Construction of truncated PSMA as a PET reporter gene for CAR T cell trafficking

In solid tumors, there are multiple barriers for a chimeric antigen receptor (CAR) T cell to surmount in order to reach the tumor site. For better understanding whether CAR T cells effectively infiltrate into tumor site, and simultaneously, whether there are off-target effects, real-time monitoring technologies need to be established. Cell-based positron emission tomography reporter genes have been developed to monitor engineered cells in living subjects. In this study, we reported the construction of a novel reporter gene truncated prostate-specific membrane antigen (Delta PSMA) pending for monitoring CAR T cells using 68Ga-PSMA-617 and a method for tracking the distribution of CAR T cells in vivo was developed. Data were provided to demonstrate that Delta PSMA was predominantly localized on the plasma membrane and could take up 68Ga-PSMA-617 in vitro in a time-dependent manner. And the expression of Delta PSMA did not affect CAR expression and cytolytic capacity of CAR T cells. CAR-Delta PSMA T cell xenografts in nude mice were clearly imaged by positron emission tomography 60 min after injection of 68Ga-PSMA-617. PSMA paired with 68Ga-PSMA-617 was capable of identifying approximately 1 x 104 engineered CAR T cells. The ability to image small numbers of CAR T cells in vivo would be helpful to accelerate the translation of cell-based therapies into the clinic, and it may reinforce our understanding of treatment success, failure, and toxicity. For better understanding whether CAR T cells effectively infiltrate into tumor site and simultaneously, whether there are off-target effects, we constructed a novel reporter gene Delta PSMA to track the distribution of CAR T cells in vivo by 68Ga-PSMA-617. Results showed that CAR T cells expressing truncated PSMA retained the cytolytic functions against target cells and approximately 1 x 104 engineered CAR T cells could be identified by the pairing of PSMA and 68Ga-PSMA-617.