Figure 1.

Conditional teratoma formation. (A) Subcutaneous teratomas generated in xenogeneic immunodeficient mice, allogenic immunodeficient mice, and syngeneic mice of either sex. sub-cu: subcutaneous injection. (B) Single intravenous administration of a high dose of induced pluripotent stem (iPS) cells did not generate teratomas in xenogeneic immunodeficient mice, allogenic immunodeficient mice, syngeneic mice of either sex, or in lung-injured mice. IV: intravenous injection. (C) Histological examination showed that the heart, lung, kidney, and liver of mice receiving intravenously injected iPSCs had no teratomas. (D) Representative histology of skin wound lesions that had topically or subcutaneously received syngeneic iPSCs. (E) Syngeneic iPSCs suspended in Matrigel generated teratomas (red arrows) when administered intraperitoneally or under the renal capsule (left panels). Replacing Matrigel with PBS prevented teratoma formation (right panels). (F) Representative gross images of the major organs of mice that had intravenously or intrapleurally received syngeneic iPSCs for 18 months (lower left and right panels). The organs harvested from mice 28 days after intra-kidney injection of syngeneic iPSCs served as positive control (upper left panel).