Joris van Dongen

127 Isolation of SVF by the FAT procedure INTRODUCTION Adipose tissue-derived stromal cells (ASCs) are a promising therapeutic cell type for regenerative purposes because of their ability to differentiate in multiple cell lineages and their ability to secrete a plurality of pro-regenerative growth factors. 1,2 ASCs are multipotent stem cell-like stromal cells, which are abundantly present in adipose tissue and easily isolated. In adipose tissue, ASCs are attached around vessels as pericytes and supra-adventitial cells in the stromal vascular fraction (SVF). 3,4 The SVF of adipose tissue contains all non-adipocyte cells ( e.g. immune cells, fibroblasts, endothelial cells, smooth muscle cells, ASCs). 5 The therapeutic potential of ASCs is thoroughly investigated clinically for bone and cartilage repair 6 , dermal wound healing and fibrosis 7,8 and myocardial infarction 9,10 , as well as in non-clinical research for tissue engineering purposes like skin tissue 11 or engineered blood vessels. 12 However, the clinical use of ASCs has become a major challenge because the ‘classical’ enzyme-based isolation methods are legally restricted in many countries. Enzymatic isolation methods are time-consuming procedures which require non-autologous materials such as enzymes and animal derived products. 13 For those reasons, there is an inherent risk of contamination of the isolated ASCs or SVF cells. Moreover, to generate sufficient numbers of ASCs, culturing and expansion of ASCs is needed. The expansion of ASCs for clinical use requires specialized culture labs (Good Manufacturing Practice facilities (cGMP)) which renders the clinical application of ASCs a costly business. Therefore, non-enzymatic intraoperative isolation procedures to yield a therapeutic cell fraction from adipose tissue, are being developed to date. 13 Non-enzymatic, mostly mechanical, isolation procedures are faster and less expensive than enzymatic isolation procedures. Furthermore, non-enzymatic isolation procedures do not require non-autologous biological materials and can therefore be used intraoperatively. Non- enzymatic isolation procedures should not be confused with emulsification procedures that are used to increase the injectabillity of adipose tissue. 13,14 In contrast to non- enzymatic isolation procedures, emulsification procedures are not able to disrupt adipocytes. Non-enzymatic isolation procedures often result in a SVF with most of the cell-cell and cell-matrix communications intact (the so-called tissue SVF or tSVF), while enzymatic isolation procedure result in a SVF with only single cells because enzymes disrupt all communication between cells and matrix (the so-called cellular SVF or cSVF). 13 Clinically, the tSVF and cSVF might have a different therapeutic effect as