Stem cells are essentially specialized cells that possess the ability to transform or differentiate into one of many different types of cells present within the body. That includes the potential ability to differentiate into cardiac, nerve, muscle, tendon, bone and many other types of cells. Stem cells are classified into two broad groups, dependent on their origin: embryonic or adult. Embryonic stem cells are the cause of much of the controversy surrounding stem cells, due to be derived from the blastocyst, which is an early stage embryo. Adult stem cells are derived from the patient themselves and usually extracted from the blood, bone marrow or adipose (fatty) tissue.
Stem cells have gained tremendous popularity in veterinary medicine and seem as if they have been the talk of the medical industry for the past couple of decades. For several years, there was much controversy regarding stem cells, especially regarding morals and ethics amongst many religious communities. So, what is all the hype about stem cells and what is their potential? 
In order to be classified as a stem cell, the cell line must demonstrate potency as well as the ability to self renew, which means that that particular stem cell can divide and produce more stem cells. Potency is by definition the ability to differentiate into specialized cells or any adult cell type. The terms generally assigned to potency in true stem cell lines are Omnipotent and Pluripotent. Omnipotent stem cells are produced as a result of the joining of an egg and sperm cell. Essentially, omnipotent stem cells yield embryonic cells and could, if allowed, produce a complete living organism. Pluripotent cells are the next step down and are a result of the further division of Omnipotent stem cells, which creates the blastocyst. Embryonic stem cells usually demonstrate Omnipotent or Pluripotent capabilities. Adult stem cells are generally classified as having multipotent capabilities, which means they can differentiate into many different cell types but usually only of closely similar cell types from which they were extracted.
Embryonic stem cells have demonstrated the highest level of capabilities and potential, mainly due to their assigned potency, however, due to their source or origin, much debate has been raised. Given their controversy, there are no approved medical therapies at this time in regards to embryonic stem cells and some research has actually been halted. The other major drawback to using embryonic stem cells is the risk for rejection as they are transplanted from one source to the next.
Adult stem (somatic) cells are present in all individuals as a means of repair and regeneration. The actual number of adult stem cells drops with age, but the hope is that with extraction, self renewal can take place in culture and increase their numbers for clinical use. The positive side to using adult stem cells is that risk of rejection is very low and in fact non-existent due to using cells derived from the patient themself. Adult stem cell therapies have been used for many years and a prime example is in patients receiving bone marrow transplants for treatment of various leukemias. There are many other potentials for adult stem cell therapies including cardiovascular disease, liver and kidney disease, bone disorders including fractures and tendon conditions. In the veterinary community, the biggest focus is on tendon therapy as well as some bone related conditions such as arthritis and OCD lesions.
Adult stem cells are most commonly obtained either through the bone marrow or fatty tissue. In my experience, the number one source, due to ease of extraction, is the fatty or adipose tissue. As mentioned, one drawback is that with age, cell numbers appear to decrease, which may yield low numbers upon extraction. The other concern regarding adult stem cells is their level of potency and ability to differentiate into the particular cell type needed. It appears, based on research, that adult stem cells are most likely to differentiate into cell types similar to that which they were extracted. Dependent on their origin, they appear to be already locked in, per se, on forming that particular cell type. Essentially, it may prove to be difficult to get a stem cell programmed for muscle or tendon repair to differentiate into a cardiac or nerve cell. This process of differentiation is rather complex and involves many signaler chemicals. Given this process of differentiation, the concern has been raised that it is possible that injection of stem cells could produce the formation of various tumors, mainly due to the process of differentiation being hard to control.
In the end, stem cells offer much hope and potential for aiding in the management of many diseases affecting humans and animals. There is much research and discovery still to be made regarding their extraction and overall usage, but right now, we are just in the infancy stages. The results thus far are promising, but overall response rate statistics are hard to find and are variable, which may reflect patient to patient variability in terms of cell line potency. The process of harvesting, culturing and re-injecting stem cells is an expensive process and one that is not covered by many insurance carriers due to their research nature, but may be a worthwhile consideration for medical conditions that are unresponsive to traditional therapies.
Tom Schell, D.V.M.
www.curost.com
(Images borrowed from Wikipedia)
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