The anti-inflammatory effects of mesenchymal stem cells and their research progress in hematopoietic stem cell transplantation: A comprehensive review.

Introduction

Hematopoietic stem cell transplantation (HSCT) is a fundamental therapeutic approach in the medical field for treating various hematologic malignancies, including acute leukemia, chronic myeloid leukemia, multiple myeloma, and lymphoma, as well as certain congenital or acquired immunodeficiency diseases, such as severe combined immunodeficiency and aplastic anemia with immune abnormalities. Since its introduction in clinical practice, HSCT has saved countless lives and significantly improved treatment outcomes for these conditions 1 . While HSCT offers curative potential for patients, it also comes with a range of severe complications that significantly affect their quality of life and can be a major factor limiting their long-term prognosis. Among these complications, acute and chronic graft-versus-host disease (GVHD), inflammatory storms, and delayed hematopoietic reconstitution are the most common and detrimental 2 . GVHD is one of the most prevalent complications following HSCT, with an incidence rate ranging from 30% to 50%. It is categorized into two types: acute GVHD (aGVHD) and chronic GVHD (cGVHD), based on when the symptoms appear. Acute GVHD typically manifests within the first 100 days post-transplantation, and in severe cases, it can lead to multiple organ failure, resulting in a mortality rate between 15% and 40%. Chronic GVHD usually develops more than 100 days after transplantation and can affect nearly all organ systems in the body, presenting with complex and varied clinical symptoms. Some patients may even exhibit autoimmune-like symptoms, which can significantly impair their daily functioning and potentially lead to long-term disability or death 3 .

In clinical practice, traditional immunosuppressive agents such as cyclosporine A, tacrolimus, and methotrexate are essential for preventing and treating GVHD 4 . While these medications can help control the onset and progression of GVHD by inhibiting the activation and proliferation of immune cells, they also carry significant side effects, most notably an increased risk of infections 5 . These infections can worsen patients’ conditions and may interact with GVHD, creating a vicious cycle that further deteriorates prognosis. Another serious complication after HSCT is a cytokine storm, which typically occurs in the early post-transplant period. This condition is often linked to tissue damage caused by conditioning regimens such as chemotherapy and radiotherapy, immune reactions during graft engraftment, and infections 6 . If not managed promptly, a cytokine storm can escalate rapidly to septic shock and multi-organ failure, posing a serious threat to patients’ lives. In addition, transplant-associated thrombotic microangiopathy (TA-TMA) and hepatic veno-occlusive disease (VOD) are also severe complications that jeopardize the safety of HSCT patients 7 , 8 . The occurrence and development of these complications are closely related to the inflammatory microenvironment after HSCT, highlighting the importance and urgency of improving this microenvironment and finding safe and effective strategies for preventing and treating complications. These issues have become key clinical challenges limiting the improvement of HSCT efficacy.

Against this backdrop, mesenchymal stem cells (MSCs), a type of non-hematopoietic stem cell with multi-directional differentiation potential and strong immune regulatory functions, have gradually become a research hotspot in the medical field 9 . MSCs are widely distributed in various organs and tissues of fetuses and adults, such as bone marrow, umbilical cord, placenta, and adipose tissue. They are relatively easy to obtain and have low immunogenicity (e.g. low expression of major histocompatibility complex class II molecules and co-stimulatory molecules on their surface, making them less likely to trigger host immune rejection), laying a solid foundation for their clinical application 10 . MSCs exert powerful immune regulatory functions through the secretion of anti-inflammatory cytokines and exosomes, mitochondrial transfer and metabolic reprogramming, and direct interaction with immune cells 11 . Based on these unique biological functions, MSCs have attracted extensive attention in the research of various inflammation-related diseases (such as rheumatoid arthritis, ulcerative colitis, and acute respiratory distress syndrome) and in the field of HSCT, providing new ideas and strategies for the prevention and treatment of post-HSCT complications. In recent years, scholars both domestically and internationally have conducted extensive basic research and clinical studies on the application of MSCs in HSCT. They have made significant progress in preventing and treating GVHD, alleviating cytokine storms, promoting hematopoietic reconstitution, and improving complications such as TA-TMA and VOD.

This article reviews the research advancements related to MSCs in HSCT, covering both basic and clinical aspects. It emphasizes the molecular mechanisms behind their anti-inflammatory effects and addresses the challenges encountered in clinical translation. By thoroughly organizing and analyzing the existing research findings, the article aims to provide valuable insights for further in-depth studies on MSCs in the HSCT field, support their clinical translation and application, and ultimately enhance the prognosis and efficacy of HSCT for patients. A graphical overview of topics related to the research field is presented in Fig. 1 , and specific details are further elaborated throughout the article’s thematic sections.

The anti-inflammatory mechanisms of MSCs

Biological characteristics of MSCs

MSCs play a crucial role in regenerative medicine and immunotherapy due to their biological origin and differentiation potential. During embryonic development, MSCs originate from the mesoderm, which gives them the ability to differentiate into various cell types and possess strong immune regulatory functions 12 . As a key germ layer in embryonic development, the mesoderm allows MSCs to develop into cells that form mesodermal tissues. This capability makes MSCs essential for maintaining the body’s immune balance, positioning them as one of the most promising types of adult stem cells in contemporary medical research 12 .

MSCs possess unique biological characteristics that enhance their proliferation and differentiation capabilities. They exhibit strong telomerase activity, which effectively slows down the shortening of telomeres. This property allows for long-term stable proliferation and enables large-scale expansion of cells in vitro , which is essential for clinical applications 13 . MSCs proliferate primarily through asymmetric cell division, a process that ensures the maintenance of the MSC population while also providing an adequate supply of cells for differentiation into various cell types. Under suitable in vivo or in vitro induction conditions, MSCs can differentiate into several mesodermal-derived cell types, including osteoblasts, chondrocytes, adipocytes, and myocytes. Furthermore, with the appropriate regulatory microenvironments, they can differentiate into non-mesodermal-derived cells, such as neural cells (including neuron-like cells and glial cells) as well as hepatocyte-like cells 14 . This extensive differentiation potential makes MSCs invaluable for tissue repair and regeneration. For instance, in bone injury repair, MSCs can differentiate into osteoblasts, secrete bone matrix, and enhance mineralization of bone tissue, thereby accelerating fracture healing. In cases of post-myocardial infarction, MSC-derived heart muscle-like cells can partially replace damaged myocardial cells, improving myocardial contractile function and reducing ventricular remodeling 15 . In research focused on treating neurological diseases, such as Parkinson’s disease and spinal cord injuries, MSC-derived neural cells can restore damaged neural cells and facilitate the reconstruction of neural synapses, offering promising avenues for recovery of neural function 16 . MSCs exert anti-inflammatory effects through multiple pathways, including regulating immune cell function, secreting anti-inflammatory factors, and inhibiting pro-inflammatory signaling pathways 17 . In vitro experiments have shown that MSCs can inhibit the functions of T cells and B cells. Vaillant et al 18 . pointed out that MSCs suppress the proliferation and cytokine release of CD8+ T cells through intercellular contact and the secretion of soluble factors. Furthermore, due to their unique immunological properties, the immunologically immature state of MSCs can reduce immune responses, improve graft acceptance in allogeneic HSCT, and lower the risk of GVHD 19 .

A key biological characteristic of MSCs is their ability to “home” to specific target areas, making them ideal as targeted therapeutic carriers. Homing ability refers to MSCs’ capacity to detect chemotactic signals—such as inflammatory factors, chemokines, and indicators of tissue damage—released by tissues or cells during pathological events like injury, inflammation, or tumors. MSCs can migrate through the bloodstream or interstitial spaces and penetrate the vascular endothelial barrier of lesions by binding to adhesion molecules on the surfaces of endothelial cells, like VCAM-1 and E-selectin. Once they reach the target tissues, they accumulate specifically in these areas. Regulated by the local microenvironment, MSCs perform biological functions such as anti-inflammatory effects and tissue repair 19 . This “active targeting” property allows MSCs to overcome the limitations of traditional drugs, which often suffer from systemic distribution and low local concentration. As a result, MSCs enable precise delivery to lesion sites, improving therapeutic efficiency and minimizing systemic side effects. Furthermore, this ability can be harnessed to deliver various genes. For instance, Han et al. 20 used MSCs as carriers for tumor-targeted suicide genes to treat lung metastases, while Kim et al. 21 created MSC-IFNβ gene complexes, both achieving promising therapeutic outcomes.

The anti-inflammatory mechanisms of MSCs

Secretion of anti-inflammatory cytokines

The anti-inflammatory and immune regulatory functions of MSCs rely significantly on their extensive “cytokine secretion network.” By precisely releasing a variety of anti-inflammatory cytokines and immune regulatory factors, MSCs can effectively target and regulate the inflammatory microenvironment, inhibit excessive immune responses, and play a crucial role in treating various inflammation-related diseases 22 . These key factors are not secreted randomly; instead, they form a synergistic “cytokine combination,” which includes Tumor Necrosis Factor-α Stimulated Gene 6 (TSG-6), Prostaglandin E2 (PGE2), interleukin-10 (IL-10), indoleamine 2,3-dioxygenase (IDO), and hepatocyte growth factor (HGF). Each of these factors participates in regulating inflammation through unique molecular mechanisms. Under inflammatory stimulation, they create a dynamically adjusted “anti-inflammatory cytokine spectrum” that ensures precise and efficient inhibition of inflammatory responses 23 .

As one of the key anti-inflammatory factors secreted by MSCs, TSG-6 functions as an “early anti-inflammatory sentinel” in situations of inflammatory injury. Initially discovered to be inducibly expressed by TNF-α, TSG-6 primarily acts by binding to hyaluronic acid (HA) in the inflammatory microenvironment, forming an HA-TSG-6 complex. This complex significantly inhibits the excessive activation of the complement system, reduces the release of complement components, and prevents tissue damage mediated by the complement pathway 24 . In acute inflammatory conditions, such as acute lung injury and traumatic inflammation, TSG-6 secreted by MSCs can quickly reach the site of injury and block the “cascade amplification effect” of inflammation through the mechanisms mentioned above, thereby creating favorable conditions for subsequent tissue repair 25 . PGE2 is another crucial anti-inflammatory factor secreted by MSCs, and its role in regulating immune cell functions has been well established. Particularly, it inhibits T-cell activation and proliferation. In research focused on preventing and treating GVHD, blocking the PGE2 secretion pathway of MSCs—such as by using cyclooxygenase-2 inhibitors—significantly weakens their inhibitory effect on GVHD, confirming the central role of PGE2 in the anti-inflammatory actions of MSCs 26 .

Importantly, the cytokine secretion by MSCs is not static but forms a “dynamic response” under inflammatory stimulation. When MSCs detect pro-inflammatory signals in the inflammatory environment, intracellular inflammatory signaling pathways (such as NF-κB and MAPK) are activated, regulating the transcription and secretion of downstream anti-inflammatory cytokines. This activation leads to a significant increase in the expression levels of factors like TSG-6 and PGE2, creating a “unique anti-inflammatory cytokine profile” tailored to specific diseases 27 . This response mechanism—“the stronger the inflammation, the more secretion”—allows MSCs to match the intensity of inflammation precisely while avoiding potential side effects from excessive cytokine secretion in non-inflammatory states 28 .

From the perspective of signaling pathway regulation, the anti-inflammatory factors secreted by MSCs directly target and inhibit core pro-inflammatory signaling pathways, effectively achieving a “blockade at the source.” For example, PGE2 can phosphorylate IκBα, the inhibitory protein of NF-κB, by activating the EP2/EP4-cAMP-PKA pathway. This phosphorylation keeps IκBα in a phosphorylated state, preventing NF-κB from being released from the cytoplasm and entering the nucleus to initiate the expression of pro-inflammatory genes 29 . More importantly, MSCs can establish a “positive feedback anti-inflammatory loop” with the inflammatory microenvironment. Pro-inflammatory cytokines, such as TNF-α and IL-6, first activate MSCs, prompting them to secrete more chemokines (like CXCL12 and CCL2) and immunosuppressive factors (including PGE2, IDO, and IL-10). The chemokines attract additional MSCs and endogenous anti-inflammatory cells, such as T regulatory (Treg) cells and M2 macrophages, to the site of inflammation, further enhancing the secretion of anti-inflammatory factors. On the other hand, immunomodulatory factors inhibit the activation of pro-inflammatory cells, reduce the release of pro-inflammatory cytokines, and amplify the anti-inflammatory effect by promoting M2 macrophage polarization 30 , 31 . This positive feedback loop ( Fig. 2 ) enables the anti-inflammatory effects of MSCs to “self-reinforce,” ensuring that these effects remain efficient even in the presence of persistent inflammation until the inflammation subsides and the microenvironment returns to homeostasis.

Mitochondrial transfer and metabolic reprogramming mechanisms

In recent years, researchers have identified mitochondrial transfer as an additional mechanism by which MSCs exert their anti-inflammatory effects. In an inflammatory microenvironment, MSCs can recognize damaged or overactive immune cells, such as CD4 + T cells, and transfer their functional mitochondria—capable of complete respiratory chain function and normal oxidative phosphorylation—into these target cells 32 . Under inflammatory conditions, CD4 + T cells often experience mitochondrial structural damage, including fragmented cristae and decreased membrane potential, or functional impairment characterized by insufficient ATP production and the excessive accumulation of reactive oxygen species (ROS). This damage typically results from oxidative stress and an increased metabolic load. However, the functional mitochondria derived from MSCs can quickly replenish the mitochondrial pool in the target cells, restoring their normal energy metabolism 33 . This process has two key benefits. First, it enhances ATP production to meet the energy demands needed for immune cell activation, thereby preventing dysfunction caused by energy deficiency. Second, it effectively inhibits the excessive activation of CD4 + T cells by clearing excess ROS and suppressing abnormal mitophagy activation. This action reduces the secretion of pro-inflammatory cytokines, such as IFN-γ and TNF-α, and hinders the escalation of inflammatory responses at their source 34 , 35 .

Mitochondrial transfer can occur through structures like tunneling nanotubes (TNTs) or extracellular vesicles (EVs). TNTs are tubular structures, measuring 50–1000 nm in diameter, that form through the extension of the cell membrane. They create direct cytoplasmic connections between MSCs and damaged cells, allowing for the active transport of mitochondria from MSCs to recipient cells. This process relies on the dynamic regulation of cytoskeletal proteins, such as microtubules and actin, as well as mitochondrial membrane transport proteins like Miro1, ensuring high targeting efficiency 36 . In contrast, EV-mediated mitochondrial transfer involves MSCs packaging mitochondria into vesicles, known as Mitochondria-Enriched EVs, which are then released into the extracellular microenvironment via paracrine signaling. These vesicles bind to specific receptors on the surface of recipient cells, such as integrins and glycoproteins, and deliver mitochondria through processes like endocytosis or membrane fusion. Compared to TNTs, EV-mediated mitochondrial transfer can reach target cells over greater distances. In addition, the vesicle structure helps protect the mitochondria from external environmental damage, thereby enhancing their stability and survival time in vivo . Together, these two pathways ( Fig. 3 ) ensure efficient mitochondrial transfer in various inflammatory microenvironments 37 .

The therapeutic potential of mitochondrial transfer has been validated through various animal and cell experiments under specific pathological conditions. In models of acute pancreatitis, mitochondrial transfer by MSCs protects cells from damage caused by the abnormal opening of mitochondrial permeability transition pores (mPTPs) 38 . In models of pulmonary GVHD, damaged alveolar epithelial cells and pulmonary vascular endothelial cells release “damage signals” (such as HMGB1 and ATP) to recruit MSCs to migrate to lung tissues. Through mitochondrial transfer, MSCs provide protective effects in two key ways: First, they inhibit the excessive activation of donor CD4 + T cells, reducing the secretion of pro-inflammatory factors and alleviating T-cell-mediated immune damage. Second, they directly repair the mitochondrial function of alveolar epithelial cells and endothelial cells, decrease oxidative stress levels, and inhibit the process of epithelial-mesenchymal transition (EMT), which helps reduce lung tissue fibrosis 39 . Current studies have shown that pretreating MSCs to enhance their mitochondrial transfer capacity—such as by overexpressing the Miro1 protein—can further improve their preventive and therapeutic effects on pulmonary GVHD. This insight offers a novel strategy for treating pulmonary complications following HSCT 40 .

Exosome-mediated miRNA regulatory network

The anti-inflammatory effect of MSCs through the secretion of exosomes (MSC-Exo) is one of the important mechanisms of their immune regulatory functions. In terms of structural and compositional characteristics, MSC-Exo are single-layer membrane vesicles with a diameter ranging from 30 to 150 nm. Their membrane structure originates from the cell membrane of MSCs, thus retaining specific surface markers of the parent cells, such as the tetraspanin proteins CD9, CD63, and CD81. These markers are not only key criteria for identifying exosomes but also ensure the precise targeting of MSC-Exo to cells at inflammatory sites through specific binding with receptors on the surface of target cells 41 . Inside the vesicles, MSC-Exo encapsulate a variety of bioactive substances from MSCs, forming a “multi-functional regulatory system.” In addition to proteins (such as heat shock protein HSP70 and precursor proteins of anti-inflammatory cytokines) and lipids (such as ceramide and phosphatidylcholine involved in membrane signaling), nucleic acids such as microRNAs (miRNA) and nuclear RNAs (nRNA) are the core functional molecules exerting anti-inflammatory effects 42 . In addition to the targeted regulation by specific miRNAs, the reshaping of macrophage function by MSC-Exo is also an important supplementary mechanism for their anti-inflammatory effects. In treatments with exosomes from bone marrow-derived MSCs, upregulation of macrophage markers such as CD206 and anti-inflammatory cytokines can be observed, promoting the polarization of macrophages toward the M2 phenotype. At the same time, the production of ROS is reduced, inhibiting oxidative stress-induced cellular damage 43 . This regulation of macrophage polarization enables MSC-Exo to not only directly inhibit inflammatory responses but also accelerate the healing of damaged tissues by promoting the anti-inflammatory and reparative functions of macrophages, forming a synergistic “anti-inflammatory-repair” effect.

The specific miRNAs enriched in MSC-Exo target different inflammatory signaling pathways, forming the core mechanism network of their anti-inflammatory effects. Among them, three miRNAs play particularly crucial roles ( Fig. 4 ):

miR-21-5p: By targeting and inhibiting the activation of programmed cell death protein 4 (PDCD4), miR-21-5p precisely blocks the NF-κB pathway, thereby suppressing the release of pro-inflammatory cytokines. In an acute lung injury model, miR-21-5p delivered by MSC-Exo can precisely target alveolar macrophages, reducing the damage caused by macrophages to alveolar epithelial cells, ultimately alleviating pulmonary edema, hemorrhage, and inflammatory infiltration in lung tissue, and improving lung function 44 , 45 .

miR-146a: This miRNA downregulates the expression of the TLR4/MyD88/NF-κB signaling axis in the inflammatory environment, inhibiting excessive immune activation. In an LPS-induced sepsis model, after the infusion of MSC-Exo rich in miR-146a, the protein levels of TLR4 and MyD88 in peripheral blood mononuclear cells and peritoneal macrophages of mice significantly decreased, the phosphorylation level of NF-κB p65 was reduced, and the secretion of pro-inflammatory cytokines was decreased. In addition, the recovery of body temperature and weight in mice was accelerated, and survival rates were significantly improved 46 , 47 .

miR-181a-5p: By targeting the STAT3 pathway, miR-181a-5p regulates the balance between Th17 and regulatory T cells, promoting the differentiation of anti-inflammatory regulatory T cells. In an autoimmune arthritis model, after the infusion of MSC-Exo carrying miR-181a-5p, the proportion of Th17 cells in the synovial tissue of mouse joints significantly decreased, while the proportion of Treg cells increased. The secretion of IL-17 was reduced, and the secretion of IL-10 increased, leading to a significant alleviation of joint swelling and cartilage damage 48 .

Moreover, MSC-Exo can be widely distributed throughout the body via the blood and lymph circulatory systems. Their membrane structure effectively protects internal active substances from degradation by nucleases and proteases in body fluids, ensuring they remain biologically active until reaching target cells, thereby laying the foundation for their subsequent effects 49 .

Mechanisms of direct interaction with immune cells

In the immunomodulatory network of MSCs, intercellular contact serves as a direct and precise mode of action. It works in synergy with the paracrine effects mediated by secreted factors to jointly regulate the function and differentiation of immune cells, playing an indispensable role in maintaining immune homeostasis and inhibiting excessive inflammatory responses. MSCs can inhibit the proliferation of T cells (especially Th1 and Th17 subsets) and the release of pro-inflammatory factors (e.g. IFN-γ, TNF-α) through intercellular contact, while promoting the differentiation of Treg cells and enhancing immune tolerance 50 .

Th1 cells mainly mediate cellular immunity by secreting pro-inflammatory factors such as IFN-γ and TNF-α, and are involved in pathogen clearance and autoimmune inflammation. Th17 cells promote neutrophil infiltration and tissue inflammatory damage by secreting IL-17 and IL-22 51 . When MSCs come into contact with Th1/Th17 cells, key molecules on their cell membrane bind to receptors on the T-cell surface, directly blocking the activation signaling pathways of T cells:

By binding to CD40L on the T-cell surface, the activation of the CD40/CD40L pathway is inhibited, reducing the “second signal” required for T-cell activation, thereby suppressing the proliferation of Th1/Th17 cells 52 .

MSCs express ligands for the Notch receptor (such as Jagged1 and Delta-like 1) on their surface. When these ligands bind to the Notch receptor on the surface of Th1/Th17 cells, they can regulate the activity of the Notch signaling pathway, blocking the pro-inflammatory functions of Th1/Th17 cells 53 .

In vitro experiments have shown that when MSCs are co-cultured with activated Th1/Th17 cells, and Transwell chambers are used to block direct cell-to-cell contact as a control, the proliferation rate of Th1/Th17 cells in the direct contact group is reduced by 40%–60% compared to the control group, and the concentrations of IFN-γ, TNF-α, and IL-17 in the cell culture medium are significantly decreased 54 . When cell-to-cell contact is blocked, the inhibitory effect of MSCs on Th1/Th17 cells is significantly weakened, proving that direct cell-to-cell contact is a key mechanism by which MSCs inhibit pro-inflammatory T-cell subtypes.

Treg cells, as “negative regulators” of immune regulation, inhibit the activation and proliferation of effector T cells through the secretion of anti-inflammatory cytokines such as IL-10 and TGF-β, thereby maintaining immune tolerance. MSCs provide “signaling support” for the differentiation of Treg cells through cell-to-cell contact, primarily by activating the TGF-β/Smad signaling pathway and signal transduction mechanisms mediated by HLA-G molecules. In a systemic lupus erythematosus model, after the infusion of MSCs, the proportion of Treg cells in the spleen and lymph nodes of mice significantly increased, and the secretion of IL-10 was enhanced, while the proportion of Th1/Th17 cells and the levels of pro-inflammatory cytokines decreased. If antibodies were used to block HLA-G or mTGF-β on the surface of MSCs, their ability to promote the differentiation of Treg cells was significantly weakened, further proving the key role of cell-to-cell contact in the regulation of Treg cells by MSCs.

MSCs can induce macrophages to shift from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype, thereby reducing the secretion of pro-inflammatory cytokines such as IL-1β and IL-6, while increasing the release of anti-inflammatory cytokines like IL-10 55 . MSCs achieve this macrophage polarization shift by activating the CD200/CD200R pathway and regulating the ICAM-1/LFA-1 pathway 56 . MSCs can actively sense changes in the inflammatory microenvironment and dynamically adjust their immune regulatory capabilities through cell-to-cell contact mechanisms 57 . They also work in concert with secreted factors to form a multi-layered immune regulatory network. This interaction is bidirectional: not only can MSCs regulate the functions of immune cells, but the inflammatory signals released by immune cells can also act back on MSCs, enhancing their immune regulatory abilities 15 . This “positive feedback” mechanism ensures that MSCs can function efficiently at sites of inflammation.

The inflammatory pathological characteristics of HSCT-associated complications

The inflammatory cascade of GVHD

GVHD is the most common and life-threatening inflammation-related complication after HSCT. The pathological process of GVHD involves a complex inflammatory cascade, triggered by mature donor T cells attacking host thymic epithelial cells, causing severe tissue damage. This mechanism plays a critical role in the transition from aGVHD to cGVHD 58 .

The core mechanism of aGVHD occurrence is that activated donor T cells trigger an “inflammatory cascade,” accompanied by the massive release of pro-inflammatory factors and infiltration of immune cells 59 . During the pre-transplant chemo-radiotherapy conditioning phase, tissue damage leads to the release of “initiating factors” such as TNF-α and IL-1β, which activate antigen-presenting cells. Antigen-presenting cells further activate donor T cells, inducing them to secrete cytokines such as IFN-γ, IL-2, and IL-17, forming a positive feedback loop to exacerbate inflammation 60 . Inflammation mainly affects target organs such as the skin, intestines, and liver: basal cells of the skin epidermis undergo apoptosis, and lymphocytes (CD4+/CD8+ T cells) infiltrate the dermis, leading to skin damage; intestinal mucosal epithelium undergoes necrosis, atrophy, and shedding, with a large number of inflammatory cells (T cells, macrophages) accumulating in the lamina propria, accompanied by intestinal barrier damage that further amplifies inflammation, leading to diarrhea and protein loss; inflammatory factors damage the bile ducts in the portal area of the liver, and a large number of lymphocytes infiltrate the bile ducts, resulting in cholestasis and elevated bilirubin, which eventually progresses to cholangitis 61 – 63 .

Chronic GVHD is the main cause of death in patients without relapse of the primary disease after HSCT. The core mechanism of its occurrence lies in the coexistence of inflammation and post-inflammatory fibrosis, combined with the superposition of B cell activation, autoantibody production, and other factors, which disrupts tissue repair. In the early stage of cGVHD, lymphocyte infiltration in target organs is the primary feature; in the late stage, it is accompanied by the activation of fibroblasts, which secrete collagen fibers and lead to tissue fibrosis. During this process, B cells become overactivated, produce autoantibodies, and attack self-tissues; Th2 cells secrete cytokines such as IL-4 and IL-13, which promote eosinophil infiltration and fibrosis 64 . Unlike aGVHD, cGVHD mostly affects the oral mucosa (presenting with dryness and ulcers), lacrimal/salivary glands (manifesting as Sjögren’s syndrome-like features), and lungs (such as bronchiolitis obliterans) 65 . The degree of inflammation varies significantly depending on the organ and individual, exhibiting heterogeneity characterized by multi-organ involvement ( Fig. 5 ).

TA-TMA

TA-TMA is a rare yet devastating complication of HSCT, characterized by an incidence of 5% to 15% among recipients, with a mortality rate exceeding 60% in severe cases—making it one of the most life-threatening non-relapse complications post-transplant 66 . Rooted in profound vascular endothelial injury, TA-TMA’s core pathological hallmark lies in “vascular endothelial inflammatory damage,” a cascade that intricately intersects with dysregulated coagulation and complement activation, ultimately leading to microvascular thrombosis, end-organ ischemia, and progressive dysfunction. Unlike other HSCT-related complications, TA-TMA exhibits a distinct predilection for damaging the microvasculature of vital organs, with the kidneys being the most frequently and severely affected, though the brain, lungs, and gastrointestinal tract can also be involved 67 .

The pathogenesis of TA-TMA is multi-factorial, with the pre-transplant conditioning phase serving as a critical initiating trigger. High-dose chemotherapy (e.g. busulfan, cyclophosphamide) and total body irradiation—cornerstones of HSCT conditioning—directly induce oxidative stress and DNA damage in vascular endothelial cells, disrupting their structural integrity and physiological function 68 . Beyond direct cytotoxicity, secondary insults further amplify endothelial injury: acute graft-versus-host disease (aGVHD) triggers systemic inflammation that targets vascular endothelium, while post-transplant infections (viral, bacterial, or fungal) release pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) that activate endothelial cells via toll-like receptor (TLR) signaling. Once activated, endothelial cells undergo a phenotypic shift: they upregulate the expression of adhesion molecules (e.g. VCAM-1, E-selectin, ICAM-1) that recruit circulating leukocytes (neutrophils, monocytes) to the vessel wall and secrete procoagulant factors (e.g. tissue factor, von Willebrand factor [vWF]) while downregulating anticoagulant proteins (e.g. thrombomodulin, protein C) 69 . This pro-inflammatory, pro-thrombotic phenotype disrupts the delicate balance of the vascular microenvironment, setting the stage for subsequent pathological events.

The kidneys are the primary target organ of TA-TMA, reflecting their dense microvascular network and high susceptibility to microthrombotic injury 70 . Pathologically, renal TA-TMA is characterized by glomerular capillary microthrombi composed of platelets and fibrin, endothelial cell swelling and detachment from the basement membrane, and widening of the subendothelial space. These changes lead to impaired glomerular filtration, resulting in clinical manifestations such as proteinuria (often in the nephrotic range), hematuria, hypertension, and progressive acute kidney injury (AKI) 71 . If left untreated, the ongoing microvascular damage and ischemia can progress to irreversible renal fibrosis, culminating in end-stage renal disease (ESRD) that requires long-term dialysis or renal transplantation 72 . Notably, extrarenal manifestations may also occur, including neurological symptoms (e.g. headache, seizures, altered mental status) due to cerebral microthrombosis, gastrointestinal bleeding or ischemia, and pulmonary hypertension—all of which contribute to the high mortality of severe TA-TMA 73 .

Beyond the core cascade of endothelial injury, thrombosis, and inflammation, TA-TMA pathogenesis is further complicated by dysregulated complement activation and impaired MSCs function. A subset of TA-TMA patients harbors congenital or acquired deficiencies in complement regulatory proteins (e.g. CD55, CD59, factor H), which normally inhibit uncontrolled activation of the alternative complement pathway 67 . In these individuals, endothelial injury triggers excessive alternative complement pathway activation, leading to the formation of membrane attack complexes (MACs) that directly lyse endothelial cells and amplify vascular inflammation 74 . This complement-mediated damage not only exacerbates the core TA-TMA pathology but also impairs the survival and function of infused MSCs—cells with potent immunomodulatory and endothelial repair capabilities 75 . Preclinical and clinical evidence suggests that the pro-inflammatory, complement-activated microenvironment of TA-TMA reduces MSCs viability, inhibits their homing to damaged vasculature, and blunts their ability to secrete anti-inflammatory cytokines (e.g. PGE2, IL-10) and pro-angiogenic factors 27 . This impaired MSCs function creates a “therapeutic gap,” as the body’s intrinsic repair mechanisms are unable to counteract the ongoing endothelial damage, further propagating the disease course ( Table 1 ).

The inflammatory microenvironment of VOD

VOD is a liver-specific complication that occurs after HSCT, characterized by occlusive inflammation and fibrosis caused by damage to the endothelial cells of the hepatic small veins and sinusoids. If not intervened in a timely manner, it can progress to liver failure or even death. The incidence of VOD after HSCT is approximately 5%–20%, while the mortality rate among patients with severe disease exceeds 80% 76 . High-dose chemotherapy or total body irradiation prior to HSCT is the primary contributing factor, as these treatments can directly damage the sinusoidal endothelial cells and small venous endothelial cells of the liver, occluding the lumens of hepatic sinusoids and small veins 77 . After endothelial cell injury within the hepatic lobules in the periportal region, pro-inflammatory factors and procoagulant factors are released; neutrophils and macrophages infiltrate the periportal region, further damaging endothelial cells and hepatocytes, and forming a vicious cycle of “injury—inflammation—thrombosis.” Clinical symptoms such as jaundice, hypoalbuminemia, and ascites occur 78 . In the inflammatory microenvironment of VOD, cholangiocyte stem cells, as a liver-specific stem cell population, have significantly impaired regenerative capacity. Clinical data show that patients with VOD may experience a recurrence of inflammatory reactions when immunosuppressants are reduced, manifesting as recurrent fever accompanied by elevated inflammatory markers. Notably, MSCs in the hepatic microenvironment of patients with VOD exhibit a unique chemokine receptor expression profile, which may affect the therapeutic efficacy of exogenous MSCs 79 .

Research on the application of MSCs in HSCT

Promoting hematopoietic reconstitution

Delayed hematopoietic reconstitution is one of the complications of HSCT, which may lead to an increased risk of infection and bleeding, seriously affecting the quality of patients’ prognosis. MSCs can differentiate into structural components that form the hematopoietic niche, such as osteoblasts, adipocytes, and vascular endothelial cells. For example, osteoblasts are located on the surface of the endosteum, forming an “endosteal niche” that provides a quiescent environment for HSCs; vascular endothelial cells form a “vascular niche” that supports the proliferation and homing of HSCs 80 , 81 . Co-transplantation of MSCs and HSCs can reconstitute the bone marrow microenvironment. As an important component of bone marrow stromal cells, MSCs can repair the bone marrow niche damaged by chemotherapy or radiotherapy and provide a scaffold for the colonization and survival of HSCs, which can shorten the engraftment time of neutrophils and platelets by approximately 3–5 days. A systematic review of 47 clinical studies (2000–2025, n = 1777) showed that co-infusion of MSCs and HSCs can shorten the engraftment time of neutrophils and platelets to 13.96 days and 21.61 days, respectively, without increasing the risk of recurrence or GVHD 82 .

Mitochondrial or metabolite transfer mediated by Connexin-43 gap junctions can reduce the level of ROS in HSCs and accelerate bone marrow niche revascularization. Adhesive junctions formed by N-cadherin between the surface of MSCs and the surface of long-term HSCs maintain HSC quiescence and inhibit ROS-induced stem cell exhaustion 83 . Recent work shows that MSC-derived microvesicles upregulate Jagged-1 and Notch-2 expression in hematopoietic stem/progenitor cells, activating the Jagged-1-Notch axis and enhancing self-renewal while restraining differentiation 84 .

MSCs can secrete hematopoietic growth factors (such as granulocyte colony-stimulating factor, erythropoietin, and chemokines) to support the proliferation and differentiation of HSCs 85 . Stem cell factor, Fms-like tyrosine kinase 3 ligand, thrombopoietin, and other factors secreted by MSCs can directly stimulate the proliferation of HSCs and inhibit their apoptosis 86 . For example, researchers have demonstrated through clinical and experimental studies that co-transplantation of MSCs can increase the number of CD34+ cells in peripheral blood and confirmed that the binding of stem cell factor (SCF) to the c-Kit receptor on the surface of HSCs can maintain the survival and self-renewal of HSCs 87 . MSCs regulate the tendency of hematopoietic differentiation by secreting granulocyte colony-stimulating factor, erythropoietin, macrophage colony-stimulating factor, and so on, and directionally promote the differentiation and maturation of hematopoietic cells such as granulocytic lineage, macrophage lineage, and erythrocytic lineage. MSCs can also secrete insulin-like growth factor, transforming growth factor-β, and other factors to regulate processes such as glucose uptake and energy metabolism of HSCs, thereby affecting the metabolic state of the bone marrow microenvironment, providing appropriate nutritional support for HSCs, and promoting their growth 88 .

MSCs can promote the migration of HSCs from peripheral blood to the bone marrow hematopoietic niche and their colonization, which in turn facilitates the homing of HSCs. MSCs can promote the migration of HSCs from peripheral blood to the bone marrow hematopoietic niche and their colonization, which in turn facilitates the homing of HSCs. MSCs are capable of secreting chemokines: after HSCT, MSCs release stromal cell-derived factor-1 (SDF-1). MSCs are capable of secreting chemokines: after HSCT, MSCs release SDF-1, which binds to the CXCR4 receptor on the surface of HSCs to form a chemical gradient, guiding the migration of HSCs to the bone marrow and accelerating their colonization 89 . In 2013, animal experiments conducted by researchers confirmed that overexpression of stromal cell-derived factor-1 (SDF-1) in MSCs can accelerate platelet recovery 90 . Immunosuppression after transplantation tends to cause infections by bacteria, viruses, and other pathogens, triggering an inflammatory response in the body. Under the stimulation of inflammatory or injury signals, MSCs can upregulate the expression of adhesion molecules such as intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1), thereby enhancing the ability to capture and anchor homing HSCs 91 . Regulating bone marrow vascular permeability is one of the essential steps in the process of hematopoietic reconstitution. By secreting factors such as vascular endothelial growth factor (VEGF), MSCs can promote an increase in vascular permeability, extracellular matrix denaturation, migration and proliferation of vascular endothelial cells, and angiogenesis 27 . These effects lead to a transient increase in the permeability of bone marrow vascular endothelium, facilitating HSCs to cross the vascular wall and enter the hematopoietic niche ( Table 2 , Fig. 6 ).

Prevention and treatment of GVHD

GVHD is one of the most severe complications after HSCT, triggered by donor T cells attacking the recipient’s tissues, and manifests as damage to multiple organs such as the skin, intestines, and liver. However, MSCs have shown significant potential in the treatment of GVHD following HSCT. The main mechanisms are as follows: MSCs can alleviate the inflammatory response of GVHD by inhibiting the activation of donor T cells, promoting the proliferation of regulatory T cells, regulating the cytokine balance (e.g. reducing TNF-α and increasing IL-10), and decreasing the release of perforin/granzyme by tissue-resident CD8+ T cells 92 .

Clinical studies have confirmed that bone marrow–derived MSCs exhibit significant efficacy in patients with aGVHD. Among relevant products, Ryoncil™ (remestemcel-L), a human bone marrow–derived MSC product, has entered the clinical evaluation phase 93 . As of 2020, more than 70 clinical trials of MSCs for steroid-refractory aGVHD have been completed or are ongoing worldwide 94 . Among these, the phase III results of Ryoncil™ (developed by Mesoblast) in 2024 showed that bone marrow–derived mesenchymal stem cells achieved an overall complete response (CR) rate of 30% and increased 6-month overall survival by 57% compared with historical controls 95 . Umbilical cord-derived MSCs have demonstrated enhanced therapeutic efficacy after interferon-gamma (IFN-γ) gene transfection. A study involving 86 patients with grade III–IV steroid-refractory aGVHD showed that umbilical cord mesenchymal stem cells treatment yielded encouraging clinical responses 96 . Prophylactic use of MSCs after haploidentical HSCT can significantly reduce the incidence of cGVHD. Studies have indicated that repeated infusions of umbilical cord mesenchymal stem cells in the early post-haploidentical HSCT period (on days +45 and +100) can effectively prevent the development of cGVHD 3 . This prophylactic strategy has also shown promising prospects in patients with severe aplastic anemia ( Table 3 ).

To enhance the therapeutic efficacy of MSCs, researchers are actively exploring combined treatment regimens. The regimen of MSCs combined with basiliximab and calcineurin inhibitors, used as second-line therapy for steroid-refractory aGVHD, has demonstrated superior efficacy compared to monotherapy in randomized phase III clinical trials 97 . In the context of haploidentical transplantation, the regimen of MSCs combined with basiliximab for the treatment of steroid-refractory aGVHD has also achieved significant effects 98 . In addition, the combined use of MSCs and immunosuppressants can produce a synergistic effect, jointly inhibiting excessive immune responses through different mechanisms. Notably, exosomes derived from MSCs can mimic the biological functions of their parent cells, alleviating GVHD symptoms while preserving the anti-leukemic effect, providing a new perspective for the development of cell-free therapeutic strategies 99 ( Fig. 7 ).

MSCs reduce the risk of infection after HSCT

After HSCT, patients’ immune defense functions are suppressed, making them prone to bacterial, viral, or fungal infections. The anti-inflammatory and immunomodulatory effects of MSCs can reduce the consumption of immune cells caused by excessive inflammation, while enhancing anti-infective capacity by promoting the functions of macrophages and natural killer cells 100 . MSCs can reduce the risk of post-transplant bacterial/viral infections by upregulating the antimicrobial peptide LL-37 and enhancing the phagocytic function of macrophages. In a 2025 clinical study on patients with severe COVID-19, results showed that MSCs significantly reduced the levels of C-reactive protein, TNF-α, and IL-6, and improved the oxygenation index—providing a reference for the combined treatment of post-transplant infectious complications 101 . In addition, antimicrobial peptides and other substances secreted by MSCs can also directly inhibit pathogens. In vitro experiments by Krasnodembskaya et al. demonstrated that human bone marrow–derived MSCs and their conditioned medium inhibited the growth of Escherichia coli by 40% and Pseudomonas aeruginosa by 70% within 6 h. This effect was dependent on the antimicrobial peptide LL-37 secreted by MSCs; when LL-37 was silenced with siRNA, the antimicrobial activity almost disappeared 102 .

MSCs secrete factors such as VEGF and fibroblast growth factor (FGF), which accelerate the healing of respiratory and gastrointestinal epithelium damaged by radiotherapy and/or chemotherapy, thereby reducing the chance of bacterial infection 103 . Latest clinical studies have found that MSC treatment can restore intestinal alpha diversity, reduce potential pathogenic bacteria, and indirectly lower the risk of bloodstream infection. Two HSCT-related prospective cohorts ( n = 128 and n = 94) showed that prophylactic infusion of MSCs (1 × 10 6 cells/kg on days +1 and +8) reduced the incidence of bacteremia within 100 days after transplantation from 27% to 11%, and the incidence of fungal infection from 9% to 2%, with no MSC-related adverse reactions observed 3 . Without compromising the body’s immunity, MSCs significantly reduce the risk of infection after HSCT and may serve as a supplement or alternative to standard infection prevention protocols in the future.

Limitations and challenges of MSCs therapy in HSCT

Despite the promising preclinical and clinical evidence, several limitations hinder the widespread application of MSCs in HSCT. First, MSCs products exhibit significant heterogeneity due to differences in tissue origin (bone marrow, umbilical cord, adipose tissue), donor variability, isolation methods, and culture conditions. This variability leads to inconsistent therapeutic outcomes and complicates cross-study comparisons 104 . At present, the lack of unified cell culture standards and quality control systems results in significant differences in MSC products obtained from different research centers. In addition, cell senescence that may occur during conventional expansion and culture further exacerbates product heterogeneity 105 . Second, MSCs possess dual immunomodulatory effects—while they typically suppress inflammation, under certain pathological conditions (e.g. high concentrations of pro-inflammatory cytokines) they may paradoxically promote inflammation or contribute to fibrosis via the secretion of pro-fibrotic factors such as TGF-β 106 . This functional plasticity makes the prediction of clinical efficacy more complex. Third, the short in vivo survival time of infused MSCs (often <72 h) limits their sustained therapeutic efficacy. Most intravenously administered MSCs become trapped in the lungs and are cleared rapidly, reducing their ability to home to target tissues 107 . Fourth, the lack of standardized protocols for dosing, timing, and administration routes leads to heterogeneity in clinical outcomes. Optimal treatment regimens (e.g. single vs. repeated infusions, cell dose) have not been established 108 .

Fifth, many clinical studies suffer from small sample sizes, lack of control groups, and short follow-up periods, limiting the generalizability and long-term safety assessment of MSCs therapy. Finally, the functional plasticity of MSCs in response to the host microenvironment—especially in the context of inflammation, aging, or comorbidities—adds another layer of complexity. Future research should focus on identifying predictive biomarkers, optimizing cell manufacturing, and conducting well-designed multicenter randomized controlled trials to address these challenges.

Conclusion and additional future directions

MSCs have emerged as a highly promising adjuvant therapy in the field of HSCT due to their significant anti-inflammatory and immunomodulatory properties. Basic research has clarified that MSCs exert anti-inflammatory effects through multiple mechanisms, including the secretion of cytokines such as prostaglandin E2 (PGE2) and interleukin-10 (IL-10), the regulation of networks via miRNA transfer through exosomes, and direct interactions with immune cells. These findings provide a solid theoretical basis for clinical applications. Through the aforementioned mechanisms, MSCs demonstrate multiple potentials in HSCT, such as preventing GVHD, promoting hematopoietic reconstitution, and reducing the risk of infection. With the deepening of basic research and clinical trials, MSCs are expected to become an important tool for adjuvant therapy in HSCT, further improving the success rate of transplantation and the quality of life of patients.

In the future, an effective translational medicine research platform can be established to address the aforementioned limitations and deficiencies. For instance, organoid models and 3D culture systems can be developed to better simulate the in vivo microenvironment, and multi-omics technologies can be used to identify biomarkers that predict therapeutic responses. Focus can also be placed on genetic modification engineering: overexpressing specific cytokines can effectively promote the transformation of macrophages to an anti-inflammatory phenotype, thereby avoiding the dual anti-inflammatory and pro-inflammatory effects of MSCs. Recent studies have confirmed that the combination of the CRISPR-Cas9 gene editing system and MSC co-culture systems can optimize the transplantation effect of HSCs 109 . In addition, non-viral vector-mediated multi-gene co-transfection technology can enhance the potential of MSCs in treating complex diseases 110 . Furthermore, greater efforts should be made to strengthen the collaborative innovation between basic research and clinical practice, promote the translation between basic research and clinical applications, and establish multi-level policy support systems to facilitate mechanism research, biomarker development, and the optimization of combined treatment strategies—ultimately advancing the clinical application of MSCs in HSCT.

Acknowledgments

The authors thank all collaborators for their valuable contributions to the development of this work.

Footnotes

ORCID iD: Li Xu https://orcid.org/0000-0002-4223-5532

Ethical Considerations: Not applicable.

Author Contributions: CZ, SM: Conceptualization, Methodology, Investigation, Writing – Original Draft, Writing – Review & Editing. WJ, NM: Data Curation, Formal Analysis. LX: Supervision, Project Administration, Funding, Acquisition. All authors read and approved the final manuscript.

Funding: The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Scientific Research Projects of the Education Department of Anhui Province (2025AHGXZK31294, 2025AHGXZK31426) and Scientific Research Project of Anhui Provincial Health Commission(AHWJ2022a003).

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement: Data sharing is not applicable to this article as no new datasets were generated or analyzed during the current study. Further information can be requested from the corresponding author.

Use of Artificial Intelligence: During the preparation of this work, the authors used Deepseek only for language polishing. No scientific data were generated or modified using AI. The authors take full responsibility for the content of the publication.

Statement of Human and Animal Rights: This study is a review and does not involve human or animal participants.

Statement of Informed Consent: There are no human subjects in this article and informed consent is not applicable.

References

1. Aljagthmi AA, Abdel-Aziz AK. Hematopoietic stem cells: understanding the mechanisms to unleash the therapeutic potential of hematopoietic stem cell transplantation. Stem Cell Res Ther. 2025;16(1):60.

2. Tamaki M, Akahoshi Y, Inamoto Y, Morita K, Uchida N, Doki N, Tanaka M, Nishida T, Ohigashi H, Nakamae H, Onizuka M, et al. Associations between acute and chronic graft-versus-host disease. Blood Adv. 2024;8(16):4250–61.

3. Huang R, Chen T, Wang S, Wang J, Su Y, Liu J, Zhang Y, Ma X, Wen Q, Kong P, Zhang C, et al. Mesenchymal stem cells for prophylaxis of chronic graft-vs-host disease after haploidentical hematopoietic stem cell transplant: an open-label randomized clinical trial. JAMA Oncol. 2024;10(2):220–26.

4. Lee H, Myoung H, Kim SM. Review of two immunosuppressants: tacrolimus and cyclosporine. J Korean Assoc Oral Maxillofac Surg. 2023;49(6):311–23.

5. Wang A, Xu Y, Fei Y, Wang M. The role of immunosuppressive agents in the management of severe and refractory immune-related adverse events. Asia Pac J Clin Oncol. 2020;16(4):201–10.

6. Cho SY, Lee HJ, Lee DG. Infectious complications after hematopoietic stem cell transplantation: current status and future perspectives in Korea. Korean J Intern Med. 2018;33(2):256–76.

7. Mouri M, Kanamori T, Tanaka E, Hiratoko K, Okubo M, Inoue M, Morio T, Shimizu M, Nishino I, Okiyama N, Mori M. Hepatic veno-occlusive disease accompanied by thrombotic microangiopathy developed during treatment of juvenile dermatomyositis and macrophage activation syndrome: a case report. Mod Rheumatol Case Rep. 2023;7(2):404–409.

8. Nusrat S, Davis H, MacDougall K, George JN, Nakamura R, Borogovac A. Thrombotic microangiopathy after hematopoietic stem cell and solid organ transplantation: a review for intensive care physicians. J Intensive Care Med. 2024;39(5):406–19.

9. Li J, Wu Z, Zhao L, Liu Y, Su Y, Gong X, Liu F, Zhang L. The heterogeneity of mesenchymal stem cells: an important issue to be addressed in cell therapy. Stem Cell Res Ther. 2023;14(1):381.

10. Krawczenko A, Klimczak A. Adipose tissue-derived mesenchymal stem/stromal cells and their contribution to angiogenic processes in tissue regeneration. Int J Mol Sci. 2022;23(5):2425.

11. Müller L, Tunger A, Wobus M, von Bonin M, Towers R, Bornhäuser M, Dazzi F, Wehner R, Schmitz M. Immunomodulatory properties of mesenchymal stromal cells: an update. Front Cell Dev Biol. 2021;9:637725.

12. Li C, Zhao H, Wang B. Mesenchymal stem/stromal cells: developmental origin, tumorigenesis and translational cancer therapeutics. Transl Oncol. 2021;14(1):100948.

13. Miclau K, Hambright WS, Huard J, Stoddart MJ, Bahney CS. Cellular expansion of MSCs: shifting the regenerative potential. Aging Cell. 2023;22(1):e13759.

14. Hoseini SM, Montazeri F. Cell origin and microenvironment: the players of differentiation capacity in human mesenchymal stem cells. Tissue Cell. 2025;93:102709.

15. Han X, Liao R, Li X, Zhang C, Huo S, Qin L, Xiong Y, He T, Xiao G, Zhang T. Mesenchymal stem cells in treating human diseases: molecular mechanisms and clinical studies. Signal Transduct Target Ther. 2025;10(1):262.

16. Peng YL, Chen J, Hu H, Liu W, Liang W, Wang J. Research progress of cell treatment strategy in Parkinson’s disease. Neurosci Appl. 2024;3:104061.

17. Li H, Dai H, Li J. Immunomodulatory properties of mesenchymal stromal/stem cells: the link with metabolism. J Adv Res. 2023;45:15–29.

18. Vaillant L, Akhter W, Nakhle J, Simon M, Villalba M, Jorgensen C, Vignais ML, Hernandez J. The role of mitochondrial transfer in the suppression of CD8(+) T cell responses by mesenchymal stem cells. Stem Cell Res Ther. 2024;15(1):394.

19. Zhou J, Shi Y. Mesenchymal stem/stromal cells (MSCs): origin, immune regulation, and clinical applications. Cell Mol Immunol. 2023;20(6):555–57.

20. Han Y, Zhu Y, Almuntashiri S, Wang X, Somanath PR, Owen CA, Zhang D. Extracellular vesicle-encapsulated CC16 as novel nanotherapeutics for treatment of acute lung injury. Mol Ther. 2023;31(5):1346–64.

21. Kim HI, Park J, Zhu Y, Wang X, Han Y, Zhang D. Recent advances in extracellular vesicles for therapeutic cargo delivery. Exp Mol Med. 2024;56(4):836–49.

22. Guan F, Wang R, Yi Z, Luo P, Liu W, Xie Y, Liu Z, Xia Z, Zhang H, Cheng Q. Tissue macrophages: origin, heterogeneity, biological functions, diseases and therapeutic targets. Signal Transduct Target Ther. 2025;10(1):93.

23. Niu T, Zhou F. Inflammation and tumor microenvironment. Zhong Nan Da Xue Xue Bao Yi Xue Ban. 2023;48(12):1899–1913.

24. Li R, Ji C, Dai M, Huang J, Xu W, Ma Y, Zhang H. An update on the role of tumor necrosis factor alpha stimulating gene-6 in inflammatory diseases. Mol Immunol. 2022;152:224–31.

25. Su W, Nong Q, Wu J, Fan R, Liang Y, Hu A, Gao Z, Liang W, Deng Q, Wang H, Xia L, et al. Anti-inflammatory protein TSG-6 secreted by BMSCs attenuates silica-induced acute pulmonary inflammation by inhibiting NLRP3 inflammasome signaling in macrophages. Int J Biol Macromol. 2023;253(Pt3):126651.

26. Hezam K, Wang C, Fu E, Zhou M, Liu Y, Wang H, Zhu L, Han Z, Han ZC, Chang Y, Li Z. Superior protective effects of PGE2 priming mesenchymal stem cells against LPS-induced acute lung injury (ALI) through macrophage immunomodulation. Stem Cell Res Ther. 2023;14(1):48.

27. Han Y, Yang J, Fang J, Zhou Y, Candi E, Wang J, Hua D, Shao C, Shi Y. The secretion profile of mesenchymal stem cells and potential applications in treating human diseases. Signal Transduct Target Ther. 2022;7(1):92.

28. Chen B, Chen Z, He M, Zhang L, Yang L, Wei L. Recent advances in the role of mesenchymal stem cells as modulators in autoinflammatory diseases. Front Immunol. 2024;15:1525380.

29. Punyawatthananukool S, Matsuura R, Wongchang T, Katsurada N, Tsuruyama T, Tajima M, Enomoto Y, Kitamura T, Kawashima M, Toi M, Yamanoi K, et al. Prostaglandin E(2)-EP2/EP4 signaling induces immunosuppression in human cancer by impairing bioenergetics and ribosome biogenesis in immune cells. Nat Commun. 2024;15(1):9464.

30. Munir H, Ward LSC, McGettrick HM. Mesenchymal stem cells as endogenous regulators of inflammation. Adv Exp Med Biol. 2018;1060:73–98.

31. Prockop DJ, Oh JY. Mesenchymal stem/stromal cells (MSCs): role as guardians of inflammation. Mol Ther. 2012;20(1):14–20.

32. Ji W, Sun L, Wang D, Zhu W. Mesenchymal stem cells alleviate inflammatory responses through regulation of T-cell subsets. Eur J Pharmacol. 2024;983:176996.

33. Wang L, Liang Y, Zhao C, Ma P, Zeng S, Ju D, Zhao M, Yu M, Shi Y. Regulatory T cells in homeostasis and disease: molecular mechanisms and therapeutic potential. Signal Transduct Target Ther. 2025;10(1):345.

34. Chen H, Chen X, Zhou ZH, Zheng JR, Lu Y, Lin P, Lin YF, Zheng YC, Xiong B, Xu RW, Cui L, et al. Mesenchymal stromal cell-mediated mitochondrial transfer unveils new frontiers in disease therapy. Stem Cell Res Ther. 2025;16(1):546.

35. Hsu YC, Wu YT, Yu TH, Wei YH. Mitochondria in mesenchymal stem cell biology and cell therapy: from cellular differentiation to mitochondrial transfer. Semin Cell Dev Biol. 2016;52:119–31.

36. Driscoll J, Gondaliya P, Patel T. Tunneling nanotube-mediated communication: a mechanism of intercellular nucleic acid transfer. Int J Mol Sci. 2022;23(10):5487.

37. Li A, Zhang T, Gao J. Progress on utilizing mesenchymal stem cells as cellular delivery system for targeting delivery of drug/gene for anti-tumor therapy. Zhejiang Da Xue Xue Bao Yi Xue Ban. 2020;49(1):20–34.

38. Hu Z, Wang D, Gong J, Li Y, Ma Z, Luo T, Jia X, Shi Y, Song Z. MSCs deliver hypoxia-treated mitochondria reprogramming acinar metabolism to alleviate severe acute pancreatitis injury. Adv Sci. 2023;10(25):e2207691.

39. Wang J, Peng X, Yuan N, Wang B, Chen S, Wang B, Xie L. Interplay between pulmonary epithelial stem cells and innate immune cells contribute to the repair and regeneration of ALI/ARDS. Transl Res. 2024;272:111–25.

40. Malekpour K, Hazrati A, Soudi S, Hashemi SM. Mechanisms behind therapeutic potentials of mesenchymal stem cell mitochondria transfer/delivery. J Control Release. 2023;354:755–69.

41. Kalluri R. The biology and function of exosomes in cancer. J Clin Invest. 2016;126(4):1208–15.

42. Wang J, Yi Y, Zhu Y. Progress of mesenchymal stem cells derived exosomes in wound repair. Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi. 2019;33(5):634–39.

43. Khayati S, Dehnavi S, Sadeghi M, Tavakol Afshari J, Esmaeili SA, Mohammadi M. The potential role of miRNA in regulating macrophage polarization. Heliyon. 2023;9(11):e21615.

44. Lu Z, Liu M, Stribinskis V, Klinge CM, Ramos KS, Colburn NH, Li Y. MicroRNA-21 promotes cell transformation by targeting the programmed cell death 4 gene. Oncogene. 2008;27(31):4373–79.

45. Lu K, Chen Q, Li M, He L, Riaz F, Zhang T, Li D. Programmed cell death factor 4 (PDCD4), a novel therapy target for metabolic diseases besides cancer. Free Radic Biol Med. 2020;159:150–63.

46. Wang JP, Dong LN, Wang M, Guo J, Zhao YQ. MiR-146a regulates the development of ulcerative colitis via mediating the TLR4/MyD88/NF-κB signaling pathway. Eur Rev Med Pharmacol Sci. 2019;23(5):2151–57.

47. Loubaki L, Chabot D, Paré I, Drouin M, Bazin R. MiR-146a potentially promotes IVIg-mediated inhibition of TLR4 signaling in LPS-activated human monocytes. Immunol Lett. 2017;185:64–73.

48. Shao B, Zhou D, Wang J, Yang D, Gao J. A novel LncRNA SPIRE1/miR-181a-5p/PRLR axis in mandibular bone marrow-derived mesenchymal stem cells regulates the Th17/Treg immune balance through the JAK/STAT3 pathway in periodontitis. Aging. 2023;15(14):7124–45.

49. Chen MY, Wang QG, Fan YJ. Research progress in promotion of tissue regeneration and reconstruction with exosomes derived from mesenchymal stem cells. Sichuan Da Xue Xue Bao Yi Xue Ban. 2021;52(3):380–86.

50. Ahn J, Kim B, Bello AB, Moon JJ, Arai Y, Lee SH. Regenerative functions of regulatory T cells and current strategies utilizing mesenchymal stem cells in immunomodulatory tissue regeneration. Tissue Eng Regen Med. 2025;22(2):167–80.

51. Dong C. Cytokine regulation and function in T cells. Annu Rev Immunol. 2021;39:51–76.

52. van Os BW, Vos WG, Bosmans LA, van Tiel CM, Toom MD, Beckers L, Admiraal M, Hoeksema MA, de Winther MP, Lutgens E. CD40L modulates CD4(+) T-cell activation through receptor for activated C kinase 1. Eur J Immunol. 2023;53(12):e2350520.

53. Lu Z, Meng S, Chang W, Fan S, Xie J, Guo F, Yang Y, Qiu H, Liu L. Mesenchymal stem cells activate Notch signaling to induce regulatory dendritic cells in LPS-induced acute lung injury. J Transl Med. 2020;18(1):241.

54. Marinescu CI, Preda MB, Burlacu A. A procedure for in vitro evaluation of the immunosuppressive effect of mouse mesenchymal stem cells on activated T cell proliferation. Stem Cell Res Ther. 2021;12(1):319.

55. Arabpour M, Saghazadeh A, Rezaei N. Anti-inflammatory and M2 macrophage polarization-promoting effect of mesenchymal stem cell-derived exosomes. Int Immunopharmacol. 2021;97:107823.

56. Li H, Wang T, Yang C, Dong W, Wu J, Zhang J, Xu F, Xie Z, Liang L, Zhang K, Zhang F, et al. Mesenchymal stem cells regulating macrophage polarization. Int Immunopharmacol. 2025;168(Pt 2):115801.

57. Wang Y, Fang J, Liu B, Shao C, Shi Y. Reciprocal regulation of mesenchymal stem cells and immune responses. Cell Stem Cell. 2022;29(11):1515–30.

58. Obana A, Akabane M, Mumtaz K, Von Stein L, Papanikolla J, Gray N, Sobotka L, Black S. Graft-versus-host disease after liver transplantation: a global review of pathogenesis, diagnosis, and treatment strategies. Transplant Rev. 2025;39(4):100942.

59. Talley S, Rademacher DJ, Campbell EM. Inflammasome activation occurs in CD4(+) and CD8(+) T cells during graft-versus-host disease. Cell Death Dis. 2023;14(9):632.

60. Moeinabadi-Bidgoli K, Babajani A, Yazdanpanah G, Farhadihosseinabadi B, Jamshidi E, Bahrami S, Niknejad H. Translational insights into stem cell preconditioning: from molecular mechanisms to preclinical applications. Biomed Pharmacother. 2021;142:112026.

61. Sacirbegovic F, Günther M, Greco A, Zhao D, Wang X, Zhou M, Rosenberger S, Oberbarnscheidt MH, Held W, McNiff J, Jain D, et al. Graft-versus-host disease is locally maintained in target tissues by resident progenitor-like T cells. Immunity. 2023;56(2):369–385.e366.

62. Ji H, Feng S, Liu Y, Cao Y, Lou H, Li Z. Effect of GVHD on the gut and intestinal microflora. Transpl Immunol. 2024;82:101977.

63. Raoufi A, Soleimani Samarkhazan H, Nouri S, Khaksari MN, Abbasi Sourki P, Sargazi Aval O, Baradaran B, Aghaei M. Macrophages in graft-versus-host disease (GVHD): dual roles as therapeutic tools and targets. Clin Exp Med. 2025;25(1):73.

64. DeFilipp Z, Alousi AM, Pidala JA, Carpenter PA, Onstad LE, Arai S, Arora M, Cutler CS, Flowers MED, Kitko CL, Chen GL, et al. Nonrelapse mortality among patients diagnosed with chronic GVHD: an updated analysis from the Chronic GVHD Consortium. Blood Adv. 2021;5(20):4278–84.

65. Nguyen JT, Jessri M, Costa-da-Silva AC, Sharma R, Mays JW, Treister NS. Oral chronic graft-versus-host disease: pathogenesis, diagnosis, current treatment, and emerging therapies. Int J Mol Sci. 2024;25(19).

66. Lazana I. Transplant-associated thrombotic microangiopathy in the context of allogenic hematopoietic stem cell transplantation: where we stand. Int J Mol Sci. 2023;24(2):1159.

67. Young JA, Pallas CR, Knovich MA. Transplant-associated thrombotic microangiopathy: theoretical considerations and a practical approach to an unrefined diagnosis. Bone Marrow Transplant. 2021;56(8):1805–17.

68. Zhang H, Fan Z, Huang F, Han L, Xu Y, Xu N, Deng L, Wang S, Lin D, Luo X, Zhang Q, et al. Busulfan plus cyclophosphamide versus total body irradiation plus cyclophosphamide for adults acute B lymphoblastic leukemia: an open-label, multicenter, phase III trial. J Clin Oncol. 2023;41(2):343–53.

69. Land WG, Agostinis P, Gasser S, Garg AD, Linkermann A. Transplantation and damage-associated molecular patterns (DAMPs). Am J Transplant. 2016;16(12):3338–61.

70. Li A, Sartain SE. Transplant-associated TMA: the conundrum of diagnosis and treatment. Hematology Am Soc Hematol Educ Program. 2024;2024(1):206–13.

71. Jalal A, Atari M, Hassanein M, Java A. Thrombotic microangiopathy and the kidney. Treasure Island (FL): StatPearls Publishing; 2025.

72. Feuer DS, Handberg EM, Mehrad B, Wei J, Bairey Merz CN, Pepine CJ, Keeley EC. Microvascular dysfunction as a systemic disease: a review of the evidence. Am J Med. 2022;135(9):1059–68.

73. Doshi K, Yusuf A, Licht C, Boyer O, Nester C, Murra A, Sharma P, Sethi S, Raina R. Extrarenal manifestations of atypical hemolytic uremic syndrome: a systematic review and meta-analysis. Pediatr Res. 2025;98(2):491–97.

74. Choi MS, Jeon H, Yoo SM, Lee MS. Activation of the complement system on human endothelial cells by urban particulate matter triggers inflammation-related protein production. Int J Mol Sci. 2021;22(7):3336.

75. Blasco M, Guillén-Olmos E, Diaz-Ricart M, Palomo M. Complement mediated endothelial damage in thrombotic microangiopathies. Front Med. 2022;9:811504.

76. Davidov Y, Shem-Tov N, Yerushalmi R, Hod T, Ben-Ari Z, Nagler A, Shimoni A, Danylesko I. Liver stiffness measurements predict sinusoidal obstructive syndrome after hematopoietic stem cell transplantation. Bone Marrow Transplant. 2024;59(8):1070–75.

77. Ans H, Amjad H, Nazir S, Cheema SS, Mistry D, Fatima T, Khan AY, Imtiaz MU, Khan FM, Khalid S, Rehman MEU, et al. Efficacy and safety of total body irradiation versus chemotherapy conditioning for hematopoietic stem cell transplant in adult acute lymphoblastic leukemia: a systematic review and meta-analysis. Clin Lymphoma Myeloma Leuk. 2025;25(4):e232–42.

78. Li ZW, Wang L. The role of liver sinusoidal endothelial cells in liver remodeling after injury. Hepatobiliary Pancreat Dis Int. 2023;22(1):22–27.

79. Bonifazi F, Ravaioli F, Iori AP, Milone G, Olivieri A, Prete A, Russo D, Santarone S, Sica S, Zecca M, Colecchia A. Operational procedure sharing pathway in veno-occlusive disease: a Delphi consensus-based recommendations. Front Oncol. 2025;15:1498782.

80. Fu W, Chen J, Hu X. Immune reconstitution following allogeneic hematopoietic cell transplantation and CAR-T therapy: dynamics, determinants, and directions. Best Pract Res Clin Haematol. 2025;38(2):101634.

81. Suresh S, Venkatesan V, Thangavel S, Marepally S. Exploring MSC and HSPC interactions: new frontiers in hematopoiesis and transplant medicine. Stem Cell Res Ther. 2025;16(1):640.

82. Pouryazdanpanah N, Moazed V, Khalilabadi RM, Dehesh T, Farsinejad A. Mesenchymal stem cell infusion to accelerate hematopoietic recovery after transplantation: a comprehensive systematic review of clinical studies (2000-2025). Crit Rev Oncol Hematol. 2025;215:104875.

83. Yang J, Liu L, Oda Y, Wada K, Ago M, Matsuda S, Hattori M, Goto T, Ishibashi S, Kawashima-Sonoyama Y, Taketani T. Extracellular vesicles and Cx43-gap junction channels are the main routes for mitochondrial transfer from ultra-purified mesenchymal stem cells, RECs. Int J Mol Sci. 2023;24(12):10294.

84. Pendse S, Kale V, Vaidya A. Microvesicles secreted by CoCl 2 -primed mesenchymal stromal cells boost the functionality of hematopoietic stem cells cultured with them. Ann Hematol. 2025;104(10):5389–5402.

85. Smallbone P, Kebriaei P, Mendt M, Shpall EJ, Olson AL, Fingrut WB. Mesenchymal stem cells in hematology: therapeutic initiatives and future directions. Best Pract Res Clin Haematol. 2025;38(1):101613.

86. Yuan X, Qin X, Wang D, Zhang Z, Tang X, Gao X, Chen W, Sun L. Mesenchymal stem cell therapy induces FLT3L and CD1c(+) dendritic cells in systemic lupus erythematosus patients. Nat Commun. 2019;10(1):2498.

87. Mei L, Yuwei Y, Weiping L, Zhiran X, Bingzheng F, Jibing C, Hongjun G. Strategy for clinical setting of co-transplantation of mesenchymal stem cells and pancreatic islets. Cell Transplant. 2024;33:9636897241259433.

88. Youssef A, Aboalola D, Han VK. The roles of insulin-like growth factors in mesenchymal stem cell niche. Stem Cells Int. 2017;2017:9453108.

89. González-González A, García-Sánchez D, Dotta M, Rodríguez-Rey JC, Pérez-Campo FM. Mesenchymal stem cells secretome: the cornerstone of cell-free regenerative medicine. World J Stem Cells. 2020;12(12):1529–52.

90. Yang D, Sun S, Wang Z, Zhu P, Yang Z, Zhang B. Stromal cell-derived factor-1 receptor CXCR4-overexpressing bone marrow mesenchymal stem cells accelerate wound healing by migrating into skin injury areas. Cell Reprogram. 2013;15(3):206–15.

91. Nitzsche F, Müller C, Lukomska B, Jolkkonen J, Deten A, Boltze J. Concise review: MSC adhesion cascade-insights into homing and transendothelial migration. Stem Cells. 2017;35(6):1446–60.

92. Zhang C, Delawary M, Huang P, Korchak JA, Suda K, Zubair AC. IL-10 mRNA engineered MSCs demonstrate enhanced anti-inflammation in an acute GvHD model. Cells. 2021;10(11):3101.

93. Giebel B. A milestone for the therapeutic EV field: FDA approves Ryoncil, an allogeneic bone marrow-derived mesenchymal stromal cell therapy. Extracell Vesicles Circ Nucl Acids. 2025;6(1):183–90.

94. Kurtzberg J, Abdel-Azim H, Carpenter P, Chaudhury S, Horn B, Mahadeo K, Nemecek E, Neudorf S, Prasad V, Prockop S, Quigg T, et al. A phase 3, single-arm, prospective study of remestemcel-L, ex vivo culture-expanded adult human mesenchymal stromal cells for the treatment of pediatric patients who failed to respond to steroid treatment for acute graft-versus-host disease. Biol Blood Marrow Transplant. 2020;26(5):845–54.

95. Mahat U, Przepiorka D, Fashoyin-Aje LA. Remestemcel-L-rknd for steroid-refractory acute graft-vs-host disease in pediatric patients. JAMA. 2025;334(1):81–82.

96. Liu DH, Yao C, Yang D, Dou L, Hou X, Qian K. Human umbilical cord derived mesenchymal stromal cell for the treatment of steroid-refractory AGVHD: a multicenter, randomized, double-blind phase 2 trial. Hemasphere. 2023;7:e8605085.

97. Zhao K, Lin R, Fan Z, Chen X, Wang Y, Huang F, Xu N, Zhang X, Zhang X, Xuan L, Wang S, et al. Mesenchymal stromal cells plus basiliximab, calcineurin inhibitor as treatment of steroid-resistant acute graft-versus-host disease: a multicenter, randomized, phase 3, open-label trial. J Hematol Oncol. 2022;15(1):22.

98. Fu H, Sun X, Lin R, Wang Y, Xuan L, Yao H, Zhang Y, Mo X, Lv M, Zheng F, Kong J, et al. Mesenchymal stromal cells plus basiliximab improve the response of steroid-refractory acute graft-versus-host disease as a second-line therapy: a multicentre, randomized, controlled trial. BMC Med. 2024;22(1):85.

99. Liu W, Chen S, Wang Y, Gong W. The rise of exosome-mediated mechanisms in MSC therapy. J Transl Med. 2025;23(1):793.

100. Feng B, Feng X, Yu Y, Xu H, Ye Q, Hu R, Fang X, Gao F, Wu J, Pan Q, Yu J, et al. Mesenchymal stem cells shift the pro-inflammatory phenotype of neutrophils to ameliorate acute lung injury. Stem Cell Res Ther. 2023;14(1):197.

101. Guo BC, Wu KH, Chen CY, Lin WY, Chang YJ, Lee TA, Lin MJ, Wu HP. Mesenchymal stem cells in the treatment of COVID-19. Int J Mol Sci. 2023;24(19):14800.

102. Krasnodembskaya A, Song Y, Fang X, Gupta N, Serikov V, Lee JW, Matthay MA. Antibacterial effect of human mesenchymal stem cells is mediated in part from secretion of the antimicrobial peptide LL-37. Stem Cells. 2010;28(12):2229–38.

103. Durand N, Mallea J, Zubair AC. Insights into the use of mesenchymal stem cells in COVID-19 mediated acute respiratory failure. NPJ Regen Med. 2020;5(1):17.

104. Zheng L, Chen W, Yao K, Lin Y, Liao C, Zhou T. Mechanism of mesenchymal stem cells in treating diabetic kidney disease. Stem Cell Res Ther. 2025;16(1):629.

105. Česnik AB, Švajger U. The issue of heterogeneity of MSC-based advanced therapy medicinal products-a review. Front Cell Dev Biol. 2024;12:1400347.

106. Zhou C, Bai XY. Strategies for the induction of anti-inflammatory mesenchymal stem cells and their application in the treatment of immune-related nephropathy. Front Med. 2022;9:891065.

107. Eggenhofer E, Benseler V, Kroemer A, Popp FC, Geissler EK, Schlitt HJ, Baan CC, Dahlke MH, Hoogduijn MJ. Mesenchymal stem cells are short-lived and do not migrate beyond the lungs after intravenous infusion. Front Immunol. 2012;3:297.

108. Regmi S, Pathak S, Kim JO, Yong CS, Jeong JH. Mesenchymal stem cell therapy for the treatment of inflammatory diseases: challenges, opportunities, and future perspectives. Eur J Cell Biol. 2019;98(5–8):151041.

109. Suresh S, Venkatesan V, Azhagiri MKK, Mahalingam G, Chandraprabha PB, Murugesan MK, Kumar S, Thangavel S, Marepally S. Engineering biomimetic bone marrow niche with gene modified mesenchymal stromal cells for ex vivo culture of human hematopoietic stem and progenitor cells. Stem Cell Res Ther. 2025;16(1):335.

110. Christoffers S, Seiler L, Wiebe E, Blume C. Possibilities and efficiency of MSC co-transfection for gene therapy. Stem Cell Res Ther. 2024;15(1):150.