What Are the Unanswered Questions and Problems?

With regard to a possible clinical application, the following criteria are relevant for stem cells:

• Reproducibility: It must be possible to multiply the stem cells in sufficient quantities in culture.
• Differentiability: It must be possible to stimulate them to differentiate into the required cell type.
• Purity: It must be possible to obtain differentiated cells of a single cell type, not cell mixtures.
• Precise integration: It must be possible to transplant the cell or tissue replacement to the correct site in the body.
• Safety against tumor formation: It must be ensured that the transplants do not continue to grow uncontrolled or form tumors.
• Long-term therapeutic effectiveness: The transplants must prove their functionality in the organism and have a therapeutic effect over a longer period of time.
• Immunocompatibility: Cell transplants should not be rejected by the immune system of the recipient organism.