Development of a stepwise screening approach to assess the intrinsic immunogenicity of drugs and chemicals

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Adverse drug reactions are a serious impediment to the development of new medicines. Approximately 1 in 16 hospital admissions in the UK are due to some form of adverse drug reaction. One of the best known, but least understood drug side-effects is hypersensitivity. Such reactions are unpredictable with respect to the chemistry of the drug and the human biology. For this reason, pre-clinical animal models fail to predict whether a novel compound will induce an immune response in humans. Thus, we have conceived a multi-disciplinary project using cells from healthy donors to define the chemical interface between drugs and immune receptors, and the checkpoints that need to be overcome for the drug receptor binding interaction to develop into an aberrant immune response. This mechanistic immunology will provide the framework for a toolbox of assays that can be used in a logical fashion to assess the quality and intensity of drug-specific immune responses. Stratification of assays will result in a screening platform to assess intrinsic immunogenicity of novel drug candidates at early and later phases of drug development.For this project to be feasible, we have established an HLA genotyped cell bank containing blood mononuclear cells from 1000 healthy donors and the culture conditions needed to study the origin of drug- and drug metabolite-specific T-lymphocyte responses. This provides the biological resource to investigate any known drug HLA association in the laboratory at the fundamental cellular, molecular and chemical level. Our initial research will focus on a panel of compounds associated with a high incidence of hypersensitivity reactions (i.e., training compounds) to generate antigen-specific T-cell responses and to define the role of HLA alleles in antigen presentation. This established protocol is time-consuming and designed for laboratory-based investigation of few variables utilizing cells from a single drug-naïve donor. In order to form a suitable platform for the screening of drugs we will focus on miniaturization to assess (1) multiple HLA-typed individuals simultaneously and (2) multiple experiments with cells from one individual within a single plate format. Established drug immunogenicity screening platforms (level 1 assays) will be transferred to our industrial partner and blinded test compounds will be assessed at both sites to define assay sensitivity and specificity.The essential knowledge of drug disposition in cell systems, immune parameters and human factors required to induce a response have not been fully defined and have therefore not been applied to a relevant test system. Thus, we will conduct mechanistic immunological investigations to elucidate (1) whether drug binding to specific HLA alleles results in the activation of naïve and/or memory T-cells, (2) the parameters that regulate activation of drug-specific T-cells (3) the drug protein adducts formed in tissue cells and whether the display of drug antigens on MHC molecules expressed on tissue cells results in T-cell activation. We have already overcome the major challenge of developing autologous tissue/immune cell co-culture systems through the generation of iPS-derived hepatocyte and keratinocyte lines and antigen-specific T-cells from the same HLA-typed healthy donors. These experiments will form the basis for level 2 assays to explore the nature of drug-specific T-cell responses and regulatory and tissue factors.Level 3 assays involve the cloning of drug- and drug metabolite-specific T-cells from level 1 and 2 assays to define cellular phenotype and functionality and to assess HLA allele restriction, cross reactivity and mechanisms of T-cell activation.The ultimate outcome of the project is to recommend a series of assays that can be used to screen for potential immunogenicity of new compounds. Working alongside our industrial partner we have a pathway for initial application of the screening assays in a real-life setting.