A Novel and Effective Strategy for the Isolation of Adipose-Derived Stem Cells

Sir: We read with great interest the article entitled "A Novel and Effective Strategy for the Isolation of Adipose-Derived Stem Cells: Minimally Manipulated Adipose-Derived Stem Cells for More Rapid and Safe Stem Cell Therapy" by Raposio et al.1 Foremost, we want to congratulate the authors for this work and this interesting concept. Indeed, these authors demonstrate the possibility of adipose-derived stromal vascular fraction graft without digestion of the tissue by proteolytic enzymes and, more importantly, without expensive specific devices.2 This is the second study that reports this possibility after the recent work conducted by Tonnard et al.3 However, in our opinion, both studies are insufficient for demonstrating that the transplanted cells are mesenchymal stromal cells. Indeed, the authors did not demonstrate the stemness of the injected stromal vascular fraction cells. Mesenchymal stromal cells have been known for four decades and were initially isolated from the bone marrow. Within the adipose tissue, mesenchymal stromal cells called adipose-derived stromal cells were first reported in 2001 by Zuk et al.4 These cells were defined in vitro by several criteria5: Mesenchymal stromal cells can be isolated based on their ability to adhere to the plastic and they are capable of significant expansion and formation of colony-forming cells, referred to as colony-forming unit-fibroblasts. This characteristic was not tested by the authors. Mesenchymal stromal cells are multipotent cells that can differentiate into various cell types derived from the mesodermal lineage (bone, cartilage, and adipose tissue). This characteristic was not tested by the authors. Mesenchymal stromal cells are characterized by the presence of CD105, CD73, and CD90 and the lack of expression of hematopoietic markers. The authors performed this experiment in their study. In our opinion, it is necessary to demonstrate that the cells produced by this method meet the in vitro criteria of the mesenchymal stromal cells. Moreover, it would be interesting to compare the adipose-derived stromal cell yield obtained with these mechanical methods to the cells obtained with specific devices. It is important, because if the cell yield is equivalent, this will reduce the cost of the stromal vascular fraction–grafted cells, which could be extremely interesting in regenerative medicine. In conclusion, the authors have limited their investigations to phenotypic characterization without realizing differentiation in the mesodermal lineage and colony-forming unit-fibroblast experiment. It seems insufficient to demonstrate that the cells obtained are adipose-derived stromal cells. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication. Nicolas Bertheuil, M.D. Department of Plastic, Reconstructive and Aesthetic Surgery Hospital Sud and INSERM U917 University of Rennes SITI Laboratory Etablissement Français du Sang Bretagne Rennes University Hospital Rennes, France Stromalab Laboratory INSERM U1031 Rangueil Hospital Toulouse, France Benoit Chaput, M.D. Stromalab Laboratory INSERM U1031 Rangueil Hospital Department of Plastic, Reconstructive and Aesthetic Surgery Rangueil Hospital Toulouse, France