Chemical-Specific T Cell Tests Aim to Bridge a Gap in Skin Sensitization Evaluation

Using new approach methodologies for the identification of a sensitizing co-formulant in a plant protection product

According to Regulation (EC) No 1272/2008, plant protection products (PPPs) can be classified for skin sensitisation by either considering the full formulation or the individual components. For a fraction of PPPs, an application of both assessment strategies results in discrepant classification results. We here aimed to resolve this discrepancy for PPP 1, an exemplary product, which was classified as sensitizing by a positive local lymph node assay but scored negative by the component-based method. We collected further data, as suggested by the regulation, based on a combination of new approach methodologies (NAMs) covering several key events (KEs) in the adverse outcome pathway model for skin sensitisation. Precisely, we employed quantitative structure activity relationship (QSAR) analysis (KE 1), the human cell line activation test (h-CLAT) complemented by Interleukin-8 release measurements (KE 3) and a novel short-term T cell test that is based on the induced expression of activation markers (KE 4). We tested the complete product, individual co-formulants (CFs) or single substances. PPP 1 tested positive in all in vitro assays. QSAR analysis revealed two CFs containing sensitizing chemicals. Only CF 1 was tested positive in the h-CLAT at a minimal induction threshold of 1.5 mg/mL, being less potent than PPP 1. In the T cell assay, both PPP 1 and CF 1 were tested positive at around 0.1 mg/mL. In conclusion, our results propose a novel integrated NAM-based strategy that should be explored further for skin sensitisation hazard identification of complex mixtures, such as PPPs.