F-11 cells were cultured in DMEM/F12 medium +20% FBS, 0.2 mM L-glutamine, 100 μM sodium hypoxanthine, 400 nM aminopterin, 16 μM thymidine (HAT supplement), and penicillin/streptomycin at 37°C (the cells were kindly provided
by Dr. S.E. Gordon, University of Washington).