FLYRD18, NKIRTIL00626 (link) and Daudi cells were cultured in IMDM (Thermo Fisher Scientific), supplemented with 8% FCS (Thermo Fisher Scientific) and penicillinstreptomycin (100 IU/mL penicillin, 100 μg/mL streptomycin; Sigma-Aldrich). FLYRD18 and NKIRTIL006 cells were passaged every 2–3 days with trypsin-EDTA (Thermo Fisher Scientific). The human NK cell line KHYG-1 (DSMZ) was cultured in RPMI supplemented with 8% FBS and penicillinstreptomycin (100 IU/mL penicillin, 100 μg/mL streptomycin) containing 500 IU/mL IL-2 (Novartis). All cell lines were tested for mycoplasma using PCR-based screening and found negative.