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.