisms and risk factors for these and other adverse drug events.

RECENT FINDINGS

In the present review we discuss currently available mechanistic information, including issues related to drug bioactivation and adduct formation, immunoresponsiveness, and immune dysregulation, for the development of sulfonamide-induced (delayed-type) cutaneous drug reactions. The potential application of findings from several related areas of research are also discussed within the context of the pathogenesis of these cutaneous reactions.

SUMMARY

Despite progress, numerous unresolved issues support the testing of novel hypotheses, the search for additional risk factors, and the need for a global approach, including links between laboratory and clinical paradigms. These issues must be addressed if we are to gain an understanding of the mechanistic bases for these cutaneous drug reactions.

Cellular and molecular pathophysiology of cutaneous drug reactions

Hypersensitivity reactions to drugs can cause a variety of skin diseases like maculopapular, bullous and pustular eruptions. In recent years increasing evidence indicates the important role of T cells in these drug-induced skin diseases. Analysis of such drug-specific T cell clones has revealed that drugs can be recognized by alpha beta-T cell receptors, not only if bound covalently to peptides, but also if the drug binds in a rather labile way to the presenting major histocompatibility complex (MHC)-peptide. This presentation is sufficient to stimulate T cells. In maculopapular exanthema (MPE), histopathological analysis typically shows a dominant T cell infiltration together with a vacuolar interface dermatitis. Immunohistochemical studies demonstrate the presence of cytotoxic CD4+ and to a lesser degree of CD8+ T cells, which contain perforin and granzyme B. They are close to keratinocytes that show signs of cell destruction. Expression of Fas ligand is barely detectable, suggesting that cytotoxic granule exocytosis may be the dominant pathway leading to keratinocyte cell damage. While in MPE, the killing of cells seems to be predominantly mediated by CD4+ T cells, patients with bullous skin disease show a strong CD8+ T cell migration to the epidermis. This is probably due to a preferential presentation of the drug by MHC class I molecules, and a more extensive killing of cells that present drugs on MHC class I molecules. This might lead to bullous skin diseases. In addition to the presence of cytotoxic T cells, drug-specific T cells also orchestrate the inflammatory skin reaction through the release and induction of various cytokines [i.e. interleukin (IL)-5, IL-6, tumor necrosis factor-alpha and interferon-gamma] and chemokines (RANTES, eotaxin or IL-8). The increased expression of these mediators seems to contribute to the generation of tissue and blood eosinophilia, a hallmark of many drug-induced allergic reactions. However, in acute generalized exanthematous pustulosis (a peculiar form of drug allergy), neutrophils represent the predominant cell type within pustules, probably due to their recruitment by IL-8 secreting drug specific T cells and keratinocytes.

Drug specific cytotoxic T-cells in the skin lesions of a patient with toxic epidermal necrolysis

Toxic epidermal necrolysis is an extremely severe drug reaction, manifesting itself by widespread apoptosis of keratinocytes, generally considered to result from Fas/CD95-FasLigand interaction, but of unknown primary mechanism. We looked at the role of cells present in the skin blisters as probable effectors of this immune reaction. In a patient suffering from cotrimoxazole-induced toxic epidermal necrolysis, blister fluid cells were phenotyped by FACS and tested without prior restimulation for cytotoxicity on autologous and allogeneic cells in the presence of the drug. Blister fluid lymphocytes were predominantly CD8+, DR+, CLA+, CD56+ T lymphocytes, perforin positive and expressing preferentially two Vbeta chains of the T cell receptor repertoire. These lymphocytes were cytotoxic only in the presence of the drug towards autologous EBV transformed lymphocytes and towards allogeneic cells sharing HLA-Cw4. Cytotoxicity occurred in the presence of either cotrimoxazole, sulfamethoxazole, or the nitroso metabolite of sulfamethoxazole, but not with the hydroxylamine metabolite of sulfamethoxazole. The lysis was blocked by an anti-MHC class I monoclonal antibody. It was abolished by EGTA and CMA, but neither by anti-fas, brefeldin A, nor by anti-TRAIL receptor monoclonal antibodies, strongly suggesting perforin/granzyme-mediated cytotoxicity, without implication of Fas or TRAIL at this stage. This is direct evidence that T lymphocytes present within the lesions of toxic epidermal necrolysis may exhibit, without any re-stimulation, a drug-specific cytotoxicity against autologous cells. Harboring the markers of classical CTL and MHC class I restriction these lymphocytes reacted against the parent drug and one of its reactive metabolites. These results challenge several current concepts and could support new therapeutic approaches.

T cells in drug allergy

In recent years, increasing evidence has indicated an important role for T cells in various drug-induced diseases. A detailed analysis of patients with various drug allergies revealed the existence of drug-specific T cells in the circulation or in eluate from skin infiltration in bullous, pustular, and maculopapular drug eruptions. The drug-specific T cells use the ab-T cell receptor CD4+ or CD8+ and react with drugs acting as haptens (covalently bound to larger molecules, such as penicillins), but also recognize drugs if they are bound only in a labile way to major histocompatibility complex molecules (noncovalent drug presentation). Functional analysis revealed a predominant IL-5 production by drug-specific CD4+ T cells in maculopapular exanthema (MPE) and bullous skin diseases, while patients with acute generalized exanthematous pustulosis have a peculiar T cell subset secreting high amounts of IL-8. Moreover, in MPE CD4+, perforin+ T cells were found in vitro and in immunohistology that had cytotoxic potential and killed keratinocytes in vitro and in vivo.

Drug metabolism, danger signals, and drug-induced hypersensitivity

One of the most difficult challenges for the practicing allergist/immunologist today is that of evaluating and managing patients who present with histories of drug-induced reactions. Adverse drug reactions are heterogeneous, and a single drug can often cause a multitude of reactions. Because the mechanisms responsible for many of these reactions are not known, they can be, and often are, difficult to classify. Moreover, for those that have features consistent with immune-mediated mechanisms, our diagnostic tools remain limited, because little is known about the relevant immunogenic determinants of most drugs. Despite these challenges, management approaches must be devised for patients who present with histories of drug-induced disease. Simply telling such a patient to avoid all drugs that have been associated with previous adverse events leaves both the patient and the referring physician frustrated. The initial part of this review focuses on exciting current research that is furthering our understanding of the mechanisms responsible for drug-induced reactions. Because it will take time to translate this new information into clinical practice, the latter part of the review focuses on ways to evaluate and manage patients who present with drug-induced reactions using the tools and the knowledge that are currently available.

Antigenicity and immunogenicity of sulphamethoxazole: demonstration of metabolism-dependent haptenation and T-cell proliferation in vivo

Sulphamethoxazole has been associated with the occurrence of hypersensitivity reactions. There is controversy as to whether the immune response is metabolism-dependent or -independent. We have therefore investigated the site of antigen formation and the nature of the drug signal presented to the immune system in vivo. Male Wistar rats were dosed with sulphamethoxazole, sulphamethoxazole hydroxylamine or nitroso sulphamethoxazole. Antigen formation on cell surfaces was determined by flow cytometry using a specific anti-sulphamethoxazole antibody. Immunogenicity was determined by assessment of ex vivo T-cell proliferation. Administration of nitroso sulphamethoxazole, but not sulphamethoxazole or sulphamethoxazole hydroxylamine, resulted in antigen formation on the surface of lymphocytes, splenocytes and epidermal keratinocytes, and a strong proliferative response of splenocytes on re-stimulation with nitroso sulphamethoxazole. Rats dosed with sulphamethoxazole or sulphamethoxazole hydroxylamine did not respond to any of the test compounds. CD4+ or CD8+ depleted cells responded equally to nitroso sulphamethoxazole. The proliferative response to nitroso sulphamethoxazole was seen even after pulsing for only 5 min, and was not inhibited by glutathione. Responding cells produced IFN-gamma, but not IL-4. Haptenation of cells by sulphamethoxazole hydroxylamine was seen after depletion of glutathione by pre-treating the rats with diethyl maleate. Splenocytes from the glutathione-depleted sulphamethoxazole hydroxylamine-treated rats responded weakly to nitroso sulphamethoxazole, but not to sulphamethoxazole or sulphamethoxazole hydroxylamine. Dosing of rats with sulphamethoxazole produced a cellular response to nitroso sulphamethoxazole (but not to sulphamethoxazole or its hydroxylamine) when the animals were primed with complete Freund's adjuvant. These studies demonstrate the antigenicity of nitroso sulphamethoxazole in vivo and provide evidence for the role of drug metabolism and cell surface haptenation in the induction of a cellular immune response in the rat.

In vitro T-cell responses to beta-lactam drugs in immediate and nonimmediate allergic reactions

BACKGROUND

beta-Lactam drugs may induce both cellular and humoral allergic reactions, and there is evidence that T cells play an important role in the pathogenesis of these reactions. The aim of this work was to assess the sensitivity and specificity of the lymphocyte transformation test (LTT) as an in vitro diagnostic tool, in patients with either an immediate or a nonimmediate reaction to penicillin G and/or amoxicillin.

METHODS

Fifty patients with a well-documented history of allergic reactions to beta-lactams (31 immediate and 19 nonimmediate) were studied by means of skin tests (prick and intradermal), radioallergosorbent test (RAST), and, when necessary, controlled administration of the drug. Twenty-eight healthy subjects with good tolerance to penicillins served as controls. LTT was performed in all subjects.

RESULTS

Skin tests were positive in 77.4% of the patients with immediate reactions and in 36.8% of those with nonimmediate reactions. The overall sensitivity of LTT in the allergic patients was 62%, but, when analyzed separately, sensitivity was 64.5% for the immediate group and 57.9% for the nonimmediate group. The LTT specificity was 92.8%.

CONCLUSION

The LTT should be considered a useful in vitro diagnostic tool to identify subjects allergic to penicillins, especially patients with nonimmediate reactions where the LTT has a better diagnostic value than skin tests. Interestingly, positive T-cell proliferative responses can be observed 10 or more years after the occurrence of the reaction without further exposure to the drug.

Characterization of T cell responses to fragrances

Fragrances are worldwide a major cause of allergic contact dermatitis (ACD), a delayed-type hypersensitivity reaction mediated by T lymphocytes. We investigated T cell responses to fragrances using peripheral blood mononuclear cells (PBMC) and T cells from skin lesions of fragrance-allergic patients. The components of a fragrance mixture (eugenol, isoeugenol, geraniol, oak moss, alpha-amyl cinnamic aldehyde, cinnamic aldehyde, cinnamic alcohol, and hydroxycitronellal) that is commonly used in the patch test were studied in vitro in the lymphocyte transformation test (LTT). PBMC from fragrance-allergic patients (n = 32) showed significant stimulations to all eight fragrances. The calculated stimulation indices (SI) varied between 2.1 and 21.8. The influence of metabolic enzymes on T cell stimulation was studied for two fragrances. Interestingly, stimulation of eugenol and isoeugenol was increased in the presence of antigen-modified human liver microsomes (CYP450) or recombinant CYP1A1 in five of seven cases. Furthermore, we established 18 T cell clones (TCC) from a skin lesion reacting specifically to eugenol. FACS analysis revealed that the majority (n = 15, 83%) of TCC were CD3(+), CD4(+), and HLA-DR(+). Seventeen percent (n = 3) of the clones were CD8(+). TCC (n = 4) released significant amounts of IL-2 and IFN-gamma but no IL-4 and IL-5. In addition, CD4(+) TCC (n = 3) showed antigen-induced cytotoxic activities against autologous B cells. In summary, we demonstrated for the first time that fragrance-specific CD4(+) and CD8(+) T lymphocytes are present in fragrance-allergic individuals. In addition, our results suggest that CYPs can be involved in the formation of the nominative antigen.

Induction of delayed-type hypersensitivity to sulfamethoxazole in mice: role of metabolites

Although cutaneous adverse drug reactions (ADRs) are relatively frequent and potentially severe, their mechanisms are poorly understood and no validated predictive experimental model is available. Sulfamethoxazole (SMX) is commonly used to treat infections in HIV-positive patients and severe cutaneous ADRs have been described. This study was undertaken to test whether sensitization to SMX could be achieved in mice using a combination of in vivo and in vitro endpoints. No delayed-type hypersensitivity (DTH) response could be evidenced following SMX injection in the back and subsequent challenge into the footpad or onto the ear. Pretreatment with the enzymatic inducers phenobarbitone and betanaphtoflavone, or depletion in CD4(+) T-lymphocytes were not successful either. In contrast, the injection of SMX/S9 mix in the back and challenge with SMX/S9 mix induced a significant increase in footpad thickness. A significant proliferation of spleen cells from SMX- or SMX/S9 mix-treated mice was evidenced following incubation with SMX/S9 mix, but not SMX alone. This study provides indirect evidence that SMX metabolites are involved and confirms previous in vitro results obtained with lymphocytes from patients with a history of SMX-induced ADRs cultured with murine microsomes. Further investigations using other drugs known to induce similar ADRs are warranted to establish the predictive value of this murine model.

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.

Phagocyte-mediated oxidation in idiosyncratic adverse drug reactions

The drug-metabolizing capacity of the liver is well known but cannot account for most idiosyncratic adverse drug reactions. Of the extrahepatic sources of reactive drug metabolites, the neutrophil has received the most attention because of its vast numbers and robust oxidizing machinery. Many drugs associated with autoimmunity are susceptible to oxidative transformation by the enzymatic action of myeloperoxidase, a protein released into the extracellular environment when neutrophils are activated. Production of the resulting drug metabolites within lymphoid organs maximizes their immune-perturbing effects. Mechanisms proposed for the initiation of drug-induced blood dyscrasias, hypersensitivity reactions, or lupus-like symptoms center around three views: (1) presentation of the implicated compound in the major histocompatibility complex of antigen-presenting cells via direct binding or after processing as a hapten bound to self-macromolecules, (2) direct cytotoxicity, or (3) interference in the development of T-cell tolerance in the thymus. How participation of reactive drug metabolites in these processes might lead to symptomatic disease is discussed.