For investigating the efficacy of CAR NK cells against HER2-positive solid tumors, we used the clinic-derived JIMT-1 [19] and an in vitro generated MDA-MB-468 variant (MDA-HER2 for short), stably expressing ectopic HER2 [18] as trastuzumab-resistant (HER2+/CD44+) and the N87 cell line as trastuzumab-sensitive (HER2+/CD44−) tumor models [8]. Here, CD44 is linked to neoplasm.