Figure 3: Evaluation of tumorigenicity in TBI rats given in situ huMSC transplantation. (A) Pathology of livers and lungs in the In Situ group (original magnification 100×). Scale bar: 200 μm. No cell degeneration, necrosis, hyperplasia or tumorigenesis was observed in the liver and lungs on days 1, 3, 7, 14 or 28, or even 12 months post-transplantation. (B) Immunohistochemical staining for EGFRvIII in the In Situ group (original magnification 200×). Scale bar: 100 μm. No positive signal was observed in huMSC-treated rats from the day of injection to 12 months after injection. (C) Immunofluorescence staining for PCNA in the In Situ group (original magnification 400×). Scale bar: 50 μm. There was no PCNA immunoreactivity (positive signal) in CFSE-labeled huMSCs (green arrows), indicating that the huMSCs do not exhibit proliferative activity. However, the adjacent neural cells are PCNA-positive (red, stained by CoraLite594, pink arrows) due to the responsive proliferation of gliocytes and nerve cells after brain injury. The cells indicated by yellow arrows are red cells that exhibit autofluorescence. CFSE: Carboxyfluorescein succinimidyl ester; EGFRvIII: epidermal growth factor receptor variant III; huMSCs: human umbilical cord mesenchymal stem cells; PCNA: proliferating cell nuclear antigen; TBI: traumatic brain injury.