**6. Role of mesenchymal stem cells in craniofacial deformities/head and neck diseases**

Majority of the craniomaxillofacial/head and neck anatomic region are formed from mesenchymal cells. Mesenchymal stem cells derived from dental and nondental sources have been effectively used for regeneration in maxillofacial region like regeneration of periodontium, salivary gland, repair of cleft lip and palate and craniofacial regeneration. These cells promote tissue regeneration and wound healing through synergistic downregulation of proinflammatory cytokines and increased production of soluble factors with antioxidant, anti apoptotic and proangiogenic properties. In oral wounds, they exhibit increased re-epithelialization, cellularity, intracellular matrix formation and neoangiogenesis, thereby accelerate wound healing. Hence mesenchymal stem cell therapy is a promising modality in healing soft tissue and hard tissue wounds of craniofacial region [7, 27].

Adipose cells with appropriate shaped scaffold can be used for reconstruct stem cells isolated from dental pulp has a potential to differentiate into osteoblasts and are a good source for bone formation. Stem cells from oral and maxillofacial region

sub sites can be combined with bone marrow stem cells to correct larger defects. Oromaxillofacial bone tissue repair with stem cells was done using collagen sponge scaffold and dental pulp stem cells [9].

Scaffold free tissue constructs to close the critical size bone defects can be used in the form of microspheres. It was found that, osteogenically differentiated microspheres with outgrowing cells can be used to fill up bone defects. This new procedure has added advantage of permitting the transplantation of more cells and better integrity compared with cell suspensions or gels ion of soft tissues. Autologous fibrin glue that holds the cells in place was prepared by cryoprecipitation. This successful technique has given new rays of hope that ADSCs can be used for difficult reconstructive procedures of craniofacial defects [9].

Mesenchymal stem cells (MSCs) are multipotent stromal cells that are present in most adult connective tissues. MSCs have been widely used in stem cell transplantation, tissue engineering, gene therapy, and immunotherapy. These cells express CD105, CD73, andCD90, and are not able to express CD45, CD34, CD14, orCD11b, CD79α or CD19 antigens. In addition, they are able to differentiate into at least 3 cell lineages (immune modulatory, angiogenesis and antiapoptosis effects) in vitro, including chondroblasts, osteoblasts, and adipocytes.

MSC reduce IL-6, tumor necrosis factor-α (TNF-α), and IL-1β levels, 3 days after fracture. This process leads to a better regeneration by limiting tissue injury and inhibiting the progression of fibrosis. The production of inflammatory cytokines, including TNF –alfa, IL-6, IL-12p 70, and IFN-gamma, by macrophages is significantly suppressed by MSCs, while the production of anti-inflammatory cytokines like IL-10 and IL-12p40 is increased. Possibly PGE2 is the key mediator for this process [1]. The anti-apoptotic effect of MSCs could also accelerate the process of bone healing. It has been suggested that faster bone healing with MSC transplantation may be especially correlated with lower levels of TNF-α expression in the callus. This may favor bone formation since it has been reported that TNF-α can have pro-apoptotic effects on osteoblasts [1, 7].

#### **6.1 Tissue engineering approaches with stem cells**

In larger bone defects the local injection of stem cells is ineffective. Controlled delivery of MSCs to the desired site is achieved by three ways [2]. Delivery of cells within injectable or prefabricated scaffolds, [3] co-delivery of cells with osteoinductive growth factors or co-culture with other cell types, and [4] Delivery of cells within a 3D dynamic environment. A refabricated bone requires 3 elements, scaffolds or carriers (a 3D support), endothelial growth factors9stimulation of neovascularisation and provision of blood supply) and, MSCs and other growth promotion factors (stimulus for osteoinduction and recruitment of endogenous MSCs). An ideal scaffold/carrier should have four charecteristics, including osteogenesis, osteoincorporation, osteoinduction and osteoconduction [10].

Co-delivery of mesenchymal stem cells with prefabricated 3 dimensional scaffolds along with growth factors that possess properties of osteogenesis, osteoincorporation, osteoinduction, osteoconduction yields better results.

Future directions: A team of professionals including stem cell biologists, molecular biologists, geneticists, polymer and materials scientists, mechanical engineers and clinicians with knowledge of oral and maxillofacial disorders is needed to develop the field of craniofacial tissue engineering.

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

Though the stem cells and gene therapy have been used in experimental animal studies, it is a major challenge to accomplish regeneration of tissues and vascularity in larger craniofacial defects, as the cells must be within 100mu.m of an oxygen source to survive. In addition to vascular supply, accurate craniofacial reconstruction demands production of tissue interface to repair structures such as joint, tooth and muscle attachments. Use of gene transfer to engineer a cell in producing protein for tissue repair overcomes limitations of recombinant protein therapy in craniofacial regeneration. Somatic cells can be genetically corrected and re-programmed into iPS stem cells that in turn differentiate into disease free cells. Gene therapy in combination with iPS cell technology has great potential use in treating congenital disorders.

Application of stem cells in craniofacial regeneration and reconstruction should be transmuted from animal models to more number human case studies and clinical trials since substantial evidence is available through animal model studies regarding their results in craniofacial regeneration. Targeted tissue engineering therapy for reconstruction of defects and deformities in various sub-units of cranio-facial skeleton with the following illustrated methodology can yield more promising results in the future.- Calvarial bone regeneration through induced pluripotent stem cells delivered by hydrogel injectable system; Cartilagenous regeneration within nasal complex with cranial suture derived stromal stem cells; Maxillary and palatal bone regeneration by mesenchymal (adipose or bone marrow derived) stem cell delivery; Mandibular defect regeneration by polyether ether ketone (PEEK) scaffold delivery of mesenchymal stem cells. Particularly of more interest is the potency of developing induced pluripotent stem cells into specific cell lineage of requirement by selectively tuning the gene expression through genetic engineering. So far fundamentally, ADSCs and BMSCs have been successful as stem cell lineages in both pre-clinical and human clinical trials, more so are ADSCs in terms of bone regeneration. Stem cells have the dual capacity as cell based carrier for drug delivery as well as gene therapy. Insightful further research is required to understand the role of stem cells in cancer therapies, with the eventual goal of eliminating the residual disease and recurrence.

### **Summary**

Autologous bone grafting has been the gold standard so far in the reconstruction of craniofacial defects and deformities. Future direction must point out towards application of stem cells for reconstruction of craniofacial defects and deformities of larger volume, thus minimizing the donor site morbidity caused by autologous hard and soft tissue grafting.
