**5. Overall potential uses of stem cells**

	- For treatment of bony and soft tissue defects due to trauma, burns, non healing wounds complicated by ischemia due to diabetes.-Scar revision, skin rejuvination, hair transplantation, breast augmentation.
	- Can reduce surgical risk in elderly patients w.r.t donor site morbidity. -Increase the survival of fat graft by cell assisted lipo-transfer.-Prevent allotransplant rejection by establishing lifelong tolerance- in composite tissue allo transplantation cases in residual defects of trauma, congenital anamolies, tumor ablation etc., thus avoiding the use of immuno suppressive agents.

Eg: Spinal cord injuries, osteopetrosis, Diabetes type I, Parkinson's, Alzeimer's, Heart and brain stroke, liver and kidney diseases, cancer and osteoarthritis, acute leukemia, CML, CLL, aplastic anemia, refractory anemia, congenital thrombocytopenia, Myelodysplastic syndrome, familial lympho histiocytosis etc. and to elicit causes of genetic defects in cells.


#### **5.1 General principles**

Autologous stem cell/bone marrow transplantation is healthy. Donor must be at least 18 years and above to give legal informed consent. Transplanted patients are required to live in isolation for 100 days while the new immune system establishes. Regenerative power of stem cells declines with age which can be modualted by food and life style habits. The number of stem cells needed varies with the treatment choice or the number of doses requested. The ideal number is 5–10 million/kg of receipient's weight per transplant dose. The minimum no. is 1–2 million stem cells/kg per transplant dose [10]. The donor's stem cells for an allogenic transplant are given to a chemotherapy/radiotherapy patient. These patients tend to have graft vs. cancer cell effect during allo- transplant. Graft failure happens when immune system rejects donor's stem cells.

If more donor stem cells are available, second transplant or with an infusion of residual lymphocytes from the donor may be done. Donors with kidney diseases such as chronic glomerulo nephritis or polycystic kidney disease, nephrectomy patients and are over 40 years old would not able to donate stem cells.

When stem cells/bone marrow are taken from donor, they must have a similar genetic make up. Usually siblings, or a parent or unrelated person should have same genetic component. The match ratio is 1 in 4(match related donor transplant). Others are unlikely to match. Stem cells from the cord blood can be used for the new born, their siblings and other relatives. Patients with genetic disorders like cystic fibrosis need cells from sibling. There is 1 in 4(25%) chance that any of sibling will have inherited the same two sets of HLA genes as the patient. For a parent to be matched, with the patient, both parents must, by chance have some HLA genes in common with each other. The blood or the cheek swab (saliva) is tested for HLA TYPE for potential donor.

Chronic Graft versus host disease (GVHD) which includes dark skin rash, dry or thickened skin, loss of appetite etc. develops after 100 days of transplant usually, but rarely before 3 months after transplant. Up to 80% success results and more than 5 plus year survival rate has been identified owing it to the compatibility of immune system. The published data shows 23 years of cryopreservation of cord stem cells with more storage life for decades. The damage or failure of stem cells is attributed to DNA damage including telomere shortening, DNA replication and failure of repair.

In treating craniofacial deformities, craniofacial fractures or neoplastic lesions, traditional craniomaxillofacial reconstructive surgery techniques along with application of tissue enigineering and regenerative medicine provide long term adequate

#### *Perspective Chapter: Role of Genetics, Stem Cells in Reconstructive Surgery—Their Perspectives… DOI: http://dx.doi.org/10.5772/intechopen.109514*

results avoiding the sequelae of tissue detrimentation. Studies have also shown that regeneration of bone in critical sized defects with periosteum preservation from a self assembling peptide nanofiber hydrogel with iPSCs. The results showed a marked increase in bone volume after 2–4 weeks with a nanofiber hydrogel scaffold with presence of medullary cavities and capillaries. This study suggests that autotransplantation of osteoprogenitor cells derived from iPSCs combined with a suitable scaffold would be a good therapy for calvarial bone regeneration [11, 12].

Mesenchymal stem cells have the capacity of modulating the immune response and promote tissue regeneration. They can be harvested from many tissues such as skin, pancreas, heart, brain, lung, kidney, cartilage, tendon and teeth, with bone marrow and adipose tissue being the most common sources. The combination of recombinant human bone morphogenic protein-2&7 with mesenchymal stem cells in correction of cleft alveolus and their long term results is yet to be established [13, 14].

Bone marrow stem cells are considered as gold standard for bone regeneration. These stem cells have potential for osteogenic and chondrogenic differentiation. Bone marrow stem cells are obtained by bone marrow aspiration under local/general anesthesia at posterior superior iliac spine, sternum or by in-vitro cultivated bone marrow stem cells. It has been noted that the in-vitro cell population is less potent than the bone marrow aspirate. It is composed of both mesenchymal and hematopoetic stemcells. The disadvantages of bone marrow stem cells is that, there is an increased risk of surgical infection, donor site pain due to invasive technique, volume deficiency in larger defects which need combination of in-vitro culture cell population which is expensive. Conversely, adipose derived stem cells are more readily available as source and can be rapidly expanded [10].

Several in-vivo studies on bone defect regeneration after cyst enucleation, alveolar cleft sugeries, maxillary sinus floor elevation and augmentation using bone marrow stem cells showed favorable results with increased bone formation compared to traditional methods. It was observed that a scaffold free approach to reconstruction with bone marrow stem cell is safe for alveolar cleft repair, but not indicated in large cleft deficiencies. Bone marrow stem cell populations with in vivo activity along with demineralized bone matrix, platelet derived growth factor in tandem with tricalcium phosphate/hydroxyapatite or platelet rich fibrin composites generating bone repair mechanisms [11, 14].

Adipose derived stem cells are a promising alternative to bone marrow stem cells or traditional autogenous bone grafts. Comprising a high cell to volume than other stem cell categories, adipose stem cells are less sensitive to aging, easy to harvest and apply (isolated stromal vascular fraction) enriched with potent growth factors for improved results. Adipose derived stem cells can directly differentiate into osteoblasts and produce chemokines that are useful in facilitating the forming of endogenous stem cells to the site of bone defect. These stem cells can survive in hypoxic environment unlike mesenchymal stem cells by secreting vascular endothelial growth factor, platelet derived growth factor which promote blood vessel formation and enhance hematopoietic cells to allow the exchange of oygen, nutrients, wastes and growth factors necessary for cell survival. ADSC are negatively impacted by donor age in older population.

The stromal vascular fraction is a single source of a diverse population of cells that include multi-potent stem cells, progenitor cells, endothelial cells, stromal cells, pericytes, peri adipocytes, hematopoetic stem cells and macrophages. This holds a promising future direction in cleft palate and craniofacial bone reconstruction and regeneration [15]. In one clinical trial, stromal vascular fraction/adipose derived

stem cells used in maxillary sinus floor elevation showed higher bone mass along with blood vessel formation compared to the control group with only adipose derived stem cells usage. ADSC in stromal vascular fraction have shown plasma membrane derived vesicles in the micro environment which establish inter cellular communication due to secretion of angiogenic molecules like FGF2, PDGF, VEGF, MMP-2, MMP-9 and osteogenic molecules like BMP2, RNA and micro RNA that impact the link with neighboring cells and the whole body. Overall, the ADSC have proved to be a multiple benefactor in safety, application and multiple cell transformation which can be collected in larger amounts in one step surgical procedure which decreases rate of infection.

ADSC are obtained through liposuction aspirate or resection of tissue fragments (buccal pad of fat). There are case reports with successful application of in vitro cultivated ADSC in alveolar cleft reconstruction, that wer seeded with demineralized bovine bone mineral and autologous bone. ADSC transferred by vehicular delivery through biphasic bone substitutes such as hydroxyl apatite-tricalcium phosphate scaffolds, poly-L-lactic acid scaffolds and bilaminate fibrin-agarose hydrogels showed significant bone regeneration compared to autologous bone grafting alone [16].

#### **5.2 Tooth derived stem cells**

Tooth derived stem cells are an interesting option in repairing bone defects of oral and dental tissues. These cells possess phenotypic characteristics similar to those of BMSCs, and they have the ability to self-renew and differentiate into multiple cell lineages, which are able to form the dentin-pulp structure when transplanted into immuno-compromised animal models. There are five classes of mesenchymal cell populations such as 1) dental pulpal stem cells 2) exfoliated deciduous teeth stem cells 3) periodontal ligament stem cells 4) dental follicle progenitor stem cells 5) stem cells from apical papilla. Of the above 5, stem cells from deciduous teeth (SHEDs) are easily extracted and isolated. They have high levels of immune stimulating and modulating chemokines, broad and multiple differentiation profile and strong proliferative capacity.

Human exfoliated deciduous teeth (SHEDs) are commonly isolated from patients between 5 and 12 years and are rich in post natal stem cells which could be induced into odontoblasts, osteoblasts, myocytes, adipocytes, and neuron-like cells. Dentin and bone could be formed when the cells are transplanted with bioactive materials in vivo. In addition, tooth derived stem cells participate in the repair and regeneration of non-dental tissues; in fact, these cells can differentiate into various types of cells, including neuron, hair follicle, hepatocyte, and cardiomyocyte like cells. Hydrogels may be a good option as a carrier for bone regeneration due to the osteoconductive characteristics of seeded MSCs as well as other advantages, such as injectability.

Dental pulpal stem cells are isolated from third molar extraction sites from teenage young adults. Both dental pulp stem cells and SHEDs are equally potent in cell regeneration and cultures with high concentration of secretomes (soluble paracrine signaling molecules) which allow for their immunomodulatory, angiogenic and neurogenic activities in vivo. SHEDs have been shown to form calvarial bone in critical size defect experiment as compared to other odontogenic tissue derived cell lines in an FGF-2 primed collagenous hydrogel deprived of oxygen, exhibiting markedly increased intramembranous ossification. Human derived dental pulp stem cells with collagen scaffold have the capacity of mature bone formation in calvarial defects with no graft rejection [17–20].

#### *Perspective Chapter: Role of Genetics, Stem Cells in Reconstructive Surgery—Their Perspectives… DOI: http://dx.doi.org/10.5772/intechopen.109514*

In vivo implantation of the porous composite scaffolds within a critically sized calvarial defect in a rat showed near complete osseous closure of the defect over 6 weeks. An in vitro amplification for harvested MSCs is almost a necessity due to the relatively low numbers of harvested cells (1 MSC/10 4–10 6 stromal cells).

Bone marrow stromal stem cells have been studied in repair of auricular cartilage and craniofacial defects, when embedded in collagen scaffold [21]. Human adipose derived stem cells (h- ADSC) without any medium were able to correct skeletal defects which clearly showed a bone turn over within 2 weeks and a stimulation of the host's reparative process. It was also noted that the bone morphogenic protein (BMP) modulated the h- ADSC through signaling during bone repair [22, 23].

Cranial suture stem cells (SuSC) isolated from calvarial sutures expressed Axin2, a marker to identify slow-cycling stem cells, which showed the ability of skeletal and cartilage repair. Direct engraftment of sutural stem cells (SuSC) to bone defect provided the benefits for cartilage repair through alteration of BMP signaling, leading the role of these cells in intramemebranous bone formation [24].

Several studies have been conducted in rabbit models for mandibular reconstruction with precise defects by integrating scaffolds such as polyether-ether-ketone (PEEK), fibrin glue, with ADSCs and MSCs transcripted with RUNX2 factor showed satisfactory promising results in terms of increase in new bone thickness, volume, compressive resistance, bone mineral density and content with good masticatory load strength [16, 23, 25].

Preliminary clinical studies have shown successful reconstruction with the combination of autologous bone grafts and human bone derived mesenchymal stem cells (BMSC) followed by distraction osteogenesis, dental implants and prosthodontic restoration. A clinical trial conducted by Gjerde et al. on 11 patients with posterior alveolar ridge resorption, evaluated mandibular regeneration using BMSCs without any additional factors like growth factors or stimulants or scaffolds. The result of this study showed successful ridge augmentation [26].

More clinical studies and trials are anticipated in mandibular and craniofacial reconstruction with larger defects using stem cells which could minimize the morbidity due to autologous bone grafting as well as provide long term results and enhance better living of patient.
