Figure 4: Evaluation of tumorigenicity in TBI rats given huMSC transplantation via tail vein injection. (A) Pathology of the liver and lung in the Tail Vein group (original magnification 100×). Scale bar: 200 μm. No cell degeneration, necrosis, hyperplasia or tumorigenesis was observed in the liver or lungs, on days 1, 3, 7, 14 or 28, or even 12 months post-transplantation. (B) Immunohistochemistry for EGFRvIII in the Tail Vein 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 Tail Vein group (original magnification 400×). Scale bar: 50 μm. The results are consistent with those of the In Situ group. There was no PCNA immunoreactivity (positive signal) in CFSE-labeled huMSCs (indicated by green arrows), indicating that the huMSCs do not exhibit proliferative activity. However, the adjacent neural cells show PCNA immunoreactivity (red, stained by CoraLite594, pink arrows) caused by the responsive proliferation of glia and neuronal 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.