In vitro techniques for hazard identification for potential sensitizers have been of increasing importance to the NTP. In FY22, BRT focused on reporting out the data for chemicals nominated by agency partners. The NTP, in collaboration with the EPA, CSPC, FDA and other federal agencies, had compiled a list of 227 chemicals for in vitro testing for the potential to cause sensitization and hypersensitivity. These compounds were nominated based on the availability of in vivo data to explore the applicability domain for several in vitro approaches including the: 1) DPRA – Direct Peptide Reactivity Assay; 2) Keratinosens – keratinocyte activation; and the 3) h-CLAT – Human cell line activation test. These assays serve as the toolbox for the NTP in vitro testing battery that is being used to evaluate the potential for chemicals to cause sensitization. The NTP has received 5 final reports from these in vitro studies which have been shared with interagency collaborators. A collaborative study was established to investigate the applicability domain for the GARDSkin assay. This assay uses gene expression profiling to discriminate skin sensitizers from non-sensitizers. A total of 31 chemicals were tested in this project. The data is under review by NTP agency partners and a report is in preparation. In FY22 BRT was asked by NTP to join the validation trial for the Electrophilic Allergen Screening Assay (EASA) as an independent validation laboratory. A total of 20 coded chemicals were provided to BRT from the validation team and were analyzed using the EASA assay under a blinded approach. Data collection for these chemicals has been completed and a draft report has been submitted to the validation team. This assay represents a valuable addition to the in vitro toolbox for hypersensitivity assessment.