It is very important to understand that there are very few adult cells in each tissue (1-100.000). They are located in specific areas, such as sternum, ribs, long bone´s epiphysis, hubcap, etc. They remain deactivated (no division) for many years until they are reactivated because of a surgery or injury.

Even though, most adult’s stem cells are designated to a specific tissue, some of them are able to differentiate into many kinds of cells, same way as embrionari cells.

The fact that an adult stem cell is able to generate specialised types of cells that are different from the tissue where the cell is located was recently understood. It was proved that hemopoietic stem cells also produce brain and skeletal muscle cells.

Even though the cellular reparation mechanism is unknown and there is also a debate on whether it occurs by plasticity (the adult stem cell obtains the characteristics of the tissue or organ that needs to be repaired) or by cellular fusion (the cell fusions with the tissue´s stem cells and stimulates them), truth is that reparation is evident.

Adult stem cells have been found in many more tissues than thought. This founding motivated the question of stem cell´s viability to be used in transplants. (Bone marrow stem cells have been being used on transplants for more than 30 years)

Bone marrow has three types of stem cells: hemopoietic, stromal and progenitor endothelial. (Fig. 215-20).

The adult stem cells that have been intensely studied are: neural, hemopoietic, epithelial, endothelial and skeletal muscle cells. There are two main types in plastic surgery :

Epithelial Cells

Epithelial cells represent 60% of the differentiated cells. They purpose is to cover body surfaces.

Skin´s epithelial cells have three different populations: follicular, glandular and epidermic. Different stem cell locations were identified in skin, follicular bulb and epidermis´ base layer.

Base layer´s stem cells produce two different types of cells when they reproduce, a stem cell able to self reproduce and an intermediate cell that will lately differentiate to a keratinocyte.

Follicular bulb stem cells are able to differentiate into several different types of cells. By differentiating into cells of the cellular matrix, they are able to produce a new hair follicle. They can also turn into epidermic cells and later be part of the different cutaneous stratums.

The knowledge of these concepts allows us to understand tissue reparation in cases of first, second, third or fourth degree burns .

Endothelial Stem Cells

Endothelial cells matter the most to plastic surgeons because they are an important tool to transfer flaps, osteogenic distraction, wound healing and graft survival, all of them depend on blood vessels remodelling.

215-20.  Obtaining the three types of stem cells. (Hemopoietic, Stromal and Progenitor) by sternum puncture.

In this section will discuss the actualization of some new concepts of neo-vascularization and the discovery of progenitor endothelial cells.

Neo-vascularization

Neo-vascularization takes place because of two different mechanisms:

Angiogenesis: the development of micro-vessels from pre-existing capillaries.

Vasculogenesis: it makes reference to blood vessels development from the endothelial stem cells or progenitor endothelial cells (PEC) that will differentiate in situ.

Before these cells were discovered, scientist thought that neo-vascularization occurred only because of angiogenesis, now with this new concept a innovating and useful window opens to reconstructive and plastic surgery.

In 1997 Asahara discovered Progenitor Endothelial Cells (PEC) and because of many investigations, there is great evidence that these cells come from bone marrow and are selectively recruited to neo-vascularization places, including myocardium, ischemic areas of diabetic foot, injury heal.

PECs respond to a very powerful stimulus: local vascular trauma, and the stimulation of granulocytes and macrophages stimulating colonies that area activated because of inflammation .

Plastic Surgery Applications

PECs can be used in many plastic surgery areas, normally in those which need vascular regeneration.

Flaps

One of the most used techniques in surgery is mobilizing flaps. Free flaps are still challenging, not only because of the transference technique, but also because of their survival.

Neo-vascularization reduces the probability of losing the flap and of cutaneous necrosis. Therefore, it is logical to think that moving these cells will provide angiogenesis to the flaps before they are transferred; but this probability has not been proved yet. It is possible to safe ischemic flaps transplanting progenitor endothelial cells, because it has been proved their capacity to move directly to ischemic places .

Injury healing

A regular problem is healing a chronic wound, such as diabetic foot. Stem cell therapy applied to these patients, whose capacity to regenerate tissues has been reduced, is a promising method. The main objective would be to replace the cells, instead of just using GF to stimulate cellular activity. There is just one study performed on diabetic patients, it was done by Tepper´s team. The results show that progenitor endothelial cells taken from patients with diabetes type II, behave in a different way when compared to progenitor endothelial cells taken from same age healthy patients. This suggests that these cell´s dysfunction in diabetic patients contributes to wound´s chronicity.

Tissue Engineering

Tissue Engineering makes reference to the development of biological substitutes to restore, maintain or improve tissue functioning. Today engineering improvements are basically bone, cartilage skin, tendon and ligament production. Engineering has not been able to generate more complex tissues like pancreas, liver or kidney. This happens because, to generate organs a micro-vasculature in vitro is needed to feed the neo-organ. Using PECs will allow the possibility to generate micro-vasculature in the cultivation, and stimulating vascular invasion of the tissue.

Interpretation: CD34 O.10% total

Fig. 215-21. Fenotypification done by Flow cytometry to demostrate hemopoieti cells.

Fig. 215-22. Stem cell Obtaining by sternum puncture.

Tissue engineering also produces synthetic grafts using endogen biomaterials like collagen, studies done in animals; show that using PECs, combined with these materials improve the attachment of the tissue with out any side effects.

Our experience

The different body areas that may be a source of stem cells are still being investigated.

Stem cells need to be:

*Non immunogenic.
* Easy to obtain.
* Able to generate a great mount of cells.

What is difficult is to have these cells reproduce themselves in a exponential way once they are obtained, to have them survive the manipulation ant to track their behaviour once attached.

Our experience is related to using stem cells combined with fat grafting and GF. It has been observed that Stem Cells application in fat transferring provides the regeneration and maintenance of such tissues in a high percentage.

We choose to obtain stem cells by sternum bone marrow aspiration because of its simple access; it can also be done while the patient is under anesthesia´s effect .

Technique

One of the pre-surgical analysis is to quantify CD34 cells in peripheral blood (hemopoietic) to establish the patient´s molecular function through Flow cytometry fenotypification (need to be at least 0.03% to guarantee the proper amount of stem cells). This allows us to measure objectively the amount of hemopoietic cells and to have a very accurate idea of the amount of stromal stem cells (Fig. 215-21).

Fig. 215-23. Bone Marrow centrifugation to obtain Stem Cells from Buffy coat.