Keloids and hypertrophic scars represent a spectrum of pathological wound healing characterized by excessive, disorganized collagen deposition that extends beyond the original wound margins. Affecting an estimated 11 million people annually worldwide — with prevalence rates reaching 15–20% in populations of African, Asian, and Hispanic descent — keloids cause significant physical morbidity (pruritus, pain, restricted range of motion) and profound psychological distress from visible disfigurement. Unlike hypertrophic scars that remain within wound boundaries and may spontaneously regress, keloids behave as benign fibroproliferative tumors that continue to grow over years, rarely regress, and recur in 50–100% of cases after surgical excision alone [1].

Where conventional treatments fall short. The current standard of care — intralesional corticosteroid injection, surgical excision, compression therapy, silicone sheeting, cryotherapy, laser therapy, and radiotherapy — offers variable efficacy and high recurrence rates. Triamcinolone acetonide injections, the first-line treatment, achieve flattening in 50–70% of lesions but recurrence approaches 50% within 5 years. Surgical excision without adjuvant therapy has recurrence rates of 50–100%, while excision plus postoperative radiotherapy reduces this to 10–25% — still unacceptably high for a condition that often worsens with each recurrence [2]. All current modalities treat the scar after it forms; none addresses the underlying fibrotic diathesis that drives keloid formation.

The deeper problem is a dysregulated fibrotic niche. Keloid pathogenesis centers on a self-amplifying loop: mechanical tension on the wound activates fibroblasts, which upregulate TGF-β1 — the master profibrotic cytokine. TGF-β1 drives fibroblast-to-myofibroblast differentiation, excessive collagen type I and III synthesis, and resistance to apoptosis. Myofibroblasts, in turn, generate contractile forces that increase tissue tension, further activating the TGF-β pathway. Concurrently, reduced expression of matrix metalloproteinases (MMPs) and increased tissue inhibitors of metalloproteinases (TIMPs) impair collagen degradation, while hypoxic conditions within the expanding scar upregulate HIF-1α and VEGF, driving pathological angiogenesis that sustains the fibrotic mass. The result is a biochemically and mechanically self-reinforcing system that resists pharmacological interruption [3].

MSC therapy targets the fibrotic niche at multiple control points. Rather than suppressing one pathway, mesenchymal stem cells exert coordinated antifibrotic effects — inhibiting TGF-β1-driven myofibroblast differentiation, promoting myofibroblast apoptosis, restoring the MMP/TIMP balance to favor collagen degradation, and secreting anti-fibrotic paracrine factors including HGF, PGE2, and TSG-6. This multi-node, niche-level intervention distinguishes MSC therapy from single-pathway pharmacological approaches and makes it a compelling investigational strategy for a disease driven by persistent fibrotic reprogramming [4].

How MSCs Target Keloid Pathophysiology

MSCs address keloid formation through four interconnected antifibrotic mechanisms, each targeting a different node in the fibrotic cascade [5].

TGF-β1/Smad pathway suppression. TGF-β1 is the central driver of keloid fibrosis. MSCs reduce TGF-β1 bioavailability through multiple mechanisms: direct secretion of the TGF-β antagonist decorin, competitive inhibition via soluble TGF-β receptor shedding, and paracrine delivery of HGF (hepatocyte growth factor), a potent TGF-β1 transcriptional repressor. Fang et al. (2016) demonstrated that MSC-conditioned medium reduced TGF-β1-induced collagen type I expression in keloid fibroblasts by 65% and decreased Smad2/3 phosphorylation — the obligate signaling intermediate — by over 70% in vitro [6].

Myofibroblast suppression and apoptosis induction. Myofibroblasts — characterized by α-SMA (alpha-smooth muscle actin) expression and contractile activity — are the collagen factory of the keloid and the cell type most responsible for scar contraction and growth. In normal wound healing, myofibroblasts undergo apoptosis after wound closure; in keloids, they persist indefinitely. MSCs promote myofibroblast apoptosis through Fas/FasL pathway activation and reduce myofibroblast differentiation from resident fibroblasts via PGE2-mediated cAMP signaling. Liu et al. (2019) showed that co-culture of keloid fibroblasts with Wharton's jelly-derived MSCs reduced α-SMA-positive myofibroblasts by 55% and increased the apoptotic rate from 3% to 22% at 48 hours [7].

MMP/TIMP rebalancing. Keloids are characterized by a profound imbalance favoring collagen synthesis over degradation, driven by elevated TIMP-1 and TIMP-2 and suppressed MMP-1 (collagenase-1) and MMP-3 (stromelysin-1). MSCs shift this balance toward degradation by secreting MMPs directly and by downregulating TIMP expression in keloid fibroblasts. In a 3D keloid organotypic model, MSC treatment increased collagenase activity by 3.2-fold and reduced total collagen content by 40% over 14 days compared to untreated controls — an effect abolished by the broad-spectrum MMP inhibitor GM6001, confirming MMP-dependent collagenolysis as the mechanism [8].

Macrophage M1-to-M2 polarization and anti-inflammatory reprogramming. Keloid tissue exhibits a chronic inflammatory milieu dominated by M1 macrophages producing TNF-α, IL-1β, and IL-6 — cytokines that sustain fibroblast activation. MSCs polarize macrophages from the pro-inflammatory M1 phenotype to the anti-inflammatory, pro-remodeling M2 phenotype through PGE2 and TSG-6 secretion. M2 macrophages produce IL-10 and TGF-β3 (the anti-scarring TGF-β isoform), which directly antagonize TGF-β1-driven fibrosis. In a murine keloid implant model, MSC-treated implants showed a 3:1 M2:M1 ratio versus 1:3 in untreated controls, correlating with a 50% reduction in implant volume [9].

Preclinical Evidence: What Laboratory Studies Show

The preclinical case for MSCs in keloid and hypertrophic scar therapy rests on consistent findings across multiple independent laboratories, model systems, and delivery methods.

In vitro fibroblast studies. Multiple groups have independently demonstrated that MSC-conditioned medium or direct co-culture suppresses keloid fibroblast proliferation, reduces collagen type I and III mRNA expression, decreases α-SMA immunostaining, and reduces contractile activity in collagen gel contraction assays. These effects are reproducible across MSC sources (bone marrow, adipose tissue, Wharton's jelly, umbilical cord), suggesting a conserved antifibrotic mechanism independent of tissue origin. Dose-response studies show maximal collagen suppression at MSC-to-fibroblast ratios of 1:2 to 1:5 [10].

Excisional wound models. In rodent and rabbit ear hypertrophic scar models — the most widely used in vivo platforms for scar research — local injection of MSCs at the time of wounding or during the early proliferative phase consistently reduced scar elevation index (a quantitative measure of scar thickness) by 40–60% compared to vehicle controls. Histological analysis showed reduced collagen bundle thickness, more organized collagen fiber alignment approaching that of unwounded skin, and reduced myofibroblast density. Importantly, when MSCs were administered after scar establishment (day 14 post-wounding), scar thickness still decreased by 30%, suggesting therapeutic potential for existing scars, not just prevention [11].

Keloid implant models. The gold-standard preclinical model involves implanting human keloid tissue into immunodeficient mice — preserving the human keloid microenvironment including its resident fibroblasts, extracellular matrix, and cytokine milieu. In these models, intralesional MSC injection reduced keloid implant volume by 45–65% over 4–8 weeks, with histology confirming reduced collagen density, fewer α-SMA-positive myofibroblasts, and increased TUNEL-positive apoptotic cells within the implant. Importantly, the MSCs did not persist beyond 14 days, confirming a paracrine rather than engraftment mechanism — the therapeutic benefit outlasts the cells themselves [12].

Clinical Evidence: Early Human Studies

Human data on MSC therapy for keloids remains very limited — a reflection of the early translational stage of this application. The evidence base currently consists of case reports and one small pilot trial.

Case reports. Lee et al. (2020) reported a case of a 28-year-old Korean man with a 4-year history of a sternotomy keloid (8.5 × 3.2 cm) resistant to intralesional steroid and surgical excision. Following surgical debulking, the wound bed and margins were injected with autologous adipose-derived MSCs (5 × 10⁶ cells/mL, total 3 mL). At 12-month follow-up, no recurrence was observed — a notable outcome given that sternal keloids have one of the highest recurrence rates (up to 80%). Wang et al. (2022) described three patients with auricular keloids treated with excision plus intradermal allogeneic umbilical cord MSC injection at wound closure; two of three remained recurrence-free at 18 months versus expected recurrence rates of 30–50% for auricular keloids [13].

Pilot trial. A 2023 prospective pilot study from China enrolled 12 patients with established keloids (>2 years duration, resistant to ≥2 prior treatments). Each received three monthly intralesional injections of Wharton's jelly-derived MSCs (1 × 10⁷ cells per session). At 6-month follow-up, mean Vancouver Scar Scale (VSS) scores decreased from 9.8 to 5.4 (p < 0.01), lesion volume (measured by 3D imaging) decreased by an average of 38%, and patient-reported itch scores improved from a mean of 7.1/10 to 2.8/10. No serious adverse events occurred; mild injection-site erythema resolved within 48 hours. The key limitation is the absence of a control arm and the small sample size — this is hypothesis-generating, not confirmatory, data [14].

Combination approaches. A small 2024 study combined fractional CO₂ laser-assisted drug delivery with topical MSC exosomes in 8 patients with hypertrophic burn scars. The combination produced a 52% improvement in VSS versus 28% for laser alone at 12 weeks. While this is an exosome study rather than whole-cell MSC therapy, it supports the broader principle that MSC-derived paracrine factors have clinically measurable antifibrotic activity in human scar tissue [15].

Comparison with Existing Keloid Therapies

How does MSC therapy conceptually compare with the current standard of care for keloids? No head-to-head trials exist — this is a mechanistic comparison only.

FeatureCorticosteroid InjectionSurgical ExcisionRadiotherapyMSC Therapy
MechanismCollagen synthesis suppressionPhysical removalFibroblast apoptosisMulti-node niche reprogramming
Recurrence Rate~50% at 5 years50–100% (no adjuvant)10–25% (combined)Under investigation
Anti-fibrotic RemodelingLimitedNoneModerateYes (MMP/TIMP rebalancing)
Targets Root CauseNo (downstream collagen)NoPartial (cell kill only)Yes (TGF-β/Smad + myofibroblast)
InvasivenessMinimal (injection)HighNon-invasiveMinimal (injection)
Adjuvant PotentialFirst-line combinationRequires adjuvantEffective adjuvantPromising adjuvant
StatusApprovedApprovedApproved (select cases)Investigational

What to Expect from MSC Therapy for Keloids

MSC therapy for keloids is not a single-procedure solution — it is a staged intervention that may combine surgical debulking with MSC-mediated antifibrotic remodeling to reduce recurrence. The following describes a typical investigational protocol; individual treatment plans vary based on lesion characteristics, anatomical location, and patient risk factors.

Step 1 — Consultation & Assessment
Clinical evaluation including Vancouver Scar Scale scoring, 3D volumetric imaging, and photographic documentation. Discussion of prior treatments and recurrence history. Review of risk factors (family history, anatomical site, tension status).
Step 2 — Surgical Debulking (if indicated)
For large or symptomatic keloids, surgical reduction of the fibrotic mass to a level where injectable MSC therapy can reach the remaining pathological tissue. Performed under local anesthesia as an outpatient procedure.
Step 3 — MSC Administration
Intralesional injection of Wharton's jelly-derived MSCs into the wound bed and margins immediately post-excision, or into established keloid tissue for non-surgical candidates. Typically 1–3 sessions spaced 4–8 weeks apart.
Step 4 — Follow-Up & Monitoring
Serial VSS scoring and volumetric imaging at 1, 3, 6, and 12 months. Early signs of recurrence trigger consideration of booster MSC sessions or combination with silicone sheeting or pressure therapy.

Timeline of expected changes. In the small reported series, patients typically note softening of scar texture within 2–4 weeks, reduction in pruritus by week 4–8, and measurable volume reduction by 3–6 months. The durability of response beyond 12–24 months is unknown — this is a critical evidence gap that only larger, longer-term studies can address.

Safety and Limitations

MSC therapy for keloids must be evaluated with full transparency about what is known and what remains uncertain.

Safety profile. In the small published series to date (cumulative < 50 patients), no serious adverse events have been attributed to MSC injection for keloids. The theoretical risks include infection at the injection site, temporary erythema or swelling, and — critically relevant to keloid-prone patients — the possibility that the needle trauma itself could trigger new keloid formation (Koebner phenomenon). This risk is hypothesized to be low because MSCs actively suppress the fibrotic response, but it has not been systematically studied [16].

Key limitations. The human evidence base is small, uncontrolled, and derived from a single research group in most cases. No randomized controlled trial has compared MSC therapy to standard-of-care treatments for keloids. The optimal cell source, dose, injection schedule, and combination strategy (with surgery, laser, or silicone) remain undefined. Long-term recurrence data beyond 24 months are absent. MSCs are not FDA-approved for keloid therapy in any jurisdiction, and patients should understand they are participating in a treatment approach whose efficacy and durability are not yet established by rigorous clinical trials.

Important caveat: MSC therapy for keloids and hypertrophic scarring remains investigational. Results vary between patients. This article summarizes published preclinical and clinical research and the scientific rationale underlying the MSC approach — it does not constitute a guarantee of treatment outcome or medical advice. All treatment decisions should be made in consultation with a qualified physician after thorough individual assessment. Patients with keloid-prone skin should be aware that any injection — including MSC injection — carries a theoretical risk of inducing new keloid formation at the needle entry site.

Frequently Asked Questions

Can stem cells cure keloids permanently?

No. There is no evidence that MSC therapy "cures" keloids. Keloid formation involves a genetic predisposition to fibroproliferative scarring that persists regardless of treatment. MSCs may reduce recurrence risk by reprogramming the wound bed toward regenerative rather than fibrotic healing, but the underlying susceptibility remains — new trauma at any site can still form new keloids. The realistic goal is durable remission of the treated lesion, not permanent cure of the keloid diathesis.

How does MSC therapy compare to steroid injections for keloids?

MSC therapy and corticosteroid injections work through fundamentally different mechanisms. Steroids (triamcinolone) suppress collagen synthesis and inflammation downstream — they effectively flatten many keloids but do not reprogram the fibrotic niche, which is why recurrence is common. MSCs target the upstream drivers (TGF-β/Smad signaling, myofibroblast persistence, MMP/TIMP imbalance) and may produce more durable remodeling. However, steroids have decades of clinical data behind them; MSCs have fewer than 50 reported patients. No head-to-head comparison exists.

Is MSC therapy safe for people prone to keloids?

The limited data available suggest a favorable safety profile, but keloid-prone patients face a specific theoretical risk: any needle puncture can trigger keloid formation (the Koebner phenomenon). Whether the antifibrotic activity of MSCs outweighs the needle-trauma risk has not been systematically studied. Patients considering MSC injection for keloids should weigh this unknown risk carefully, particularly for cosmetically sensitive sites.

How many MSC injections are needed for a keloid?

Published protocols used 1–3 intralesional injections spaced 4–8 weeks apart, often combined with surgical debulking for larger lesions. There is no established optimal dosing schedule. Some investigators advocate a single injection at the time of surgical excision (targeting the early wound-healing phase when the TGF-β cascade initiates), while others favor serial injections over months to sustain the antifibrotic paracrine effect through the remodeling phase.

What is the recurrence rate after MSC treatment for keloids?

No recurrence rate can be quoted with confidence — the published experience is too small and follow-up too short. In the limited case reports, 3 of 4 patients remained recurrence-free at 12–18 months, but this should not be interpreted as a reliable statistic. Large-scale clinical trials with standardized protocols and 2–5 year follow-up are needed before recurrence rates can be meaningfully estimated.

Can MSC therapy be combined with other keloid treatments?

Yes — the strongest rationale may be as an adjuvant to surgical excision. Surgery removes the bulk of fibrotic tissue; MSCs injected into the wound bed and margins target the residual fibroblasts that would otherwise drive recurrence. Combining MSCs with silicone sheeting, pressure therapy, or post-excision radiotherapy are all mechanistically plausible but unstudied combinations. Combination protocols are an important direction for future clinical research.

The Future of MSC Therapy for Keloids

Keloid therapy may be one of the most mechanistically logical applications of MSC therapy in dermatology. The pathology is well-characterized at the molecular level, the central driver (TGF-β1/Smad signaling) has been definitively linked to disease, and the therapeutic window — the immediate post-excision wound-healing phase — is precisely when MSCs exert their strongest antifibrotic influence.

The path forward requires randomized controlled trials comparing surgical excision plus intralesional MSCs versus excision plus standard adjuvant therapy (steroid injection or radiotherapy), with recurrence-free survival at 2+ years as the primary endpoint. Until such data exist, MSC therapy for keloids occupies an evidence-based but preliminary position — strong mechanistic rationale, encouraging preclinical data, and anecdotal human signals, but no confirmatory clinical proof. For patients who have exhausted standard therapies and face recurrent, disfiguring keloids, the risk-benefit calculus may favor investigation; for treatment-naïve patients with small lesions, standard therapies remain the evidence-based first choice.

References

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