IL-15 boosts mesothelin- and CD70-CAR NK cell potency in PDAC without added benefit from dual targeting

Chimeric antigen receptor (CAR) therapies have shown great success in hematological malignancies but remain largely ineffective against solid tumors such as pancreatic ductal adenocarcinoma (PDAC). A key obstacle among various aspects, is the dense stromal barrier formed by cancer-associated fibroblasts (CAFs), providing a rationale for simultaneously targeting stroma and tumor cells. Using immunohistochemistry of primary PDAC tumors and liver metastases, we confirmed high mesothelin (MSLN) expression on tumor cells, and CD70 expression on tumor cells and predominantly CAFs. Based on these results and the favorable safety profile of CAR natural killer (NK) cells over CAR T cells, we generated MSLN- and CD70-targeting IL-15-armored CAR NK cells. Both constructs mediated cytotoxicity against different pancreatic cancer and CAF cell lines with varying antigen expression in vitro, demonstrating that both, the CAR-molecule and IL-15 were required to increase functionality against more treatment-resistant cell lines. Interestingly, pooled MSLN- and CD70-CAR NK cells did not significantly improve cytolysis compared to monotherapies in an advanced 3D in vitro model or in vivo. Together these findings highlight the limitations of dual-targeting approaches and underscore the need for advanced engineering strategies to improve CAR NK cells beyond antigen targeting and cytokine support in the PDAC microenvironment.