Reply: Mechanical Micronization of Lipoaspirates

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We appreciate the letter from van Dongen et al. regarding our article, “Mechanical Micronization of Lipoaspirates: Squeeze and Emulsification Techniques.”1 In response to their suggestion stating that stromal vascular fraction isolated from adipose tissue should be classified into “cellular-derived stromal vascular fraction,” which means enzymatically derived stromal vascular fraction, and “tissue-like stromal vascular fraction,” which means mechanically derived stromal vascular fraction, we would like to make the following comments.
The first sentence of their letter, “the article of Mashiko et al., in which … to obtain a stromal vascular fraction” is wrong; the procedures we described are performed to remove adipocytes from lipoaspirates and micronize the connective tissue, not to obtain the stromal vascular fractions. We need to reaffirm the criteria defining stromal vascular fraction to avoid any confusion. The scientific term, “stromal vascular fraction” has been historically used since 40 years ago.2 Stromal vascular fraction has been used to express cellular fractions (heterogeneous cell mixture), which are biologically isolated from the original stromal tissue (adipose tissue, in this case). According to the joint statement of the International Federation for Adipose Therapeutics and Science and the International Society for Cellular Therapy published in 2013,3 the stromal vascular fraction is the released elements separated from the mature adipocytes following enzymatic digestion, which can differ substantially according to the protocols.
It is true that mechanical, nonenzymatic techniques can release a small number of isolated cells,4 which can be called stromal vascular fraction. However, no efficient mechanical (nonenzymatic) methods to isolate stromal vascular fraction have been developed so far. The products obtained from previously reported mechanical methods, such as those using red blood cell lysis buffer, aggressive shaking, vortexing,5 or syringe transfer (including their published procedure, fractionation of adipose tissue procedure6), are not isolated cells, but are micronized tissue fragments. In the products, the majority of cells remain integrated in the tissue fragments and bound to the extracellular matrix, and cannot be analyzed by flow cytometry. It is not appropriate to use the term “tissue-like stromal vascular fraction,” in which stromal vascular cells are not isolated from the tissue fragments. Thus, we referred to it as “micronized tissue fragments” in our article. We agree, however, that the stromal vascular fraction may be obtained by more sophisticated mechanical methods in future studies.
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