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

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

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

Drug-induced skin toxicity: gaps in preclinical testing cascade as opportunities for complex in vitro models and assays

Skin is the largest organ of the body and serves as the principle barrier to the environment. Composed of multiple cell types arranged in stratified layers with highly specialized appendages, it serves sensory and immune surveillance roles in addition to its primary mechanical function. Several complex in vitro models of skin (i.e. microphysiological systems (MPS) including but not limited to 3D tissues, organ-on-a-chip, organoids), have been developed and assays validated for regulatory purposes. As such, skin is arguably the most advanced organ with respect to model development and adoption across industries including chemical, cosmetic, and to a somewhat lesser extent, pharmaceutical. Early adoption of complex skin models and associated assays for assessment of irritation and corrosion spurred research into other areas such as sensitization, absorption, phototoxicity, and genotoxicity. Despite such considerable advancements, opportunities remain for immune capabilities, inclusion of appendages such as hair follicles, fluidics, and innervation, among others. Herein, we provide an overview of current complex skin model capabilities and limitations within the drug development scheme, and recommendations for future model development and assay qualification and/or validation with the intent to facilitate wider adoption of use within the pharmaceutical industry.

[Delayed-type cutaneous drug reactions. Pathogenesis, clinical features and histology]

BACKGROUND

Cutaneous reactions to drugs can be subdivided in different ways. In addition to the standard classification according to the etiopathogenesis there are also classifications based predominantly on morphological criteria. The majority of drug-related cutaneous adverse reactions are immunological reactions which are collectively classified under the term hypersensitivity. These reactions are based on drug-specific immunoglobulin E (IgE) or cell-mediated mechanisms, not on the mechanism of action of the drug and are unpredictable. Delayed type reactions to drugs are forms of type IV T-cell mediated hypersensitivity. A prerequisite is a stable association of a pharmaceutical substance with a protein so that hapten-protein conjugates can be produced. The most common clinical symptom is maculopapular (morbilliform) drug-related exanthema. This article also examines lichen planus like drug reaction and drug-induced (hematogenic) allergic contact dermatitis in more detail.

DIAGNOSTICS

The diagnostics are never trivial but also include the differentiation from viral exanthema and initial phases of severe cutaneous adverse reactions, such as toxic epidermal necrolysis. In addition to the morphological classification, the final diagnosis encompasses the interpretation of histopathological alterations in the skin biopsy, analysis of patient medication history, laboratory results and inclusion of data from the literature. Patch tests can also have additional diagnostic benefits. In vitro tests which involve the cellular incubation of the drug responsible should be reserved for specialized laboratories. A prerequisite for successful treatment is immediate termination of the drug responsible.

THERAPY AND PROGNOSIS

Therapy is symptomatic with topical and also short-term systemic steroids and antihistamines. The prognosis is very good.

The role of cytokines in the mechanism of adverse drug reactions

Cytokines are thought to play a role in acute and/or immune-mediated adverse drug reactions (ADRs) due to their ability to regulate the innate and adaptive immune systems. This role is highly complex owing to the pluripotent nature of cytokines, which enables the same cytokine to play multiple roles depending on target organ(s) involved. As a result, the discussion of cytokine involvement in ADRs is organized according to target organ(s); specifically, ADRs targeting skin and liver, as well as ADRs targeting multiple organs, such as drug-induced autoimmunity and infusion-related reactions. In addition to discussing the mechanism(s) by which cytokines contribute to the initiation, propagation, and resolution of ADRs, we also discuss the usefulness and limitations of current methodologies available to conduct such mechanistic studies. While animal models appear to hold the most promise for uncovering additional mechanisms, this field is plagued by a lack of good animal models and, as a result, the mechanism of cytokine involvement in ADRs is often studied using less informative in vitro studies. The recent formation of the Drug-Induced Liver Injury Network, whose goal is collect thousands of samples from drug-induced liver injury patients, has enormous potential to advance knowledge in this field, by enabling large-scale cytokine polymorphism studies. In conclusion, we discuss how further advances in this field could be of significant benefit to patients in terms of preventing, predicting, and treating ADRs.

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.

A mechanistic investigation into the irreversible protein binding and antigenicity of p-phenylenediamine

Exposure to the skin sensitizer p-phenylenediamine (PPD) is associated with allergic contact dermatitis; however, the ability of PPD to modify protein has not been fully investigated. The aims of this study were to characterize the reactions of PPD and the structurally related chemical 2,5-dimethyl-1,4-benzoquinonediamine with model nucleophiles, a synthetic peptide (DS3) containing each of the naturally occurring amino acids and His-tagged glutathione-S-transferase pi (GSTP), and to explore the effect of dimethyl substitution on PPD-specific T-cell responses using lymphocytes from allergic patients. The reductive soft nucleophiles N-acetyl cysteine and glutathione prevented PPD self-conjugation reactions and Bandrowski's base formation, but no adducts were detected. N-Acetyl lysine, a hard nucleophile, did not alter the rate of PPD degradation or form PPD adducts. With PPD and 2,5-dimethyl-1,4-benzoquinonediamine, only cysteine was targeted in the DS3 peptide. PPD and 2,5-dimethyl-1,4-benzoquinonediamine were also found to selectively modify the reactive Cys 47 residue of GSTP, which has a pK(a) of 3.5-4.2 and therefore exists in a largely protonated form. Glutathione formed mixed disulfides with the DS3 peptide, reducing levels of PPD binding. Lymphocytes from PPD allergic patients proliferated in the presence of PPD but not with 2,5-dimethyl-1,4-benzoquinonediamine. These results reveal that PPD and 2,5-dimethyl-1,4-benzoquinonediamine bind selectively to specific cysteine residues in peptides and proteins. Lymphocytes from PPD allergic patients were capable of discriminating between the different haptenic structures, suggesting that the hapten, but not the peptide moiety associated with MHC, is an important determinant for T-cell recognition.

Role of epidermal dendritic cells in drug-induced cutaneous adverse reactions

Drug-induced adverse reactions (ADR) include any undesirable pharmacological effect that occurs following drug administration at therapeutic doses. The appearance of ADR significantly limits the use of drugs in as much as their clinical symptoms may range from very mild discomfort such as cutaneous rash, up to very severe, or even fatal tissue necrolysis such as the Stevens Johnson syndrome.One of the most frequently involved organ during ADR is the skin. Drug-induced cutaneous reactions (CDR) incidence is variable but they may appear in 2-3% of ambulatory patients, and it may increase to 10-15% when patients are hospitalized, or even be as high as 60% when co morbidity includes the presence of virus, bacteria, or parasites.Due to the fact that skin is one of the organs most frequently involved in ADR, in this work we analyze and propose a mechanism by which epidermal dendritic cells operating as the sentinels of the skin neuro-immune-endocrine system may contribute to CDR via either immunogenic or tolerogenic immune responses towards drugs, whenever they are administered topic or systemically.

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.