DNMT1 and neoplasm: And, ectopic expression of DNMT1 Del(155–163), but not its C1229S mutant reduced the sphere formation of CD133+ cells at passage 2 (Figure 4D,E), inhibited the stem cell activity by limited dilution assay (Figure 4F,G), and inhibited the tumor‐initiating capacity of CD133+ cells (Figure 4H).