Teratoma Formation in Immunocompetent Mice After Syngeneic and Allogeneic Implantation of Germline Capable Mouse Embryonic Stem Cells

Background: Embryonic stem cells (ESCs) have the potential to form teratomas when implanted intoimmunodeficient mice, but data in immunocompetent mice are limited. We therefore investigated teratomaformation after implantation of three different mouse ESC (mESC) lines into immunocompetent mice. Materialsand
Methods: BALB/c mice were injected with three highly germline competent mESCs (129Sv, BALB/c andC57BL/6) subcutaneously or under the kidney capsule. After 4 weeks, mice were euthanized and examinedhistologically for teratoma development. The incidence, size and composition of teratomas were compared usingPearson Chi-square, t-test for dependent variables, one-way analysis of variance and the nonparametric Kruskal-Wallis analysis of variance and median test.
Results: Teratomas developed from all three cell lines. The incidenceof formation was significantly higher under the kidney capsule compared to subcutaneous site and occurred inboth allogeneic and syngeneic mice. Overall, the size of teratoma was largest with the 129Sv cell line and underthe kidney capsule. Diverse embryonic stem cell-derived tissues, belonging to the three embryonic germ layers,were encountered, reflecting the pluripotency of embryonic stem cells. Most commonly represented tissueswere nervous tissue, keratinizing stratified squamous epithelium (ectoderm), smooth muscle, striated muscle,cartilage, bone (mesoderm), and glandular tissue in the form of gut- and respiratory-like epithelia (endoderm).
Conclusions: ESCs can form teratomas in immunocompetent mice and, therefore, removal of undifferentiatedESC is a pre-requisite for a safe use of ESC in cell-based therapies. In addition the genetic relationship of theorigin of the cell lines to the ability to transplant plays a major role.