CD56 on intratumoral NK cells: orchestrating NK cell-mediated anti-tumor effects in bladder cancer.

Bladder cancer (BCa) exhibits favorable responses to immunotherapy, but a significant percentage of patients fail to show a response owing to an inadequate tumor-immune landscape. We previously showed that NK cells are one of the predominant tumor-infiltrating lymphocytes in BCa and correlate with improved patient survival. However, that link was observed only with CD56(bright) NK cells while the CD56(dim) subset exhibited reduced cytotoxicity and higher accumulation in advanced BCa stages. The role of CD56 in NK cell functionality in BCa, however, remains unclear. Using flow cytometry and cytotoxicity assays, we demonstrated a significant decrease in cytotoxicity and activation of NK92 cells against BCa upon CD56 deletion. Further, migration assays and atomic force microscopy showed CD56 deletion impaired NK92 cell migration and adhesion to bladder tumor cells, reducing NK92 cell-mediated apoptosis of BCa cells. Prolonged exposure to bladder tumors led to CD56 loss in NK92 cells, suggesting tumor-induced NK92 cell dysfunction via CD56 reduction, consistent with our previous findings. Confocal microscopy revealed an overlap of CD56 and phosphorylated Pyk2, a critical kinase at the tumor-immune synapse, potentially mediating the downstream cytotoxicity effects. Blocking Pyk2 phosphorylation decreased CD56-mediated NK92 cell activation and reduced NK92 cell-mediated cytotoxicity against BCa. Finally, we showed that CD56 is also expressed by BCa cells and may be a predictive biomarker for NK cell-based immunotherapy, with its shedding indicating a mechanism for NK cell evasion. Our study identifies a novel innate-immune axis in BCa, leading to a better understanding of intratumoral NK cell biology and advancing NK cell-targeted treatments.