Current Status of ADSCs-Enriched Fat Grafts in Plastic Surgery

Yating YIN ,Jianhua LI ,Hao WANG,3 ,Pingping WANG,4 ,Wanling ZHENG,5 ,Qiang LI,* ,Peisheng JIN,*

SUMMARY Autologous fat grafting is an increasingly popular technique in plastic surgery for volume augmentation and rejuvenation.However,the unpredictability of long-term volume retention limits its clinical application.Various animal studies have documented the positive effects of adipose tissue-derived stem cells (ADSCs) on the acceleration of lipofilling.However,the results have been inconsistent,and there is an insufficient number of high-quality clinical studies to formulate evidence-based recommendations for ADSC-enriched fat grafts.Moreover,related technical standards,such as the final count of harvested ADSCs and the enrichment ratio,have not yet been established.This systematic review included all clinical trials on ADSC-enriched fat grafts in plastic surgery from PubMed in the past 10 years,as well as all registered clinical trials on ClinicalTrials.Gov.To examine the current landscape of ADSCs harvest,we summarize the current applications of ADSCs in the field of plastic surgery and discuss the current barriers to universal clinical use.

KEY WORDS Adipose tissue-derived stem cells;Stromal vascular fraction;Fat graft;Cell-assisted lipotransfer;Plastic surgery

INTRODUCTION

In plastic surgery,autologous fat is considered the ideal filler for soft-tissue defects caused by aging,trauma,chronic wounds,and cancer resection.There is a consensus among plastic surgeons that fat grafting is useful for a variety of reconstructive procedures and that it is a safe procedure with a low complication rate and high patient satisfaction.In addition,autogenous fat is increasingly being used to improve skin quality,especially in cases of scarring secondary to acne,burns,and radiation injury[1-2];however,its high reabsorption rate limits its long-term therapeutic effect.

Various methods to enhance the survival rate of fat transplantation are currently under exploration,and the use of stem cell constituents,initially described by Zuk et al.[3],are of particular interest.Cell-assisted lipotransfer (CAL) refers to the addition of the ADSC-rich component of the stromal vascular fraction (SVF) to lipoaspirate with promising results.In 2006,Matsumoto D et al.[4]proved that CAL fat survived better than non-CAL fat after transplantation and that revascularization was significantly increased in CAL fat transplants.

Many animal studies have documented the positive effects of ADSCs in accelerating lipofilling.The ability of stem cells to self-renew[5],to secrete trophic factors[6],and to differentiate into different cell types[7]has allowed for the development of more flexible therapies to redefine the classic“autologous fat transplant”and offer more customizable treatment options.

In recent years,ADSCs have been used in various clinical fields,such as for the treatment of chronic wounds[8],multiple sclerosis[9],Crohn’s disease[10],chronic discogenic low back pain[11],stress urinary incontinence[12],and myocardial ischemia[13],many of which are registered on ClinicalTrials.Gov.Although CAL is commonly used in aesthetic procedures,there is currently no consistency across therapeutic avenues.As our understanding of ADSCs grows,several key aspects,such as the optimal isolation procedure,application approach,and cell quantity,remain unclear in the field of autologous ADSC grafts.Therefore,in the current study,we surveyed the research from the last decade to clarify these aspects.

MATERIAL AND METHODS

To identify the relevant clinical trials,we searched PubMed for original studies using the following search terms:(“adipose-derived stem cells”O(jiān)R“adipose stem cells”O(jiān)R“stromal vascular fraction”) AND (“fat graft”O(jiān)R“l(fā)ipofilling”O(jiān)R“cell-assisted lipotransfer”).Articles from 2010 to 2020 were included.The study designs,application methods of ADSCs,graft survival rates,aesthetics outcomes,and complications of the published studies were analyzed.

We also examined registered clinical trials on Clinical Trials.Gov.,although only seven relevant registered trials were included.The study designs and application methods of ADSCs were analyzed.

RESULTS

Published Clinical Studies

The clinical trials included in this review were as follows:study 1,Charles-de-Sa L[14];study 2,Gontijo-de-Amorim NF[15];study 3,Tissiani LA[16];study 4,Schendel SA[17];study 5,Koh KS[18];study 6,K?lle SF[19];study 7,Gentile P[20];study 8,Castro-Govea Y[21];study 9,Mazur S[22];study 10,Aronowitz JA[23];study 11,Peltoniemi HH[24];study 12,Yin Y[25].Table 1 shows the clinical trials worldwide from 2010 to 2020 that utilized ADSCs or SVF as a therapeutic in reconstructive and aesthetic surgery.Table 2 details the isolation and application methods of ADSCs and the autograft preparation protocol.

Table 1 Clinical studies on ADSC-enriched autologous fat grafts

Table 2 CAL clinical data:cell isolation and autograft preparation

Study Design

Most of the articles involved in this review are prospective controlled,with the exception of studies 4,8,9,and 10.The size of the sample ranged from 6 to 174.The patients suffered soft tissue defects caused by aging (studies 1,2,4,and 12),atrophy (studies 3,5,and 8),cancer resection (studies 7 and 9),and others (studies 10 and 11).The follow-up period ranged from 3 to 36 months.

Application Method

Most of the studies used adipose tissue harvested from the abdomen using negative-pressure liposuction.The most commonly published method of ADSC isolation involves enzymatic digestion of lipoaspirate to release the SVF,except in studies 1 and 2,in which SVF was separated mechanically,rather than by enzymatic processing.Different types of stem cells were used in these studies.Freshly isolated stem cells (SVF) were used in studies 1,2,3,4,7,8,9,10,11,and 12,and expanded ADSCs were used in studies 1,5,and 6.Uncultured ADSCs were reinjected on the same day of liposuction,while cultured ADSCs were reinjected 14 days after expansion.

Different methods of liposuction were used.Classic Coleman standard liposuction was used in studies 5,6,8,9,and 12.Study 2 used the superwet technique,study 4 used the Lipivage Closed System,and studies 7 and 11 used the Celution System.In studies 7 and 11,the overall process was controlled through automated sensors and processing algorithms that ensured standard handling of the tissue and cells.The diameter of the cannula applied for liposuction varied from 1.5-4 mm.The diameter of the cannula applied for fat reinjection varied from 1.4 mm to 14 G.In addition,study 1 used a 30-G needle to reinject the ADSC-suspension,and study 7 used 1-2 mmdiameter specific microcannulas for implantation.

The total amount of harvested fat ranged from 25-900 cc.The enrichment ratio of SVF-enriched fat in studies 1,2,7,9,and 11 was 1:1;in study 3,it was 2:1;in study 4,it was 2.7:1;in study 8,it was 1:1.5-2.5;and in study 12,it was 3:1.The quantities of ADSCs used in each trial varied considerably.The number of expanded ADSCs ranged from 2 × 106to 8.58 × 108(studies 1,5,and 6) and that of SVF was between 0.16 × 105and 8 × 107(studies 1,3,4,9,and 10).

Clinical Outcomes

ADSCs-CAL increased the survival rate of fat grafts

The cut-off time for measuring the fat volume was different,and the longest was at 36 months.The volume was mainly measured by computed tomography (CT) (study 2),magnetic resonance imaging (MRI) (studies 3,6,7,and 11),and 3D photogrammetric scan (studies 4,5,and 12).The results show a significant increase in the survival rate of fat grafts among the studies on ADSCs-(including SVF-)enriched autologous fat grafts.The retention rate of CAL was between 63% and 90.4%.The retention rate of simple lipofilling was between 24% and 79%.Most of the studies showed a higher survival rate of CAL compared to the traditional fat graft.In study 6,the survival rate in the ADSCs-CAL group was nearly 5 times that of the control group.The high residual volume is encouraging with respect to the possible use of enriched fat grafts in reconstructive surgery.However,study 11 indicated that stem cell enrichment does not warrant a higher graft survival in lipofilling of the breast.

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ADSCs-CAL improved the overlying skin quality

Skin quality tests were mainly performed by biopsy and histological detection (study 1).Evaluations of aesthetic outcomes were conducted by peers and patients themselves (studies 2,3,7,8,and 12).Other assessment forms used,included a semiquantitative scale and a modified Michigan’s questionnaire (studies 1 and 2).Study 1,in which fat/SVF mixture and ADSCs were compared for their use in facial rejuvenation,showed similar results to SVF-CAL and ADSCs alone,and both modified the pattern of the dermis.In this study,facial skin showed an increase in fibrils and the reappearance of new oxytalan elastic fibers in the papillary dermis after treatment.The proliferation of small blood vessels in the reticular dermis and subcutaneous fat layer was also noted.In study 12,the skin quality of both the SVFenriched and control groups was improved in terms of spots,wrinkles,texture,pores,UV spots,brown spots,and red areas compared with the preoperative skin qualities.In terms of skin texture,the cuticle groove became more even,and the skin became fuller.The longterm cosmetic outcomes were generally satisfactory and remarkable (studies 2,3,5,7,8,and 12).These results confirmed that ADSCs-CAL plays a role in promoting skin regeneration and rejuvenation.

ADSCs-CAL did not have an increased complication rate compared to autologous fat transplantation alone

In the long-term follow-up,most of the articles in this review did not report severe adverse events.In study 3,fat necrosis was present in four patients in the SVF group,three of which were surgically removed.One patient was observed without the need for intervention.In study 6,the amount of necrosis was significantly lower in the ADSCs-CAL group than in the control grafts (4.6% vs.16.1%).Study 9 showed that cancer recurrence in the ASC-enriched fat group (3.7%) was not significantly different from that in the control group (4.13%).There were no major complications in study 10,and six minor complications (3.7%) and three oil cysts (1.8%) were observed in the postoperative follow-up after fat grafting.In study 11,there were no complications or abnormal findings on postoperative MRI.However,in the long term,there was one case in each group in whom several small oil cysts were detected approximately 1.5-2 years postoperatively;this may be related to the originally small and thin breasts of both patients.

Registered Clinical Trials

All relevant clinical trials that were registered at www.ClinicalTrials.Gov were included.A full overview of the studies is presented in Table 3.

Most registered clinical trials are either ongoing,not yet recruiting patients,or have exceeded the completion date.Studies C,D,K,and O were complicated and the study designs varied;studies A,C,H,J,K,and M were randomized and controlled;studies B,D,E,G,and O were single group assignments;studies F,L,N,and O were non-randomized;study I was an observational,prospective,and case-control study.The estimated patient enrollment ranged from 3 to 80,and the followup period ranged from 3 to 36 months.ADSCs were used as the SVF type in most of the studies,except thatex vivoexpanded stem cells were applied in study L.The conditions of patients included skin abnormalities or aging (studies A,D,and G),wounds (studies E,J,and O),scars (study E),soft tissue defects (studies B,C,E,F,H,I,K,L,M,and N),and others (study J).

DISCUSSION

As shown in the tables above,the classic Colemanstandard fat graft is the most widely recognized.Despite similar grafting practices and processes,the improvement rates of fat survival vary,ranging from 24% and 79% in this review.The popularity of CAL has proved conducive to the development of new systems through which SVF is extracted from adipose tissue for immediate use in the operating room as a means of enriching the tissue to be transferred,with the aim to improve fat retention.However,the complexity of SVF components makes the results more uncertain,and it may well become clear that these therapies will need to be individually evaluated.Freshly isolated ADSCs,also known as SVF,are considerably more heterogeneous than the quite homogeneous cells harvested from purified ADSCs[26].This variability of ADSCs makes their clinical application exceptionally challenging.

Table 3 Registered clinical trials

The culturing of ADSCs takes several days or weeks and cannot be performed as a same-day procedure.While some techniques use simple centrifugation to isolate stem cell pellets,others are more complex and involve,for example,enzymatic dissolution of the adipose tissue.After isolation,it takes approximately 2 weeks of culture before reinjection.Moreover,in plastic surgery,it is difficult to envisage the extraction of adipose tissue,a cell culture phase,and a second intervention with MSC-enriched tissue in accordance with indications for reconstruction;multiple constraints,for the most part economic,render this type of operation impractical.In line with this,the quantity of cells reinjected after a culture phase with SVF extraction and direct utilization in a clinical setting is disproportionate.Last but not least,the expensiveness of industrial systems for enzymatic isolation of SVF,and the cost price of academic studies render these treatments difficult to provide routinely in clinical practice.However,this review of 12 studies and 428 patients came to the conclusion that fat graft enrichment with SVF cells actually improved graft survival for small-scale reinjected volumes.Therefore,it will be necessary to find new and cost-efficient means of producing SVF cells that are usable in the operating room,either with the goal of increasing the volumetric retention of the graft or in order to undertake reconstructive surgery.

Although not all ongoing clinical trials are registered on ClinicalTrials.Gov,there is no doubt that a considerable amount of research in this field is currently being conducted.However,the patient populations are limited in size,and the lack of blinding in all studies,as well as the limited randomization,significantly increases the risk of bias.In terms of volumetry,some studies used MRI and CT,but none showed how accurately the volume of the graft could be calculated by evaluating the width of the graft in a single image.Given the consistent findings of these studies in spite of their shortcomings,they highlight the efficacy of ADSCs in the treatment of fat transfer.

New mechanical digestion of adipose tissue was first described in 2013[27],a process the authors imperfectly termed“nanofat grafting”.In this technique,the adipose tissue is emulsified and filtered at 500 mm to produce SVF cells.The term“nanofat grafting”is imprecise because no adipocytes are involved,and that the cells involved,which are not nanometer-sized,correspond according to the authors to ADSCs.The diameter of ADSCs is on the order of microns.

Numerous technical variants may modify the SVF composition and require characterization studies of the products used in a clinical setting.As previously underlined,it will behoove researchers to agree on a definition of extraction techniques and on the main lines of future research in view of analyzing the reinjected product.

ETHICS DECLARATIONS

Ethics Approval and Consent to Participate

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Consent for Publication

All the authors have consented to the publication of this article.

Competing Interests

The authors declare that they have no competing interests.The authors state that the views expressed in the article are their own and not the official position of the institution or funder.