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

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.

Background: Drug-specific T-lymphocytes participate in drug hypersensitivity reactions. To model such responses ex vivo we have generated an HLA-typed bank of PBMC from 1000 healthy donors and designed methods to study the activation of T-cells with drugs. Despite this, essential knowledge of drug antigens and the immune and human factors required to convert the antigenic signal into an immune response is missing. Therefore, predictive test systems have not yet been developed.

Objectives: We propose a radical new approach to study the bioscience underpinning drug immunogenicity based around our HLA-typed PBMC bank. The project will define key chemical and immunological parameters associated with the development of a T-cell response. These mechanistic studies provide the framework for a toolbox of assays that will be transferred to our industrial partner for assessment of the quality and intensity of the antigen-specific T-cell response induced by existing and novel drug candidates.

Methods: We will study the priming of naïve T-cells and activation of memory T-cells with training compounds (drugs and synthetic metabolites) using 3 methods. HLA-restriction, cellular phenotype and function and cross reactivity will be assessed. Immune checkpoint inhibitors will be utilized to increase sensitivity of the assays. Established autologous HLA-typed iPS-derived hepatocytes and keratinocytes will be used to measure qualitative/quantitative differences in drug protein binding profiles and to relate drug exposure to T-cell activation.

Impact: Currently, there are no established methods to predict drug immunogenicity. The scientific knowledge that we will generate will provide assays to assess the quality and intensity of the antigen-specific T-cell response induced by existing and novel compounds. Our industrial partner provides access to novel drugs for testing and a pathway for initial application of the newly established assays in a real-life setting.

Immunological drug reactions cannot be predicted; this is largely because the relationship between the chemistry of the drug antigen and the development of an immune response has not been defined. Through an interdisciplinary approach that relates donor genotype and phenotype to the chemical characteristics of the antigen we will conduct the fundamental bioscience underpinning drug immunogenicity. The project will help to integrate academic and industry scientists with expertise in immunological drug reactions to successfully characterize the activation of naïve T-cells from healthy donors by drugs. This will place us at the forefront in the field studying immunological drug reactions and allow us to make a real impact, by translating laboratory findings into a toolbox of assays that can be used to assess intrinsic immunogenicity of drugs and chemicals.

Who are the beneficiaries of the research?

1. Pharma: Due to their nature, drug hypersensitivity reactions are usually not detected until a drug is administered to a large population, such as phase III clinical trials, or the market. As well as a risk to human safety, the withdrawal of drugs at such a late stage is of great cost to Pharma, and also prolongs the time for the patient until a safer drug is developed. The cost of discovering and developing a drug is estimated to be about $900 million, and takes approximately 13 years (Kola et al. Nat Rev Drug Disc. 2004; 3(8):711-5). Thus reducing late-stage drug withdrawals through the development of assays to assess immunogenicity of drugs would reduce the cost and time to bring safer drugs to the market, benefitting the pharmaceutical industry and patients (timeline 3-5 years).

2. Chemical/cosmetics industries: The project will provide us with basic insights into immunology which will engage researchers in the field of environmental chemical and cosmetic allergy. Improved assays that predict sensitization potential of cosmetics is timely since the testing of cosmetic ingredients in animals is subject to an EU ban (timeline 3-5 years).

3. Diagnostics sector: The diagnostics sector will benefit indirectly from our project. By relating drug antigen formation to immune responses we will develop a clearer understanding of why certain compounds are associated with a high incidence of serious adverse reactions. Lessons learned from our project will pave the way for the development of sensitive and specific diagnostic tests that increase drug safety by stratification of drug use. The concept of such tests would be attractive to diagnostic companies for future development and commercialisation (timeline 5-10 years).

4. Patients and health service providers: Patients and health service providers will benefit from our project if newly marketed drug are associated with a lower number of immune-mediated adverse drug reactions. It was estimated in 2004 that the annual cost of admissions to the NHS because of adverse drug reactions was £466m. Since immune-mediated reactions are often the most severe and result in the longest hospital stay and most intensive treatment, our project has the potential to significantly reduce NHS costs (timeline 5-10 years).

5. Drug regulators: Scientific outputs from the project will better inform drug regulators and will thereby contribute towards better benefit-risk assessments for the use of drugs (timeline 5 years+).