An In Vivo Tiered Approach to Test Immunosensitization by Low Molecular Weight Compounds

New chemical entities are tested in general toxicity assays during development before entering clinical trials. However, immunosensitization of these entities is not tested on a standard basis. There are no in vitro or in vivo standardized methods available for testing immunosensitization or immunostimulation. In this chapter, we describe a tiered strategy oral exposure model for assessing immunosensitization or immunostimulation capacity of low molecular weight compounds. The strategy starts from a set of data that may provide information on bioactivation, conjugation (hapten–protein conjugate formation), cytotoxicity and signs of inflammation in any of the animals in a 28 day-toxicity study. In case of concern, a reporter antigen–popliteal lymph node assay (RA–PLNA) and, subsequently, an oral exposure experiment with the reporter antigen can be performed. Based on the presence of RA-specific immune responses an indication for immunosensitization can be found.