For therapeutic purposes, ASCs are typically isolated from human adipose tissue. However, they can be obtained from the adipose of other mammals, offering a wealth of potential for the preclinical study of ASCs [11]. Here we will review ASC heterogeneity among large mammalian species such as cattle, pigs, and dogs. It has been noted that large mammals more closely reflect human physiology than rodents, despite the increased ethical concerns of using these more intelligent animals in research [12]. If ASCs from large mammals prove useful, they could significantly advance our understanding and treatment of diseases, offering new hope for patients and researchers alike.

Most ASCs sourced from mammalian species are evaluated using the same criteria for characterization and differentiation capacity as those derived from humans. Most published studies have utilized ASCs from large, land mammals. Interestingly, fat extraction sites are inconsistent between species and even among research of the same species (Table 1, Ref. [13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]). In two independent studies of ovine-derived ASCs, cells were extracted from the embryonic tail fat [13] or omental fat tissues [14]. Despite the difference in depot site, both cell types undergo adipogenesis and osteogenesis [13, 14]. The embryo fat-derived, and omental fat-derived ASCs were capable of myogenesis [13] and chondrogenesis [14], respectively, indicating differences in differentiation capacity. Neither study induced chondrogenesis and myogenesis, but the ASCs likely become chondrocytes and myocytes, despite the extraction site. However, more research needs to be done to confirm this assumption.

In bovine research, extraction sites are not standardized. However, adipogenic and osteogenic differentiation potential is maintained in ASCs from both the tailhead region [15] and the abdomen [16]. Notably, cell surface marker expression is more heavily contested. Ishida et al. [4] included CD26, CD54, and CD146 as surface markers for detecting ASCs, but other bovine-derived ASCs were not evaluated using the same standards [15, 16], complicating comparison among studies. While positive and negative surface markers varied, CD44 and CD73 positivity remained required for ASC identification in both studies [15, 16]. Since previous literature is inconsistent regarding positive and negative selection markers, the resulting studies reviewed herein are also inconsistent regarding selectivity markers. This phenomenon eludes to the need for protocol standardization in ASC research.

Similarly to ASCs extracted from ovine and bovine models, porcine models are also inconsistent regarding fat depot extraction sites. However, the criteria for ASC detection were consistent, with CD29, CD44, CD90, and CD105 as positive markers, and CD14, CD31, and CD45 as negative markers [17, 18, 19, 20]. Abdominal and dorsal fat-derived ASCs could undergo adipogenesis and osteogenesis [17, 18, 19]. Dorsal fat-derived ASCs can differentiate into chondrocytes [18, 19, 20], but not myocytes [18], despite expressing muscle-specific genes in the presence of fully differentiated myotubes [18]. Moreover, differentiation capacity and resulting transcriptomic profiles are heavily reliant upon the breed of the porcine model [25], indicating a need for uniformity across studies.

Consistent with other non-human mammalian ASCs, canine-derived ASCs can undergo adipogenesis [21, 22, 26], osteogenesis [21, 22, 26], and chondrogenesis [22, 26]. However, Rashid et al. [21] demonstrated that the extraction site of ASCs affects differentiation capacity. While ASCs from the canine infrapatellar fat pad, perirenal, inguinal, and omental regions can differentiate into osteocytes and adipocytes as evidenced by alizarin red and Oil Red O staining, respectively, omental fat-derived ASCs showed significantly increased Oil Red O staining compared to undifferentiated controls than ASCs from other depots. However, omental-derived ASCs are larger than infrapatellar fat pad-derived ASCs, so they may be able to form larger lipid droplets, become larger adipocytes, and therefore retain more Oil Red O stain [21]. Also, this difference may be due to the proximity of omental fat to the abdominal region compared to the other derivation sites. Similarly, omental-derived ASCs showed more significant alkaline phosphatase (ALP) activity in cells undergoing osteogenesis compared to other depot-derived ASCs. However, although ALP activity was significantly elevated in all differentiated cells compared to the undifferentiated controls [21]. Interestingly, the proliferation of ASCs from the infrapatellar fat pad of canines was higher than that of cells from other sites [21].

Non-human primate-derived ASCs can undergo adipogenic [23, 24, 27, 28, 29], osteogenic [23, 24, 28, 29], and chondrogenic [23, 24, 28] differentiation, regardless of isolation from abdominal [23] or mesenteric [24] depot sites. Further, another study showed the differentiation of ASCs into neural cells [29]. The span of in vitro ASC differentiation experiments is seven to 21 days; however, differentiation times differed amongst lineages between studies, making comparison across experiments difficult. Non-human primate adipogenesis studies were carried out for seven [24] or 21 [23] days, while chondrogenesis and osteogenesis studies were consistently 21 days [23, 24]. Although these discrepancies in differentiation times are interesting, the International Federation for Adipose Therapeutics and Science (IFATS) does not recommend a specific time frame for differentiation of ASCs [30], leaving interpretation up to the investigators.

All mammalian-derived ASCs reviewed were capable of adipogenesis and osteogenesis, and all cells induced to undergo chondrogenesis could do so. However, in a study by Milner et al. [18], porcine ASCs were incapable of myogenesis. In this study, porcine ASCs were differentiated using a medium that caused murine myoblasts to differentiate into myotubes [18]. Therefore, based on the intrinsic differences that may be present between species, it is probable that the myogenesis-inducing medium will also vary from species to species. Thus, more studies need to be performed to confirm the ability of porcine-derived ASCs to undergo myogenesis. Otherwise, ASC protocols, including differences in depot sites and positive and negative selection markers, vary among species, leading to conflicting results. The discrepancies in surface marker expression may be due to expression differences amongst various species, leading researchers to identify other positive and negative markers [31]. A standardized approach to ASC research is needed to harness the translational potential of mammal-derived ASCs fully.

While large mammal-derived ASCs are crucial for better understanding the role of ASCs in preclinical models, human-derived ASCs are the most critical consideration for future therapeutic applications. However, adipose from different anatomical locations exhibits unique biological and physiological properties, indicating the need to review the behaviors of ASCs from various human depots. For example, fat accumulation in an android or truncal distribution is associated with obesity-related cardiometabolic diseases, whereas gynoid peripheral fat in the gluteal and femoral regions is metabolically protective [32]. Subcutaneous white adipose tissue (WAT) is the body’s predominant adipose that stores and releases energy through lipids. Compared to visceral adipose, subcutaneous adipose comprises a more significant percentage of ASCs [33]. Mounting interest in ASCs has emerged due to their utility in cell-assisted lipotransfer and bone regeneration and their role in tumor-promoting interactions with cancer cells, especially in the breast. Here, we discuss human adipose progenitor cells which demonstrate heterogeneity in function depending on the subcutaneous anatomical depot from which they are derived (Fig. 1).

Fig. 1.

ASCs from various human-derived depots. Adipose-derived stem cells (ASCs) from the buccal fat pad, breast, flank, abdominal, gluteal, and thigh depots have varying differentiation capacities. These cells differ in proliferative abilities and gene and protein expression of various markers. Created with BioRender.com.

Human ASCs have been isolated from subcutaneous depots, including the abdomen, gluteal region, breast, arm, thigh, flank, back, and buccal fat pads, and cultured in vitro. The anatomical niche ASCs are derived from can dictate lineage differentiation potential into adipocytes, osteocytes, or chondrocytes. In comparison to ASCs isolated from the abdomen (abASCs), breast-derived ASCs (brASCs), preferentially differentiate from the osteogenic lineage, suggesting that brASCs could be more suitable for bone regeneration applications. On the other hand, abASCs are preferred to brASCs for adipocyte generation in cell-assisted fat grafting for breast reconstruction. These findings significantly impact the selection of ASCs for specific regenerative medicine applications [34].

For cell-assisted fat grafting, ASCs with the highest adipogenic potential are desired to supplement fat growth in the engrafted areas [34]. Therefore, determining differentiation capacity differences among ASC depots is crucial to selecting the most effective ASC type. Among flank-, arm-, abdomen-, and thigh-derived ASCs, thigh-derived ASCs (thASCs) exhibited the highest adipogenic potential out of the four depots [35]. Similarly, a study comparing thASCs and abASCs from age-, BMI-, and passage-matched tissues showed that thASCs expressed significantly higher gene and protein expression of mature adipocyte markers than abASCs after one week of adipogenic differentiation [36], confirming the results of the previous study. Thus, thigh adipose could be superior to abdominal adipose for fat grafting. However, ASCs were not obtained from all depots in all patients, which may limit the conclusions drawn from the depot-specific differences in this study [35]. Conversely, flank ASCs (flaASCs) exhibited the lowest gene expression of mature adipocyte markers adipocyte protein 2 (AP2) and lipoprotein lipase (LPL) after one week of in vitro adipogenic differentiation compared to the abdominal-derived ASC controls [35]. When comparing abASCs and gluteal ASCs (gluASCs), gluASCs exhibited enhanced adipogenesis compared to abASCs, as evidenced by Sudan staining. However, mature adipocyte gene marker fatty acid binding protein 4, also known as AP2, was not significantly different between the depots after 28 days of adipogenic differentiation [37]. Gluteal adipose is anatomically close to the thigh, which may explain its functional similarities and enhanced adipogenesis compared to abASCs, which are closer to visceral organs.

Due to their osteogenic differentiation potential, ASCs represent promising tools in bone regeneration procedures correcting periodontal defects and facial reconstruction. ASCs with the highest osteogenic differentiation capacity are ideal for such applications. The buccal fat pad, a small fat pocket in the cheek, yields ASCs (bfpASCs) with enhanced osteogenic differentiation compared to abASCs, as demonstrated by the increased gene expression of ALP and collagen I after two weeks of in vitro osteogenic differentiation. BfpASCs and abASCs had similar abilities to adhere to periodontal engraftment resorbable materials. BfpASCs displayed enhanced osteogenic stimulation in response to amelogenin, a porcine enamel derivative used for periodontal defect corrections, as bfpASCs exhibited upregulation of ALP and collagen I compared to abASCs. The difference in response of bfpASCs to amelogenin is potentially due to the buccal fat pad niche location, which is closer to dental enamel, and abdominal fat is located distal to dental enamel [38]. However, bfpASCs and abASCs displayed similar adipogenic differentiation potential, growth kinetics, and proliferation in response to human sera, suggesting that the utility of bfpASCs is most relevant in bone regeneration, especially in periodontal and facial reconstruction [38]. However, Broccaioli et al. [38] did not delve into the detailed mechanisms behind the different behaviors exhibited by abASCs and bfpASCs.

Furthermore, in a comparison of flank-, arm-, abdomen-, and thigh-derived ASCs, flaASCs and thASCs had the highest osteogenic potential evidenced by alizarin red and ALP staining, as well as gene expression of mature osteoblast markers. Gene expression of bone morphogenetic protein 4 (BMP4) was highest in flaASCs and thASCs, suggesting that the bone morphogenic proteins (BMPs), which stimulate osteogenesis, could be responsible for the increased differentiation in these depots [35]. Compared to abASCs, gluASCs have higher osteogenic potential after 28 days of osteogenic differentiation. GluASCs showed significant upregulation of ALP, but no depot difference was seen in other gene markers of mature osteoblasts [37]. The differences in differentiation capacity could be due to niche-specific differences in levels of osteogenic precursors present in adipose to alterations in signaling pathways like the BMP pathway.

In mouse models, ASCs have enhanced survival compared to adipocytes under hypoxic conditions. This suggests supplementing ASCs in fat grafting procedures through cell-assisted lipotransfer may prevent hypoxia and necrosis in the newly grafted fat. Enhanced survival may result from ASCs being needed to initiate tissue repair post-damage [39]. ThASCs exhibit higher angiogenic potential than abASCs, making them a potentially preferred candidate for cell-assisted fat grafting over abASCs [36]. After three weeks of in vitro induced endothelial differentiation, thASCs expressed significantly higher angiogenic vascular endothelial growth factor (VEGF) pathway gene and protein markers, as well as endothelial cell marker CD31. When endothelially differentiated thASCs and abASCs were seeded on Matrigel, thASCs exhibited significantly greater tube formation, with extensive tubes and junctions, evidenced by phase-contrast microscopy [36]. It is postulated that the thigh adipose microenvironment is primed by exercise compared to the abdominal adipose environment, and the biomechanical fluid shear stress from exercise induces differentiation to the endothelial lineage [40]. In shear stress conditions, murine progenitor C3H/101/2 cells express greater levels of von Willebrand Factor (vWF), a protein expressed in endothelial cells. Similarly to the previous study, shear stress also induces tube formation on Matrigel. Shear stress induces upregulation of VEGF and VEGFR-1 mRNA expression, indicating a potential mechanism by which these cells differentiate into endothelial cells during mechanical stress [40]. These observations may contribute to thASC predisposition to angiogenesis over abASCs.

When considering the safety and efficacy of cell-assisted fat grafting, it is necessary to consider ASC growth kinetics and self-renewal. BrASCs exhibit a higher self-renewal capacity, as evidenced by significantly increased colony-forming units, suggesting that brASCs may retain an undifferentiated state and thus have enhanced stem cell populations [34]. The growth kinetics of brASCs differ from abASCs, indicating that priming from the original anatomical niche can dictate the long-term growth kinetics of ASCs. BrASC doubling time was progressively faster with each passage, while abASCs had a stable doubling time [34]. Furthermore, in comparing abdomen-, arm-, flank-, and thigh-derived ASCs, flaASCs exhibited the highest proliferation capacity by BrdU incorporation [35]. Further investigation revealed 2–4-fold higher fibroblast growth factor 2 (FGF2) gene expression in flaASCs compared to abASCs, identifying the FGF2 pathway as a potential mechanism by which flaASC proliferation is increased [35]. Meanwhile, in two studies, abASCs exhibited proliferation profiles similar to that of gluASCs [37] and bfpASCs [38]. Additionally, in a study comparing ASCs from the upper abdomen, lower abdomen, flanks, dorsum (dorsal upper back), and thighs, the colony formation capacity (reflecting self-renewal capacity) and doubling times did not differ between depots [41]. These findings underscore a unique cellular growth profile of brASCs compared to ASCs from other adipose depots. Thigh, flank, and arm-derived ASCs had comparable proliferation capacities, but flaASCs were highly proliferative [35]. Therefore, the results of these studies indicate that adipose tissue depot sites can influence the proliferation of ASCs, indicating the importance of a thorough assessment of proliferative abilities before selecting a depot site for ASC extraction for clinical use.

Investigating the effects of ASCs on surrounding cells via secretion of cytokines, growth factors, or exosomes is important for predicting long-term activity in engrafted sites and understanding how ASCs interact with nearby tumors. The effects of abASC and thASC secretomes were evaluated by applying ASC-conditioned media to human fibroblasts. The protein secretome of ASCs from these two depots increased VEGF protein expression compared to the control; however, there was no significant difference in VEGF protein expression between thASCs and abASCs [41]. VEGF is a mediator of wound healing and has been shown to play a role in migration, proliferation, and angiogenesis. No significant difference was found between the migration of fibroblasts treated with media from either abASCs or thASCs, despite both ASC depot secretomes increasing fibroblast migration compared to the control [41]. Therefore, VEGF signaling must play a role in both abASC and thASC migration. This data highlights similarities in thigh and abdominal ASC secretomes and their impact on surrounding fibroblasts, suggesting that both abASCs and thASCs could be equally effective in promoting wound healing and angiogenesis, which could have implications for tissue engineering and regenerative medicine.

ASCs from different human anatomical niches display various expression profiles, differentiation potentials, and proliferative abilities. To curate the desired effect for therapies, the ASC-derivation site must be considered (Fig. 2). Although the mechanisms behind differentiation, angiogenesis, and proliferation of ASCs are well-characterized [42], there is a lack of detailed discussion of underlying mechanism in several of the articles herein. When these differences between ASCs from each depot are thoroughly characterized, there will be new applications for using stem cells in regenerative medicine.

Fig. 2.

Considerations for Site-Specific ASC Applications. Differentiation potential, gene expression profile, self-renewal, and survivability must be noted when choosing depot-derivation site of ASCs for a particular clinical application.

Chemokines and cytokines for tissue repair and disease drive mobilization of ASCs. For example, one study revealed that C-C chemokine receptor type 7 (CCR7) drives ASC migration. In ASCs transduced with a CCR7-containing lentivirus, migration to secondary lymph organs increased, and rats could maintain transplants for a longer period, reflecting a positive outcome of ASC migration [43]. This migration is crucial to ASCs’ role in tissue repair, allowing them to reach damaged areas and initiate the repair process. However, C-X-C Motif Chemokine Ligand 1 (CXCL1), a chemokine, drives the migration of obASCs to prostate cancer via C-X-C motif chemokine receptor 1 (CXCR1), thereby promoting poorer prostate cancer outcomes that are associated with obesity. In this model, signaling via CXCR1 promotes alpha-smooth muscle actin ($\alpha$-SMA) signaling, which drives angiogenesis [44]. Another study expounds upon this model, indicating that tumor-infiltrating lymphocytes’ interleukin-22 (IL-22) secretion may drive ASCs to the tumor site [45]. These studies suggest that cytokines and chemokines may be driving ASCs to sites of disease, thereby both positively and negatively impacting different disease outcomes.

In another paper studying migration of both lean and obese ASCs, monocyte chemoattractant protein -1 (MCP-1) and interleukin 8 (IL-8) induced migration of mouse-derived ASCs from both lean (lnASCs) and obese (obASCs) donors through a Boyden chamber. Interestingly, High Mobility Group Box 1 (HMGB1) caused significant migration of obASCs, and stromal-derived factor 1 (SDF-1) caused lnASC migration [46]. However, these results were not exactly paralleled in human studies. In lnASCs from human donors, SDF-1, tumor necrosis factor alpha (TNF-$\alpha$), MCP-1, and HMGB1 induced migration, but IL-8 did not. Compared to the control, SDF-1, TNF-$\alpha$, MCP-1, HMGB1, and IL-8 all caused obASC migration through a Boyden chamber. This study highlights the mechanistic differences that may be driving ASC migration in both lean and obese patients. Interestingly, even migration of the lnASC and obASC control groups were significantly different, with lnASC migration being over two-fold higher than the obASC control, indicating an inherent difference in both human and mouse ASC migration in obese conditions [46].

Age impacts the migration and angiogenic potential of ASCs significantly as well. In ASCs from older patients, migration patterns were diminished compared to ASCs from younger patients [47]. In a study looking at tube formation of ASCs on Matrigel, there was a significant difference in the number of tube branch points between early (less than 20) and late (greater than 20) passage human-derived ASCs that were not stimulated to form tubes, indicating the potential of age to impact angiogenic potential in these cells as well [46].

Lastly, ASC-driven angiogenesis and neovascularization can promote tumor growth, especially in TME priming, potentially making it easier for tumors to receive nutrients from non-neoplastic cells. Hypoxic conditions have been shown to promote ASC regenerative capabilities, thereby inducing angiogenesis [48]. In a study by Kalinina et al. [49], abdominal ASCs from ten female patients were cultured in both hypoxic and normoxic conditions to analyze proteins that may play a role in regeneration. Over 600 proteins were secreted by the ASCs from both groups, of which 100 played pivotal roles in tissue regeneration, wound healing, and vessel formation [49]. In murine ASCs with experimentally upregulated VEGF expression, there was an increase in blood vessel formation in implants compared to control groups. More specifically, there was a significantly greater number of SMA-positive blood vessels present as well. The VEGF-overexpressed ASCs showed upregulation of angiopoietin-1, indicating a potential mechanistic process by which VEGF contributes to angiogenesis in ASCs [50]. Similarly, in a separate experiment in immunodeficient mice, injection with murine preadipocytes showed the formation of vessel plexuses with adipocyte maturation, suggesting interplay between vascular growth factors secreted by adipocytes as well as surrounding endothelial cells, leading to new vessel growth [51]. The potential of ASCs to communicate with cancer cells through growth factors and cytokines, allowing them to migrate to damaged areas, is an intriguing aspect of their role in tumor pathogenesis [6].

With compelling evidence supporting the immunomodulatory effects of ASCs on cancer microenvironments, ASC vectors have garnered more attention as a potential solution for slowing cancer progression and recurrence. Malekshah et al. [86] used an ASC-vectored gene therapy to encourage tumor cells to die. ASCs expressing an enzyme capable of converting the inactive irinotecan to its active form (SN-38) were injected into mice. At the ovarian cancer site, cells activated the pro-drug, resulting in cancer cell death [86]. The vector platform improved prognosis in approximately 80% of human ovarian cancer xenograft mice cohorts. Growth suppression was achieved even in metastatic disease with associated ascites and cancer spheroid leakage into the abdominal cavity, which has historically challenged therapeutic approaches with resistance to traditional chemotherapeutic agents. This vector platform effectively reduced side effects typically associated with conventional chemotherapeutics, which are only effective at doses that cause significant weight loss and organ damage [86]. Another study aimed to integrate ASCs into a broader approach to cancer therapy. Researchers from University College London used MSC extracellular vesicles (MSC-EVs) to deliver TNF-related apoptosis-inducing ligands (TRAIL) in several cancer cell types, including lung, pleural, renal and breast. Notably, this therapeutic platform partially induced apoptosis in TRAIL-resistant cancer lines, providing a potential therapeutic option for patients with refractory disease [87]. Interestingly, this study provides a baseline for nontraditional ASC-vectored therapies for cancer treatment, which would be an unprecedented use of these cells in the clinic.

More recently, ASC vectored therapies have been applied to metabolic disorders like type 2 diabetes mellitus, non-alcoholic fatty liver disease, high cholesterol, and triglyceride disorders. Wang et al. [88] suggest that harvesting ASCs from diabetic donors may offer a new avenue to treat type 2 diabetes mellitus. While diabetic ASCs had poorer proliferative ability and reduced release of HGF compared to non-diabetic controls, they provided other therapeutic benefits in the study. When processed and introduced into mice with type 2 diabetes mellitus, diabetic ASCs improved insulin sensitivity and pancreatic beta cell mass. Utilizing stem cells in this way provides an alternative therapy to classical medication management with metformin, GLP-1 agonists, and SGLT2 inhibitors [88].

Furthermore, ASC therapeutics have been generated in the context of obesity. Researchers compared brown adipose tissue (BAT)-derived and WAT-derived ASCs and their immunomodulating activity on diet-induced, obese mice. Mice were injected weekly for three weeks with either type of therapy. Compared to the saline-injected control, both inducible brown and white ASC therapies improved weight and glucose control and promoted adipose tissue browning. Mice treated by the inducible brown ASC therapy demonstrated superior inflammatory control, evidenced by diminished mRNA levels of pro-inflammatory cytokines like IL-6 and TNF-$\alpha$, and better protected pancreatic beta islet insulin production, offering an alternative option for obesity treatments. However, the short span of this study is limiting since human candidates in a clinical trial would adhere to this regimen for a longer period [89].

While ASC vector therapy research has grown substantially with many studies boasting promising results, translation into clinical practice has been challenging. The safety of these therapies has been questionable without the availability of compelling evidence in clinical trials that these cell therapies provide patients with a favorable risk-to-benefit ratio. In a different approach using the properties of ASCs as therapeutics, a Japanese clinical trial measured the ability of ASCs to improve prognosis in liver cirrhosis patients. Autologous subcutaneous ASCs were infused into the liver circulation, and patients were followed closely over six months to one year. No serious adverse events were reported upon subsequent follow-ups at 1-month, 6-month, and 1-year intervals. Liver function tests improved or remained stagnant at 6 months post-therapy. Interestingly, this ASC therapy caused an increase in HGF and IL-6 with subsequent liver regeneration. These findings highlight the potential of ASC-based liver regeneration as an alternative to total liver transplant. However, the trial sample size was small, which limits the generalizability of the results [90].

Other clinical trials have shown conflicting results regarding the effect of ASCs on various disease states. ASC injection showed great promise in a phase III clinical trial monitoring the effect of ASCs on the osteoarthritic knee. In patients injected with ASCs, there were significant improvements to daily life and osteoarthritis-related pain compared to the control group. Minimal adverse effects were reported, and less than three percent of patients receiving ASC treatment reported any pain and swelling post-injection [91]. In contrast, in a separate clinical trial, ASCs had no significant effect on function in patients suffering from a shoulder tendon tear compared to a control group [92]. Interestingly, in another study, ASC-derived exosomes were administered to Alzheimer’s Disease patients intranasally twice weekly for twelve weeks. At a moderate dose, impairment levels were lower than in the higher and lower exosome dose groups following final administration. There was no difference in tau protein accumulation amongst groups, but the moderate dose group displayed lower rates of hippocampal shrinkage, although not significant [93]. In a separate phase I clinical trial, ASCs were assessed for their effect on spinal cord injuries. Patients displayed minor adverse effects after injection of ASCs into the subarachnoid space, but no serious events. Patients showed slight improvements to impairment a year after treatment; however, this must be investigated in subsequent clinical trials to confirm effectiveness [94]. Overall, ASCs show potential as therapeutics in contexts outside of obesity, cancer, and related diseases, including but not limited to osteoarthritis, muscle repair, and even neurological disorders like Alzheimer’s Disease. However, the beforementioned clinical trials highlight the importance of continuation of studies surrounding ASCs to confirm the specific applications that will maximize ASC therapeutic potential in patients, as they seem to have different effects in various anatomical environments and disease states.

ASCs boast benefits compared to their bone marrow-derived counterparts (BMSCs). The ratio of ASCs in adipose is greater than BMSCs in bone marrow, resulting in greater stem cell yield from adipose tissue than from the bone marrow. Another advantage of ASCs over BMSCs is the ease of extraction from patients, as bone marrow extraction is more invasive than adipose tissue extraction [95]. Despite these advantages and others, as well as the promising clinical outcomes of ASCs thus far, there are some challenges to ASC use as therapeutics. As evidenced by the impact both obesity and the presence of cancer has on the behavior of ASCs, they are directly influenced by their environment. To reflect this phenomenon, Paino et al. [96] (2017) cultured ASCs in the presence and absence of breast cancer cells and bone cancer cells. The ASCs cultured in the presence of cancer cells were able to differentiate into adipocytes as well as form tubes on Matrigel. However, the ASCs cultured in the absence of cancer cells were not able to undergo adipogenesis or angiogenesis [96]. Therefore, because ASCs may act differently depending on the presence of hypoxia [54, 82], cancer [54], or another stressor, it may be challenging to fully understand how ASCs will behave in separate individuals. Another consideration is regarding tumorigenicity. Based on a recent study monitoring MSC engulfment by breast cancer cells, the resulting hybrid cells were more senescent, which ultimately promoted a more metastatic phenotype [62]. Taken together with the conflicting results of recent clinical trials surrounding ASCs, the challenges imposed by ASC clinical use initiates hesitation amongst physicians and patients alike. Therefore, much research needs to be done before ASCs are regularly used as a treatment for a range of diseases.