Automation and Standardization o f the Stromal Vascular Fraction

Clinical application of SVF cells requires that they be prepared using a clinical-grade processing system and reagents within a standardized methodology. Ideally, the system, reagents, and methods used will generate a consistent, reproducible cell SVF cell product with a reliable safety and efficacy profile. We refer to cells processed in such a manner as adipose-derived regenerative cells (ADRCs) as a means of distinguishing them from the cell population obtained using non-clinical-grade enzyme reagents, open non-automated system processes, or where consistent cell product composition has not been validated.

Our approach led to the development of the Celution System, an automated system designed to digest, extract, wash, and concentrate SVF cells from adipose tissue. The Celution System is a CE marked medical device in the European Union and an investigational device in several FDA-approved clinical trials in the United States. This system was designed to provide high-quality, reproducible, standardized, validated cell processing so that the end product could be relied on to meet a clearly defined composition and thus a more predictable safety and efficacy profile. The Celution System consists of a stand-alone reusable hardware unit: the Celution Device, the Celution Consumable Set, and Celase Reagent. The Celase Reagent is a proprietary enzymatic reagent that digests the extracellular matrix to release the entrapped SVF cells. In accordance with the need to apply only medical-grade reagents, Celase is manufactured as a sterile product under pharmaceutical standards using a mammalian product-free system to eliminate concern regarding transmissible spongiform encephalopathic agents. This ensures safety and provides consistent, reproducible tissue digestion activity. Adipose tissue is introduced into the tissue collection chamber of the Celution Device, where it is washed to remove red blood cells and debris, and then digested with Celase. The device subsequently moves cells and fluids through a closed system of tubing and reservoirs, concentrates cells through the use of centrifugation technology, and subsequently removes the waste through the use of the same pumps and tubing used to deliver the fluids and cells.

Since the release of the Celution System, many other automated, semiautomated, and manual adipose tissue processing systems have been developed, such as the Cha-Station (CHA Biotech, Kangnamgu, Republic of Korea) and Icellator (Tissue Genesis, Honolulu, HI). The Sepax system (Biosafe, Eysins, Switzerland), a product originally designed to process umbilical cord blood, has also been used to concentrate adipose tissue cells after digestion with collagenase. ¹¹ A comparison of these four systems is provided in Table 7-1. It is important to note that although each of these systems processes adipose tissue, intrinsic differences in their design and reagents mean that the cell product prepared by one system is often very distinct from any other in terms of yield, composition of cell types, and in residual enzyme level. ¹² These reasons make it extremely difficult to extrapolate safety and efficacy data obtained with one system to that of another and emphasizes the importance of accurate characterization of the product.

Although many systems are now available, very few studies have evaluated different devices in a controlled, head-to-head comparison. Furthermore, differences in the techniques used to characterize the cell population produced by these approaches frequently confound comparison between published studies. The most comprehensive head-to-head comparison so far was published by Aronowitz and Ellenhorn in 2013. ¹² In their study, the authors compared four different systems: Multi Station, Cha-Station, Celution System, and Lipokit with MaxStem (Medi-Khan, West Hollywood, CA). The results showed considerable differences in cell yield (viable nucleated cells per gram of input adipose tissue), residual enzyme levels, and what is very important, in the composition of the cell product. For example, CD34+ stromal cells (defined as cells expressing CD34 but not the endothelial marker CD31 or the hematopoietic marker CD45) composed, on average, approximately 43% of the cell product produced by the Celution System, but only approximately 20% to 28% of the cells with the other systems. Similarly, the frequency of CD34+/CD31+ vascular endothelial cells in the cell product prepared with the Celution System was, on average, fourfold higher than that obtained with the other systems. Stem cell frequency, as assessed by the CFU-F assay, was also fourfold higher. The most important conclusion of this paper was that when using the same starting adipose tissue and the same cell characterization assays, different processing systems yield very different products. This clearly demonstrates the importance of standardized characterization approaches. This need has also been recognized by the professional societies involved in bringing this form of cell therapy to the clinic. ¹³