Stem cells grow into all the different types of cells comprising the human body and are produced from the inner cells of blastocysts, a hollow microscopic ball of cells. For obtaining cloned embryonic stem cells, i) the nucleus is extracted from a matured human egg (called enucleation); ii) the somatic cells of the subject (e.g. patient) that is to be cloned is transferred to enucleated oocytes; and iii) through electric fusion and an activation process, embryo development is induced as normal fertilization of sperm and egg.

Ethical controversies emerged in the international community because human cloning would be possible if the cloned embryos are implanted in the womb. Nonetheless, cloned embryonic stem cells cause no immunological rejection when transplanted into patients because they are acquired from the patient's own somatic cells, offering new hope to the many suffering from heart diseases, Alzheimer's disease, Parkinson's disease, diabetes, spinal cord disease and other incurable diseases.