Potential therapeutic applications of antler stem cells and their derivatives

Abstract

Deer antlers are the only mammalian organs that regenerate annually, driven by antler stem cells (AnSCs) in the pedicle periosteum. In the past two decades, AnSCs have shifted from a topic of comparative biology to a potential source for regenerative treatments. The cell type has evolved from periosteum-derived multipotent cells to the identification of antler blastema progenitor cells and RXFP2-positive mesenchymal stem cells. In parallel, two distinct translational routes have emerged: Transplantation of living AnSCs and cell-free administration of their derivatives, including conditioned medium, extracellular vesicles (EVs)/exosomes, and AnSC-derived peptides. Across the skin, bone, cartilage, liver, lung, nervous system, and cardiovascular system, both routes have produced promising pro-regenerative and anti-fibrotic effects, and recent work in non-human primates has extended these findings to systemic aging. This review integrates current evidence on the redefined AnSC taxonomy, distinguishes the evidence base and regulatory implications of the cellular vs cell-free routes, summarizes shared molecular mechanisms, and argues that companion-animal veterinary medicine represents a uniquely tractable near-term translational arena. We identify the main barriers to human clinical translation: EV standardization, immunogenicity, dose-response uncertainty, and long-term safety.

Key Words: Antler stem cells; Regeneration; Extracellular vesicles; Conditioned medium; Bone; Wound healing; Aging; Regenerative medicine

Core Tip: This review highlights antler stem cells (AnSCs) through three main points. First, it examines distinct populations, such as antler blastema progenitor cells and RXFP2-positive periosteal cells, which are related in the context of antler development and regeneration. Second, it differentiates between living-cell transplantation and cell-free derivatives, noting that the latter currently face fewer manufacturing and safety challenges. Lastly, it compares AnSCs with established mesenchymal stromal cell sources, emphasizing advantages such as strong osteochondral activity and renewable sourcing, while also tackling concerns such as immunogenicity, donor variability, and a lack of human clinical evidence.

INTRODUCTION

Among mammals, deer antlers best exemplify true epimorphic regeneration of an entire organ. Each year, the antler is shed and completely regrown, achieving a remarkable growth rate of 1-2 cm per day, making it the fastest-growing bony structure in the animal kingdom[1-3]. This unique ability challenges the general mammalian belief that complex appendages cannot be regenerated. Research indicates that antler regeneration is a stem-cell-based epimorphic process, rendering it a valuable model for studying organ regeneration and a potential source of regenerative cells and molecules[1,2,4-6].

Antler stem cells (AnSCs) are multipotent and highly proliferative. They can expand significantly without clear signs of tumor formation in short-term rodent and xenograft studies. However, these studies did not run long enough to rule out delayed tumor development. Although evidence on their long-term safety remains limited, AnSCs remain appealing for therapeutic applications[5,7,8]. Importantly, AnSCs and their secreted products exert pro-regenerative effects not only in deer but also across mammalian species, including rodent, lagomorph, and primate models, suggesting that AnSCs may exert their regenerative effects partly through signaling pathways shared across mammalian species, although the extent of their functional conservation remains to be established[9-11].

In this review, we first organize the field around the recent redefinition of the AnSC cell type based on their reported anatomical locations, phenotypic features, and regenerative functions[12,13]. Second, we treat the living-cell route and the cell-free route as two parallel translational pipelines with different evidence bases, manufacturing logics, and regulatory paths, rather than blending them. Third, we explicitly propose companion-animal veterinary medicine as a potential near-term translational setting, an application area that has received limited attention in previous reviews. Veterinary medicine may provide a potential investigational setting, but direct veterinary efficacy, safety, and regulatory evidence for AnSC-derived products remains lacking. Throughout the review, we distinguish indications with immediate in vivo evidence from those that remain biologically plausible but experimentally unaddressed.

This selective narrative minireview draws on peer-reviewed literature identified through searches of PubMed, Web of Science, and Scopus from database inception to July 15, 2025. Representative search terms included “antler stem cell”, “antlerogenic periosteum”, “pedicle periosteum”, “reserve mesenchyme”, “antler blastema progenitor cell”, “RXFP2”, “conditioned medium”, “extracellular vesicle”, “exosome”, “regeneration”, “wound healing”, “bone”, “cartilage”, “fibrosis”, and “aging” used individually or in combination. It examines reported AnSC populations within a provisional working framework, compares the regenerative potential and translational requirements of living-cell and cell-free strategies, and identifies barriers to future applications, including in companion-animal medicine, without aiming to provide a systematic review or meta-analysis.

DISCOVERY AND IDENTIFICATION OF ANSCS

From the periosteum to a defined stem cell population

The essential insight of the field is that antler regeneration is governed by the periosteal tissues rather than by dedifferentiation of mature pedicle stump cells. The pedicle is a permanent bony protuberance from which antlers are cast and regenerated. Tissue deletion and membrane insertion experiments showed that total deletion of the pedicle periosteum (PP) abolishes future antler regeneration (Figure 1A and B), whereas partial deletion of the PP, for example, the distal 1/3, antler regeneration occurs from the cut end of the residual PP on the pedicle shaft, a place distant from the natural regeneration plane (Figure 1C and D)[14,15]. Therefore, PP must be the primary tissue type for antler regeneration, and the pedicle bone may play only a subsidiary role. In the next experiment, a piece of non-permeable membrane was inserted into the space between the PP and the pedicle skin (Figure 1E), and the inserted membrane effectively blocked the pedicle skin from participating in antler regeneration, but antler regeneration still took place, and the regenerated antler was wrapped with a scab (Figure 1F).

Figure 1 Outcomes following pedicle periosteum deletion and membrane insertion. A: Total pedicle periosteum (PP) (arrow) deletion; B: Failure in antler regeneration from the PP-less pedicle stump (left), whereas the sham-operated pedicle regenerated a multi-branched antler (right); C: Partial PP (arrow) deletion (distal third); D: Regenerating antler bud (velvet antler) from the cut end of PP on the pedicle shaft. Note that this place is distant from the natural regeneration plane (arrow); E: Membrane (arrow) insertion between the PP and the enveloping skin in a pedicle stump; F: Scab-wrapped regenerating antler (arrow). Note that the inserted membrane prevented the pedicle skin from participating in antler regeneration, but failed to stop antler regeneration. PP: Pedicle periosteum; VA: Velvet antler; SC: Scab-wrapped regenerating antler.

Deer are not born with pedicles and first antlers, but these develop postnatally when male deer approach puberty from the frontal crests[16]. It is known that the periosteum overlying the crests gives rise to the pedicles and the first antler, which was termed antlerogenic periosteum (AP)[1,2,4,5]. Classic tissue deletion (Figure 2A) and transplantation (Figure 2B) experiments showed that removal of the AP will abolish the pedicle and antler formation, whereas transplantation of the AP elsewhere will induce ectopic antler formation[6]. A key conceptual nuance, demonstrated by Li et al[6], is that the cells in the PP responsible for antler regeneration in the adult cannot recapitulate the cells for the initial development of the pedicle and first antler, when transplanted ectopically, indicating that regenerative and developmental programs, while related, are not identical.

Figure 2 Antlerogenic periosteum deletion and transplantation, and histological structure of a growing antler tip. A: Antlerogenic periosteum (AP) deletion (right side). Note that the deleted AP will be transplanted autologously onto the forehead region; B: Outcomes of AP deletion and transplantation. Note that the AP-less crest region failed to develop a pedicle and antler (arrow), but the transplanted forehead region initiated ectopic antler formation (arrowhead); C: Histological structure of a growing antler tip. Note that the reserve mesenchyme layer is located in the outermost position and immediately under the dermis of velvet skin. AP: Antlerogenic periosteum; D: Dermis; RM: Reserve mesenchyme; PC: Pre-cartilage; CA: Cartilage; HA: Hypertrophic cartilage; BO: Bone.

Once these cells were isolated and expanded by our group, they satisfied the practical criteria for mesenchymal stem cells (MSCs): Adherent growth, characteristic surface marker expression (such as CD90, CD107 and CD73), and tri-lineage differentiation potential (chondrocytes, adipocytes, and osteoblasts), along with expression of key pluripotency-associated and embryonic-type markers, such as OCT4, Nanog, and SOX2, that distinguish them from conventional bone-marrow MSCs[5,8]. Independent groups isolating “antler-derived multipotent stem cells” and “antlerogenic stem cells” reached concordant conclusions about their multipotency and proliferative vigor[5,10]. The competence of these cells was strikingly demonstrated by the cloning of viable red deer from the AnSCs, which showed that AnSCs retain full nuclear developmental potential and can give rise to differentiated progeny in vivo[17].

Another prominent feature of deer antlers is their ability to undergo rapid elongation at an unprecedented rate (up to 2 cm a day) during their rapid growth period[18]. Our group showed via a BrdU incorporation study that it is the outermost layer of the growing antler that is mainly responsible for this growth rate. Because this layer contains most of the mesenchymal cells (Figure 2C), Newbrey and Banks[19] termed this layer the reserve mesenchyme (RM). Cells isolated from the AP, PP, and RM are hereafter referred to as AP-derived cells (APCs), PP-derived cells (PPCs), and RM-derived cells (RMCs), respectively.

The re-definition: Antler blastema progenitor cells and RXFP2-positive stem cells

Two recent contributions have substantially updated the field’s understanding of “what an antler stem cell is”. First, Qin et al[12] used single-cell lineage tracing to identify a specific population of antler blastema progenitor cells (ABPCs) that arises during early regenerative blastema formation. These cells show particularly strong osteogenic and regenerative capabilities, making them the primary drivers of rapid antler growth. They have also been shown to maintain their regenerative potential even in different contexts. The accompanying commentary rightly emphasized that this evidence supports the idea that stem cells, rather than dedifferentiation, drive antler regeneration. Second, Ba et al[13] discovered RXFP2+ MSCs within the AP, highlighting their important role in postnatal antler development. This finding links a specific receptor-defined cell type to the initiation of antler developmental programs.

Reconciling the various AnSC populations is essential and offers the most valuable clarification in this review. Instead of competing definitions, APCs/PPCs, RMCs, ABPCs, and RXFP2+-APCs should be viewed as distinct states along a single developmental or regenerative pathway. During development, periosteal stem cells in the resting niche (AP) activate at male puberty, leading to pedicle formation and initial antler growth. In regeneration, resting periosteal cells (PP) activate after hard antler casting and differentiate into blastema progenitors for subsequent antler regeneration. A summary of this classification is presented in Table 1. However, direct lineage-tracing evidence linking all these populations is currently lacking. Therefore, their proposed relationships should be regarded as testable hypotheses rather than established developmental continuity.

Table 1 Antler stem/progenitor cell populations.

Population	Anatomical/temporal location	Defining or associated markers	Functional role	Ref.
AP cells	Frontal crest before the pedicle initiation in deer calves	MSC markers; embryonic-type markers	Initiate pedicle and first antler formation	[1,5,6]
PP cells	Pedicle in puberty and adulthood	MSC markers; STRO-1-type profile	Cell source of annual regeneration	[2,4,5]
RM cells	The distal regenerating antler, the outermost layer beneath the skin	Proliferative MSC profile	Provide progenitors during elongation	[5,42]
Antler blastema progenitor cells	Early stage of RM tissue	PTN, TNN, TNC, DLX5	Strong osteogenic/regenerative driver	[12]
RXFP2+ cells	A key sub-population of AP cells	RXFP2	Postnatal antler development	[13]

Antlerogenic periosteum cells, pedicle periosteum cells, and reserve mesenchyme cells are primarily defined by anatomical origin, whereas antler blastema progenitor cells and RXFP2-positive antlerogenic periosteum cells were identified using more specific molecular or single-cell approaches. AP: Antlerogenic periosteum; MSC: Mesenchymal stem cell; PP: Pedicle periosteum; RM: Reserve mesenchyme.

THERAPEUTIC APPLICATIONS OF ANSCS AND THEIR DERIVATIVES

The therapeutic literature falls into two delivery paradigms. The first involves transplantation of living AnSCs, which may act through transient tissue retention, direct differentiation, and sustained paracrine signaling. The second is cell-free AnSC derivatives, including conditioned medium (CM), extracellular vesicles (EVs), extracellular matrix (ECM), peptides, and metabolites. In this review, EV is used as the general term because exosomes represent only one EV subtype. We use the term “exosome” only when it directly reflects the terminology and characterization used in the original study. Improved tissue repair after cell transplantation does not confirm donor-cell engraftment or differentiation. Direct cellular participation is only supported by donor-cell tracing or specific markers. Studies involving CM, EVs, ECM, peptides, or metabolites are classified as cell-free and mainly paracrine. Table 2 summarizes this distinction.

Table 2 Summary of preclinical applications of antler stem cells and related antler-derived products.

Organ/indication	Preparation	Model	Intervention route	Principal effect	Mechanism (where defined)	Evidence for engraftment or paracrine action	Ref.
Skin/acute wound	CM; living AnSCs	Rat; radiation wound	Local perilesional delivery	Scarless regenerative healing	Anti-myofibroblast; regenerative substances	Living AnSCs: Donor-cell retention in healing dermis demonstrated, supporting partial direct participation; CM/EV studies: Paracrine	[20-23]
Skin/diabetic, burn	Exosomes; CM-hydrogel	Mouse/rat; full-thickness wound	Local (perilesional injection or topical hydrogel)	Accelerated healing	miR-21-5p/STAT3; angiogenesis; M2 polarization	Cell-free; paracrine modulation of fibroblasts, endothelial cells and macrophages	[24-26]
Bone	EVs; CM; peptides; grafts	Mouse, macaque, rabbit, rat; bone injury/osteoporosis	Local biomaterial implantation or systemic intravenous EV delivery	Bone regeneration; reversal of bone loss	Runx2/Cbfa1; JUN	Stable donor-cell differentiation not conclusively established; CM, EV, peptide and graft effects are host-mediated	[9,10,29-33]
Cartilage/OA	Exosomes; CM; ECM	Rat, mouse; full-thickness osteochondral defect/osteoarthritis	Local scaffold implantation or intra-articular exosome injection	Osteochondral & cartilage repair; anti-OA	miR-140/MMP13; anti-senescence	Predominantly cell-free; stimulation of host chondrocytes and resident progenitors	[35-39]
Liver	AnSCs; thymosin β10	Rat; CCl4-induced liver fibrosis	Intravenous cell transplantation or antler thymosin β10 (intraperitoneal protein delivery)	Reduced fibrosis	TGF-β1/SMAD inhibition	Living-cell treatment, but donor-cell differentiation not demonstrated; transwell evidence supports paracrine action	[43,44]
Lung	Exosomes	Mouse; bleomycin-induced pulmonary fibrosis	Intravenous tail-vein injection	Reduced pulmonary fibrosis	Blocked monocyte/macrophage recruitment	Cell-free EV-mediated immunomodulation	[45]
Nervous system/SCI	Engineered EVs; exosomes; peptides	Rat; postoperative cognitive dysfunction and acute spinal cord trauma	Systemic or local delivery	Neuroprotection; SCI repair	TLR2/TLR4 inhibition	Cell-free EV or peptide effects; no donor-cell engraftment	[47,48]
Diabetes (T1DM)	CM	Mouse; streptozotocin-induced T1DM	Intraperitoneal injection	Disease alleviation	NF-κB inhibition	CM-mediated paracrine effect	[49]
Cancer	AnSC medium; EV carriers	Human prostate cancer cell lines, glioma cell lines, mouse	In vitro cell incubation/intravenous tail-vein injection	Anti-tumor; drug delivery	-	Cell-free anti-tumor activity or EV-mediated drug delivery	[50-52]
Aging	EVs; extract; metabolite	Mouse, macaque; senescence, aging-associated bone loss, skin aging, osteoarthritis	Delivery routes included intravenous, intra-articular, local wound injection or topical application	Anti-senescence; systemic rejuvenation	Uridine; anti-senescence	Cell-free systemic effects; no cellular engraftment	[9,11,28,39]

CM: Conditioned medium; AnSCs: Antler stem cells; EV: Extracellular vesicle; STAT3: Signal transducer and activator of transcription 3; OA: Osteoarthritis; ECM: Extracellular matrix; MMP13: Matrix metalloproteinase-13; TGF: Transforming growth factor; SCI: Spinal cord injury; TLR: Toll-like receptor; T1DM: Type 1 diabetes mellitus; NF-κB: Nuclear factor kappa B.

Skin and wound healing

Skin was the first major non-skeletal tissue in which AnSC products demonstrated regenerative, rather than merely reparative, healing. The defining feature reported across studies is scarless or scar-reduced closure, resembling fetal-type regenerative healing. AnSC-CM accelerated cutaneous wound healing in rats and shifted the outcome toward regeneration rather than fibrotic scarring[20]; identifying specific regenerative substances active during antler renewal provided a mechanistic rationale for this scarless restoration[21]. Living AnSC transplantation promoted regenerative healing of radiation-induced cutaneous wounds in rats[22]. In this study, fluorescent lineage tracing detected substantial numbers of administered AnSCs in the dermal layer of the healing tissue, supporting at least partial direct cellular participation. Nevertheless, the study did not demonstrate that the donor cells permanently differentiated and incorporated into all regenerated skin-cell types. The altered expression of wound-healing and extracellular-matrix genes also suggests an important paracrine and microenvironmental contribution.

In contrast, the subsequent CM- and EV-based studies were entirely cell-free, and their effects therefore resulted from modulation of recipient/residential cells rather than donor-cell engraftment. AnSC-derived exosomes promoted regenerative wound healing specifically by inhibiting the fibroblast-to-myofibroblast transition, an anti-fibrotic mechanism central to scar prevention[23]. Exosomes from AnSC-RM cells accelerated wound healing via a miR-21-5p/signal transducer and activator of transcription 3 axis[24]. In burn injury, AnSC-derived exosomes promoted angiogenesis and M2 macrophage polarization, linking vascular and immune responses[25]. Engineering approaches have begun to combine these derivatives into delivery platforms: A dual-network hydrogel loaded with AnSC-CM and EGCG promoted diabetic wound healing through combined antibacterial, antioxidant, anti-inflammatory, and angiogenic actions[26], and an injectable hydrogel constructed from antler mesenchyme matrix promoted regenerative healing by recreating a fetal-like niche[27]. Cosmetically oriented studies have also reported anti-aging effects of AnSC cell extract on the skin in a murine model of cutaneous aging[28].

Bone repair and regeneration

Given that the growing antler is a rapidly mineralizing bony organ, bone repair is a biologically plausible application. AnSCs show strong osteogenic and chondrogenic differentiation in vitro, and endochondral ossification depends partly on Cbfa1/Runx2 signaling[29]. In a rabbit mandibular-defect model, both living AnSCs and cell-derived preparations, including cell homogenate and culture supernatant, promoted bone formation[10]. However, these studies did not conclusively demonstrate stable donor-cell engraftment and differentiation into mature host bone because the techniques used were insufficient. The efficacy of cell-free preparations in the same model suggests that paracrine signaling contributed substantially to the observed repair.

The remaining CM-, EV-, peptide-, material-, and graft-based studies represent cell-free or biomaterial-mediated approaches. AnSC-CM accelerated the regeneration of alveolar bone defects in rats, indicating clear dental and craniofacial relevance[30]. Mechanistically, deer antler material promoted osteogenic differentiation of human MSCs via JUN modulation, providing a human-cell mechanistic anchor[31], and isolated antler polypeptides enhanced proliferation and osteogenic differentiation of bone-marrow MSCs[32]. Two recent contributions are especially significant for translation. First, an “antler-inspired” bone graft engineered to mimic antler biology triggered rapid bone regeneration, indicating how the biological principles of antler growth can be applied to a synthetic device[33]; a complementary biomechanical study showed that the longitudinal tubular, transversely interconnected microarchitecture of antler bone itself can guide repair of critical-sized long-bone defects[34]. Second, and most consequentially, EVs from ABPCs reversed bone loss in mice and, critically, in macaques, while lessening broader aging phenotypes[9]. The inclusion of a non-human primate model in this study materially raises the translational credibility of the bone and systemic indications. Based on the available evidence, it is one of the most important pieces of evidence in the field.

Cartilage and osteoarthritis

Cartilage repair has emerged as one of the strongest indications for AnSCs and their derivatives, in part because antler growth is a natural model of chondrogenesis and because anti-inflammatory and chondroprotective actions converge well in osteoarthritis (OA). AnSC ECM supported high-quality repair of osteochondral defects in rats[35], and AnSC-CM provided an effective approach to cartilage regeneration in vivo[36]. AnSC-derived exosomes repaired mechanical cartilage damage and, specifically in OA, ameliorated disease via a miR-140/matrix metalloproteinase-13 (MMP13) axis that simultaneously dampened inflammation and promoted cartilage regeneration, a combined mechanism well suited to a disease with both inflammatory and degenerative components[37,38]. A conceptually important contribution linked the antler system to cellular aging biology: Exosomes from AnSCs alleviated human MSC senescence and OA, suggesting that AnSC derivatives act in part by counteracting the senescent phenotype of resident joint cells[39]. Engineering efforts have also integrated antler-derived materials into structured scaffolds for osteochondral repair[40]. Thymosin β10 supports chondrogenesis in this system and functions as a factor for angiogenesis and chondrogenesis during antler growth[41]. Nutritional factors can modulate it, as arginine promoted AnSC proliferation and chondrogenesis via Wnt/β-catenin and mammalian target of rapamycin signaling[42]. Except for the studies using living-cell implants, the cartilage and OA studies summarized here used CM, EVs, ECM, peptides, or scaffolds. Their effects therefore reflect stimulation of host chondrocytes, resident progenitor cells, and immune cells rather than donor-cell engraftment.

Liver

In the liver, the dominant therapeutic theme is anti-fibrosis. AnSCs were proposed as a novel cell source for reducing liver fibrosis, with in vivo evidence of attenuated fibrosis[43]. Transwell co-culture experiments, in which AnSCs were physically separated from hepatic stellate cells, support a predominantly paracrine mechanism involving inhibition of stellate-cell activation and pro-fibrotic signaling. The mechanism was then refined: Antler thymosin β10 reduced liver fibrosis by inhibiting the transforming growth factor (TGF)-β1/SMAD pathway, the canonical pro-fibrotic axis, identifying a specific antler-derived molecule responsible for part of the effect[44]. The convergence of anti-fibrotic activity in skin, liver, and lung, frequently traceable to suppression of TGF-β/SMAD signaling and myofibroblast activation, is one of the most consistent cross-organ signatures of AnSC derivatives.

Lung

In pulmonary fibrosis, AnSC-exosomes alleviated the disease, and a mechanistic study showed that the benefit derived chiefly from inhibiting the recruitment of monocyte-derived macrophages rather than from polarization of resident M2 macrophages[45]. This finding is worth highlighting because it shows that the immunomodulatory mechanism of AnSC EVs is organ- and context-specific: M2 polarization is central in burn wounds but not in lung fibrosis, and it cautions against assuming a single universal mode of action[25].

Nervous system and spinal cord injury

Although the nervous system is not an obvious target for a bone-regenerating cell, AnSC derivatives have shown notable neuroprotective and neuroregenerative activities. It is known that AnSCs are initially derived from neural crest cells during embryo development. Velvet antler polypeptides exerted biological effects on neural stem cells from embryonic rat brain, an early indication of neural activity[46]. More clinically oriented work demonstrated that AnSC-exosomes improved postoperative cognitive dysfunction in cardiopulmonary bypass rats by inhibiting Toll-like receptor 2 (TLR2)/TLR4 signaling[47]; we note that this is a neurocognitive rather than a cardiac-tissue indication, and it should be classified accordingly. The most advanced contribution in this domain is the use of engineered EVs from ABPCs as a therapy for spinal cord injury, a high-impact and notoriously refractory condition; using engineered rather than naïve EVs also signals the field’s maturation toward designed therapeutics[48].

Metabolic, oncologic, and other applications

AnSC-CM alleviated type 1 diabetes mellitus in vivo, possibly by inhibiting nuclear factor kappa B (NF-κB) signaling, extending the anti-inflammatory mechanism into an autoimmune-metabolic context[49]. In oncology, AnSC products display an intriguing duality. On one hand, AnSC-CM inhibited prostate cancer cells, indicating intrinsic anti-tumor activity[50]; on the other hand, EVs from three-dimensional (3D)-cultured AnSCs have been used as a drug-delivery vehicles for osteosarcoma and glioma[51,52], leveraging them as carriers rather than as therapeutic agents per se. This vehicle role is an important, distinct application class that should not be confused with regenerative effects. In dentistry, AnSC-CM reduced periodontal destruction in a murine periodontitis model, complementing the alveolar bone data[53].

Aging and senescence

A unifying recent theme is that AnSC-derivatives counteract aging at both cellular and systemic levels. Beyond MSC senescence in joints[39], the macaque study showed that ABPC-derived EVs mitigated aging-related phenotypes, reversed bone loss, and exerted cutaneous anti-aging effects[9,28]. A cross-species metabolomic analysis added a small-molecule dimension, identifying uridine as a potent, species-conserved regeneration-promoting factor[11]. Collectively, these data position the antler system not only as a source of tissue-specific repair signals but as a reservoir of geroprotective activity, an interpretation that, although promising, currently rests on a small number of studies and requires independent replication and validation.

Shared molecular mechanisms

Although the indications above span many organs, the basic mechanisms converge on a limited set of pathways, and it is useful to view these as a single mechanistic undercurrent rather than as organ-specific phenomena (Figure 3). Anti-fibrotic effects across skin, liver, and lung are repeatedly traced to suppression of TGF-β/SMAD signaling and inhibition of the fibroblast-to-myofibroblast transition[23,44,45]. Immunomodulation operates through NF-κB suppression in autoimmune-metabolic disease[49], TLR2/TLR4 suppression in neuro-cognitive injury[47], and context-specific macrophage modulation in wounds vs lung[25,45]. Osteogenic and proliferative control involves Runx2/Cbfa1[29], JUN[31], and Wnt/β-catenin signaling, the latter further regulated by the blood vessel epicardial substance gene, which controls AnSC homeostasis[42,54]. Niche- and growth-control signaling implicates PTN-PTPRZ in tissue regeneration and thymosin β10 in angiogenesis and chondrogenesis[41,55]. Finally, defined molecular cargoes, miR-21-5p[24], miR-140[38], and conserved metabolites such as uridine[11] provide the transferable, “drug-like” effectors that make the cell-free route feasible. The breadth of these conserved pathways explains both the cross-organ efficacy and the cross-species activity of AnSC derivatives.

Figure 3 Simplified proposed model of signaling pathways associated with antler stem cell- and derivative-mediated tissue repair. Antler stem cells (AnSCs), antler blastema progenitor cells (ABPCs), and their cell-free derivatives regulate tissue repair through interconnected anti-fibrotic, immunomodulatory, osteochondral, angiogenic, and anti-senescence pathways. Suppression of transforming growth factor-β/SMAD signaling and the fibroblast-to-myofibroblast transition reduces alpha-smooth muscle actin expression and collagen deposition. Nuclear factor kappa B and Toll-like receptor 2 (TLR2)/TLR4 inhibition, together with context-dependent regulation of macrophage recruitment and polarization, mediates immunomodulation. Runx2/Cbfa1, Wnt/β-catenin, JUN, and the miR-140/matrix metalloproteinase-13 axis regulate bone and cartilage regeneration. PTN/PTPRZ and thymosin β10 contribute to niche regulation, angiogenesis, and chondrogenesis, whereas the miR-21-5p/signal transducer and activator of transcription 3 axis and uridine are associated with wound healing and anti-senescence activity, respectively. TGF: Transforming growth factor; α-SMA: Alpha-smooth muscle actin; AnSCs: Antler stem cells; ABPCs: Antler blastema progenitor cells; NF-κB: Nuclear factor kappa B; TLR: Toll-like receptor; STAT3: Signal transducer and activator of transcription 3; EVs: Extracellular vesicles; ECM: Extracellular matrix; MMP13: Matrix metalloproteinase-13; SASP: Senescence-associated secretory phenotype.

Comparison with established mesenchymal stromal cell sources

AnSCs should not be regarded as universally superior to established human mesenchymal stromal cell sources. Rather, they provide a biologically distinctive but translationally immature platform. Compared with bone marrow MSCs, selected AnSC populations, particularly ABPCs, have shown greater proliferation, lower senescence-marker expression, stronger osteochondral differentiation, and higher EV production under defined experimental conditions[9,12]. Antler tissue is also renewable and can be collected repeatedly without sacrificing the donor animal. In addition, AnSC-derived EVs contain potentially distinctive proteins, miRNAs, and metabolites, including regeneration-associated factors such as miR-21-5p, miR-140, and uridine[11,24,38].

These advantages are probably counterbalanced by important limitations. Human bone marrow-, adipose-, umbilical-cord-, Wharton’s-jelly-, and dental-pulp-derived MSCs have substantially greater clinical and manufacturing experience. Umbilical-cord and dental-tissue MSCs may also proliferate rapidly and show low immunogenicity, whereas adipose tissue provides a comparatively abundant adult-cell source. In contrast, living AnSCs and their EVs are xenogeneic for human recipients, and direct one-on-one comparisons using identical culture, purification, and potency assays are scarce but needed. Consequently, the most defensible advantage of AnSCs is their unique regenerative biology and candidate molecular cargo, rather than demonstrated general advantage over human MSC products. Table 3 shows a qualitative comparison of AnSCs with other established MSC sources.

Table 3 Qualitative comparison of antler stem cells with established mesenchymal stem cell sources.

Cell source	Proliferative capacity	Immunogenicity	Differentiation tendency	Secretome/EV characteristics	Translational maturity
AnSCs	High in selected populations; prolonged expansion and low senescence reported	Living cells are xenogeneic; EV immunogenicity remains insufficiently defined	Strong osteogenic and chondrogenic activity; population-dependent heterogeneity	Regeneration-associated proteins, miRNAs and metabolites; relatively high EV production reported	Preclinical; no human trials
Bone marrow MSCs	Moderate; decreases with donor age and passage	Generally low but not absent in allogeneic use	Well-established osteogenic, chondrogenic and adipogenic differentiation	Extensively characterized immunomodulatory and trophic secretome	Extensive preclinical and clinical experience
Adipose-derived MSCs	Moderate to high; relatively abundant source	Generally low but not absent	Strong adipogenic potential; osteogenic and chondrogenic capacity	Angiogenic and immunomodulatory secretome	Extensive preclinical and growing clinical experience
Umbilical cord/Wharton’s jelly MSCs	High; relatively low senescence	Generally low among human allogeneic sources	Multilineage differentiation, although protocol-dependent	Strong immunomodulatory and trophic activity	Advanced preclinical and clinical development
Dental pulp MSCs	High in some comparative studies	Generally low but source- and activation-dependent	Strong odontogenic and neuroectoderm-associated potential; variable adipogenesis	Neurotrophic, angiogenic and immunomodulatory factors	Mainly preclinical and early clinical development

This table provides a qualitative overview based on heterogeneous published studies rather than standardized head-to-head comparisons. The comparisons are context-dependent and should be interpreted cautiously. EV: Extracellular vesicle; AnSCs: Antler stem cells; miRNAs: MicroRNAs; MSCs: Mesenchymal stem cells.

Quality and limitations of the current evidence

To interpret the current evidence base for AnSCs cautiously, most therapeutic studies have used rodent models, while rabbit studies are less frequent and large-animal validation remains rare. The macaque study of ABPC-derived EVs represents an important advance, but it included only three animals per treatment group and was not designed as a thorough regulatory toxicology study[9]. No completed human clinical trial of AnSCs or AnSC-derived products has yet been reported.

Reproducibility is another concern. Few research groups have reported findings, and independent replication applying standardized cell definitions, EV-isolation methods, doses, and outcome measures continues to be uncommon. Heterogeneous nomenclature and variable use of the terms EV and exosome add to the complexity of comparison. In addition, publication bias toward positive results may affect the literature, while ineffective doses, negative findings, and toxicity observations may be underreported. Most mechanistic conclusions rely on pathway associations or inhibitor experiments rather than rigorous cargo-specific loss-of-function and rescue studies. Future studies should use preregistered protocols, blinded outcome assessment, adequate power calculations, dose-response designs, standardized reporting, and independent multicenter validation. Comparative studies against clinically established MSC or MSC-EV products are also required before concluding AnSC-specific superiority.

Overall, wound and musculoskeletal repair currently have relatively direct preclinical support, whereas evidence for systemic aging, neurological disorders, cancer, and other systemic indications remains more preliminary. Local administration may offer a more favorable, controllable risk-benefit profile than systemic delivery, though this requires indication-specific evaluation. EVs and peptides may provide practical manufacturing advantages over living cells, but their safety or superiority has not been established. Similarly, companion-animal applications may offer a useful translational setting but still require rigorous assessment of xenogeneic immunogenicity, pathogen control, and jurisdiction-specific veterinary regulations.

TRANSLATIONAL OUTLOOK AND FUTURE CLINICAL STRATEGIES

Choosing between the cellular and cell-free routes

The most consequential strategic decision for the field is the relative emphasis on living-cell transplantation vs cell-free derivatives. Living AnSCs offer durable engraftment, in situ differentiation, and sustained paracrine output, and they remain the most faithful reproduction of the natural regenerative process[5,22]. However, they carry the full regulatory weight of an advanced-therapy cellular product: Requirements for cell-line provenance, karyotypic stability, sterility, and the management of xenogeneic immunogenicity when cervid cells are used in non-cervid recipients. Immortalization strategies, such as hTERT modulation, which also alter the small-EV characteristics of AnSCs, may help standardize a cell source but simultaneously raise the bar for tumorigenicity testing[56]. Above all, many transplanted cells may not survive in recipients in vivo, and the main functions of the injected cells may be mediated through paracrine pathway[57,58].

The cell-free route, including CM, EVs/exosomes, ECM, and purified peptides largely circumvent these concerns. EVs are non-replicative, can be sterilized and characterized as a defined product, are more amenable to storage and dosing, and provoke less immunogenicity than living xenogeneic cells[59,60]. The field’s trajectory, evident in the dominance of EV and CM studies, suggests growing interest in cell-free products. Nevertheless, neither their clinical readiness nor their superiority over living-cell or established human MSC products has been demonstrated. Future studies should prioritize clinical development with well-characterized EV or peptide products, reserving living-cell approaches for indications where durable engraftment is indispensable.

Barriers that must be addressed

A credible translational program must address manufacturing, immunogenicity, pharmacology, and evidence-quality limitations. First, AnSC-derived products require GMP-compatible donor qualification and cell banking. Deer identity, species, age, health status, infectious-disease status, nutrition, medication exposure, collection season, timing after hard antler casting, antler growth stage, and precise tissue compartment should be documented. Available studies suggest inter-animal variation in self-renewal and growth-stage-dependent differences in differentiation potential, but the direct effects of donor age, season, and nutrition on EV cargo and therapeutic potency remain largely unknown[3]. These variables should be treated as potentially critical material attributes until they are formally exclude.

Establish a qualified master cell bank and working cell bank from selected donors. Culture variables, including passage number, seeding density, oxygen tension, medium composition, serum-free or xeno-free supplements, harvest interval, and 2D vs 3D culture, must be fixed. 3D culture can alter EV yield and cargo; therefore, EVs produced under 2D and 3D conditions cannot automatically be considered interchangeable[51]. Scale-up will probably require closed bioreactor culture combined with scalable concentration and purification methods, such as tangential-flow filtration and size-exclusion chromatography.

Product-release criteria should include cell-bank identity and stability; EV particle number and size distribution; EV-enriched and contaminant markers; purity; sterility; mycoplasma; endotoxin; residual DNA and host-cell proteins; aggregation; storage stability; and freeze-thaw sensitivity. Depending on the route of administration, also assess tissue-factor activity, thrombin generation, hemolysis, and complement activation. Most importantly, each product requires an indication-specific potency assay linked to its proposed mechanism, such as inhibition of TGF-β/SMAD signaling for anti-fibrotic products, enhancement of osteogenic differentiation for bone indications, or suppression of MMP13 for cartilage indications. General particle counts or total protein concentration alone are not sufficient measures of potency.

Second, EVs are non-replicative but not necessarily non-immunogenic. AnSC-EVs may retain MHC molecules, membrane proteins, glycans, or other cervid antigens that can induce innate or adaptive immune responses, particularly after repeated systemic administration. Aged female macaques received 15 mg of EVs per administration every two weeks for ten administrations over 20 weeks. The study reported no significant changes in routine blood counts or liver and kidney biochemical indices, and no overt adverse immunological reactions[9]. However, the study included only three macaques per group and did not comprehensively assess EV-specific immunoglobulin G (IgG) or IgM, complement activation, acute cytokine release after each dose, immune-organ histopathology, or long-term immune memory. Thus, these results show preliminary repeat-dose tolerability but do not rule out immunogenicity. Repeat-dose studies should longitudinally measure anti-EV antibodies, complement split products, cytokine release, immune-cell phenotypes, and changes in circulation time. This matters because repeated EV administration may accelerate blood clearance even without overt clinical inflammation[61]. Direct comparisons among autologous, allogeneic, and xenogeneic EVs would help determine whether the cervid origin adds clinically meaningful immunological risk.

Third, biodistribution and pharmacokinetics remain poorly defined. The short-term SPECT/CT analysis showed EV distribution at 1 hour, 4 hours, and 8 hours after administration, but it did not define full circulation half-life, tissue exposure, metabolism, or long-term clearance[9]. Future studies should use validated, stable labeling methods; distinguish intact EVs from released labels; and evaluate blood half-life, tissue accumulation, clearance organs, dose proportionality, and changes after repeated dosing. Dose-response and dose-frequency studies are also required because most current studies use a single empirically selected dose.

Finally, long-term safety studies should evaluate inflammatory toxicity, thrombogenicity, ectopic tissue formation, reproductive toxicity where relevant, and tumor-promoting potential. Engineered EVs additionally require assessment of cargo-related off-target effects and altered tissue distribution. These studies, together with validated potency assays and batch-comparability testing, are prerequisites for clinical translation.

Sourcing, ethics, and supply

A practical advantage of the antler system is that source tissue can be harvested from regenerating velvet antler, a renewable structure, without harming the animal. Each year, farmed deer antlers are removed for medicinal use, allowing readily available AnSC to be obtained from these commercially harvested velvet antlers. Consequently, this source would be ethically and logistically preferable to many other animal-derived primary cell sources. The demonstrated cross-species potency of AnSC derivatives in rodents and primates suggests that a well-characterized cervid cell bank could potentially provide a renewable source of EV or peptide products. However, the feasibility of this model will depend on donor qualification, xenogeneic pathogen control, batch comparability, and demonstration that prolonged cell expansion does not alter product potency or safety[9-11]. The recent establishment of sika deer-induced pluripotent stem cells offers a further route to a renewable, genetically defined, and editable cell source that could standardize derivative production while reducing reliance on primary tissue[62].

Companion-animal and veterinary applications as a translational proving ground

Companion-animal medicine may provide a useful setting in which to investigate AnSC-derived products, particularly for naturally occurring OA, bone defects, tendon injuries, and difficult-to-heal wounds. However, no direct clinical evidence currently demonstrates the efficacy or safety of AnSC-derived products in client-owned dogs, cats, or horses. Consequently, veterinary application should be regarded as a research opportunity rather than an established or necessarily accelerated translational pathway[9-11,38].

Regulatory requirements are jurisdiction-specific and depend on product composition, processing, intended use, and donor-recipient relationship. In the United States, animal stem cells, conditioned media, and exosomes intended for disease treatment may fall within the regulatory framework for animal cell-, tissue-, and tissue-based products. Development therefore requires attention to donor eligibility, product characterization, manufacturing controls, safety, effectiveness, and investigational-use requirements. Cervid-derived products additionally require assessment of xenogeneic immunogenicity and species-specific pathogen transmission. Initial studies should therefore use standardized products in controlled veterinary trials with prespecified clinical outcomes, dose escalation, adverse-event monitoring, and long-term follow-up. Food and Drug Administration guidance specifically emphasizes that donor-recipient relationships, including xenogeneic use, influence the safety, effectiveness, and quality profile of veterinary cell- and tissue-based products.

Engineering and combination strategies

Research on AnSCs is progressing from naïve derivatives toward designed products. Engineered EVs have been deployed for spinal cord injury[48], EVs have been used as targeted drug carriers[51,52], and antler-derived materials and biomimetic architectures have been incorporated into scaffolds, hydrogels, and grafts for bone and cartilage repair[26,27,33,34,40]. The logical convergence is a combination product: A standardized AnSC-derived EV or peptide payload delivered within a niche-recreating biomaterial that provides spatial control, sustained release, and a regeneration-permissive microenvironment. Given the demonstrated importance of the niche to AnSC function[27,63-65], such integrated designs are likely to outperform either component alone.

Future research priorities

Future development should focus on indication-specific product engineering rather than just descriptive studies. Main points include: (1) Engineered EVs with tissue-targeting ligands or defined cargo are able to enhance delivery and safety, requiring renewed testing for biodistribution, immunogenicity, and off-target effects; (2) Gene editing in AnSCs may improve cargo but needs in-depth examination of genomic stability and tumorigenicity, making it a long-term strategy; (3) Combining AnSC-derived EVs with hydrogels and biomaterials can support local retention and tissue-specific applications, particularly in bone and wound healing; (4) Artificial intelligence analysis of cellular and EV data can identify quality attributes and optimize donor cell selection, though biological assays stay essential; and (5) An individualized approach, taking into account factors such as disease stage and immune status, may be more effective than a universal treatment.

CONCLUSION

AnSCs provide a distinctive model to understand repeated mammalian organ regeneration and a potential source of regenerative cells and molecular products. The field has progressed from identifying periosteal stem-cell populations to single-cell and molecular definitions involving ABPCs and RXFP2+ cells. These populations may represent related developmental and regenerative states, although their complete lineage relationships require additional confirmation. Both living-cell and cell-free approaches have shown therapeutic activity in preclinical models. However, the current evidence is dominated by rodent studies, with limited large-animal validation, no human clinical trials, and insufficient independent replication. Living-cell transplantation may involve both direct cellular participation and paracrine signaling, whereas CM-, EV-, peptide-, metabolite-, and ECM-based approaches act primarily by modulating host cells and the tissue microenvironment. The proposed relationships among AnSC populations still require direct lineage validation, while companion-animal applications should be regarded as a potential research opportunity rather than an established clinical pathway.

AnSCs are not yet demonstrably superior to established human MSC sources. Possible benefits include complete organ regeneration, strong osteochondral activity, renewable sourcing, prolonged expansion of selected populations, and distinctive regenerative cargo. These features must be balanced against xenogeneic immunogenicity, donor and seasonal variability, uncertain pharmacokinetics, and limited translational maturity. Future progress will depend on GMP-compatible cell banking and manufacturing, mechanism-linked potency assays, standardized dose metrics, rigorous biodistribution and repeat-dose immunogenicity studies, and independent large-animal validation. Companion-animal medicine may provide a useful translational setting, particularly for OA, bone defects, and wound healing, provided that the same standards of product quality and safety are maintained. With these requirements addressed, AnSC-derived products may contribute to the development of new regenerative strategies.

ACKNOWLEDGEMENTS

The authors sincerely thank Professor Peter Fennessy for his careful proofreading and review of the grammar and language of this manuscript.