MSLN and malignant pleural mesothelioma: Based on promising results from their preclinical studies [25, 42], the University of Pennsylvania completed two phase I trials in MM, testing their second generation anti-MSLN CAR T cell therapy carrying a murine derived SS1 scFv targeting MSLN region I. In the first trial against malignant pleural mesothelioma (MPM) and pancreatic ductal adenocarcinoma (PDAC) (NCT01355965), T cells were transfected with mRNA to express the CAR transiently and thus limit potential ‘on target/off tumor’ toxicities (Fig. 2e).