GDF2 and neoplasm: Two weeks later, BMP9‐MBs (20 ng/250 μL) were administered by tail vein injection and destroyed in the tumour by ultrasound stimulation (once every 3 days for a total of four times), and then the mice received an intravenous tail vein injection of 1.0 × 107 NK cells and an intra‐abdominal injection of an anti‐PD‐L1 antibody (0.2 mg/mouse).