Adipose tissue as a living drug: Stromal vascular fraction and adipose tissue-derived stem cells in regenerative medicine

Table 1 Comparison of traditional drugs, living drugs and extracellular vesicles

Characteristic	Conventional drugs	Living drugs	Acellular methods
Composition	Chemical compounds (e.g., small molecules, biologics)	Viable, metabolically active cells (e.g., stem cells, T cells)	Purified growth factors, EVs, cytokines
Mechanism of action	Act as inert agents to exert biochemical effects	Two mechanisms: (1) Secretion of trophic and immunomodulatory factors; and (2) Direct cell replacement or structural contribution	Mimic paracrine signaling but lack adaptive cellular activity
Cellular activity	Inert, no real-time interaction with cells	Senses surroundings, adapts to the microenvironment, integrates with physiological processes	Cannot sense environment, grow, or interact with other cells
Adaptive response	No adaptive response	Adaptive paracrine signaling and, in some cases, lineage contribution	No adaptability or real-time response
Examples	Small-molecule drugs, biologics (e.g., monoclonal antibodies)	Stem cells, T cells, NK cells, MSCs, CAR-T, TILs, iPSC-derived products	ASC-derived EVs, growth factors, cytokines
Therapeutic effects	Target specific biochemical pathways	Replicate, migrate to injury sites, secrete therapeutic factors, modulate immune response	Provide paracrine benefits but cannot replace or integrate into tissues
Sustained effect	Short-term effects, often require repeated administration	Potential for sustained therapeutic outcomes (e.g., CAR-T)	Limited sustained effect without live cell interactions
Integration with body	Does not integrate with body systems beyond biochemical effects	Integrates with body, modulates tissue repair, and immune response	No integration with body; only mimics certain therapeutic benefits
Regenerative potential	Limited regenerative capability	Can promote tissue repair, angiogenesis, and immunomodulation	Limited regenerative potential; mainly offers supportive factors
Safety concerns	Risk of side effects and toxicity	Risks related to cell survival, fate control, and immune rejection	Reduced safety concerns compared to whole cells but lacks dynamic response capabilities
Examples in therapy	Pain relief, antibiotics, cancer biologics	MSCs, CAR-T, TILs, NK cells in regenerative and oncological therapies	EVs from stem cells, purified cytokines in regenerative medicine

EVs: Extracellular vesicles; NK: Natural killer; MSCs: Mesenchymal stem cells; CAR-T: Chimeric antigen receptor T-cell; TILs: Tumor-infiltrating lymphocytes; iPSC: Induced pluripotent stem cell; ASC: Adipose-derived stem cell.

Table 2 Adipose tissue types and characteristics

Adipose tissue	Primary function	Morphology	Location in humans	Metabolic role	Plasticity	Regenerative potential	Prevalence in adult humans
WAT	Energy storage, endocrine regulation	Unilocular adipocytes	Subcutaneous, visceral depots	Lipid storage and mobilization (lipolysis)	High	Rich source of SVF and ASCs for clinical use	Abundant
BAT	Non-shivering thermogenesis	Multilocular adipocytes	Supraclavicular and paravertebral regions	Oxidative metabolism for heat production	Low-moderate	Endocrine activity (less used as a cell source clinically)	Limited, depot-specific
Beige adipose tissue (brite or brown-in-white)	Inducible thermogenesis	Inducible multilocular adipocytes	Scattered within WAT, mainly subcutaneous	Adaptive energy expenditure upon recruitment	Moderate	Paracrine recruitment potential	Present, recruitable

WAT: White adipose tissue; SVF: Stromal vascular fraction; ASCs: Adipose-derived stem cells; BAT: Brown adipose tissue.

Table 3 Summary of protocols used in different studies for enzymatic and mechanical isolation of stromal vascular fraction

Ref.	Protocols
	Enzymatic isolation of SVF
Tiryaki et al[28]	Digestive agent	Collagenase NB6, 0.1 U/mL, 1:1 (enzyme:fat, v/v)
	Incubation	37 °C for 45 minutes, gentle agitation
	Centrifugation	300 × g for 5 minutes
Agostini et al[29]	Digestive agent	Collagenase NB6 (SERVA, GMP grade), 0.15 U/mL
	Incubation	37 °C for 60-70 minutes
	Centrifugation	400 × g, for 10 minutes at 4 °C
Winnier et al[30]	Digestive agent	Matrase reagent (transpose RT kit)
	Incubation	Kit-specified
	Centrifugation	Closed system separation/filtration per kit protocol
	Mechanical isolation of SVF
Tiryaki et al[28]	Digestive agent	Pass lipoaspirate through sequential blade grids (1000 μm, 750 μm, 500 μm). Ca/Mg balanced buffer, fat:buffer, 1:3
	Incubation	10 minutes shaking after buffer addition
	Centrifugation	2000 × g for 10 minutes
Solodeev et al[25]	Digestive agent	Run actuator-driven rotating blades to mechanically disrupt tissue with 350 mL prewarmed saline
	Incubation	< 15 minutes mechanical agitation inside a closed system
	Centrifugation	400 × g for 15 minutes
Yaylacı et al[27]	Digestive agent	Pass fat repeatedly through blade grids (2.4 mm → 1.2 mm → 0.6 mm)
	Incubation	Sequential 31 + 101 passes
	Centrifugation	400 × g for 10 minutes

SVF: Stromal vascular fraction.

Table 4 Comparison of stromal vascular fraction and adipose-derived stem cells

Features	SVF	ASCs
Definition	A heterogeneous cell mixture obtained directly from adipose tissue enzymatically or mechanically, comprising diverse stromal and immune cell populations	A relatively homogeneous mesenchymal stromal cell population derived from adherent culture and expansion of SVF
Composition	Fibroblasts, endothelial cells, pericytes, smooth muscle cells, blood-derived cells, immune cells (T-cells, macrophages), and progenitor and stem cells (ASCs)	Enriched in plastic-adherent multipotent MSCs with a fibroblast-like morphology, showing minimal hematopoietic contamination after passaging
Heterogeneity	Highly heterogeneous	Relatively homogeneous
Markers	CD34, CD45, CD31	CD73, CD90, CD105
Isolation methods	Single-step procedure following collagenase digestion or mechanical dissociation, without the need for culture or expansion	Requires isolation from SVF followed by culture expansion over many days to weeks to enrich the adherent cell population
Mechanism of action	Vascular/immune cells drive angiogenesis, immunomodulation, and tissue support, while ASCs contribute differentiation	Combination of direct differentiation and strong paracrine effects (secretion of VEGF, HGF, IGF-1, extracellular vesicles)
Differentiation potential	Variable potential (due to cellular heterogeneity)	Multilineage potential (adipogenic, osteogenic, chondrogenic)
Timeframe for use	Immediate use application (cells can be reinjected within the same procedure)	Not immediate use (requires laboratory processing and expansion)
Yield per gram of AT	Yields approximately 500000 to 2000000 nucleated cells per gram of fat but only 1%-10% are progenitors/stem cells[50]	Yields approximately 5000-200000 ASCs per gram of fat after culture expansion depending on passages and technique[51]
Scalability	Constrained by harvest volume and regulatory restrictions, as large-scale expansion is not feasible with same-day isolations	Easily scalable through in vitro expansion, allowing production of large cell doses from relatively small adipose samples
Clinical readiness	Used in autologous cell therapies (especially for cosmetic and orthopedic applications) as regulatory approval easier since it regarded as minimally manipulated	Ongoing clinical trials in diverse fields (cardiovascular, musculoskeletal, inflammatory) as this requires GMP culture facilities
Key advantages	Quick, cost-effective, and maintains cellular diversity	More defined, reproducible, and expandable population
Current limitations	Batch variability, lower predictability of outcomes and regulatory debate on enzymatic methods	Time-consuming, cost-intensive, requires GMP conditions for clinical use

SVF: Stromal vascular fraction; ASCs: Adipose-derived stem cells; MSC: Mesenchymal stem cell; VEGF: Vascular endothelial growth factor; HGF: Hepatocyte growth factor; IGF-1: Insulin-like growth factor 1; GMP: Good manufacturing practice.