An alternative in vivo model to evaluate pluripotency of patient-specific iPSCs

The generation of autologous human induced pluripotent stem cells (hiPSCs) from a patient’s somatic cells and the sub­sequent differentiation of these cells into desired cell types offer innovative treatment options for tissue regeneration. The hiPSCs obtained are usually implanted in immunodeficient mice, and teratoma formation is analyzed after 4 to 6 weeks to assess the cells’ pluripotency. In this study, an alternative in vivo model based on chicken egg chorioallantoic membrane (CAM) was established to analyze the pluripotency of newly created hiPSCs. 0.5, 1, 2, 4 x 106 hiPSCs gen­erated from urine-derived renal epithelial cells were seeded on CAM and incubated for 9 days. Teratoma formation was detected in 70% of eggs inoculated with 2 x 106 hiPSCs and in 100% of eggs inoculated with 4 x 106 hiPSCs. All teratomas exhibited vascular structures. The robustness of the CAM model was confirmed using two additional hiPSC lines derived from human fibroblasts (NuFFs) or jaw periosteal cells. The presence of all three germ layers within the teratomas was successfully verified by histochemical and immunofluorescence staining and gene expression analysis of germ layer-specific markers. Urine-derived renal epithelial cells were used as negative control and showed no teratoma formation. The CAM-based in vivo model provides an optimal in vivo test environment for the pluripotency evaluation of newly generated hiPSC lines. This simple, fast, inexpensive and reproducible method reduces the suffering of animals and thus implements the principles of the 3Rs (replacement, reduction, and refinement).