In practice, stem cells are identified by whether they can regenerate tissue. For example, the defining test for bone marrow or hematopoietic stem cells .
Stem cell treatments may require immunosuppression because of a requirement for radiation before the transplant to remove the person’s previous cells, or because the patient’s immune system may target the stem cells. One approach to avoid the second possibility is to use stem cells from the same patient who is being treated.
Pluripotency in certain stem cells could also make it difficult to obtain a specific cell type. It is also difficult to obtain the exact cell type needed, because not all cells in a population differentiate uniformly. Undifferentiated cells can create tissues other than desired types.
Some stem cells form tumors after transplantation pluripotency is linked to tumor formation especially in embryonic stem cells, fetal proper stem cells, induced pluripotent stem cells. Fetal proper stem cells form tumors despite multipotency.