Joris van Dongen

105 tSVF acts anti-inflammatory on chondrocytes in vitro INTRODUCTION Autologous adipose tissue transplantation is frequently used for a variety of different clinical indications,suchasdermal scarring,fatatrophy,bodycontouring,woundhealing, burn wounds, osteoarthritis and perianal fistulas. 1-6 The therapeutic efficacy of adipose tissue is ascribed to the stromal vascular fraction (SVF) containing a heterogeneous mixture of non-adipocyte cell types e.g. immune cells, fibroblasts, endothelial cells, pericytes and adipose derived stromal cells (ASCs). 7,8 ASCs reside in SVF as progenitor cell types attached around vessels as pericytes or supra-adventitial cells. 9,10 In vitro, ASCs secrete a plethora of growth factors, cytokines, chemokines, matrix proteases and extracellular vesicles which stimulate different regenerative processes such as angiogenesis, fibroblast migration and proliferation, matrix remodeling as well as immune modulation. 11-13 These trophic effects illustrate the regenerative potential of ASCs as a source for cell-based therapy to repair different types of damaged tissue. 14 Nowadays, SVF is often mechanically derived instead of enzymatically isolated because the use of enzymes for medicinal products is highly regulated in many countries. Mechanical preparation of SVF results in a tissue-like SVF (tSVF) containing SVF cells and intact cell-cell communications including ECM. Enzymatically isolated SVF yields a single cell suspension of SVF (cellular SVF or cSVF). ECM acts as a pro- regenerative scaffold to bind and release growth factors, matrix metalloproteinases (MMP), proteins and cytokines in a controlled way. 15,16,17 Several growth factors or enzymes, like transforming growth factor-beta (TGF- β ), fibroblast growth factor (FGF) and matrix metalloproteinase 13 (MMP-13), are involved in cartilage homeostasis. 18-20 A disbalance between these growth factors and enzymes play an important role in cartilage degradation, synovitis and osteophyte growth and thus osteoarthritis (OA). 18- 20 Osteoarthritis is chronic progressive disease, wherein damaged joints lead to pain, stiffness and disability. 21 ASCs might decrease these clinical symptoms by influencing growth factor stimulated processes involving cartilage degeneration such as blocking TGF- β 1-induced fibrosis and reducing collagenase 3 (MMP-13) expression in vitro. 22,23 Furthermore, ASCs can induce immune suppressive effects in OA by exciting macrophages in the synovium to produce interleukin (IL)-10 or induce a switch to M2 macrophages via secretion of prostaglandin-E 2 (PGE2). 24 This could beneficially contribute to the treatment of OA. Hence, tSVF as a source for ASC-cell-based therapy potentially harbors more therapeutic capacity than ASCs alone in the treatment of OA. Multiple studies have already shown safety and efficacy e.g. improved functionality, less instability and reduction of pain of using ASCs and cSVF as a treatment of OA in humans and animals. 25-31 More recently, a case series with tSVF as a treatment for