Activity of His-ILFAC transgene in vivo. HSC536 lymphoblasts transfected with pDR2–His-ILFAC or pDR2-FAC were selected for stable expression of the episomal vectors by Hygromycin B, followed by analysis of their growth in the presence of MMC. Growth inhibition was measured by cell counting after 3 days (approximately 3 cell divisions) of continuous exposure to MMC and compared with untreated cells. The final cell count of untreated cultures was set at 100%. The mean values of duplicate sets of experiments are shown.