Stem cells are the primordial or original cells that give rise to life and being of a living thing, from animals and humans. Zygote formed from the fusion of sperm and oocyte is the first line of stem cell that is “totipotent” meaning it gives rise to embryonic stem cells and from there to epiblast and embryonic germ stem cells, that are all “pluripotent” meaning they form all the differentiated cell types of a given tissue. These pluripotent stem cells lineage give rise to the primordial germ cells that form all the tissues from skin to bone marrow and all other body tissues. The aim of stem cell therapy over the past half a century has been to induce pluripotent stem cells (IPS) in different body tissues to repair or replace the damaged tissues and cells of specific organ or parts of the body in vitro (in lab) and in vivo (in live beings) (1-2).
Bone marrow transplant has been the earliest stem cell therapy in the treatment of leukemia and lymphoma and has been widely clinically practiced over almost half of a century all over the world with quite success. Later on umbilical cord blood storage and use for transplants has been clinically practiced, while other forms of stem cell therapy such as the use of induced pluripotent stem cells (IPS) for a wider treatment of cancers and autoimmune disorders of different organs and tissues have been mostly experimental. Another common clinical use of bone marrow transplants has been in chemotherapy of cancers, to introduce the hematopietic stem cells within the bone marrow to replace the destroyed healthy cells by chemotherapy. The most common side-effects of bone marrow and other transplants traditionally has been graft vs. host reaction that rejects the transplant. Another stem cell therapy, “Prochymal” based on allogenic stem cells therapy using mesenchyme stem cells has been used recently in the management of such transplant rejections (3-4).
While in the past it was thought that the stem cells are basically in bone marrow and umbilical cords and most organs and tissues unlike the epidermis of the skin do not possess the capacity of renewal, in recent years it has become apparent that some other tissues in fact contain stem cells for potential renewal (5). One main reason of the delay in the stem cells therapy has been lack of recognition of different stem cells across different tissues with different potential capacities unlike the progenitor bone marrow and umbilical cord stem cells. As explained above while many of these stem cells are pluripotent, most are multipotent or unipotent, meaning having the capacity of their own specific tissue cells regeneration (6-7). In fact and with a comprehensive perspective, cancer cells could be considered as stem cells for their capacity of turnover and proliferation. This fact has been known and discussed as early as late 80s, but only recently has received widespread attention and acceptance. The cancer stem cell concept is important for opening a new venue to the novel approaches in anti-cancer therapies that instead of killing all or partial cancer cells with the potential of regrowth, to target the cancer stem cells for final cure with no possibility of relapse (8-9).
The advancement in stem cell research over years has led to the distraction and culture of progenitor or totipotent stem cells in vitro first from the animal models such as mouse, and now from the human’s blastocysts, with the ability of generation all the differentiated cells of a being such as human, hence “cloning” that puts the science in the jeopardy of Frankenstein as it has long been anticipated and infuriated (10-11). Other than blastocysts, the progenitor or embryonic stem cells with capacity of generating differentiated tissues of the whole being, it has been shown that epiblasts first from mouse and now humans could created such pluripotency (12-14). Moreover and morally riskier is the capability of adult stem cells to be reprogrammed to a pluripotent state, through transferring the adult nucleus into an oocyte or by fusion with a pluripotent cell. The most famous example of this cloning has the creation of “Dolly” the sheep by transferring of a somatic nucleus into an oocyte (15-18).
From a therapeutic not creational standpoint, the ability of regenerating new cells in the damaged and destroyed tissues is the art and science of IPS (induced pluripotent stem cells). Despite knowing for long that some amphibians could naturally regenerate limbs, eye or other injured body parts, therapeutic regeneration or regrowth of damaged or destroyed tissues medically by IPS is quite recent (2, 19-20). Since the original retrovirus-mediated induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by some defined factors in 2006-2007 (21), rapid progress has been made to generate iPS cells from adult human cells (22), a range of tissues that can be reprogrammed (23), and from patients with specific diseases (24). The number of transcription factors required to generate iPS cells has also been reduced (25), and the efficiency of iPS cell generation has increased (26), and techniques have been devised without viral vectors integration (27).
From Research to the bed side:
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Stem Cell Therapy: Does it work and for what?