Phenotypic Analysis of Stromal Vascular Fraction after Mechanical Shear Reveals Stress-Induced Progenitor Populations
The intersyringe processing allows preparation of two distinct products. The first is the unfiltered emulsified fat, which contains mainly dead adipocytes and extracellular matrix. This whitish product, which has a paste aspect, can be used for volume defects but requires a minimum of 25-gauge needles for injection because of the extracellular matrix that can block finer needles. Banyard et al. analyzed this product, which is different from nanofat graft. Indeed, the nanofat grafting product is filtered before use to remove the remaining connective tissue. Here, the authors have filtered after enzymatic digestion, which does not reflect the nano fat grafting. The use of collagenase before filtration will therefore yield a completely different cell population. In their Discussion, the authors are aware of it but, clinically, this cannot be the same use, as several times we experienced that this product does not pass through needles smaller than 24- to 25-gauge.
The second product obtained after intersyringe processing and filtration is a mechanically isolated stromal vascular fraction, which differs from the one obtained after collagenase digestion. Indeed, we recently analyzed this second product obtained after the Tonnard procedure without collagenase digestion, and we obtained different results compared with Banyard et al.3,4 Indeed, even when we used different phenotypic markers, we demonstrated that stromal vascular fraction obtained after intersyringe processing contains significantly fewer hematopoietic, endothelial, and red blood cells (CD235a+ cells) than stromal vascular fraction obtained after enzymatic digestion, and we conclude that this technique produces an adipose-derived stem cell–enriched stromal vascular fraction (579,195 adipose-derived stem cells/g versus 47,859 adipose-derived stem cells/g; p < 0.001). The reduction in cell viability is a problem we also found, and the work of Osinga et al. was somewhat surprising.5 Thus, we noted twofold less viable stromal vascular fraction after mechanical digestion compared with enzymatic stromal vascular fraction digestion.
Finally, the authors concluded that intersyringe processing increases the number of CD105+/SSEA3+ muse cells in the stromal vascular fraction. However, muse cells exhibit characteristics of both mesenchymal and pluripotent stem cells. They are double-positive for CD105 and stage-specific embryonic antigen-3, but they also express pluripotency markers, including Oct3/4, Nanog, and Sox2, and are capable of differentiating into cells of ectodermal, endodermal, and mesodermal lineages.6 It would be necessary to test the differentiation capacities and the expression of pluripotency markers of these cells before concluding that intersyringe processing induces multilineage differentiating stress-enduring cells. Then, the authors conclude that there is a significant up-regulation of the mesenchymal stem cell population in stress-induced stromal vascular fraction compared with control stromal vascular fraction. However, the CD34+/CD45− cell population consists of not just mesenchymal stem cells but also contains endothelial cells.7 Moreover, it would be interesting to determine the progenitor capacities (colony-forming units) of these enduring stress cells compared with conventional adipose-derived stem cells obtained after enzymatic digestion.
We congratulate the authors for this study that opens new perspectives regarding the regenerative potential of mechanical adipose tissue processing. It seems necessary to investigate the actual regenerative potential of these stress-induced progenitor obtained after intersyringe processing.