Adipose-derived stem/stromal cells (ADSCs) were first characterised in 2001, and have since already been widely studied and used as a major source of tissue with regenerative potential, with characteristics similar to that of mesenchymal stem/stromal cells (MSCs) [ 1 – 4 ]. ADSCs are remote as part of the aqueous fraction derived from enzymatic digestion of lipoaspirate (the product of liposuction). This aqueous fraction, a mixture of ADSCs, endothelial precursor cells (EPCs), endothelial cells (ECs), macrophages, smooth muscle cells, lymphocytes, pericytes, and pre-adipocytes among others, is what is known as the stromal vascular fraction (SVF).
ADSCs, such as MSCs, have shown promise in regenerative and reconstructive medication [ 5 – 8 ]. Recent advances in the area of tissue regeneration have got put SVF on a par and at times even over ADSCs [ 9 – 17 ]. For instance, in a study of erection function in a rat model of cavernous nerve injury, SVF treatment showed superior statistically significant results compared to ADSC treatment alone, especially in smooth muscle/collagen ratio and in endothelial cell content [ 12 ]. The advantage of SVF over ADSCs is believed to be in two fundamental areas. Firstly, even though similar in properties such as immunomodulation, anti-inflammatory, angiogenesis, and so on, the distinctive, heterogeneous cellular composition of SVF might be responsible for the better therapeutic outcome observed in comparative animal research [ 9 – 12 ]. Secondly, unlike ADSCs, SVF is much more very easily acquired, without the need for any cell separation or culturing situations. Thus, the therapeutic cellular product is instantaneously obtained and it has minimal contact with reagents making it comparatively safer and susceptible to the fulfilment of lesser regulatory criteria. It should be mentioned that, whereas ADSCs find utility in both allogeneic plus autologous treatments, SVF, owing to the presence of various cell varieties known to cause immunological rejection, is suitable for autologous remedies only.
Even though almost all ADSCs are derived from the white adipose tissues (WAT), as covered in this review, the identification associated with progenitor cells in brown adipose tissue (BAT) associated with adult humans is fascinating and worth a point out [ 18 , 19 ]. Termed as BADSCs (brown adipose-derived stem cells), these have been isolated from BAT deposits present in fairly inaccessible regions such as the mediastinum, and are capable of differentiating in order to metabolically active BA cells with differences in surface antigen expression as compared to WAT-originating ADSCs [ 18 ]. Current knowledge of WAT and BAT define these cells with specific functionalities, and thus translational avenues for ADSCs from possibly source should be compared to identify specific therapeutic targets plus potential advantage of one over the other. Understanding of the molecular mechanisms behind either cell fate and the possibility of inter-conversion are interesting avenues of research with basic plus translational implications [ 20 , 21 ].
Despite the potential of SVF in regenerative medicine there are challenges to overcome. First is remoteness of SVF, which needs a specialised infrastructure such as a thoroughly clean room facility, equipment, reagents, and technical capabilities. These types of conditions limit the reach of SVF to only main hospitals in tier 1/2 cities, especially in a nation such as India. In this regard, the up and coming point-of-care biomedical gadgets which can take lipoaspirate as their input and produce clean and sterile, injectable SVF as output will be beneficial. Secondly, the technique of isolating SVF is a vital roadblock in the accepted use of SVF for therapeutic applications. Digestion of lipoaspirate is achieved by collagenase, and the presence of collagenase within the injectable product does not bode well with regulatory specialists such as the US Food and Drug Administration (FDA) [ 3 ]. Consequently, alternative methods are being explored with some encouraging results [ 22 – 25 ]. Finally, characterisation of the regenerative cells associated with SVF has not reached a wide consensus. Organisations such as the Worldwide Federation for Adipose Therapeutics and Science (IFATS) as well as the International Society of Cellular Therapy (ISCT) have been upgrading the surface antigen-based definition of SVF cells, where CD34 antigen, primarily associated with haematopoietic stem cells (HSCs), became an essential marker of regenerative, MSC-like cells of the SVF [ 1 , 26 , 27 ].
In this particular review, using the broader topics of isolation and characterisation of SVF, we will touch upon some of the challenges plus innovations in the field and comment upon the future of SVF.