CD19 and cancer: Of note, compared with CLDN6-CAR NK cells, NK-92MI and CD19-CAR NK cells contacting cancer cells also underwent morphological changes, namely, short membrane extension, flap-shaped membrane extension or vesicular protrusion, and partial morphology elongation, indicating that natural biological characteristics of NK cells still exist, but they lacked the ability to specifically recognize antigens and showed little cytotoxicity.