Stem Cells

They are undifferentiated cells that are pluripotent or multipotent, meaning they have the capacity to give rise to diverse specialized cell and tissue types (such as muscular, neural, bone, or epithelial tissue). Whereas totipotent cells (such as the early zygote) can generate an entire living organism, multipotent stem cells can only generate specific tissue lineages. In physiological wound healing, for example, adult stem cells naturally intervene to regenerate damaged tissue.

They can be grouped into several primary sources:

• In the human embryo.- Either in the 5-day-old blastocyst (comprising 150–200 pluripotent cells), or in specific developing organs of a more mature fetus (liver, brain, bone marrow...).
• In umbilical cord blood harvested after childbirth.
• In various tissues of adult humans, such as bone marrow, adipose tissue, and peripheral blood (termed adult stem cells).
• Through scientific reprogramming of somatic cells (induced pluripotent stem cells, or iPSCs).

The goal of regenerative medicine is to direct these cells to produce healthy tissues that can replace cells damaged by severe degenerative diseases (Parkinson's disease, Alzheimer's, multiple sclerosis, spinal cord injuries, diabetes, cardiac infarction, etc.). When derived autologously from the patient's own body or through adult stem cells, they carry the decisive advantage of avoiding immune rejection.

Significant clinical successes in human patients have been achieved using adult stem cells and umbilical cord blood in treating numerous blood disorders and tissue injuries. Conversely, embryonic stem cells have presented serious clinical risks, notably the formation of teratomas and malignant tumors, due to their uncontrolled proliferative tendencies; adult stem cells, once differentiated, reliably produce the targeted tissue. Consequently, sound medical research points to adult and induced pluripotent stem cells as the most promising therapeutic path. In addition, embryonic stem cell harvesting poses insurmountable moral and ethical dilemmas (conscience).

The ethical issues vary fundamentally depending on the source:

• The destruction of human embryos to harvest embryonic stem cells is gravely immoral, for obtaining them requires the intentional killing of a living human embryo.
• The use of adult stem cells presents no ethical objections whatsoever, as they are harvested without harming the donor.
• Likewise, obtaining stem cells from umbilical cord blood after a healthy birth poses no moral objection, although clinical applications require careful medical assessment.
• Even more morally reprehensible is so-called therapeutic cloning.

So-called therapeutic cloning involves somatic cell nuclear transfer: an enucleated human oocyte is fused with the nucleus of a donor's somatic cell via cloning to produce a cloned human embryo genetically identical to the donor. The living cloned human embryo is then deliberately destroyed in the laboratory to harvest its stem cells for research or treatment.