The present invention generally relates to specificity assays using cell cultures, in particular to chimeric antigen receptor (CAR) expressing reporter T (CAR-T) cell assays to test novel antigen binding moieties in different formats. Furthermore, the present invention relates to the use of CAR-T cells, transfected/transduced with an engineered chimeric antigen receptor (CAR) comprising a target antigen binding moiety capable of specific binding to a recognition domain of an antigen binding molecule. The invention also relates to methods and kits for specificity testing of a candidate antigen binding moiety and/or nucleic acid molecules and vectors expressing engineered CARs.