Joris van Dongen

27 Comparison of SVF isolation procedures: a systematic review INTRODUCTION Adipose tissue seems to be an outstanding source for regenerative therapies, since it is an easy accessible source for adipose-derived stem or stromal cells (ASCs). Adipose tissue can easily be harvested with liposuction, a low risk procedure that can be performed under local anesthesia. Several clinical trials have been published using ASCs for soft tissue reconstruction 1 , cardiac repair 2 , pulmonary repair 3 and cartilage repair 4 . All these trials show promising results for future use of ASCs in tissue repair and regeneration. To harvest ASCs, adipose tissue or lipoaspirate is subjected to enzymatic dissociation followed by several centrifugation steps 5 , which is a relative long-lasting procedure that cannot be performed during surgery. The cell population obtained by this enzymatic digestion and centrifugation is the stromal vascular fraction (SVF), containing ASCs, endothelial cells, supra-adventitial cells, lymphocytes and pericytes 5,6 . ASCs in vivo are characterized as CD31min/CD45min/CD34pos/CD90pos/CD105low cells 7 . After isolation, the SVF can either be used directly in clinical procedures or can be cultured to increase the number of cells before using them in the clinic 8,9 . In case of cell culturing, only ASCs and their precursor cells (supra-adventitial cells and pericytes) are able to adhere and survive 10,11 . Upon passaging in vitro , the phenotype of ASCs starts to deviate from their in vivo phenotype (Spiekman et al., 2016): in this process CD34 surface expression is lost, while CD105 expression is up-regulated to mention a few 7,12 . Alternatively, administration of the enzymatically prepared vascular stromal fraction of adipose tissue might have a therapeutic capacity that is similar to cultured ASCs. Although, no formal scientific evidence exists, the consensus is, that the therapeutic benefit of SVF predominantly relies on the abundantly present ASCs. The current protocol to isolate and cultureASCs fromadipose tissue involves enzymatic digestionwith collagenase.This is a laborious and time consuming protocol and requires a specialized culture lab (Good Manufacturing Practice facilities (cGMP)), which is not available in most peripheral hospitals 13 . Therefore, intraoperative procedures for SVF isolation are warranted, in particular systems that do not employ enzymatic treatment, such as mechanical dissociation. At present, several (commercial) procedures are available for intraoperative isolation of SVF 14,15 . These intraoperative isolation procedures differ in various aspects: isolation of a single cell SVF (cellular SVF (cSVF)) resulting in a pellet with hardly any volume or isolation of SVF cells containing intact cell-cell communications (tissue SVF (tSVF). Most of the enzymatic intraoperative isolation procedures result in a cSVF, because