Generation of iPSCs and NK Cells

Human peripheral blood mononuclear cell (PBMC)-derived iPSC lines were generated as reported previously [11 , 22 (link)]. iPSCs were cultured with mTeSR1 (StemCell Technologies, Vancouver, BC, Canada) on six-well plates coated with Matrigel (BD Biosciences, Franklin Lakes, NJ) and mechanically passaged every 7 days by treating with 1 mg/ml Dispase (StemCell Technologies) at 37 °C for 5 min. Murine bone marrow-derived stromal cell line OP9-DLL1 (Riken BRC Cell Bank, Ibaraki, Japan) was cultured in Minimum Essential Medium α (MEM α) (Gibco, Waltham, MA) supplemented with 20% foetal bovine serum (FBS, Gibco). Tumour cell lines including breast ductal carcinoma cell line BT474 (ATCC HTB-20), breast metastatic carcinoma cell line MDA-MB-453 (ATCC HTB-131), breast adenocarcinoma cell line MCF7 (ATCC HTB-22) and breast ductal metastatic carcinoma cell line MDA-MB-435S (ATCC HTB-129) were cultured as recommended by ATCC. Primary NK cells were expanded from fresh PBMCs by co-culturing with inactivated modified K562 feeder cells as described previously [23 (link)]. NK cells were harvested as population of over 90% CD3-CD56+ cells after the co-culture.