The infiltrative capacity of murine and human embryonic stem cells in in vitro assays

Objectives: A realistic way for obtaining local tissue regeneration is by local application of cells, known as cell therapy. Embryonic stem cells (ES) are often considered for this. As a basic step towards cell therapy, we evaluated the infiltrative behavior of murine and human embryonic stem cells in two known in vitro assays, the PHF (precultured heart fragment) assay and the Coll I (Collagen I) assay. Two different application strategies were investigated: multicellular spheroids, as a model for cell patch applications and single cells, as a model for local cell injections. Materials and methods: The B6D2 mES cell line and the H1 hES cell line were used. The PHF assay consists of precultured chick embryonic heart fragments and is a general accepted model for studying tumor invasion in a 3D setting. The Coll I assay consists of a native Collagen I gel, a model for evaluating infiltration in the extracellular matrix. Analysis was done by light microscopy. A two-sided Students t-test (99,9%) was used for calculating significant differences in infiltration. Results and discussion: In the PHF assay, the mES spheroids showed a gradual infiltration of the mES cells and massive expansion, resulting in a reduction in the size of the original PHF. The hES spheroids showed a non infiltrative behavior and did not interact with the host tissue. The mES single cells were infiltrative and expansive, but did not reduce the size of the original PHF. The hES single cells were infiltrative, but didn’t show expansive behavior. These results were confirmed by the Coll I assay. mES spheroids had a infiltration index of 62%, hES spheroids of 32%, mES single cells of 51% and hES single cells of 25% (significant difference). As indicated by these results, mES cells can’t be used as a model system for hES cell infiltration. The use of hES cells as a tissue patch for local application seems dangerous. The use of single hES cells for injection shows good infiltration and is a viable option for cell therapy. In conclusion, these two models are an easy screening tool for the infiltration capacity of different cell types