MKI67 and cancer: As the proliferated cells are characterized by high expression of Ki67, which is regarded as a marker of dysplasia of cancer cells, we performed IHC staining of Ki67 on lung tissue sections (Figure 2E), and statistical analysis of Ki67 positive cells (Figure 2F), showing that repeated transplantation of UC-MSCs for 2 weeks would not increase the ratio of proliferating alveolar epithelial cells (Figure 2F).