Innovative strategies for immune thrombocytopenia treatment: immunomodulatory mechanisms and clinical potential of mesenchymal stem cells

Abstract

Immune thrombocytopenia (ITP) is a heterogeneous autoimmune disorder characterized by increased platelet destruction and impaired megakaryopoiesis within a dysregulated bone marrow niche. Conventional therapies often achieve only transient platelet recovery, failing to restore immune tolerance, thereby underscoring the need for mechanism-based therapeutic strategies. Mesenchymal stem cells (MSCs) have emerged as promising candidates due to their ability to modulate immune responses and repair the hematopoietic microenvironment. This review synthesizes current evidence regarding the biological properties, immunomodulatory mechanisms, and therapeutic applications of MSCs in ITP, emphasizing intrinsic abnormalities of patient-derived MSCs and the corrective potential of exogenous MSCs from distinct tissue sources. It further integrates emerging insights into MSC functional heterogeneity, optimization of culture conditions, priming strategies, and cellular engineering approaches that may enhance therapeutic efficacy and safety. By highlighting the interplay between immune tolerance restoration and bone marrow niche remodeling, this review provides a translational framework that links mechanistic understanding to the future clinical development of MSC-based therapies for ITP.

Introduction

Immune thrombocytopenia (ITP) is an autoimmune blood disorder defined by platelet counts below 100 × 10⁹/L, leading to an increased risk of bleeding [1]. The primary pathogenic mechanism involves the breakdown of immune tolerance, predominantly driven by impaired function of regulatory cells, including Tregs, Bregs, and myeloid-derived suppressor cells. Consequently, when this regulatory network is compromised, autoreactive immune cells become activated, producing anti-platelet antibodies and cytotoxic T cells, which simultaneously destroy circulating platelets and inhibit platelet production in the bone marrow [2]. These insights into the underlying mechanisms of ITP underscore the necessity for treatments specifically targeting these pathological processes to achieve sustained responses and improved quality of life [3].

MSCs, particularly bone marrow-derived MSCs (BMSCs), are multipotent stromal cells known for their immunomodulatory properties across various diseases [4, 5]. Recent evidence highlights their crucial involvement in ITP pathogenesis, in which impaired BMSCs exhibit deficient regulation of macrophage polarization, a key mechanism in the immune dysregulation observed in ITP [6]. Studies indicate that BMSC administration can effectively correct the imbalance between M1/M2 macrophages, reduce proinflammatory cytokine levels, and subsequently increase platelet counts in ITP model [7]. Furthermore, the HMGB1-TLR4 pathway has been identified as a potential therapeutic target to restore the immunoregulatory function of BMSCs in ITP. This review comprehensively examines the pathophysiological and therapeutic roles of MSCs in ITP, highlighting their potential as a novel treatment strategy for this complex autoimmune disorder.

While previous reviews have summarized the general therapeutic potential of MSCs in ITP, a unified framework integrating intrinsic MSC abnormalities, functional heterogeneity, and translational optimization strategies remains insufficiently defined. Distinct from prior descriptive overviews, this review places particular emphasis on the dual role of MSCs as both contributors to bone marrow niche dysregulation and as therapeutic agents capable of restoring immune tolerance. By synthesizing emerging evidence on patient-derived MSC dysfunction, tissue source–specific characteristics, culture optimization, priming approaches, and cellular engineering strategies, we propose a translational perspective that bridges mechanistic insights with future clinical development. This positioning highlights the interplay between immune tolerance restoration and microenvironmental remodeling, thereby offering an updated conceptual framework that complements and extends existing literature.

Biological characteristics and immunomodulatory properties of MSCs

Definition, criteria, and cellular sources

MSCs are multipotent stromal cells characterized by self-renewal and differentiation capacity into various mesenchymal lineages, including osteocytes, chondrocytes, and adipocytes [5]. They can be isolated from diverse tissues such as bone marrow, adipose tissue, umbilical cord, and various oral tissues, with each source exhibiting distinct biological properties that influence their therapeutic potential [8, 9]. According to criteria proposed by the International Society for Cellular Therapy (ISCT), MSCs are defined as a heterogeneous population of cells adhering to plastic surfaces under standard culture conditions. These cells express CD73, CD90, and CD105 but lack CD34, CD45, CD14/CD11b, CD79a/CD19, and HLA-DR, and retain the capacity for osteogenic, adipogenic, and chondrogenic differentiation in vitro [10]. Among various MSC sources, bone marrow-derived MSCs (BMSCs), the earliest identified and most extensively studied subtype, demonstrate robust differentiation potential toward osteogenic, chondrogenic, and adipogenic lineages [11].

Key biological properties

Research has demonstrated that specific bone morphogenetic proteins (BMPs) can guide MSC differentiation; for example, BMP9 is recognized as one of the most potent inducers of osteogenesis [12]. This differentiation capability underpins the critical role of MSCs in tissue repair and regeneration. However, the functional potency of MSCs is limited by factors such as cellular aging and prolonged in vitro expansion, which impair their biological properties. A representative example is observed in human umbilical cord-derived MSCs (hUC-MSCs), where late-passage cells (P8) exhibit reduced proliferative and differentiation potential compared with early-passage cells (P2). This highlights a critical consideration for clinical-scale expansion and therapeutic application [13]. Beyond differentiation capacity, MSCs exert significant therapeutic effects through their robust secretory profile, releasing a wide spectrum of bioactive molecules. These include growth factors such as VEGF, which promotes angiogenesis, and TGF-β, which is involved in growth regulation and immunomodulation [14]. Notably, MSCs also secrete extracellular vesicles (EVs), particularly exosomes, which function as key mediators of intercellular communication. These vesicles contain proteins, lipids, and nucleic acids (e.g., mRNAs and microRNAs) that can be transferred to recipient cells, thereby modulating cellular behavior [15]. For instance, MSC-derived exosomes inhibit cancer progression in non-small cell lung cancer by targeted gene regulation and attenuate inflammatory responses in endothelial cells [16]. The development of exosome-mimetic nanovesicles derived from umbilical cord MSCs further underscores the therapeutic potential of leveraging paracrine mechanisms across diverse diseases, ranging from osteoarthritis to inflammatory conditions. Such approaches represent promising cell-free alternatives to conventional cell-based therapies [17]. Recent reviews further suggest that biomaterial-assisted delivery strategies, such as hydrogel-encapsulated MSC-derived EVs, may enhance the stability and therapeutic efficacy of cell-free MSC products, supporting their future clinical application in immune-mediated diseases [18].

Immunomodulatory functions

A defining characteristic of MSCs is their inherently low immunogenicity, primarily due to minimal MHC-I expression and the absence of MHC-II and essential costimulatory molecules such as CD40, CD80, and CD86 [19]. Nevertheless, this immune-privileged phenotype is not absolute and can be compromised by inflammatory microenvironments or suboptimal manufacturing and culture conditions [19]. Beyond their recognized regenerative potential, MSCs exhibit potent immunomodulatory effects through multiple mechanisms, including suppression of T-cell proliferation, modulation of macrophage polarization toward anti-inflammatory phenotypes, and promotion of regulatory T-cell differentiation. These multifaceted regulatory actions, mediated by paracrine signaling and direct cell-cell interactions, establish MSCs as promising therapeutic candidates for diverse immune-mediated disorders. However, their clinical efficacy is influenced by factors such as tissue origin, processing strategies, and the host immune context [20].

Accumulating evidence increasingly underscores MSCs as dynamic regulators of immune homeostasis. Through direct cellular interactions and the secretion of bioactive mediators, MSCs can suppress excessive immune activation, particularly by modulating T lymphocytes and dendritic cells (DCs) [21, 22]. In inflammatory settings, MSCs inhibit pro-inflammatory Th17 differentiation by activating the SOCS3 pathway through IFN-γ/STAT1 signaling, thus suppressing downstream STAT3 activity [23]. Emerging studies further indicate that MSCs influence T-cell fate through epigenetic mechanisms. These mechanisms include alterations in histone lactylation at specific gene promoters, ultimately promoting a more tolerogenic immune phenotype [24, 25]. In addition, MSC-derived small extracellular vesicles (MSC-sEVs) effectively reduce endothelial senescence and promote angiogenesis in models of aging and type 2 diabetes. These effects are primarily mediated by the transfer of miR-146a, which inhibits Src phosphorylation and related signaling pathways [26]. Beyond direct cellular interactions, the MSC secretome plays a crucial role in reshaping inflammatory microenvironments. MSCs release anti-inflammatory mediators such as prostaglandin E2 (PGE2), indoleamine 2,3-dioxygenase (IDO), and TGF-β, thus shifting local cytokine networks toward an anti-inflammatory state. In addition to autoimmune modulation, cytokines secreted by bone marrow–derived MSCs can directly regulate hematopoietic and malignant progenitor cells, highlighting the broad paracrine activity of MSCs within the bone marrow niche [27]. This phenomenon has been clearly demonstrated in certain experimental models, where MSCs derived from umbilical cord and adipose tissue markedly reduce TNF-α, IL-6, and IL-1β levels and simultaneously enhance IL-10 production (Fig. 1). Consequently, these MSCs facilitate tissue repair and resolve inflammation [28].

Fig. 1.

MSC-mediated immune and hematopoietic regulation in ITP. MSCs promote immune tolerance by inhibiting Th1/Th17 responses and enhancing Tregs, Bregs, and tolerogenic dendritic cells. They also modulate macrophage polarization and cytotoxic T-cell activity. Simultaneously, MSC-secreted factors and extracellular vesicles support bone marrow niche repair and megakaryocyte differentiation via CXCL12–CXCR4 signaling and growth factor pathways. Together, these effects decrease platelet destruction and improve thrombopoiesis

Application of MSCs in various autoimmune diseases

MSCs are increasingly recognized for their notable capacity to modulate immune responses and facilitate tissue repair, making them a promising therapeutic option for numerous autoimmune diseases [29, 30] (Table 1). MSCs exert integrative effects across multiple immune cell populations rather than functioning through a single pathway. These effects include suppression of Th1/Th17 responses, enhancement of regulatory T-cell activity, modulation of B-cell function, and reprogramming of inflammatory cytokine networks. These shared immunomodulatory mechanisms have supported the investigation of MSC-based therapies in conditions such as rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease, and autoimmune diabetes [30–33].

Table 1.

MSC clinical trials in autoimmune diseases

Disease	MSC type	Mechanisms	Clinical outcomes	Trial NCT	Refs.
SLE	UC-MSC, BM-MSC; IV infusion	B-cell modulation; Treg↑; IFN signature↓; microenvironment repair	SLEDAI↓, proteinuria↓, steroid-sparing effect; sustained remission in some patients	NCT00698191; NCT03171194	[34, 35]
RA	UC-MSC, BM-MSC, AD-MSC; IV infusion	↓Th1/Th17;↓TNF-α/IL-6; ↑Treg/Breg	DAS28↓, HAQ↓, CRP/ESR↓; good safety profile	NCT03186417; NCT03333681; NCT03798028	[36]
Crohn’s Disease	AD-MSC (Darvadstrocel/Cx601); Local injection	Local immune modulation; tissue repair	ADMIRE-CD: ~50% remission vs. 34% placebo at 24 weeks	NCT01541579; NCT02405285	[37]
SSc	BM-MSC, AD-MSC; IV infusion	Anti-fibrotic effects; improved microvasculature; Treg↑	mRSS↓; ulcer healing; stabilization of lung function	NCT00962923; NCT02975960; NCT02213705	[38]
MS	BM-MSC IV; MSC-NP intrathecal administration	Neuroprotection; immune reset; oligodendrocyte repair	Confirmed safety; stabilization/improvement of EDSS in some patients	NCT01854957; NCT03355365	[39, 40]
pSS	BM-MSC, AD-MSC; IV infusion; exploratory gland injection	↓B-cell activation; ↓autoantibodies; Th17/Treg modulation	ESSDAI↓, improvement of xerostomia/keratoconjunctivitis	NCT00953485	[41, 42]
T1D	Autologous BM-MSC; IV infusion	Immune tolerance; β-cell protection/regeneration	Preserved C-peptide; ↓insulin requirement	NCT02057211; NCT04078308; NCT03484741	[43]
ITP	hUC-MSC; IV infusion	Restoration of MSC function; ↓Th1/Th17; ↑Treg; ↓autoantibodies; megakaryopoiesis support	ORR ~ 40–50%; bleeding improvement; sustained responses in some patients	NCT04014166; NCT06813157	[44, 45]

Clinical and preclinical studies consistently demonstrate that MSC therapies lead to decreased inflammatory activity, better clinical outcomes, and favorable safety profiles across various disease contexts. These findings underscore a common immunoregulatory framework that extends beyond individual diseases. Importantly, MSCs are viewed less as disease-specific treatments and more as regulators of immune homeostasis and promoters of stromal microenvironmental repair. Within this broader autoimmune context, applying MSCs to ITP represents a logical extension of their established immunomodulatory properties.

Considerations and optimization strategies for MSC production with therapeutic potential in ITP

Optimizing MSC manufacturing methods for ITP is essential to enhance their immunomodulatory function, regenerative potential, and clinical applicability. Traditional two-dimensional monolayer cultures remain common due to technical simplicity. However, MSCs cultured under these conditions frequently experience passage-dependent senescence and functional deterioration, which may compromise their ability to restore immune tolerance in ITP. In contrast, three-dimensional spheroid cultures better mimic the native microenvironment, significantly improving anti-inflammatory and immunoregulatory properties. This approach may strengthen MSCs’ capacity to modulate Th1/Th17 balance and regulatory T-cell responses involved in ITP pathogenesis [46] (Figure. 2).

Fig. 2.

Precision-engineering strategies and source-dependent immunomodulatory properties of MSCs. Bone marrow–, adipose-, and umbilical cord–derived MSCs display distinct immunomodulatory profiles. Through the secretion of IDO, PGE2, and TSG-6, MSCs regulate macrophage polarization and inflammatory signaling. Engineering approaches, including TLR priming, cytokine preconditioning, genetic modifications, and hypoxic culture, enhance immune tolerance and reduce autoantibody-mediated inflammation

To comply with clinical-grade standards, serum-free or xeno-free culture conditions are increasingly utilized, enabling GMP-compatible MSC expansion and reducing safety risks. These conditions are particularly important for repeated administration in patients with refractory autoimmune cytopenias. Additionally, priming techniques—including inflammatory stimulation using IFN-γ and TNF-α, functional polarization through TLR signaling, small-molecule treatments, and genetic modifications—can further enhance MSC homing, survival, and expression of key immunoregulatory factors like IDO, PGE2, and TSG-6 [47, 48]. Emerging evidence indicates that responsiveness to priming may vary depending on the MSC source. For example, BMSCs frequently demonstrate enhanced activation of immunometabolic pathways upon inflammatory priming, whereas hUC-MSCs often exhibit greater resilience against senescence and retain proliferative capacity under hypoxic or cytokine-based conditions. Such differences between MSC sources must be considered when developing optimized manufacturing protocols and could partly explain variability observed across clinical studies. These functional improvements may be especially relevant in ITP, where impaired immune tolerance, abnormal antigen presentation, and compromised bone marrow niche support sustain disease progression. Although optimization approaches strengthen the rationale for MSC therapy in autoimmune diseases, they also raise challenges related to standardization, batch consistency, and potentially increased immunogenicity. Therefore, careful selection of culture and priming methods is vital for designing MSC-based therapies aimed at durable efficacy in ITP (Table 2).

Table 2.

Overview of MSC culture and induction strategies

Method	Advantages	Disadvantages	Typical applications	Refs.
Conventional 2D monolayer culture	Simple, low cost, easy to monitor morphology and phenotype; widely used and standardized for basic research.	Does not recapitulate the 3D in vivo environment; extended culture induces senescence, phenotypic drift, and decreased immunomodulatory capacity.	Basic MSC biology, early-phase in vitro experiments, proof-of-concept studies.	[49]
3D spheroid/aggregate culture	Enhances anti-inflammatory and immunomodulatory properties (e.g., TSG-6↑); improves survival and stress resistance; better mimics in vivo conditions.	Controlling spheroid size and oxygen/nutrient gradients is technically demanding; scale-up and standardization are complicated.	Optimization of MSC immunomodulation in models of autoimmune diseases and sterile inflammation.	[50]
Serum-free / xeno-free GMP-compatible culture	Avoids animal-derived components; improves safety and regulatory compliance; suitable for clinical-grade MSC manufacturing.	Higher cost; lot-to-lot variation between commercial formulations; effects on MSC phenotype require validation.	Clinical-grade MSC expansion for human trials and approved cell therapy products.	[51]
Hypoxic culture / hypoxic preconditioning	Mimics the bone marrow niche; enhances proliferation, survival, paracrine factor secretion, and immunomodulation; improves resistance to ischemic/hypoxic injury.	Requires dedicated equipment and precise oxygen control; effects vary by context and exposure duration.	Preconditioning MSCs for ischemic/inflammatory indications and improving cell persistence and function in vivo.	[52]
Inflammatory cytokine priming	Strongly boosts immunosuppressive mediators (e.g., iNOS/IDO, chemokines, PGE2); switches MSCs into a highly immunomodulatory state.	May increase HLA class II expression and immunogenicity; excessive exposure can impair MSC viability or induce dysfunction.	Generation of highly immunosuppressive MSCs for autoimmune diseases, GVHD, and inflammatory disorders.	[53]
TLR-based polarization	Allows functional “polarization” into pro-inflammatory MSC1 or immunosuppressive MSC2 phenotypes; provides mechanistic insight into MSC plasticity.	Responses are ligand- and dose-dependent, with batch variability; TLR4 priming can enhance pro-inflammatory activity, posing potential risks in autoimmune conditions.	Fine-tuning MSC function in preclinical models; dissecting mechanisms of MSC-mediated immune regulation.	[54]
Genetic engineering of MSCs	Enables targeted enhancement of homing, survival, paracrine signaling, or specific pathways; can significantly amplify therapeutic potency.	Falls under gene therapy regulations; potential safety concerns (insertional mutagenesis, persistent gene expression); manufacturing and approval processes are complex.	Next-generation, indication-tailored MSC products for critical illnesses, cardiovascular, and neurological diseases.	[55]
Secretome / extracellular vesicle (EV, exosome)-based approaches	Cell-free; lower risk of tumorigenicity and immunogenicity; easier storage and handling; captures key immunomodulatory and regenerative signals from MSCs.	Standardization of isolation, dosing, and characterization is still evolving; may not fully reproduce the complexity of whole-cell therapy.	Development of safer “off-the-shelf” MSC-derived products for immunomodulation and tissue regeneration.	[56]

Role of MSCs in the pathogenesis of ITP

In ITP, MSCs derived from bone marrow display three major dysfunctions critical to disease progression. First, MSCs from ITP patients (ITP-MSCs) show impaired proliferation and increased apoptosis. These changes result from disrupted signaling pathways (e.g., Wnt, PI3K/Akt), oxidative stress, and epigenetic modifications affecting genes regulating cell cycle progression and survival [57, 58]. Second, their immunoregulatory capacity is severely diminished. They fail to adequately suppress pathogenic T-cell proliferation, have impaired generation of Tregs and tolerogenic DCs, and show abnormal cytokine secretion. These defects collectively exacerbate autoimmune destruction of platelets [59]. Third, intrinsic and immunological defects impair their ability to effectively support megakaryopoiesis and platelet formation within the bone marrow niche. Dysfunctional unfolded protein responses and insufficient platelet-derived growth factor-BB (PDGF-BB) signaling further impair these supportive functions [60]. Consequently, ITP pathology involves not only immune dysregulation but also fundamental defects in the bone marrow stromal microenvironment, where compromised MSCs are unable to maintain immune equilibrium and facilitate hematopoiesis [61]. Table 3 summarizes the functional domains and associated molecular abnormalities in ITP-MSCs.

Table 3.

Functional defects, molecular mechanisms, and consequences of MSCs derived from ITP patients

Functional domain	Defective manifestations	Dysregulated molecules / pathways	Consequences in ITP	Refs.
Proliferation/survival	Reduced proliferative capacity; Replicative senescence; Increased apoptosis; Reduced colony-forming ability	Signaling Pathways: ↓Wnt/β-catenin, ↑ PI3K/Akt, ↓ Notch pathway (Notch-1, Jagged-1) Apoptosis Markers: ↓ Bcl-2, ↑ Bax, ↑ Caspase-3/9 miRNAs: ↓miR-155-5p (SOCS1 axis), ↑miR-628-3p (TRAF3 axis)	Impaired MSC self-renewal; Reduced number of functional MSCs in the BM niche.	[60, 62–64]
Immunomodulation (T cells)	Failure to inhibit CD4 + T-cell proliferation; Impaired induction of Tregs; Inability to correct Th1/Th2 imbalance	↓ IL-35 secretion, ↓ TGF-β expression, Defective adenosine signaling (↓CD39/CD73), ↑ Caspase-9 mRNA	Loss of peripheral immune tolerance; Sustained T-cell activation and autoimmune responses.	[45, 65, 66]
Immunomodulation (APCs)	Failure to suppress DC maturation; impaired polarization of macrophages towards an M2 phenotype	General defect in paracrine signaling and cell-to-cell interactions	Enhanced antigen presentation; Increased platelet destruction by M1 macrophages.	[7]
Hematopoietic Support	Impaired support for megakaryocyte differentiation and maturation; Ineffective platelet production	↓ CXCL12 (SDF-1), ↓ PDGF-BB, VEGF, SCF, Altered expression of actin cytoskeleton-related genes	Thrombopoiesis failure; contributes to thrombocytopenia despite elevated TPO levels.	[67, 68]

Impaired proliferation and excessive apoptosis of ITP-MSCs

ITP-MSCs frequently harbor intrinsic abnormalities in intracellular signaling pathways [45]. Several critical pathways for MSC proliferation and survival, such as Wnt, TGF-β/BMP, and PI3K/Akt, appear disrupted, directly hindering cellular growth and promoting apoptosis [58]. Regulatory elements such as microRNAs and long non-coding RNAs (lncRNAs), essential mediators of gene expression, also exhibit dysregulation in ITP-MSCs. This dysregulation may repress cell-growth-associated genes and activate pro-apoptotic pathways [69, 70]. Oxidative stress further exacerbates these defects by damaging vital cellular components [71]. In addition, genetic predispositions and aberrant epigenetic changes, including altered DNA methylation and histone modifications, may permanently silence crucial cell-cycle genes (e.g., cyclins), while simultaneously activating apoptotic signaling pathways [72].

Given these fundamental impairments and heightened apoptosis, therapeutic strategies focus on correcting these intrinsic defects. For instance, repurposing drugs like statins, known for broad beneficial effects on cell proliferation, may help modulate the growth and gene expression profiles of ITP-MSCs [73]. If autologous MSCs are intrinsically defective, therapeutic strategies might involve replacing or regenerating them. Advanced approaches include generating induced tissue-specific stem cells (iTSCs), which can differentiate into healthy MSCs for transplantation. Enhancing engraftment and survival of transplanted MSCs within recipient bone marrow is crucial. Such enhancement may require preconditioning of either the recipient niche or the transplanted cells themselves [74, 75]. Additionally, developing novel therapies, ranging from biologics and gene therapies employing viral vectors to deliver corrected genes into patient-derived MSCs, to investigating natural compounds targeting similar cell survival and renewal pathways in other refractory diseases, represents a promising therapeutic avenue [76, 77].

Abnormal immunomodulatory function of ITP-MSCs

A fundamental defect in ITP-MSCs is their inability to function effectively as master immune regulators [59]. These cells show significant impairment in suppressing activated T-cell proliferation, resulting in unchecked autoimmune platelet destruction. Crucially, they fail to adequately induce and support key regulatory T-cell populations [45]. They have reduced capability to generate Tregs, essential cells for immune tolerance, and also poorly generate CD8 + CD28- suppressor T-cells. This loss of immune regulation is further exacerbated by their inability to properly educate DCs [78]. Instead of promoting tolerogenic DCs (regDCs), ITP-MSCs allow DCs to mature with elevated co-stimulatory molecules and increased IL-12 secretion. These hyperactivated DCs further drive Th1 differentiation and fail to induce T-cell anergy. Additionally, cellular senescence contributes directly to these immunoregulatory deficiencies, as senescent MSCs cannot adequately deliver signals required to suppress overactive immune responses [79].

This cellular dysfunction is driven by a complex and abnormal inflammatory microenvironment in the bone marrow, characterized by dysregulated cytokines and chemokines. For example, levels of IL-35, a critical anti-inflammatory cytokine, are notably reduced, partly due to impaired induction of IL-35-producing regulatory T-cells (iTr35) by ITP-MSCs [80]. Simultaneously, decreased secretion and impaired function of IL-6 reduce MSCs’ ability to induce suppressive T-cells (Ts cells) and regulate the expression of IL-10 [81]. Additionally, ITP-MSCs exhibit downregulated CXCL12, disrupting megakaryocyte migration within the bone marrow niche and reflecting broader stromal support deficiencies [67]. Furthermore, vital molecular pathways mediating cell-to-cell communication, such as the Notch-1/Jagged-1 signaling axis, are significantly impaired in ITP. Reduced Jagged-1 expression and downstream signaling directly impair the formation of tolerogenic regDCs [65]. The pro-inflammatory protein High Mobility Group Protein 1 (HMGB1) further impairs MSC-mediated macrophage polarization via the HMGB1-TLR4-MyD88 pathway, exacerbating inflammatory responses. Chen et al. [82] reported that the chemokine SDF-1α markedly promotes MSC migration, homing, and microenvironmental remodeling; thus, impaired homing capacity likely contributes significantly to functional defects in ITP-derived MSCs.

Impaired capacity of ITP-MSCs to support platelet production

ITP-MSCs show intrinsic defects, including altered proliferation, increased apoptosis and senescence, and impaired immunoregulatory function. These abnormalities disrupt the immune balance within the bone marrow niche essential for normal megakaryopoiesis [60]. Additionally, ITP-MSCs display elevated intracellular iron concentrations, adversely affecting megakaryocyte development in the marrow microenvironment. Interestingly, treatment with eltrombopag has been shown to mitigate this iron accumulation [83, 84]. Integrated mRNA and miRNA profiling further reveals dysfunctions in fundamental cellular processes, such as the unfolded protein response (UPR) and DNA transcription, underlying these observed impairments. The interaction between platelets and MSCs also appears critical in this dysfunction [85]. Notably, platelet-derived growth factor-BB (PDGF-BB) protects MSCs against apoptosis, senescence, and impaired immunomodulation, potentially through the p53/p21 signaling pathway. This protective feedback mechanism appears deficient in the ITP microenvironment [60]. Therefore, impaired MSC functionality represents a critical mechanism underlying insufficient platelet production in ITP, linking immune dysregulation to hematopoietic niche failure [67].

Current evidence suggests that MSC-mediated effects occur via multiple targets. A comprehensive overview of these mechanisms, including direct cellular interactions and exosome-mediated regulation, is summarized in Table 3.

Table 4.

Molecular mechanisms, target cells, and therapeutic mediators of MSC-based therapy in ITP

Target cell / process	Therapeutic effect of MSCs	Key mediators/signaling pathways	Clinical/biological outcome	Refs.
Regulatory T cells	Promotes CD4 + T-cell differentiation into Foxp3 + Tregs.	Notch Pathway: Notch-1 / Jagged-1 interaction. Cytokines: TGF-β1, PGE2, IL-10. Direct Contact: Cell-to-cell interactions.	Restores immune tolerance; suppressed autoreactive T-cell responses.	[22, 85, 86]
Helper T cells	Rebalancing Subsets Suppresses Th1/Th17 differentiation; promotes shift toward Th2.	Cytokine Modulation: ↓ IFN-γ, IL-17 (Pro-inflammatory) ↑ IL-4, IL-10 (Anti-inflammatory) Enzymes: Indoleamine 2,3-dioxygenase (IDO).	Reduced cytokine storm; decreased T-cell assistance for autoantibody production by B cells.	[87–90]
Macrophages	M2 Polarization Shifts phenotype from Pro-inflammatory (M1) to Anti-inflammatory (M2).	Soluble Factors: PGE2, TSG-6. Exosomes: Transfer of regulatory miRNAs. Metabolic: IDO-mediated tryptophan depletion.	Reduces Fcγ receptor-mediated phagocytosis of opsonized platelets.	[91, 92]
B Cells/ plasma cells	Inhibition of Activation Suppresses proliferation and differentiation into antibody-secreting cells.	Indirect: Through inhibition of T-helper cells and DC maturation. Direct: Cell cycle arrest (G0/G1 phase); Soluble factors (e.g., CCL2).	Decreased production of anti-GPIIb/IIIa and other platelet-specific autoantibodies.	[93, 94]
DCs	Inhibition of Maturation Maintains DCs in an immature, tolerogenic state.	Surface Markers: ↓ CD80, CD86, CD83, HLA-DR expression. Cytokines: ↓ IL-12, ↑ IL-10.	Impaired antigen presentation to T cells; Induction of T-cell anergy.
Bone marrow Niche	Microenvironment Repair Restores structural and functional support for hematopoiesis.	Trophic Factors: ↑ CXCL12 (SDF-1) ↑ SCF, VEGF, PDGF-BB ↑ Angiopoietin-1	Enhanced megakaryocyte maturation and thrombopoiesis (platelet production).	[22, 63, 67, 78, 80, 81]
Exosome-mediated Targeting	Genetic Regulation Post-transcriptional modulation of inflammatory gene expression.	miRNAs: • miR-146a-5p: Targets IRAK1/TRAF6 to inhibit NF-κB signaling. • miR-125a-3p.	Precision molecular targeting without using whole cells; Reduced inflammation.	[95, 96]

Mechanistic study of MSCs derived from different sources for treating ITP

In recent years, MSCs have emerged as a promising therapy, especially for refractory or chronic ITP, due to their dual roles in immune modulation and hematopoietic support. MSCs can be isolated from various tissues, each possessing distinct biological characteristics and practical advantages, potentially influencing their functional mechanisms and clinical efficacy [44]. Bone marrow-derived MSCs (BMSCs) are the most extensively studied. They correct T-cell imbalance, enhance Treg function, and restore megakaryocyte differentiation [95]. Notably, recent findings indicate that lysosomal dysfunction and activated cGAS-STING signaling in aging hematopoietic stem cells (HSCs) contribute to inflammatory dysfunction. These findings offer new insights into optimizing the hematopoietic-supportive role of BMSCs by targeting lysosomal activity or related inflammatory pathways [96, 97]. Adipose-derived MSCs (AD-MSCs) are easily accessible and exhibit strong immunomodulatory effects, including suppression of pathogenic T-cell activity and mitigation of senescence-associated defects in patient-derived MSCs [98]. Preclinical studies using ITP mouse models confirm that AD-MSCs effectively restore Th17/Treg balance and regulate cytokine profiles and transcription factors (T-bet/GATA-3). This underscores their value as a convenient source for immune normalization [87]. Human umbilical cord MSCs (hUC-MSCs), characterized by low immunogenicity and high proliferative capability, also show promising outcomes in refractory ITP, primarily through anti-inflammatory cytokine release and microenvironmental repair [87].

Recent research further highlights MSC-derived EVs, especially those from primed MSCs, as beneficial in enhancing hematopoietic stem cell function and immune modulation. This suggests their potential as novel cell-free therapeutic agents [99]. By comparing the distinct properties and advantages of BMSCs, AD-MSCs, and hUC-MSCs, we aim to provide a comprehensive understanding of optimizing MSC-based interventions to restore immune tolerance and improve platelet production in ITP (Table 5).

Table 5.

Preclinical and clinical studies of MSCs from different sources in the treatment of ITP patients

MSC source	Study level / model	Study type / model	Key findings / mechanisms	Refs.
BMSCs	Preclinical (animal model)	Mouse Model	Significantly increased platelet counts; elevated frequency of Treg cells and suppressive cytokines (IL-10, TGF-β1); upregulated Foxp3 expression.	[100]
	Preclinical (animal model)	Mouse Model of Pregnancy ITP	BMSC-derived exosomal miR-146a-5p regulated Th1/Th2 balance, promoted platelet production, and alleviated ITP by inhibiting the CARD10/NF-κB signaling pathway.	[101]
AD-MSCs	Clinical (human)	Case Report (Refractory ITP)	Haploidentical AD-MSC transplantation led to complete and sustained remission (platelet count > 100 × 109/L) for over 15 months, with no relapse.	[102]
hUC-MSCs	Clinical trial (human)	Prospective Phase I Trial (Refractory ITP)	Overall response rate of 44.4% (8/18 patients); dose-dependent effect observed; the highest dose (2.0 × 106 cells/kg) achieved platelet counts of ~ 50 × 109/L for up to 28 weeks; bleeding symptoms relieved in 60–75% of patients; only mild adverse events reported.	[44]
	Clinical (human)	Case Report (ITP in pregnancy)	Platelet counts during pregnancy were maintained between 41–94 × 109/L and rose to 154 × 109/L postpartum. No infusion-related adverse events were observed.	[103]

Immunomodulatory mechanisms: comparative analysis across MSC sources

MSCs derived from various tissues share fundamental immunomodulatory characteristics. However, emerging evidence highlights significant differences in their potency, stability, and mechanisms, influencing their therapeutic utility in ITP (Fig. 3). All MSC types effectively suppress pathogenic T-cell responses in preclinical models [104]. Nonetheless, hUC-MSCs and AD-MSCs typically demonstrate stronger inhibition of Th1/Th17 polarization, possibly due to their inherently greater secretion of anti-inflammatory mediators (e.g., IDO, PGE2, TGF-β) [105]. In contrast, BMSCs provide more balanced immune regulation by combining T-cell suppression with niche-supportive signaling. This balanced effect might be advantageous for restoring immune tolerance without causing extensive immunosuppression [106]. Treg induction is central to the immunomodulatory action of all MSC sources, yet variations in efficiency exist. hUC-MSCs consistently promote robust Foxp3⁺ Treg expansion, possibly because of enhanced paracrine activity and lower donor-age-related senescence. Conversely, BMSCs may achieve sustained yet comparatively slower immune reprogramming [107]. With high levels of immunoregulatory cytokines such as TGF-β and IL-10, hUC-MSCs might more rapidly restore disrupted Treg/Th17 balance observed in ITP patients. AD-MSCs exhibit promising anti-inflammatory effects clinically, though comparative long-term Treg stability data remain limited [104]. In addition to regulating lymphocytes, MSCs modulate innate immunity by shifting macrophages toward an anti-inflammatory M2 phenotype, potentially reducing platelet destruction in ITP. The extent of this effect likely varies depending on differences in secretome profiles and priming conditions [108]. Collectively, although core mechanisms are consistent, source-specific differences in immunomodulatory strength and durability must be considered in designing MSC-based therapies for ITP.

Fig. 3.

Translational roadmap for MSC-based therapy in ITP. Selection of MSC sources, multi-omics–based quality control, and engineered preclinical strategies facilitate clinical translation. However, donor variability, safety concerns, and manufacturing complexities remain significant challenges. Integrated optimization involving efficacy validation, standardized production methods, and bioinformatic profiling may increase therapeutic consistency and precision

Support for hematopoiesis and bone marrow niche restoration

Besides immune regulation, MSCs also support hematopoiesis by maintaining the bone marrow microenvironment, a critical function for ITP, where defective megakaryopoiesis and stromal dysfunction are increasingly recognized [109]. As natural components of the hematopoietic niche, BMSCs strongly secrete supportive factors such as CXCL12 and stem cell factor (SCF), promoting megakaryocyte survival and maturation [110]. This niche-restorative capability distinguishes BMSCs from MSC sources outside the marrow. While hUC-MSCs are not native to bone marrow, they possess robust paracrine and proliferative abilities, rapidly secreting trophic factors that indirectly facilitate hematopoietic recovery [111]. AD-MSCs present intermediate properties, combining accessibility with a secretome capable of modulating stromal and immune signaling. Experimental evidence further indicates MSC-derived EVs may enhance megakaryocyte differentiation and platelet production. This suggests a shared but variably expressed mechanism among MSC sources [112]. Taken together, MSC-based therapy in ITP appears to function through dual mechanisms, restoring immune tolerance and repairing the microenvironment, where BMSCs primarily favor niche support and hUC-MSCs exhibit stronger systemic immunomodulation.

Translation and practical implications in clinical settings

From a translational viewpoint, critical factors influencing MSC source selection for ITP treatment include availability, manufacturability, and clinical scalability (Table 6). hUC-MSCs offer significant benefits such as large-scale expansion capability, lower immunogenicity, and consistent donor quality, making them highly suitable for allogeneic use and early clinical trials [113, 114]. AD-MSCs provide convenient autologous accessibility, although therapeutic consistency may be affected by donor metabolic variability [115]. BMSCs remain biologically significant due to their intrinsic hematopoietic regulatory function but are limited by invasive collection methods and age-associated functional decline [116].

Table 6.

Comparative translational profile of MSC sources in ITP

Feature	BM-MSCs	hUC-MSCs	AD-MSCs	Mechanistic notes / evidence basis	Refs.
Niche support	Strong interaction with bone marrow niche (CXCL12⁺ microenvironment)	Moderate stromal support	Limited hematopoietic niche data	BM-MSCs regulate hematopoiesis and megakaryocyte development via niche-mediated signaling.	[118]
Treg induction	Robust induction via direct contact and cytokine secretion	Strong paracrine-driven expansion (TGF-β, IL-10)	Moderate, donor-dependent	MSC-derived cytokines promote Foxp3⁺ Treg expansion, promoting immune tolerance.	[119]
Accessibility	Invasive (bone marrow aspiration)	Non-invasive (perinatal tissue source)	Minimally invasive (liposuction)	Collection methods affect scalability and clinical applicability.	[120]
Clinical translation focus	Hematopoietic support / refractory ITP contexts	Immunomodulatory reset strategies under investigation	Emerging applications	Evidence from preclinical and initial clinical MSC studies in ITP.	[109]
Macrophage modulation	Contact + cytokine-mediated polarization	Secretome-driven M2 polarization	Variable, influenced by donor metabolism	MSC secretome composition and priming influence innate immune responses.	[121]

Comparative clinical evidence (Table 5) indicates that hUC-MSC therapy achieves promising response rates and favorable safety profiles in refractory ITP. Data on AD-MSCs and BMSCs are comparatively limited or context-dependent. These findings suggest that therapeutic choices could eventually depend on specific patient phenotypes. For example, younger patients exhibiting predominant immune dysregulation and intact marrow function might particularly benefit from hUC-MSCs, given their robust immunomodulatory properties and scalability [113]. Conversely, patients with clear stromal or hematopoietic impairment might gain theoretical advantages from BMSC-based approaches, owing to their niche-restoring capabilities [117]. Overall, integrating mechanistic insights with practical considerations could shift MSC therapy in ITP from empirical applications toward personalized, mechanism-based strategies.

Risks and limitations

Despite their therapeutic promise, MSC-based treatments for ITP entail critical safety considerations and translational challenges. These vary according to tissue origin, manufacturing approaches, and clinical scenarios. Evidence from studies involving hematopoietic transplant complications, graft-versus-host disease, and other immune-related conditions shows that intravenous administration of BMSCs is generally well-tolerated short-term. Such studies indicate no significant increase in acute toxicity or malignancy incidence. However, long-term safety data remain insufficient, and considerable variability exists across manufacturing methods, culture conditions, and dosing protocols [122, 123]. Although systematic reviews indicate that MSC therapy under strict quality-control measures does not typically induce new solid or hematologic malignancies, prolonged in vitro expansion may cause chromosomal instability or spontaneous cellular transformation. This emphasizes the need for ongoing surveillance, particularly in chronic diseases such as ITP [124].

AD-MSCs exhibit a distinct safety profile influenced by donor characteristics and metabolic status. Clinical studies indicate generally favorable tolerability, with most short-term adverse events limited to mild fever or localized discomfort. However, isolated cases of thrombotic events, fibrotic progression, and focal structural abnormalities have been reported during follow-up [125]. Notably, the “donor background effect” is particularly relevant for AD-MSCs. Cells obtained from obese or metabolically dysregulated donors may display a more pro-inflammatory secretome. This shift could reduce their tolerance-inducing potential or disrupt immunomodulatory balance in autoimmune conditions [126]. Accordingly, international consensus statements recommend rigorous phenotypic characterization and careful patient selection to reduce risks such as thromboembolism, infection, or unintended immune activation [127].

hUC-MSCs demonstrate favorable short-term tolerability and encouraging preliminary efficacy. However, challenges remain, including limited follow-up duration, small cohort sizes, and insufficient disease-specific safety data in thrombocytopenic populations. Cohort analyses and systematic reviews across various indications suggest that UC-MSC infusion does not significantly increase serious adverse events or mortality during early follow-up. These findings support their classification as relatively safe allogeneic products. Nevertheless, their long-term safety in ITP remains inadequately defined [128].

The safety profile of MSC therapy in ITP must also be considered in the context of autologous versus allogeneic transplantation. Autologous MSCs, commonly AD-MSCs or patient-derived BMSCs, may lower the risk of alloimmune reactions. However, they may exhibit functional impairment or a pro-inflammatory bias linked to the patient’s underlying disease or metabolic condition, potentially reducing therapeutic reliability. In contrast, allogeneic MSCs provide advantages in manufacturing consistency and immunological potency. Yet, they raise theoretical concerns regarding immunogenicity, microvascular obstruction, and thrombotic complications after intravenous administration. These concerns are particularly relevant in ITP, where profound thrombocytopenia and coagulation imbalance are already present. Therefore, careful risk–benefit evaluation and individualized dosing strategies are essential.

Conclusion

MSC-based therapy represents a promising approach in ITP, shifting treatment goals from symptomatic platelet replenishment toward modulating the immune microenvironment and restoring bone marrow niche stability. A critical priority is the comparative evaluation of MSCs from various tissue sources. Current evidence indicates that no single MSC source is universally superior; rather, each presents distinct functional trade-offs. BMSCs are extensively characterized for hematopoietic support and provide valuable mechanistic insights. hUC-MSCs offer enhanced proliferative potential, reduced senescence related to donor age, and lower immunogenicity, facilitating large-scale allogeneic applications. AD-MSCs are practical due to accessibility and ease of autologous harvesting, but donor metabolic status may introduce variability. These differences suggest that future therapeutic strategies will likely focus on individualized MSC selection based on patient characteristics, disease progression, and treatment history rather than a universal approach. Additionally, therapeutic methods are evolving from simple MSC infusion toward optimized cellular products. Preconditioning techniques, inflammatory priming, and genetic engineering to enhance MSC homing, persistence, and immunomodulatory activity are increasingly important. Such advancements may overcome current challenges of therapeutic inconsistency and limited clinical efficacy observed in early studies.

Despite promising initial outcomes, several challenges remain before MSC therapy can be standardized in ITP management. Variability in manufacturing processes, dosing, and administration methods complicates study comparisons and limits the interpretation of effectiveness. Furthermore, the in vivo fate and long-term survival of infused MSCs are poorly understood. Advanced imaging and cell-tracking technologies could provide essential insights into MSC biodistribution, persistence, and interactions within the hematopoietic niche, guiding future protocol improvements. The field is thus shifting from early mechanistic studies toward clinical refinement and precision therapy. Progress will depend on rigorously designed, adequately powered randomized controlled trials (RCTs) defining standardized parameters for MSC source selection, manufacturing quality, dosing strategies, and patient stratification. In particular, future head-to-head RCTs comparing MSC sources under consistent manufacturing and dosing protocols are necessary to clarify differences in efficacy, response durability, and safety profiles in ITP. With ongoing advances in cell engineering and biomarker-driven therapeutic designs, MSC-based interventions offer potential for sustained disease control and enhanced quality of life in patients with refractory ITP.

Abbreviations

ITP

Immune thrombocytopenia

AITP

Autoimmune thrombocytopenic purpura

MSCs

Mesenchymal stem cells

BMSC

Bone marrow-derived mesenchymal stem cell

AD-MSC

Adipose tissue-derived mesenchymal stem cell

hUC-MSC

Human umbilical cord-derived mesenchymal stem cell

UCMSCs

Umbilical cord mesenchymal stem cells

EV

Extracellular vesicle

HSC

Hematopoietic stem cell

NSCLC

Non-small cell lung cancer

UPR

Unfolded protein response

GMP

Good manufacturing practice

ISCT

International society for cellular therapy

DC

Dendritic cell

GVHD

Graft-versus-host disease

RA

Rheumatoid arthritis

SLE

Systemic lupus erythematosus

SSc

Systemic sclerosis

MS

Multiple sclerosis

pSS

Primary Sjögren’s syndrome

T1D

Type 1 diabetes

T2DM

Type 2 diabetes mellitus

CD

Crohn’s disease

ORR

Overall response rate

VEGF

Vascular endothelial growth factor

TGF-β

Transforming growth factor beta

PGE2

Prostaglandin E2

IDO

Indoleamine 2,3-dioxygenase

TSG-6

Tumor necrosis factor-stimulated gene-6

TNF-α

Tumor necrosis factor alpha

IFN-γ

Interferon gamma

IL

Interleukin

CXCL12-C-X-C

motif chemokine ligand 12

SDF-1

Stromal cell-derived factor 1

SCF

Stem cell factor

PDGF-BB

Platelet-derived growth factor-BB

BMP

Bone morphogenetic protein

BMP9

Bone morphogenetic protein 9

GILZ

Glucocorticoid-induced leucine zipper

NF-κB

Nuclear factor kappa-light-chain-enhancer of activated B cells

SMAD

Sma- and Mad-related protein

TNFAIP3

TNF alpha-induced protein 3

PI3K

Phosphoinositide 3-kinase

Akt

Protein kinase B

cGAS

Cyclic GMP-AMP synthase

STING

Stimulator of interferon genes

IRAK1

Interleukin-1 receptor-associated kinase 1

CARD10

Caspase recruitment domain family member 10

ATRA

All-trans retinoic acid

TPO-RA

Thrombopoietin receptor agonist

Author contributions

XZ wrote the manuscript and created the figures. XZ and NS conceived the final approval of the version to be submitted. All authors read and approved the final manuscript.

Funding

The work was supported by grants from the Taishan Youth Scholar Foundation of Shandong Province (tsqn201812140), Shandong University Horizontal Project (6010225019).

Data availability

No datasets were generated or analysed during the current study.

Ethics approval and consent to participate

Not applicable.

Competing interests

The authors declare no competing interests.