PSMA-Specific Car-Engineered T Cells for Prostate Cancer: CD28 outperforms combined CD28-41BB "Super- stimulation"
Despite advances in the understanding of its molecular pathophysiology, prostate cancer remains largely incurable, highlighting the need for novel therapies. We developed a chimeric antigen receptor (CAR) specific for prostate specific membrane antigen (PSMA), a glycoprotein that is overexpressed in prostate cancer, which expression involves neovasculature of several tumor entities, thus envisaging an additional antiangiogenic effect. To optimize the CAR design, we compared two CARs with
... wo CARs with signaling domains containing one or two T cell costimulatory elements, in addition to CD3ζ. Conversely, what has been described for other CARs, a third-generation CAR (containing CD28 and 41BB co-signaling domains) induced a potent antitumor effect similar to a second-generation CAR (containing CD28 co-signaling domain), though we observed a detrimental effect of the additional costimulatory domain that was attributed to increased activation-induced cell death (AICD). This “super-stimulation” resulted in exhaustion of cells, higher frequencies of cell death and, more importantly, the impossibility of sufficiently expanding the CAR cells to obtain the minimum number of cells requested for in vivo therapies. While the superiority of 2nd and 3rd generation over 1st generation CAR T cells has been clearly shown in both preclinical and clinical studies, the optimal combination of costimulatory domains for 3rd generation CAR-T cells must still be defined and should be evaluated case-by-case in order to fine-tune immunotherapy approaches.