CAR 422 T-cells targeting mesothelin stump overcome shedding, boost efficacy in ovarian and pancreatic cancer models.

Current CAR T-cell therapy targeting mesothelin (MSLN) in solid tumors like ovarian cancer and pancreatic cancer faces significant challenges. A major issue is the natural proteolytic shedding of most cell surface mesothelin, leaving only a short juxtamembrane "stump." This shedding creates two problems: reduced target antigen on tumor cells and the presence of soluble, shed mesothelin in the tumor microenvironment and circulation, which acts as a decoy, binding to CAR T cells and diminishing their engagement with tumor cells. This has limited efficacy and raised safety concerns in clinical trials for CAR T cells targeting membrane-distal mesothelin regions.

Researchers engineered novel CAR 422 T cells utilizing phage display-derived antibodies specifically targeting the mesothelin "stump" domain, making them resilient to antigen shedding. They evaluated the cytotoxicity and in vivo activity of CAR 422 T cells, comparing them to conventional anti-mesothelin CAR T cells. Efficacy was assessed against tumor cells known to be resistant to conventional CAR T approaches. Furthermore, on-target/off-tumor toxicity was evaluated in a human mesothelin knock-in mouse model to assess safety profiles.

CAR 422 T cells, designed to target the mesothelin stump, demonstrated cytotoxicity and in vivo activity that were comparable to previously studied anti-mesothelin CAR T cells. Importantly, this novel design proved effective against tumor cells that exhibited resistance to conventional anti-mesothelin CAR T cells, which typically target the shed domain. This suggests a significant advantage in overcoming a key mechanism of therapeutic failure. Furthermore, in a human mesothelin knock-in mouse model, CAR 422 T cells showed reduced on-target/off-tumor toxicity, addressing a critical safety concern associated with mesothelin-targeted therapies.

CAR 422 T cells were effective against tumor cells that were resistant to conventional anti-mesothelin CAR T cells and showed reduced on-target/off-tumor toxicity in a human mesothelin knock-in mouse model.