NK cell expansion was performed in vitro by using VarioMACS (Miltenyi Biotec GmbH, Bergisch Gladbach, Germany) and cultured in MEM medium (Thermo Fisher Scientific, Inc., Waltham, MA, USA) for 72 h at 37°C. On day 5, MEM medium (Thermo Fisher Scientific, Inc.) was refreshed with the addition of autoplasma (1%) (Sigma-Aldrich; Merck KGaA) and interleukin-2 (500 IU/ml) (Sigma-Aldrich; Merck KGaA). Culture continued for 14 days at 37°C. Cells were then fixed with 4% paraformaldehyde for 15 min at 37°C and the viability of expanded NK cells was determined by 5% propidium iodide staining for 2 h at 37°C as described previously (25 (link)). In vitro-expanded NK cells were stained with primary antibodies and analyzed using a flow cytometer with antibodies and FCS Express™ 4 IVD software (De Novo Software, Glendale, CA, USA), as described in a previous study (24 (link)).