hNK cells induce caspase activity in K14⁺ invasive cells, and hNK cell cytotoxicity can be increased by using a CD44 antibody specific to K14⁺ cells. (A and B) Representative confocal images of tumor organoids (A) and tumor clusters (B) stained for caspase activity (green) and K14 (white) among tumor organoids cultured alone (top) or in coculture with hNK cells (bottom). Scale bar, 10 µm. (C) Representative confocal images of staining tumor cell clusters for CD44 and K14. Scale bar, 10 µm. (D) Schema for the ADCC assay. Tumor clusters were isolated from MMTV-PyMT mammary tumors and incubated with a CD44 antibody before being in coculture with hNK cells at a reduced ratio of 10 NK cells to 1 tumor cell. (D′) Boxplot of the normalized colony count. Error bars represent 5th to 95th percentile. ns, not significant; *, P < 0.05; ***, P < 0.001 by Mann–Whitney U test.