2.1 Tissue culture
Human embryonic kidney (HEK) 293F cells (Thermo Life Technologies) were cultured in FreeStyle 293 Expression Medium (Thermo Fisher Scientific) containing penicillin-streptomycin (10 µg/mL) (Thermo Fisher Scientific). CHO-K1 cells were cultured in F-12K medium containing 10% fetal bovine serum (FBS), L-glutamine (2 mM), and penicillin-streptomycin (500 µg/mL). CHO-K1 cells (ATCC) stably transduced with PD-L1 were kindly provided to us by Dr. Sridhar Nimmagadda (Department of Oncology at Johns Hopkins Medicine) and cultured in F-12K medium (Thermo Life Technologies) containing 10% FBS, L-glutamine (2 mM), G418 Sulfate (2 mg/mL) (Thermo Fisher Scientific), and penicillin-streptomycin (500 µg/mL). H2444 cells were cultured in RPMI-1640 medium with 10% FBS, L-glutamine (2 mM), and penicillin-streptomycin (500 µg/mL). MDA-MB-231 cells were cultured in DMEM medium with 10% FBS, L-glutamine (2 mM), and penicillin-streptomycin (500 µg/mL). All cells were grown at 37°C with a humidified atmosphere and 5% CO2.