Figure 1. Serial xenotransplantation enriches self-renewal and tumorigenicity of osteosarcoma cells.

(A) Self-renewal and tumorigenicity were assessed by the amount of cells injected and the time of tumor formation. Cells from the first U2OS xenograft were re-transplanted to yield the 1^st, 2^nd and 3^rd generations of U2OS cells (designated as UT1, UT2, and UT3). (B) HE staining determined that UT2 cells retained histological features of U2OS cells, as reflected by cellular polymorphism, nuclear hyperchromasia, and mitotic activities, together with osteoid formation that recapitulated the hallmark histological phenotype of the parental osteosarcoma. (C) UT2 cells remained capable of tumorigenicity in the bone. Tumor formation occurred in the right legs of mice with injection of UT2 cells (section ii). (D) HE staining of osteosarcoma xenograft formed in the femurs of the right legs (panel C), focally breaching the cortex, and extending into soft tissue (arrow and inset).