Autologous Keratinocyte Suspension Versus Adipose-Derived Stem Cell-Keratinocyte Suspension for Post-Burn Raw Area

Burn injuries are complicated wounds to manage with a relative high mortality rate in especially large area burns and elderly patients.

Substantial tissue damage and extensive fluid loss can cause impaired vital functions of the skin. When healing is delayed, the potential short term common complications include wound infection affecting the local healing process or systemic inflammatory and immunological responses which subsequently can cause life threatening sepsis and multi-organ failure.

Fortunately, survival rates have improved drastically over the last century due to advancements in burn care such as early surgical intervention, critical care support and wound care.

For many years the "gold standard" for treating wounds of burn patients has been transplantation with an autologous split skin graft. In patients with extensive burn wounds donor sites may be limited. In order to cover all the wounds, the patients often need multiple operations and/or the skin had to be expanded as much as possible.

However, the current different expansion techniques and treatments [mesh and Meek-Wall] frequently lead to scar formation, especially in the large mesh intersites.

The rate of wound closure depends on how quickly epidermal cells migrate out of the meshed auto graft and/ or wound edges to close the wound. Accelerating re-epithelialization could potentially improve the outcome of the healing process in terms of reducing granulation tissue formation, reducing the healing time, and thereby reducing the risk of colonization and infection, as well as scar formation.

Since clinical cases were first successfully treated with cultured epithelial layers, keratinocyte sheets have become an important tool in burn wound treatment. However, the clinical application can be limited by long culture time and fragility of the keratinocyte sheets. There is, therefore, a clinical demand for other options to cover large areas of burn wounds in the absence of viable donor sites.

A novel concept consists of treating wounds with epithelial cell suspensions. In 1998, Fraulin et al. developed a method of spreading cell suspension on to wounds using an aerosol spray in a porcine model.

The use of non-cultured keratinocyte suspensions was first reported by Hunyadi et al., showing that a group of patients with burn wounds or chronic leg ulcers, treated with a fibrin matrix containing keratinocytes, healed completely, as opposed to the control group.

In porcine wound models, non-cultured keratinocyte suspensions have been shown to accelerate wound healing, improve quality of epithelialization, and restore melanocyte population, compared to the respective control group.

Major advantages in the use of non-cultured cell suspensions are a drastic reduction of preparation time and possibly easier handling compared to keratinocyte sheets. Particularly, scar quality may be improved by enhancing the speed of epithelialization and fading of mesh patterns in split skin grafts.

On the other hand, stem cell-based therapies have gained interest as a promising approach to enhance tissue regeneration.

Stem cells are characterized by their multipotency and capacity for self-renewal. Their therapeutic potential is largely due to their ability to secrete proregenerative cytokines, making them an attractive option for the treatment of chronic wounds.

Stem cells from numerous sources are currently being tested in preclinical and clinical trials for their ability to faster wound healing and tissue regeneration. These trials have not only proven autologous stem cell therapy to be safely tolerated, but also demonstrated positive clinical outcomes.

According to the International Society of Cellular Therapy, mesenchymal stem cells are defined by their ability to adhere to a plastic surface, by their expression of the surface markers CD73, CD90, and CD105, by their lack of expression of hematopoietic markers CD14, CD34, CD45, CD11b/CD79, and CD19/HLA-DR, and by their ability to differentiate along osteoblastic, adipocytic and chondrocytic pathways.

Isolated from tissues including bone marrow, adipose tissue, umbilical cord blood, nerve tissue, and dermis, MSCs have been administered both systemically and locally for the treatment of cutaneous wounds.18 Although mesenchymal stem cells have been shown to exhibit low levels of long-term incorporation into healing wounds, a growing body of research suggests that their therapeutic benefit is attributed to their release of trophic mediators, rather than a direct structural contribution.19 Through the release of vascular endothelial growth factor, stromal cell-derived factor-1, epidermal growth factor, keratinocyte growth factor, insulin-like growth factor, and matrix metalloproteinase-9, mesenchymal stem cells promote new vessel formation, recruit endogenous progenitor cells, and direct cell differentiation, proliferation, and extracellular matrix formation during wound repair.

Mesenchymal stem cells also exhibit key immunomodulatory properties though the secretion of interferon-λ, tumor necrosis factor-α, interleukin-1α and interleukin-1β, as well as through the activation of inducible nitric oxide synthase. Mesenchymal stem cells secretion of prostaglandin E2 further regulates fibrosis and inflammation, promoting tissue healing with reduced scarring.

Finally, Mesenchymal stem cells display bactericidal properties through the secretion of antimicrobial factors and by upregulating bacterial killing and phagocytosis by immune cells.

Adipose-derived mesenchymal stem cells are a pluripotent, heterogeneous population of cells present within human adipose tissue.

However, isolation of adipose-derived mesenchymal stem cells is readily accomplished using liposuction aspirates or excised fat samples, which are obtainable with minimal donor morbidity.

Adipose-derived mesenchymal stem cells can be differentiated into adipogenic, chondrogenic, myogenic, and osteogenic cell lineages in response to specific stimuli. Alternatively, adipose-derived mesenchymal stem cells may be immediately administered without in vitro expansion or differentiation in culture.

The extraordinarily high cell yield from lipoaspirate (as many as 1*107 cells from 300 ml of lipoaspirate with at least 95% purity), as compared with bone marrow aspiration, makes Adipose-derived mesenchymal stem cells a particularly attractive cell source for the acute wound setting.