Characterization of drug-specific T cells in lamotrigine hypersensitivity

Drug-induced hypersensitivity syndrome: clinical and biologic disease patterns in 24 patients

Drug-induced hypersensitivity syndrome (DIHS), also called drug rash with eosinophilia and systemic symptoms (DRESS), is a severe reaction usually characterized by fever, rash, and multiorgan failure, occurring 1-8 weeks after drug introduction. It is an immune-mediated reaction involving macrophage and T-lymphocyte activation and cytokine release, although no consensus has been reached as to its etiology. The skin, hematopoietic system, and liver are frequently involved. DIHS can mimic severe sepsis, viral infection, adult-onset Still disease (AOSD), or lymphoproliferation.We describe 24 consecutive patients with DIHS who were hospitalized between September 2004 and March 2008. Criteria for inclusion in this observational study were suspected drug reaction, eosinophilia >or=500/microL and/or atypical lymphocytes, involvement of at least 2 organs (skin being 1 of them), with suggestive chronology and exclusion of other diagnoses. Our cohort of 12 women and 12 men had a median age of 49 years (range, 22-82 yr), and 11 had skin phototype V or VI. Patients with mild or no rash were immunocompromised (7/24)- defined as treatment with prednisone (>or=10 mg/d) and another immunosuppressant drug, or human immunodeficiency virus infection. All patients were febrile (>38 degrees C), 14 had localized or generalized edema, 7 had pharyngitis, 8 had lymphadenopathy, 22 had hepatitis, 4 had nephritis, 2 had noninfectious and nonlithiasic angiocholitis or cholecystitis. Ten patients were hypotensive, 5 of whom had associated laboratory signs and/or imaging findings suggestive of acute myocardial dysfunction. Half of the patients had hemogram abnormalities, including eosinophilia. Nine DIHS patients fulfilled the Fautrel criteria for AOSD diagnosis, including glycosylated ferritin <20% in 4/11, with or without laboratory characteristics of hemophagocytosis. Twenty DIHS episodes occurred during the less sunny months of October to March.We determined 25-hydroxyvitamin D3 (25[OH]D3) levels in 18 patients and found that 9 patients had vitamin D deficiency (<25 nmol/L or <10 microg/L) and 5 had vitamin D insufficiency (25-50 nmol/L). Moreover, 25(OH)D3 levels were inversely correlated with ferritin values. After culprit-drug withdrawal, outcomes were favorable for all patients, including those with cardiac abnormalities under slow tapering of glucocorticoids.We recommend looking for the frequent but underdiagnosed hypersensitivity myocarditis with noninvasive diagnostic tools, such as N-terminal probrain natriuretic peptide, and promptly withdrawing the culprit drug and starting glucocorticoids. Vitamin D deficiency might be a DIHS risk or severity factor, especially for patients with high skin phototype and during the winter. Because DIHS clinical and laboratory patterns share similarities with AOSD and hemophagocytosis, DIHS should be included in their differential diagnoses.

Investigation of the immunogenicity of p-phenylenediamine and Bandrowski's base in the mouse

p-Phenylenediamine (PPD) exposure is associated with T-cell mediated contact dermatitis. T-cells from allergic patients proliferate following exposure to PPD and the oxido-conjugation product Bandrowski's base (BB). Both compounds are classified as sensitizers in the local lymph node assay; however, because of their instability the nature of the antigenic determinant remains ill-defined. The aim of this study was to explore the immunogenic potential of PPD and BB in mice. Spleen cell proliferation and cytokine secretion was measured ex vivo following antigen recall with soluble PPD or BB and either irradiated or glutaraldehyde fixed, antigen pulsed dendritic cells from syngeneic mice. Glutathione was added to certain incubations. LC-MS analysis and solvent extraction were used to monitor the fate of [(14)C]BB in culture and the extent of BB binding, respectively. Spleen cells from BB exposed, but not PPD- or vehicle-exposed, mice proliferated when stimulated with BB. Proliferating cells secreted high levels of IFN-gamma, GM-CSF and IL-2. Stimulation with PPD instigated low levels of proliferation. Irradiated, but not fixed, dendritic cells pulsed with BB stimulated proliferation signifying a classical hapten mechanism involving irreversible BB binding to protein and processing. BB bound preferentially to serum protein when incubated together with cells and serum. Degradation of BB in the presence of glutathione was associated with a stronger stimulation of specific T-cells at higher BB concentrations. These data demonstrate that BB is a potent immunogen in the mouse.

[Diagnostic methods for confirming drug-allergy--the lymphocyte transformation test in dermatology]

Recognizing the adverse drug reactions and confirming the role of the drug causing the symptoms is a great challenge for a medical team. The aim of this article is to review the diagnostic methods for confirming drug-allergy and to evaluate the lymphocyte transformation test according to dermatological aspect. Lymphocyte transformation test relies on the observation that specific T-cells divide and expand after encountering the antigen. T-cell sensitization is measured by 3H-thymidine uptake in dividing cells. The main advantage of this test is its applicability with many different drugs in different immune reactions, as drug-specific T-cells are almost always involved in drug hypersensitivity reactions. Its disadvantage is that the test is cumbersome and technically demanding. The method is not unequivocally accepted, it is necessary to carry out a systematic evaluation of its sensitivity and specificity to make the test more widely appreciated. Despite of its deficits, the lymphocyte transformation test plays an important role in diagnosing drug-hypersensitivities.

CD69 upregulation on T cells as an in vitro marker for delayed-type drug hypersensitivity

BACKGROUND

T cells play a key role in delayed-type drug hypersensitivity reactions. Their reactivity can be assessed by their proliferation in response to the drug in the lymphocyte transformation test (LTT). However, the LTT imposes limitations in terms of practicability, and an alternative method that is easier to implement than the LTT would be desirable.

METHODS

Four months to 12 years after acute drug hypersensitivity reactions, CD69 upregulation on T cells of 15 patients and five healthy controls was analyzed by flow cytometry.

RESULTS

All 15 LTT-positive patients showed a significant increase of CD69 expression on T cells after 48 h of drug-stimulation exclusively with the drugs incriminated in drug-hypersensitivities. A stimulation index of 2 as cut-off value allowed discrimination between nonreactive and reactive T cells in LTT and CD69 upregulation. T cells (0.5-3%) showed CD69 up-regulation. The reactive cell population consisted of a minority of truly drug reactive T cells secreting cytokines and a higher number of bystander T cells activated by IL-2 and possibly other cytokines.

CONCLUSIONS

CD69 upregulation was observed after 2 days in all patients with a positive LTT after 6 days, thus appearing to be a promising tool to identify drug-reactive T cells in the peripheral blood of patients with drug-hypersensitivity reactions.

Alendronate-induced esophagitis: possible pathogenic role of hypersensitivity to alendronate

Upper gastrointestinal tract mucosal irritations, such as esophagitis, have been reported as rare adverse events due to a variety of aminobisphosphonates, including alendronate sodium, which have been widely used to treat osteoporosis. Although the pathogenesis of aminobisphosphonate-induced esophageal mucosal irritation has not been clearly understood, direct chemical esophageal irritation with prolonged local mucosal exposure to the drug with gastric contents might be the most plausible mechanism according to the previously reported literature. Here we report a young adult man with severe ulcerative esophagitis due to alendronate who demonstrated a strongly positive result on a drug lymphocyte stimulation test against alendronate. This case report provides the new concept that T-cell mediated delayed hypersensitivity to the drug may be involved in the pathogenesis of alendronate-induced esophagitis.

Utility of the lymphocyte transformation test in the diagnosis of drug sensitivity: dependence on its timing and the type of drug eruption

BACKGROUND

Lymphocyte transformation test (LTT) is a safety and reproducible test to assess activation of drug-specific T cells in vitro; however, there are several practical concerns such as the time of testing and the influence of treatment. Our aim was to define the right timing to perform LTT for determining the causative agent in various types of drug reactions.

METHODS

Lymphocyte transformation test was performed at different time points during the evolution of three types of drug reactions, maculo-papular type of drug eruptions (MP), Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN), and drug-induced hypersensitivity syndrome/drug rash and eosinophilia with systemic symptoms (DIHS/DRESS).

RESULTS

Positive LTT reactions were obtained when the test was performed at the acute stage but not the recovery stage in MP and SJS/TEN, while positive LTT reactions were obtained at the recovery stage but not the acute stage in DIHS/DRESS, regardless of treatment with systemic prednisolone.

CONCLUSIONS

Lymphocyte transformation test is a reliable method to define the causative agent, when LTT is performed at the right timing depending on the type of drug reactions. Lymphocyte transformation test should be performed within 1 week after the onset of skin rashes in patients with MP and SJS/TEN; and 5-8 weeks after in patients with DIHS/DRESS, respectively.

Antiviral activity of diverse classes of broad-acting agents and natural compounds in HHV-6-infected lymphoblasts

BACKGROUND

HHV-6 replication requires complex and poorly understood interactions between viral and cellular factors.

OBJECTIVES

Several natural compounds or broad-acting pharmacological agents were studied in an attempt to discover new targets for anti-HHV-6 therapy.

STUDY DESIGN

The antiviral activity was determined in human T-lymphoblasts, using HHV-6A (GS)-infected HSB-2 cells, HHV-6B (Z29)-infected MOLT-3 cells and HHV- 6B (HST)-infected MT4 cells. Virus replication was measured by CPE and qPCR assay. Foscarnet was included as the reference compound.

RESULTS

Among the 15 natural compounds tested, only 'red marine algae' (an extract rich in sulfated polysaccharides) exhibited strong activity when added during virus adsorption. Among the broad-acting pharmacological agents, chloroquine, artemisinin, hypericin, ribavirin, resveratrol and glycyrrhizic acid were all inactive. Amantadine produced a reproducible inhibition of HHV-6 replication, albeit at relatively high concentrations. Except for lamotrigine, which was moderately active against HHV-6B, several antiepileptic drugs were shown to have no activity. We included several compounds which we previously described as potent HHV-6 inhibitors, i.e., the non-nucleoside inhibitor CMV423 and the acyclic nucleoside phosphonate analogues cidofovir and 9-(S)-[3-hydroxy-2-(phosphonomethoxy)propyl]-3-deazaadenine. The latter compound exhibited remarkable anti-HHV-6 activity.

CONCLUSION

Further optimization of compounds belonging to diverse classes of antiherpetic agents, for their specific action against HHV-6, is warranted.

HLA-B*1502-bound peptides: implications for the pathogenesis of carbamazepine-induced Stevens-Johnson syndrome

BACKGROUND

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) can involve MHC-restricted presentation of a drug or its metabolites for T-cell activation. HLA-B(*)1502 tightly associated with carbamazepine (CBZ) induced these conditions in a Han Chinese population.

OBJECTIVE

We sought to identify HLA-B(*)1502-bound peptides that might be involved in CBZ-induced SJS/TEN.

METHODS

Soluble HLA-B(*)1502 was used to identify bound peptides in the presence and absence of CBZ by using liquid chromatography-tandem mass spectrometry. Peptide-binding assays were performed to detect the specific interaction between the HLA molecule and the identified peptides. Mass spectra were compared to detect CBZ-modified peptides.

RESULTS

We identified more than 145 peptides bound to HLA-B(*)1502. In 13 of 15 peptides examined, we functionally confirmed their specificity with binding assays. Preferable uses of these peptides at the anchoring residues P2 and P9 were similar to those observed in other HLA-B alleles in the Han Chinese population. However, the preferable use of serine residues at the nonanchoring position (P) 5, P6, P7, and P8 appeared to be unique for the B(*)1502 peptides. No specific CBZ-modified peptides were detected when we compared the mass spectra of peptides detected in the presence or absence of the drug.

CONCLUSION

Noncovalent interaction between a drug and an HLA complex might contribute to cytotoxic T cell-mediated cell death in patients with SJS/TEN.

CLINICAL IMPLICATIONS

An understanding of pharmacologic interaction of drugs with an HLA complex might lead to safer drugs that avoid SJS/TEN.

Delayed drug hypersensitivity reactions ? new concepts

Immune reactions to small molecular compounds such as drugs can cause a variety of diseases mainly involving skin, but also liver, kidney, lungs and other organs. In addition to the well-known immediate, IgE-mediated reactions to drugs, many drug-induced hypersensitivity reactions appear delayed. Recent data have shown that in these delayed reactions drug-specific CD4(+) and CD8(+) T cells recognize drugs through their T cell receptors (TCR) in an MHC-dependent way. Immunohistochemical and functional studies of drug-reactive T cells in patients with distinct forms of exanthems revealed that distinct T cell functions lead to different clinical phenotypes. Taken together, these data allow delayed hypersensitivity reactions (type IV) to be further subclassified into T cell reactions, which by releasing certain cytokines and chemokines preferentially activate and recruit monocytes (type IVa), eosinophils (type IVb), or neutrophils (type IVd). Moreover, cytotoxic functions by either CD4(+) or CD8(+) T cells (type IVc) seem to participate in all type IV reactions. Drugs are not only immunogenic because of their chemical reactivity, but also because they may bind in a labile way to available TCRs and possibly MHC-molecules. This seems to be sufficient to stimulate certain, probably preactivated T cells. The drug seems to bind first to the fitting TCR, which already exerts some activation. For full activation, an additional interaction of the TCR with the MHC molecules is needed. The drug binding to the receptor structures is reminiscent of a pharmacological interaction between a drug and its (immune) receptor and was thus termed the p-i concept. In some patients with drug hypersensitivity, such a response occurs within hours even upon the first exposure to the drug. The T cell reaction to the drug might thus not be due to a classical, primary response, but is due to peptide-specific T cells which happen to be stimulated by a drug. This new concept has major implications for understanding clinical and immunological features of drug hypersensitivity and a model to explain the frequent skin symptoms in drug hypersensitivity is proposed.

Idiosyncratic adverse reactions to antiepileptic drugs

Idiosyncratic drug reactions may be defined as adverse effects that cannot be explained by the known mechanisms of action of the offending agent, do not occur at any dose in most patients, and develop mostly unpredictably in susceptible individuals only. These reactions are generally thought to account for up to 10% of all adverse drug reactions, but their frequency may be higher depending on the definition adopted. Idiosyncratic reactions are a major source of concern because they encompass most life-threatening effects of antiepileptic drugs (AEDs), as well as many other reactions requiring discontinuation of treatment. Based on the underlying mechanisms, idiosyncratic reactions can be differentiated into (1) immune-mediated hypersensitivity reactions, which may range from benign skin rashes to serious conditions such as drug-related rash with eosinophilia and systemic symptoms; (2) reactions involving unusual nonimmune-mediated individual susceptibility, often related to abnormal production or defective detoxification of reactive cytotoxic metabolites (as in valproate-induced liver toxicity); and (3) off-target pharmacology, whereby a drug interacts directly with a system other than that for which it is intended, an example being some types of AED-induced dyskinesias. Although no AED is free from the potential of inducing idiosyncratic reactions, the magnitude of risk and the most common manifestations vary from one drug to another, a consideration that impacts on treatment choices. Serious consequences of idiosyncratic reactions can be minimized by knowledge of risk factors, avoidance of specific AEDs in subpopulations at risk, cautious dose titration, and careful monitoring of clinical response.

Immunological principles of T-cell-mediated adverse drug reactions in skin

Drug hypersensitivity reactions in skin are an immune-mediated phenomenon associated with significant patient mortality and morbidity. Antigen-specific T cells, which have been isolated from the peripheral circulation and target organs of hypersensitive patients, are thought to propagate and regulate the development of clinical symptoms. The investigation of clinical cases with respect to the basic cellular and chemical mechanisms that underpin drug hypersensitivity has resulted in: i) the need to redress some aspects of present immunological dogma; and ii) additional fundamental immunological questions. Thus, the aim of this review article is to summarise present opinion on how and why drugs initiate a pathogenic T-cell response in a small section of the population and subsequently reflect on gaps in basic immunology and where future research might lead.

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.

Antibodies to voltage-gated potassium and calcium channels in epilepsy

OBJECTIVE

To determine the prevalence of antibodies to ion channels in patients with long standing epilepsy.

BACKGROUND

Although the CNS is thought to be protected from circulating antibodies by the blood brain barrier, glutamate receptor antibodies have been reported in Rasmussen's encephalitis, glutamic acid decarboxylase (GAD) antibodies have been found in a few patients with epilepsy, and antibodies to voltage-gated potassium channels (VGKC) have been found in a non-paraneoplastic form of limbic encephalitis (with amnesia and seizures) that responds to immunosuppressive therapy.

METHODS

We retrospectively screened sera from female epilepsy patients (n=106) for autoantibodies to VGKC (Kv 1.1, 1.2 or 1.6), voltage-gated calcium channels (VGCC) (P/Q-type), and GAD. All positive results, based on the values of control data [McKnight, K., Jiang, Y., et al. (2005). Serum antibodies in epilepsy and seizure-associated disorders. Neurology 65, 1730-1735], were retested at lower serum concentrations, and results compared with previously published control data. Demographics, medical history, and epilepsy related information was gathered.

RESULTS

The studied group consisted predominantly of patients with long standing drug resistant epilepsy. VGKC antibodies were raised (>100 pM) in six patients. VGCC antibodies (>45 pM) were slightly raised in only one patient. GAD antibodies were <3 U/ml in all patients. The clinical features of the patients with VGKC antibodies differed from previously described patients with limbic encephalitis-like syndrome, and were not different with respect to seizure type, age at first seizure, duration of epilepsy, or use of anti-epileptic drugs from the VGKC antibody negative patients.

CONCLUSION

The results demonstrate that antibodies to VGKC are present in 6% of patients with typical long-standing epilepsy, but whether these antibodies are pathogenic or secondary to the primary disease process needs to be determined.

Current understanding of delayed anticonvulsant hypersensitivity reactions

Hypersensitivity syndrome (HSS) reactions are one of the most feared idiosyncratic drug reactions and are most common with exposure to antiepileptic drugs (AEDs), sulfonamides, nonsteroidal antiinflammatory drugs, corticosteroids, and allopurinol. HSS is associated with chemotoxic and T-cell-mediated inflammatory injuries in barrier tissue systems that contain cytochrome oxidases (e.g., skin, mucosa, liver, and lungs) and can be seen as a derangement in the defense system against xenobiotics-bioactive foreign molecules. The mechanisms for anticonvulsant HSS are incompletely understood but involve genetic susceptibility, with accumulation of AEDs and oxidized metabolites causing major histocompatibility complex (MHC) and non-MHC-dependent clonal activation of T cells and subsequent cytokine/chemokine production in T cells, keratinocytes, and other target cells. This review discusses the classification and possible mechanisms for anticonvulsant HSS.

Transfection of drug-specific T-cell receptors into hybridoma cells: tools to monitor drug interaction with T-cell receptors and evaluate cross-reactivity to related compounds

In the context of drug hypersensitivity, our group has recently proposed a new model based on the structural features of drugs (pharmacological interaction with immune receptors; p-i concept) to explain their recognition by T cells. According to this concept, even chemically inert drugs can stimulate T cells because certain drugs interact in a direct way with T-cell receptors (TCR) and possibly major histocompatibility complex molecules without the need for metabolism and covalent binding to a carrier. In this study, we investigated whether mouse T-cell hybridomas transfected with drug-specific human TCR can be used as an alternative to drug-specific T-cell clones (TCC). Indeed, they behaved like TCC and, in accordance with the p-i concept, the TCR recognize their specific drugs in a direct, processing-independent, and dose-dependent way. The presence of antigen-presenting cells was a prerequisite for interleukin-2 production by the TCR-transfected cells. The analysis of cross-reactivity confirmed the fine specificity of the TCR and also showed that TCR transfectants might provide a tool to evaluate the potential of new drugs to cause hypersensitivity due to cross-reactivity. Recombining the alpha- and beta-chains of sulfanilamide- and quinolone-specific TCR abrogated drug reactivity, suggesting that both original alpha- and beta-chains were involved in drug binding. The TCR-transfected hybridoma system showed that the recognition of two important classes of drugs (sulfanilamides and quinolones) by TCR occurred according to the p-i concept and provides an interesting tool to study drug-TCR interactions and their biological consequences and to evaluate the cross-reactivity potential of new drugs of the same class.

Drug-Specific T Cells in An HIV-Positive Patient with Nevirapine-Induced Hepatitis

Background

Nevirapine is associated with idiosyncratic reactions such as skin rash, hepatitis and hypersensitivity syndrome, which have the hallmarks of being immune mediated. However, there is little laboratory evidence to support an immune pathogenesis.

Methods

A HIV-positive individual who developed hepatitis within 6 weeks of starting nevirapine, in the absence of any cutaneous manifestations, is described. Other causes of hepatitis were excluded, and the patients liver function normalized on withdrawal of nevirapine. Lymphocytes from the patient, and six individuals with HIV who were on nevirapine without adverse effects, were exposed to nevirapine and its metabolites, and lymphocyte proliferation assessed by 3H-thymidine incorporation on day 5.

Results

The T cells taken from the nevirapine-hypersensitive patient proliferated in the presence of nevirapine with a stimulation index of greater than 2. There was no proliferation with nevirapine metabolites. T cells taken from HIV-positive control individuals showed no proliferation with either nevirapine or its metabolites.

Conclusion

The results from our patient suggest that T cells may be involved in the pathogenesis of nevirapine-induced hepatitis. Larger numbers of patients need to be studied to fully evaluate the role of T cells in nevirapine-induced hepatitis and nevirapine hypersensitivity syndrome.

Long-lasting reactivity and high frequency of drug-specific T cells after severe systemic drug hypersensitivity reactions

BACKGROUND

Drug-reactive T cells are involved in most drug-induced hypersensitivity reactions. The frequency of such cells in peripheral blood of patients with drug allergy after remission is unclear.

OBJECTIVE

We determined the frequency of drug-reactive T cells in the peripheral blood of patients 4 months to 12 years after severe delayed-type drug hypersensitivity reactions, and whether the frequency of these cell differs from the frequency of tetanus toxoid-reactive T cells.

METHODS

We analyzed 5 patients with delayed-type drug hypersensitivity reactions, applying 2 methods: quantification of cytokine-secreting T cells by enzyme-linked immunospot (ELISpot), and fluorescent dye 5,6-carboxylfluorescein diacetate succinimidyl ester (CFSE) intensity distribution analysis of drug-reactive T cells.

RESULTS

Frequencies found were between 0.02% and 0.4% of CD4(+) T cells reacting to the respective drugs measured by CFSE analysis, and between 0.01% and 0.08% of T cells as determined by ELISpot. Reactivity was seen neither to drugs to which the patients were not sensitized nor in healthy individuals after stimulation with any of the drugs used.

CONCLUSION

About 1:250 to 1:10,000 of T cells of patients with drug allergy are reactive to the relevant drugs. This frequency of drug-reactive T cells is higher than the frequency of T cells able to recognize recall antigens like tetanus toxoid in the same subjects. A substantial frequency could be observed as long as 12 years later in 1 patient even after strict drug avoidance. Patients with severe delayed drug hypersensitivity reactions are therefore potentially prone to react again to the incriminated drug even years after strict drug avoidance.

Noncovalent interactions of drugs with immune receptors may mediate drug-induced hypersensitivity reactions

Drug-induced hypersensitivity reactions are instructive examples of immune reactions against low molecular weight compounds. Classically, such reactions have been explained by the hapten concept, according to which the small antigen covalently modifies an endogenous protein; recent studies show strong associations of several HLA molecules with hypersensitivity. In recent years, however, evidence has become stronger that not all drugs need to bind covalently to the major histocompatibility complex (MHC)-peptide complex in order to trigger an immune response. Rather, some drugs may bind reversibly to the MHC or possibly to the T-cell receptor (TCR), eliciting immune reactions akin to the pharmacological activation of other receptors. While the exact mechanism is still a matter of debate, noncovalent drug presentation clearly leads to the activation of drug-specific T cells. In some patients with hypersensitivity, such a response may occur within hours of even the first exposure to the drug. Thus, the reaction to the drug may not be the result of a classical, primary response but rather be mediated by existing, preactivated T cells that display cross-reactivity for the drug and have additional (peptide) specificity as well. In this way, certain drugs may circumvent the checkpoints for immune activation imposed by the classical antigen processing and presentation mechanisms, which may help to explain the idiosyncratic nature of many drug hypersensitivity reactions.

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.

Pharmacological interaction of drugs with immune receptors: the p-i concept

Drug-induced hypersensitivity reactions have been explained by the hapten concept, according to which a small chemical compound is too small to be recognized by the immune system. Only after covalently binding to an endogenous protein the immune system reacts to this so called hapten-carrier complex, as the larger molecule (protein) is modified, and thus immunogenic for B and T cells. Consequently, a B and T cell immune response might develop to the drug with very heterogeneous clinical manifestations. In recent years, however, evidence has become stronger that not all drugs need to bind covalently to the MHC-peptide complex in order to trigger an immune response. Rather, some drugs may bind directly and reversibly to immune receptors like the major histocompatibility complex (MHC) or the T cell receptor (TCR), thereby stimulating the cells similar to a pharmacological activation of other receptors. This concept has been termed pharmacological interaction with immune receptors the (p-i) concept. While the exact mechanism is still a matter of debate, non-covalent drug presentation clearly leads to the activation of drug-specific T cells as documented for various drugs (lidocaine, sulfamethoxazole (SMX), lamotrigine, carbamazepine, p-phenylendiamine, etc.). In some patients with drug hypersensitivity, such a response may occur within hours even upon the first exposure to the drug. Thus, the reaction to the drug may not be due to a classical, primary response, but rather be mediated by stimulating existing, pre-activated, peptide-specific T cells that are cross specific for the drug. In this way, certain drugs may circumvent the checkpoints for immune activation imposed by the classical antigen processing and presentation mechanisms, which may help to explain the peculiar nature of many drug hypersensitivity reactions.

Role of bioactivation in drug-induced hypersensitivity reactions

Drug-induced hypersensitivity reactions are a major problem in both clinical treatment and drug development. This review covers recent developments in our understanding of the pathogenic mechanisms involved, with special focus on the potential role of metabolism and bioactivation in generating a chemical signal for activation of the immune system. The possible role of haptenation and neoantigen formation is discussed, alongside recent findings that challenge this paradigm. Additionally, the essential role of costimulation is examined, as are the potential points whereby costimulation may be driven by reactive metabolites. The relevance of local generation of metabolites in determining the location and character of a reaction is also covered.

Mechanisms of drug-induced liver injury

The idiosyncratic nature and poor prognosis of drug-induced liver injury (DILI) make this type of reaction a major safety issue during drug development, as well as the most common cause for the withdrawal of drugs from the pharmaceutical market. The key to predicting and preventing DILI is understanding the underlying mechanisms. DILI is initiated by direct hepatotoxic effects of a drug, or a reactive metabolite of a drug. Parenchymal cell injury induces activation of innate and/or adaptive immune cells, which, in turn, produce proinflammatory and tissue hepatotoxic mediators, and/or mount immune reactions against drug-associated antigens. Understanding the molecular and cellular elements associated with these pathways can help identify risk factors and may ultimately facilitate the development of strategies to predict and prevent DILI.

T cell-mediated hypersensitivity to quinolones: mechanisms and cross-reactivity

BACKGROUND

Quinolones are widely used, broad spectrum antibiotics that can induce immediate- and delayed-type hypersensitivity reactions, presumably either IgE or T cell mediated, in about 2-3% of treated patients.

OBJECTIVE

To better understand how T cells interact with quinolones, we analysed six patients with delayed hypersensitivity reactions to ciprofloxacin (CPFX), norfloxacin (NRFX) or moxifloxacin (MXFX).

METHODS

We confirmed the involvement of T cells in vivo by patch test and in vitro by means of the lymphocyte proliferation test (LTT). The nature of the drug-T cell interaction as well as the cross-reactivity with other quinolones were investigated through the generation and analysis (flow cytometry and proliferation assays) of quinolone-specific T cell clones (TCC).

RESULTS

The LTT confirmed the involvement of T cells because peripheral blood mononuclear cells (PBMC) mounted an enhanced in vitro proliferative response to CPFX and/or NRFX or MXFX in all patients. Patch tests were positive after 24 and 48 h in three out of the six patients. From two patients, CPFX- and MXFX-specific CD4(+)/CD8(+) T cell receptor (TCR) alphabeta(+) TCC were generated to investigate the nature of the drug-T cell interaction as well as the cross-reactivity with other quinolones. The use of eight different quinolones as antigens (Ag) revealed three patterns of cross-reactivity: clones exclusively reacting with the eliciting drug, clones with a limited cross-reactivity and clones showing a broad cross-reactivity. The TCC recognized quinolones directly without need of processing and without covalent association with the major histocompatability complex (MHC)-peptide complex, as glutaraldehyde-fixed Ag-presenting cells (APC) could present the drug and washing quinolone-pulsed APC removed the drug, abrogating the reactivity of quinolone-specific TCC.

CONCLUSION

Our data show that T cells are involved in delayed immune reactions to quinolones and that cross-reactivity among the different quinolones is frequent.

Mechanisms of drug-induced delayed-type hypersensitivity reactions in the skin

Cutaneous drug reactions (CDRs) are the most commonly reported adverse drug reactions. These reactions can range from mildly discomforting to life threatening. CDRs can arise either from immunological or nonimmunological mechanisms, though the preponderance of evidence suggests an important role for immunological responses. Some cutaneous eruptions appear shortly after drug intake, while others are not manifested until 7 to 10 days after initiation of therapy and are consistent with delayed-type hypersensitivity. This review discusses critical steps in the initiation of delayed-type hypersensitivity reactions in the skin, which include protein haptenation, dendritic cell activation/migration and T-cell propagation. Recently, an alternative mechanism of drug presentation has been postulated that does not require bioactivation of the parent drug or antigen processing to elicit a drug-specific T-cell response. This review also discusses the role of various immune-mediators, such as cytokines, nitric oxide, and reactive oxygen species, in the development of delayed-type drug hypersensitivity reactions in skin. As keratinocytes have been shown to play a crucial role in the initiation and propagation of cutaneous immune responses, we also discuss the means by which these cells may initiate or modulate CDRs.

Carbamazepine-induced acute liver failure as part of the DRESS syndrome

Carbamazepine is a widely used drug. It is commonly associated with hepatic abnormalities, ranging from an asymptomatic rise in liver function tests to acute liver failure. The most severe reaction occurs as part of a generalised hypersensitivity reaction, also known as drug reaction, eosinophilia and systemic symptoms (DRESS). We describe a case of a young adult who presented with non-specific symptoms, which progressed to fulminant hepatic failure, displaying the hallmarks of DRESS. We highlight the need for awareness of such an association.

The usefulness of skin tests to prove drug hypersensitivity

BACKGROUND

Suspected drug hypersensitivity is common. Only a minority of cutaneous adverse drug reactions (CADRs) are allergic in origin and will reappear after the next exposure. Methods to confirm suspected CADRs are needed and skin testing could serve as one possibility.

OBJECTIVES

To analyse the usefulness of skin tests in revealing drug allergy. The relevance of skin test results was evaluated with drug provocation studies.

METHODS

During 1989-2001, 947 patients with a history of suspected CADR were examined with skin tests including patch tests (PTs) (826 patients), skin prick tests (SPTs) (935 patients) and photopatch tests (12 patients). The occurrence of positive and negative test reactions to different drugs was correlated with clinical history. Drug provocation was carried out in 246 patients.

RESULTS

Antimicrobial drugs were suspected and tested most often. A positive PT reaction to one or more drug was seen in 89 of 826 (10.8%), most often to beta-lactams, clindamycin and trimethoprim. A positive SPT reaction was seen in 10 of 935 (1.1%) patients. Challenge was carried out in 17 patients with positive skin test results. Thirteen of 16 (81.2%) PT positives developed exanthema, three remained negative and one SPT-positive patient developed urticaria. Among skin test negatives, 207 of 229 (90.4%) challenges were negative and 22 of 229 (9.6%) were positive, 12 with exanthema, three with fixed drug eruptions and seven with urticaria.

CONCLUSIONS

Skin testing, especially the PT, was a useful screening method to find a cause of CADR if the reaction was exanthema and if antimicrobial, cardiovascular or antiepileptic drugs were suspected. The SPT detected occasional positives with antimicrobials. In cases of fixed drug eruption, PTs performed at the earlier reaction site were useful. When skin tests are negative or dubious, oral challenge should be carried out to confirm the association.

Cross-reactivity among drugs: clinical problems

Cross-reactivity among drugs is either mediated by immunologic mechanisms or not. The former kind is usually explained by the presence of common antigenic determinants in the cross-reacting drugs. In the case of compounds provoking non-allergic hypersensitivity reactions, cross-reactivity is explained by a common pharmacological characteristic, such as the inhibitory effect of non-steroidal anti-inflammatory drugs on cyclooxygenase-1 and the capability of muscle relaxants or contrast media to release histamine through a non-immunologic mechanism. The main clinical problem deriving from cross-reactivity among drugs is the compelling need to choose a potentially cross-reactive compound and, therefore, to assess cross-reactivity by diagnostic tests. In choosing alternative compounds, skin testing has been used in evaluating IgE-mediated cross-reactivity between penicillins and cephalosporins, as well as among muscle relaxants. In assessing T cell-mediated cross-reactivity among contrast media, corticosteroids, anticonvulsants and heparins, delayed-reading intradermal tests and patch tests, together with lymphocyte transformation tests, can be performed. Because of the limited sensitivity of in vivo and in vitro testing, the most prudent way of establishing the tolerability of a compound of the same group in patients who especially require one is a graded challenge when other allergologic tests are negative.

Cellular mechanisms of T cell mediated drug hypersensitivity

Noncovalent drug presentation leads to the activation of drug-specific T cells. In some patients with hypersensitivity, such a response occurs within hours even upon the first exposure to the drug. Thus, the reaction to the drug might not be due to a classical, primary response, but rather mediated by existing, preactivated T cells that are cross specific for the drug, and have an additional (peptide) specificity as well.

Characterization of the T-cell response in a patient with phenindione hypersensitivity

The oral anticoagulant phenindione [2-phenyl-1H-indene-1,3(2H)-dione] is associated with hypersensitivity reactions in 1.5 to 3% of patients, the pathogenesis of which is unclear. We describe a patient who developed a severe hypersensitivity reaction that involved both the skin and lungs. A lymphocyte transformation test showed proliferation of T-cells from the hypersensitive patient, but not from four controls on exposure to phenindione in vitro. Drug-specific T-cell clones were generated and characterized in terms of their phenotype, functionality, and mechanism of antigen presentation. Forty-three human leukocyte antigen class II restricted CD4(+) alphabeta T-cell clones were identified. T-cell activation resulted in the secretion of interferon-gamma and interleukin-5. Five of seven clones proliferated with phenindione alone, whereas two clones also proliferated with 2-phenylindene. Certain T-cell clones were also stimulated by R- and S-warfarin; computer modeling revealed that warfarin can adopt a phenindione-like structure. Phenindione was presented to T-cells via two pathways: first, bound directly to major histocompatibility complex and second, bound to a processed peptide. Our data show that CD4(+) T-cells are involved in the pathophysiology of phenindione hypersensitivity. There may be cross-sensitivity with warfarin in some phenindione hypersensitive patients.

The immunological and clinical spectrum of delayed drug-induced exanthems

PURPOSE OF REVIEW

Drug-induced exanthems are the most common manifestations of drug hypersensitivity and are observed in as much as 2-3% of hospitalized patients. Here we summarize new concepts of the immune mechanisms underlying various forms of drug-induced exanthems.

RECENT FINDINGS

Alpha-betaTCR+, CD4 and CD8+ T cells are involved in different drug hypersensitivity reactions. Their function determines the clinical picture. In maculopapular, bullous and pustular exanthems cytotoxic T cells are involved, while a high IL-5 and eotaxin production by tissue cells is frequently found in maculopapular and occasionally in bullous and in pustular exanthems. High IL-8 (CXCL-8) and granulocyte-macrophage colony stimulating factor production by T cells is a hallmark of pustular drug exanthems. In the most severe and potentially life-threatening forms of exanthems (Stevens-Johnson syndrome/toxic epidermal necrolysis) cytotoxic CD8+ T cells with natural killer cell markers can be found in the blister fluid.

SUMMARY

These findings are the basis for a new subclassification of delayed, type IV hypersensitivity reactions into type IVa (T helper type 1 cells, e.g. tuberculin reaction and contact dermatitis), IVb (T helper type 2 cells, maculopapular exanthem with eosinophilia), IVc (cytotoxic T cells, contact dermatitis, maculopapular and bullous exanthem), and IVd reactions (CXCL-8/granulocyte-macrophage colony stimulating factor-producing T cells and neutrophil attraction, pustular exanthems), by which, in most reactions, various mechanisms occur together but one reaction dominates the clinical picture.

Immune mechanism of drug hypersensitivity

Drug hypersensitivity reactions can lead to a great variety of different diseases. The main cause is a specific interaction of antibodies or T cells with a drug. In addition to the hapten concept, some drugs can bind directly to T-cell receptors and stimulate them. Based on recent investigation on different exanthemas, an extended classification of the Gell and Coombs type IV reaction is proposed.

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.

Advances in allergic skin disease, anaphylaxis, and hypersensitivity reactions to foods, drugs, and insect stings

This review highlights some of the research advances in allergic skin disease, anaphylaxis, and hypersensitivity reactions to foods, drugs, and insect venom that were reported primarily in the Journal of Allergy and Clinical Immunology from 2002 through 2003. Among the topics highlighted are new insights into the pathogenesis of atopic dermatitis and potential strategies for more effective treatment of the atopic march. Patients should remain supine with raised legs during anaphylactic shock because upper body elevation could result in sudden death from loss of venous return to the heart. A major advance in food allergy was that humanized, monoclonal anti-IgE antibody showed protection against peanut-induced anaphylaxis. In addition to studies elucidating mechanisms of drug hypersensitivity, a clinical study showed patients with a history of prior penicillin allergy with negative penicillin allergy test results are unlikely to experience reactions or resensitization on subsequent oral courses of penicillin. Lastly, there are new recommendations for patients with convincing insect sting reaction histories but negative skin test responses to venom.

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.

Drug-induced autoimmunity

PURPOSE OF REVIEW

Presentation of different mechanism of drug-induced autoimmunity and highlighting of new developments.

RECENT FINDINGS

Drugs can induce autoimmune diseases by their pharmacological properties. Injection of certain drugs into the thymus can alter positive selection in the thymus and elicit autoimmune reactions. Peripheral tolerance can be broken by increasing the expression of LFA-1 adhesion molecule on T cells. This can be related to the inhibition of intracellular kinases. Alternatively, a drug specific immune response might elicit autoimmunity by cross-reactivity: the drug reactive T cells might be cross-reactive with certain peptide antigens and possibly autoantigens.

SUMMARY

Drug-specific immune responses are well described. They have a great tendency to be cross-reactive with peptide antigens. This 'immunological' cause of autoimmunity elicited by drugs may occur more frequently than thought. It connects the field of drug hypersensitivity with drug-induced autoimmunity.

Characterization of sulfamethoxazole and sulfamethoxazole metabolite-specific T-cell responses in animals and humans

Sulfamethoxazole (SMX) is associated with hypersensitivity reactions. Identification of drug-specific lymphocytes from hypersensitive patients suggests involvement of the immune system. Lymphocytes from humans recognize SMX and nitroso-SMX (SMX-NO), whereas cells from sensitized rats recognize only SMX-NO. In this investigation, we study the nature of SMX-specific T cells in four species. Male rats, mice, and rabbits were immunized with SMX (50 mg kg-1) or SMX-NO (1 mg kg-1). Lymphocytes and/or splenocytes were isolated and incubated with SMX, SMX-hydroxylamine or SMX-NO and proliferation were measured. Lymphocytes were also isolated from SMX-hypersensitive patients (n = 3) and drug-specific proliferation was measured. In addition, rabbits were bled fortnightly for 4 months to determine whether SMX-NO-specific T cells cross-react with SMX. To confirm that SMX-NO responses were due to covalent binding and not cross-reactivity, cells were pulsed with SMX-NO and/or coincubated with glutathione. Splenocytes from mice, rats, and rabbits proliferated when stimulated with SMX-NO, but not SMX. A 2-h pulse with SMX-NO was sufficient for proliferation, whereas cells coincubated with SMX-NO and glutathione did not proliferate. Rabbit lymphocytes proliferated in the presence of SMX-NO and SMX-hydroxylamine, but not SMX. SMX-hydroxylamine was converted to SMX-NO in culture. The SMXNO-specific response of rabbit lymphocytes was maintained for at least 4 months and the cells did not cross-react with SMX. Human lymphocytes from hypersensitive patients proliferated in the presence of SMX and both metabolites. These results highlight important differences in T-cell recognition of drug (metabolite) antigens in animals that have been sensitized against a drug metabolite and patients with hypersensitivity to the drug.