T-cell recognition of chemicals, protein allergens and drugs: towards the development of in vitro assays

Abstract

Chemicals can elicit T-cell-mediated diseases such as allergic contact dermatitis and adverse drug reactions. Therefore, testing of chemicals, drugs and protein allergens for hazard identification and risk assessment is essential in regulatory toxicology. The seventh amendment of the EU Cosmetics Directive now prohibits the testing of cosmetic ingredients in mice, guinea pigs and other animal species to assess their sensitizing potential. In addition, the EU Chemicals Directive REACh requires the retesting of more than 30,000 chemicals for different toxicological endpoints, including sensitization, requiring vast numbers of animals. Therefore, alternative methods are urgently needed to eventually replace animal testing. Here, we summarize the outcome of an expert meeting in Rome on 7 November 2009 on the development of T-cell-based in vitro assays as tools in immunotoxicology to identify hazardous chemicals and drugs. In addition, we provide an overview of the development of the field over the last two decades.

Fig. 1

Modes of chemical recognition by T cells. T cells interact with their TCR with MHC class I or class II molecules that present chemicals covalently bound to peptides in the binding groove of the MHC molecules (classical haptens), complexed to amino acids in MHC molecules and TCR with or without participation of MHC-bound peptides (metal ions) or noncovalently associated with MHC and/or TCR in a peptide-dependent or -independent manner (p-i concept, some drugs)

Fig. 2

Modes of chemical delivery in T-cell assays. Chemicals that are used to stimulate T cells in T-cell assays can be either added directly or used to modify APC such as DC (hapten modification). Alternatively, chemical-coupled proteins (hapten–protein conjugates) such as HSA can be added to the T-cell/DC cocultures

Fig. 3

Schematic protocol for in vitro T-cell priming assays. In the in vitro T-cell priming assay, sorted naive human T cells are primed with immature DC plus chemical. Proliferation can be measured on days 5 and 10. The culture is restimulated with fresh DC plus chemical on day 10 to assess antigen-specificity and to perform additional functional testing such as cytokine secretion assays or intracellular cytokine staining (ICS)