Adipose Tissue as a New Source of Adult Stem Cells

The major sources of adult stem cells are bone marrow and umbilical cord blood. Mesenchymal stem cells (MSCs) isolated from cord blood are low in number and fairly restricted in plasticity.¹ Bone marrow is rich in MSCs and is the predominant source of these cells. Bone marrow isolated MSCs can consistently differentiate into fat, cartilage, and bone cells.² Until recently, no real alternative to bone marrow isolation was available.

The lipoaspirate from liposuction procedures has long been considered medical waste, much like umbilical cord blood was in the past. It is now widely recognized that adipose tissue is also an abundant source of adult stem cells.² Lipoaspirate is processed into a heterogeneous, non-adipocyte cell population, referred to as the stromal vascular fraction (SVF). Under specific culture conditions, a subpopulation of the SVF cells adheres and proliferates into a more homogenous cell population referred to as adipose-derived stem cells (ADSCs). To date, ADSCs have consistently demonstrated their phenotypic and functional similarities to bone marrow-derived cells.

The number of stem cells that can be isolated per unit volume of lipoaspirate is approximately 10-fold greater than that from bone marrow.³ Functionality or potency of mesenchymal cells is often established using colony-forming unit (CFU) assays, the most general of which is the fibroblast colony-forming unit assay (CFU-F). ADSCs are capable of forming CFU-F at an approximate frequency of 1 in 4 cells by passage two,⁴ compared to 1 in 50,000 for marrow-derived cells.⁵

ADSCs are phenotypically very similar to bone marrow-derived MSCs after 1 to 2 passages. Functionally, ADSCs and bone marrow MSCs are also very similar.3 Comparable efficacies have been observed for both sources of cells in preclinical applications. However, phenotypic differences observed on ADSCs at isolation and early passage may indicate a more primitive progenitor status. Primitive status would lend support to several groups who have reported successful transdifferentiation of ADSCs into endodermal vasculature and ectodermal neural progenitors.

Interest in ADSCs is continuing to grow in the scientific community, as evidenced by the ever-growing number of research journal publications. The demand for adult stem cells will certainly increase as the field of cellular medicine progresses into the future. Adipose tissue is an accessible, plentiful, and renewable source of adult stem cells.

References

1. Panksy, A., Roitzheim, B., and Tobiasch, E. (2007) Differentiation potential of adult human mesenchymal stem cells. Clin Lab. 53: 81-4.

2. Schaffler, A., and Buchler, C. (2007) Concise Review: Adipose Tissue Derived Stromal Cells - Basic and Clinical Implications for Novel Cell Based Therapies. Stem Cells 25: 818-827.

3. Wagner, W., Wein, F., Seckinger, A. et al. (2005) Comparative characteristics of mesenchymal stem cells from human bone marrow, adipose tissue and umbilical cord blood. Exp Hematol. 33: 1402-16.

4. Mitchell, J.B., McIntosh, K., Zvonic, S. et al. (2006) Immunophenotype of Human Adipose-Derived Cells: Temporal Changes in Stromal-Associated and Stem Cell-Associated Markers. Stem Cells 24: 376-385.

5. Castro-Malaspina, H., Ebell, W., Wang, S.(1984) Human bone marrow fibroblast colonyforming units (CFU-F). Prog Clin Biol Res. 154: 209-36.