Growth of ALK-A5 retrovirally infected cells is inhibited in presence of low FCS concentration or cytotoxic agents. (A) ALK-A5 or ALK-A6 pSRG– or pSRG-infected cells were cultured in the presence of different concentrations of FCS. The percentages of EGFP⁺ cells were calculated over time. Data are reported as ratios of ALK-A5 versus ALK-A6 pSRG EGFP⁺ cells. (B) Retrovirally infected cells (3 days after transduction) were cultured with different concentration of bleomycin (B) or cyclophosphamide (C). Percentages of EGFP⁺ cells were obtained by flow cytometry and ratios between ALK-A5 versus ALK-A6 pSRG EGFP⁺ cells were calculated. In A-C, ▪ represents pSRG-A5; □, pSRG-A6.