Molecular basis of drug recognition by specific T-cell receptors

Drug-induced lupus

INTRODUCTION

Drug-induced lupus (DIL) refers to an idiosyncratic side effect of numerous, apparently unrelated, medications, in which symptoms overlap with those of systemic lupus erythematosus. DIL is reversible by discontinuation of the medication. The etiological mechanism underlying DIL is linked to the inherent susceptibility of the adaptive immune system to lapse into auto-reactivity.

AREAS COVERED

Clinical and laboratory features of DIL will be compared with those of idiopathic systemic lupus and with other types of drug reactions with overlapping features. Formerly commonly-used drugs conferred very high risk of developing DIL, although the probability of developing DIL has not been established with most lupus-inducing drugs. Pharmacological or physiochemical properties of the parent compounds are uninformative, but the importance of reactive drug metabolites in initiating autoimmunity will be discussed. As with most systemic autoimmune diseases, the pathogenesis of DIL is complex and obscure. The role of complement and human leukocyte allotypes as well as drug acetylator phenotype inform the underlying mechanism, and several of these non-mutually exclusive concepts will be described.

EXPERT OPINION

The pros and cons of proposed mechanisms for DIL will be discussed in the context of current understanding of autoimmunity and immune tolerance to self.

Delayed Allergic Reaction to Suxamethonium Driven by Oligoclonal Th1-Skewed CD4+CCR4+IFN-γ+ Memory T Cells

BACKGROUND

Muscle relaxants represent the drugs most frequently involved in intraoperative anaphylaxis during surgical procedures. Our aim was to report the case of a delayed reaction to suxamethonium and analyze specific T cell lines with regard to their specificity, phenotype and cytokine profile.

METHODS

We generated a drug-specific T cell line from a biopsy at the site of positive intradermal reactions and analyzed the immunophenotype, T cell receptor Vbeta domain expression and cytokine profile.

RESULTS

T cells isolated from positive intradermal test reactions to suxamethonium showed a strict dose-dependent proliferation in response to drug-pulsed autologous antigen-presenting cells. The drug-specific CD4+ T cells were oligoclonal memory CD3+CD4+ T cells and expressed the skin homing receptors cutaneous lymphocyte antigen (CLA) and CCR4. Furthermore CD4+ suxamethonium-reactive T cell lines were IFN-gamma-positive and synthesized high levels of IFN-gamma and TNF-alpha.

CONCLUSION

The study describes a delayed hypersensitivity to suxamethonium, driven by an oligoclonal T helper cell 1-skewed CD4+ memory T cell population, expressing the skin homing receptors CLA and CCR4.

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.

Direct T-cell stimulations by drugs--bypassing the innate immune system

Some drug induced immune mediated side effects appear rapidly (6-<48hrs) and are hard to reconcile with the generation of a new immune response to the drug. By extending the previously presented p-i concept (pharmacological interaction with immune receptors), I propose that drugs might stimulate memory T-cells via their T-cell receptors, which happen to react not only with a peptide antigen, but also with a (chemically inert) drug. In this model, the generation of a new, drug specific immune response is actually bypassed: the innate immune system must not be stimulated, as no naive T-cells are stimulated. Only previously activated memory T-cells are re-activated, as they have a lower threshold of reactivity to a T-cell receptor transmitted signal, whereby certain cofactors like an ongoing immune response to a virus might facilitate reactivity to the drug. This concept has major implications for preclinical testing of the allergenic potential of a drug, which normally is measured by the ability of the drug to cause a new immune response.

Thrombo-ischaemic pinnal necrosis associated with fenbendazole treatment in a dog

An 11-week-old, female West Highland white terrier was presented with necrosis of the distal third of both pinnae. Haematology, biochemistry and urinalysis, Coombs test, antinuclear antibody and cold autoagglutinin antibody tests were normal. A drug reaction to fenbendazole was diagnosed. The necrotic ear tips were surgically removed. Histopathology revealed extensive coagulative necrosis of the epidermis and superficial to mid-dermis, a moderate interstitial neutrophilic infiltrate and complete thrombotic occlusion and necrosis of blood vessels. There was also endothelial cell activation and proliferation with endothelial cell cushions protruding into the vascular lumen. Immunohistochemistry for factor VIII-related antigen confirmed endothelial cell involvement. This case represents an unusual, drug-induced, thrombo-ischaemic necrosis of the pinnae. It is also, to the authors' knowledge, the first report of fenbendazole sensitivity in a dog. The histopathology is similar to previous cases of proliferative thrombovascular pinnal necrosis, suggesting that drug reactions should be considered in this condition.

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.

Successful intravenous human immunoglobulin treatment of drug-induced Stevens-Johnson syndrome in a dog

A two-year-old, male English springer spaniel developed severe mucocutaneous ulceration following treatment with trimethoprim-potentiated sulphadiazine. The clinical signs were consistent with Stevens-Johnson syndrome (SJS): there were no target or arciform lesions typical of erythema multiforme minor and major; more than one mucosal surface was affected; epidermal detachment affected less than 10 per cent of the body surface area; and there was a clear history of drug exposure. Systemic signs included a severe hepatopathy, dyspnoea, pyrexia and cachexia. Glucocorticoid therapy was associated with secondary infection by Pseudomonas aeruginosa. The clinical signs rapidly resolved following a single intravenous infusion of 0.51 g/kg human immunoglobulin (ivHIG) as a 5 per cent solution. By blocking FAS/FAS ligand (CD95/CD95L) interactions, ivHIG is thought to prevent keratinocyte apoptosis. It also binds to immunoglobulin G Fc receptors, inhibiting cell activation and cytokine synthesis, neutralises autoantibodies and immune complexes, blocks complement activity, is antimicrobial and increases colloid osmotic pressure. To the authors' knowledge, this is the first report of successful treatment of canine SJS using ivHIG, although it has been used to treat erythema multiforme in a cat and toxic epidermal necrolysis in a dog.

Drug interaction with T-cell receptors: T-cell receptor density determines degree of cross-reactivity

BACKGROUND

Immune-mediated adverse reactions to drugs are often due to T-cell reactivity, and cross-reactivity is an important problem in pharmacotherapy.

OBJECTIVE

We investigated whether chemical inert drugs can stimulate T cells through their T-cell receptor (TCR) and analyzed the cross-reactivities to related compounds.

METHODS

We transfected human TCRs isolated from two drug-reactive T-cell clones (TCCs) by PCR into a TCR-negative mouse T-cell hybridoma. The TCCs were isolated from a patient with drug hypersensitivity to the antibacterial sulfonamide sulfamethoxazole (SMX).

RESULTS

The transfectants reacted to SMX only in the presence of antigen-presenting cells (APCs). Glutaraldehyde-fixed APCs, however, were sufficient to elicit T-cell stimulation, indicating a processing-independent direct interaction of the drug with the TCR and MHC molecule. The transfected hybridomas secreted IL-2 in a drug dose-dependent manner, whereas the degree of reactivity was dependent on the level of TCR expression. One transfectant reacted not only to SMX but also to related sulfonamide compounds. Interestingly, high TCR expression increased cross-reactivity to other structurally related compounds. In addition, SMX-specific TCR cross-reacted only with sulfonamides bearing a sulfanilamide core structure but not with sulfonamides such as celecoxib, furosemide, or glibenclamide.

CONCLUSIONS

These results demonstrate that the T-cell reactivity to drugs is solely determined by the TCR. Moreover, these results show that cross-reactivity of structurally similar compounds correlates with the density of the TCR. Stably transfected T-cell hybridomas may represent a powerful screening tool for cross-reactivity of newly generated sulfonamide-containing compounds such as celecoxib.

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.

Distinct delayed T-cell response to beta-methasone and penicillin-G in the same patient

BACKGROUND

Multiple drug allergy syndrome is a clinical condition characterized by reactions against more than one different class of, both pharmacologically and structurally, unrelated drugs. Scanty data are available to date about a multiple drug delayed hypersensitivity syndrome. Our aim was to report the case of a delayed reaction to both beta-methasone (beta-MT) and penicillin-G (pen-G) occurring in the same patient, and analyse beta-MT- and pen-G-specific T-cell Lines (TCLs) with regard to their specificity, phenotype and cytokine profile.

METHODS

We generated two drug-specific TCLs from biopsies at the site of positive intradermal reactions, and analysed their immunophenotype, T-cell receptor Vbeta (TCR-Vbeta) domains expression and cytokine profile.

RESULTS

We demonstrated the specificity of the T cells isolated from positive intradermal test reactions to pen-G and beta-MT through the strict dose-dependent proliferation in response to drug-pulsed autologous antigen presenting cells. Fluorescence activated cell sorter (FACS) analysis revealed a predominance of CD4+ cells in the inflammatory cell infiltrate of intradermal test with beta-MT, while a predominance of CD8+ T cells in the site of delayed reaction to pen-G was found. The drug specific CD4+ and CD8+ T cells were heterogeneous, with regard to TCR-Vbeta usage. CD8+ pen-G-TCL displayed a preferential T helper 2 (Th2) profile, while a substantially heterogeneous pattern of cytokine production characterized specific beta-MT TCL.

CONCLUSION

The study describes the coexistence in the same patient of a delayed hypersensitivity to both penicillin G and beta-MT, driven, respectively, by pen-G-specificTh2-skewed CD8+ and beta-MT specificTh0 CD4+ T cells. This case further support the existence of a multiple drug allergy syndrome also for delayed hypersensitivity.

Modes of presentation of chemical neoantigens to the immune system

The immune system can interact with small molecular compounds like drugs. Drugs are not only immunogenic because of their chemical reactivity, but also because they may bind in a labile way to MHC-molecules and fit into available T-cell receptors. This seems to be sufficient to stimulate T-cells. Such structural features of a drug have to be considered in the evaluation of drug hypersensitivity reactions and should be taken into account in predictive drug allergy testing.

Mechanisms of idiosyncratic drug reactions: the case of felbamate

Idiosyncratic drug reactions (IDR) are a specific type of drug toxicity characterized by their delayed onset, low incidence and reactive metabolite formation with little, if any, correlation between pharmacokinetics or pharmacodynamics and the toxicological outcome. As the name implies, IDR are unpredictable and often result in the post marketing failure of otherwise useful therapies. Examples of drugs, which have failed as a result of IDR in recent years, include trovafloxacin, zileuton, troglitazone, tolcapone and felbamate. To date there exists no pre-clinical model to predict these adverse drug reactions and a mechanistic understanding of these toxicities remains limited. In an attempt to better understand this class of drug toxicities and gain mechanistic insight, we have studied the IDR associated with a model compound, felbamate. Our studies with felbamate are consistent with the theory that compounds which cause IDR undergo bioactivation to a highly reactive electrophilic metabolite that is capable of forming covalent protein adducts in vivo. In additon, our data suggest that under normal physiological conditions glutathione plays a protective role in preventing IDR during felbamate therapy, further emphasizing a correlation between reactive metabolite formation and a toxic outcome. Clinical studies with felbamate have been able to demonstrate an association between reactive metabolite formation and a clinically relevant toxicity; however, additional research is required to more fully understand the link between reactive metabolite formation and the events which elicit toxicity. Going forward, it seems reasonable that screening for reactive metabolite formation in early drug discovery may be an important tool in eliminating the post-marketing failure of otherwise useful therapies.

Non-covalent presentation of sulfamethoxazole to human CD4+ T cells is independent of distinct human leucocyte antigen-bound peptides

BACKGROUND

It has been shown that drugs comprise a group of non-peptide antigens that can be recognized by human T cells in the context of HLA class II and that this recognition is involved in allergic reactions. Recent studies have demonstrated a MHC-restricted but processing- and metabolism-independent pathway for the presentation of allergenic drugs such as lidocaine and sulfamethoxazole (SMX) to drug-specific T cells. However, there is little information so far on the precise molecular mechanisms of this non-covalent drug presentation.

OBJECTIVE

The aim of this study was to evaluate the requirements for a specific peptide occupying the groove of the MHC class II molecule for the efficient presentation of non-covalently bound drugs to CD4+ T cells.

METHODS

We analysed the effect of coincubation or prepulse of antigen presenting cells (APC) with different peptides on the proliferative responses of SMX-specific CD4+ T cell clones. In a second series of experiments, we eluted HLA-bound peptides from the surface of antigen presenting cells by mild acid treatment. Successful removal of peptides was tested directly using labelled peptides and functionally by monitoring activation and proliferation of peptide-specific T cell clones. Finally, the presentation of SMX to SMX-specific T cell clones before and after elution of MHC class II bound peptides was tested.

RESULTS

We found that neither peptide coincubation nor peptide prepulse of APC altered the proliferative response of SMX-specific T cells. APC treated with the acid for a short time retained cell viability, MHC class II expression and antigen presenting cell function. However, defined peptides could be eluted from surface MHC class II molecules nearly quantitatively. Nevertheless, the chemically non-reactive drug SMX could still be presented to specific T cells independent of the presence of distinct self-peptides.

CONCLUSION

Our data suggest that small molecules like drugs can bind to a multitude of HLA-bound peptides or that, similar to superantigens, they might bind directly to HLA.

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.

mRNA expression of multiple cytochrome p450 isozymes in four types of cultured skin cells

BACKGROUND

Many drugs are known to induce allergic reactions in the skin. The metabolic activation of drugs resulting in the formation of protein adducts is thought to be a first step in the induction of these allergic reactions. We postulated that dermal tissue might be a site of drug activation by cytochrome P450 (CYP) isozymes.

METHODS

Messenger RNA was extracted from cultured Langerhans cells, keratinocytes, fibroblasts and melanocytes from 6 individuals, and CYP mRNA expression was analyzed by RT-PCR.

RESULTS

CYP1A1, 1B1 and 2E1 were found in all four cell types. CYP2A6, 2C, 2D6, 3A5, 3A7 and 4B1 mRNA was expressed in a cell-type- and/or individual-specific manner. CYP1A2, 2A7, 2B6 and 3A4 mRNA was not detectable.

CONCLUSIONS

The mRNA for a variety of CYP isozymes was expressed in all four types of skin cells examined. These CYP enzymes may be involved in the pathogenesis of drug-induced allergic reactions in the skin.

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.

Predictive drug allergy testing: an alternative viewpoint

T- and B-cells recognise drugs when bound as haptens to carrier molecules. Recent studies suggest that drugs might also bind in a non-covalent form to MHC-peptide complexes and T cell receptors, and are thereby able to stimulate T cells. This has, however, only been shown for drug-specific T cell clones. Functional analysis revealed that drug-reactive T cells secrete high amounts of IL-5 and are cytotoxic. Cytotoxicity is mediated by drug-specific CD4(+) and CD8(+) cells and, as revealed by the immunohistochemical analysis of drug-induced exanthems, might be involved in the killing of keratinocytes thus explaining the drug-induced exanthem. Further work is needed to clarify the type and exact location of the rather labile drug binding to MHC and T cell receptors, and to evaluate what drug allergies might be caused by such an unusual presentation and immune stimulation. This new model as well as findings from the analysis of clinical drug allergies may have major implications on how to test and predict the allergenic potential of drugs. A change and expansion of currently performed test procedures is required to predict the allergenic potential of drugs.

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.

Recognition of sulfamethoxazole and its reactive metabolites by drug-specific CD4+ T cells from allergic individuals

The recognition of the antibiotic sulfamethoxazole (SMX) by T cells is usually explained with the hapten-carrier model. However, recent investigations have revealed a MHC-restricted but processing- and metabolism-independent pathway of drug presentation. This suggested a labile, low-affinity binding of SMX to MHC-peptide complexes on APC. To study the role of covalent vs noncovalent drug presentation in SMX allergy, we analyzed the proliferative response of PBMC and T cell clones from patients with SMX allergy to SMX and its reactive oxidative metabolites SMX-hydroxylamine and nitroso-SMX. Although the great majority of T cell clones were specific for noncovalently bound SMX, PBMC and a small fraction of clones responded to nitroso-SMX-modified cells or were cross-reactive. Rapid down-regulation of TCR expression in T cell clones upon stimulation indicated a processing-independent activation irrespective of specificity for covalently or noncovalently presented Ag. In conclusion, our data show that recognition of SMX presented in covalent and noncovalent bound form is possible by the same TCR but that the former is the exception rather than the rule. The scarcity of cross-reactivity between covalently and noncovalently bound SMX suggests that the primary stimulation may be directed to the noncovalently bound SMX.