Bone marrow-derived MSCs were the first MSCs to be described, known as BM-MSCs. BM-MSCs can be isolated from the sternum, vertebrae, iliac crest, and femoral shaft (123–125). Compared to other types of MSCs, the process of obtaining BM-MSCs is invasive. BM-MSCs are collected through specific bone marrow aspiration, and stem cell isolation can be quickly and efficiently performed using flow cytometry and MACS technology based on the expression of cell surface markers (126, 127). In addition to meeting the ISCT standards, BM-MSCs express other surface markers, such as STRO-1, CD146, SSEA-4, CD271, MSCA-1, and PDGFRα (128, 129). Among these, STRO-1 is highly expressed in fresh and young BM-MSCs and decreases during expansion cultures, making STRO-1-positive BM-MSCs suitable for clinical applications (129). BM-MSCs exist in very low quantities in bone marrow tissue and undergo rapid proliferation after seven days of culture, achieving a 500-fold expansion in 50 passages (130). Under phase-contrast microscopy, the dominant cells appear spindle-shaped or pool-like with abundant cytoplasm and large, dark nucleoli. After in vitro expansion, a sufficient number of cells can be obtained for therapeutic doses.

A-MSCs were first isolated from human adipose tissue through plastic adherence before MSCs were formally defined (131). In 2001, Zuk et al. identified MSCs in human adipose tissue and characterized them (132), which led to the recognition that MSCs isolated from adipose tissue could serve as an alternative to BM-MSCs. Adipose tissue consists mainly of adipocytes organized into lobules. It is a highly complex tissue composed of mature adipocytes that account for over 90% of the tissue volume, along with a heterogeneous group of cells surrounding and supporting the adipocytes. After enzymatic digestion and/or mechanical disruption, single-cell populations can be released from adipose tissue, forming the stromal vascular fraction (SVF) (133). Centrifugation separates the SVF from mature adipocytes. The supernatant contains low-density, floating adipocytes, while the SVF forms a denser cell pellet. The SVF is a heterogeneous mixture of various cell populations with different levels of maturity and function, including pericytes, smooth muscle cells, and A-MSCs (134). A-MSCs are further isolated from the SVF through expansion and plastic adherence, similar to BM-MSCs, to deplete most hematopoietic cell populations. Factors such as donor age, donor BMI, tissue type (white or brown adipose tissue), and tissue harvesting procedures and locations can affect the yield, proliferation rate, and differentiation capacity of A-MSCs (134–138). Compared to A-MSCs from older patients, A-MSCs from younger patients exhibit higher proliferation rates and more effectively differentiate into mature adipocytes (134). Increased BMI reduces A-MSCs proliferation and may impair in vitro osteogenic potential (135). Although there are two types of adipose tissue (brown and white), white adipose tissue is the source of A-MSCs used in most studies (136). Additionally, ultrasound-assisted liposuction reduces the proliferation frequency of A-MSCs and prolongs their population doubling time compared to excision methods (137). The yield of A-MSCs also depends on the tissue harvest site, with the abdomen being more suitable for A-MSCs collection than the hip/thigh region (138). A-MSCs possess the same characteristics as standard MSCs, meeting ISCT criteria. However, CD34 expression has been a unique feature of A-MSCs, with studies showing that a significant portion of A-MSCs are CD34-positive, although negative results for CD34 have also been reported (139). Evidence suggests that CD34 is expressed in tissue-resident A-MSCs, with negative findings being the result of cell culture, indicating that CD34 expression may be reversible (140). A report by Suga et al. indicated that CD34 expression is associated with immature, pro-angiogenic gene expression and greater replicative potential (141). It is speculated that CD34 is a niche-specific marker of immature/early progenitor cells that is lost under in vitro conditions (133, 142).

The placenta is a transient maternal-fetal organ that is highly abundant and easily accessible. Since it is discarded after delivery, its collection does not involve invasive procedures, making it more ethically acceptable. This has garnered significant interest in the placenta as a source of MSCs. P-MSCs can be isolated from various parts of the placenta, such as the chorion, basal decidua, top decidua, amnion, and amniotic fluid (143–146). P-MSCs are typically isolated using explant or enzymatic methods. In the explant method, tissue is dissected from the respective source, washed with cold phosphate-buffered saline to remove excess blood, minced into small pieces, and allowed to adhere to culture dishes. The plates are incubated at 37 °C with MSCs proliferation medium. In the enzymatic method, the tissue is similarly minced and treated with trypsin, DNase, and collagenase. The isolated cells are then plated and maintained similarly to explant cultures. P-MSCs exhibit high immunoregulatory properties by secreting soluble factors and modulating the immune functions of macrophages and dendritic cells, thereby inhibiting T cell activity and enhancing their immunosuppressive capabilities (144). Current literature suggests that P-MSCs hold great potential as a cell source for therapeutic angiogenesis. P-MSCs secrete a large number of cytokines and chemokines crucial for angiogenic signaling, promoting angiogenesis by modulating niche cells (147).

The human umbilical cord is an extra-embryonic connective tissue located between the mother and fetus, consisting of two arteries, one vein, vascular connective tissue, and umbilical epithelium. The connective tissue, also known as Wharton's jelly, is a spongy structure woven from collagen fibers, proteoglycans, and embedded stromal cells. The umbilical cord is a rich source of MSCs, with minimal ethical concerns. Its collection and isolation process is painless, minimally invasive, and the tissue is easy to store and transport (148). HUC-MSCs can be isolated from different parts of the umbilical cord, including blood, endothelial cells of the umbilical vein, and Wharton's jelly (149). Similar to P-MSCs, HUC-MSCs are typically isolated using explant or enzymatic methods (150). The surface markers of HUC-MSCs are similar to those defined by the ISCT for MSCs, although they are negative for CD133 (151). The phenotypic characteristics of HUC-MSCs may be influenced by the number of culture passages, culture medium, and methods used. HUC-MSCs can exert immunosuppressive effects by inhibiting the proliferation of T cells, B cells, and NK cells, and by directing monocytes and dendritic cells towards an immature state (152, 153).

Flow cytometric analysis using MSCs from different tissues revealed that all cell types exhibit similar immunophenotypes. MSCs are positive for CD29, CD44, CD73, CD90, and CD105, which are known MSC markers, with positive markers expressed across all cell types (154). These results confirm that MSCs from different sources express the surface markers defined by the ISCT. However, CD90, a typical MSC marker, is less pronounced in P-MSCs compared to other cells (154). In addition to surface markers, MSCs from different tissue sources have varying lineage differentiation capabilities. When MSCs from bone marrow, umbilical cord, adipose tissue, and placenta are cultured in vitro, BM-MSCs exhibit a longer population doubling time than other MSC types (154). P-MSCs can undergo more passages compared to other MSC types during passaging (154). In colony-forming unit (CFU) assays, BM-MSCs and HUC-MSCs produce more colonies than other MSC types when an equal number of MSCs are plated, indicating stronger self-renewal characteristics (154). After differentiation, BM-MSCs and AT-MSCs exhibit significant differentiation potential, generating osteoblasts, adipocytes, and chondrocytes, whereas MSCs derived from umbilical cord blood and placenta show weaker differentiation potential (154).

Early studies on the differentiation of MSCs into cardiomyocytes demonstrated that specific microenvironmental conditions, such as treatment with 5-azacytidine and platelet-derived growth factor-β, could induce MSCs differentiation into cardiomyocytes (155, 156). However, in another study, rat BM-MSCs failed to differentiate into cardiomyocytes following 5-azacytidine treatment (157). In fact, the regulatory mechanisms of MSCs multipotency are highly complex. Nevertheless, increasing evidence suggests that the activation or inhibition of certain transcription factors can guide MSCs towards specific lineage differentiation. Through exogenous overexpression or knockout of candidate genes, some key transcription factors, such as GATA4, Nkx2.5, myocardin, thioredoxin-1, and Notch1, can specifically promote the differentiation of MSCs into cardiomyocytes expressing ANP and cTnI (158, 159). Additionally, pre-treatment with TGF-β1 has been shown to enhance the differentiation of rat BM-MSCs into cardiomyocytes and improve cardiac function in a rat heart failure model (160). For stable and efficient cardiomyocyte generation from MSCs, co-treatment with 5-Aza, BMP-2, and DMSO can induce MSCs differentiation into cardiomyocyte-like cells within 24 h (161). Recent studies have shown that human amniotic MSCs (hAMSCs) can also be chemically induced to differentiate into cardiomyocyte-like cells in vitro using a chemical induction protocol that includes BMP4, Activin A, 5-azacytidine, CHIR99021, and IWP2 (162). These studies were conducted in vitro, but MSCs can also differentiate into functional cardiomyocytes in vivo under appropriate conditions. For instance, when human MSCs expressing the β-galactosidase reporter gene were transplanted into immunodeficient mice with experimental myocardial injury, β-galactosidase-expressing cardiomyocytes were found in the host myocardium, indicating that xenografted MSCs had differentiated into cardiomyocytes (163). Moreover, in gender-mismatched cell therapy experiments using porcine models of acute and chronic myocardial infarction, transplanted male MSCs were found to differentiate into cardiomyocytes in female host myocardium. This was confirmed by the co-localization of the Y chromosome with the cardiac transcription factors GATA-4, Nkx2.5, and the structural cardiac protein α-sarcomeric actin (164–166). These findings suggest the potential for MSCs to differentiate into cardiomyocytes in vivo.

Although MSCs can exert beneficial effects on the heart through various mechanisms, the paracrine activity of MSCs has recently become a focal point of therapeutic research. Multiple growth factors and cytokines are secreted together as part of the “secretome.” These factors can be water-soluble or encapsulated in EVs or exosomes cultured in “conditioned media.” The secreted paracrine factors have diverse effects, such as antifibrotic, anti-apoptotic, and angiogenic properties, which improve local vascularization and reduce cardiomyocyte death. The paracrine function of MSCs is primarily attributed to their derived exosomes, which will be discussed in detail later.

Exosomes are EVs with diameters ranging from 40 to 160 nm (169). They are secreted by various cell types, including dendritic cells, mast cells, platelets, and MSCs, and are present in most human and animal body fluids, such as plasma, serum, saliva, amniotic fluid, breast milk, and urine (170). Exosomes were first discovered by Pan and Johnstone while studying how sheep reticulocytes mature into red blood cells (171). They carry crucial information and macromolecules from their source cells, playing a vital role in intercellular communication. These macromolecules, which include various proteins, enzymes, transcription factors, lipids, ECM proteins, receptors, and nucleic acids, can be found inside or on the surface of exosomes (170). Initially, exosomes were considered to be cellular debris or waste and were thought to be indicators of cell death (172, 173). Since their discovery, the biological properties, functions, and potential clinical applications of exosomes have been extensively studied. Typical biomarkers of exosomes include proteins such as CD9, CD81, CD63, ceramide, tumor susceptibility gene 101 (TSG101), and apoptosis-linked gene 2-interacting protein X (ALIX), all of which are involved in exosome origin and biogenesis (170, 174). The most common and traditional method for isolating exosomes is ultracentrifugation/differential ultracentrifugation, which separates exosomes based on size and density (175). Other methods include ultrafiltration, size-exclusion chromatography (SEC), and molecular weight-based exosome separation (175). Immunoaffinity chromatography and precipitation can also be used to enhance the purity of isolated exosomes (174).

MSCs promote angiogenesis and possess the ability to restore ischemic tissues, making them highly attractive for treating cardiovascular diseases (176). The beneficial effects of MSCs in tissue repair are largely attributed to paracrine signaling, including secreted vesicles, mainly exosomes (177). Since exosomes contain various regulatory RNAs, they have the potential to reduce tissue damage after myocardial infarction (178). Exosomes derived from different MSCs sources generally have common therapeutic effects, though their specific mechanisms vary slightly, likely due to differences in their microRNA (miRNA) content (179, 180). miRNAs, important gene expression regulators, are abundant in exosomes. They can suppress the expression of pro-apoptotic proteins, increase anti-apoptotic protein expression, improve angiogenic gene expression, mitigate oxidative stress, limit the proliferation of cardiac fibroblasts, create an anti-inflammatory microenvironment, and enhance cardiac function. These effects promote cardiomyocyte survival and improved function in various myocardial infarction or heart failure models (178, 181). Interestingly, recent studies have demonstrated that exosomes secreted by MSCs can replace MSCs-based stem cell therapy in various injury and disease models (182, 183). For example, MSC-derived exosomes (MSC-Exos) have been shown to induce repair in mouse models of wound healing and myocardial infarction (184–186). Our next aim is to elucidate the molecular mechanisms of MSC-derived exosomes to facilitate their clinical translation (as shown in Figures 1–4).

One of the major challenges in MSCs-based therapy for HF is the pronounced heterogeneity in treatment outcomes and the incomplete understanding of the underlying mechanisms. Numerous clinical trials have reported variable results, likely stemming from a complex interplay among factors such as cell processing methods, therapeutic regimens, and patient-specific pathological conditions. For instance, the C-CURE trial utilized bone marrow-derived MSCs preconditioned with a cardiogenic cocktail, leading to notable improvements including a 7% increase in LVEF, a 24.8 ml reduction in end-systolic volume, and a 62-m gain in 6-min walk distance (221). In contrast, the CHART-1 trial, which employed a fixed high-dose regimen of bone marrow-derived MSCs in end-stage HF patients, failed to meet its primary endpoints and showed only limited benefit in certain subgroups (222, 223). Further analysis suggests that the cardiopoietic preconditioning strategy in C-CURE may have significantly enhanced the reparative potential of the cells, while individualized dosing based on body weight may be more advantageous than fixed dosing schemes. Additionally, the pathological microenvironment in end-stage HF may compromise the viability and functionality of transplanted cells.

Significant variation in therapeutic efficacy is also observed among MSCs derived from different tissue sources. In the RIMECARD trial, umbilical cord-derived MSCs (UC-MSCs) led to greater improvements in LVEF compared with placebo, and UC-MSCs were found to express hepatocyte growth factor (HGF) at levels 55 times higher than bone marrow-derived MSCs, suggesting that differences in the paracrine profiles of MSCs may influence therapeutic outcomes (224). The MSC-HF trial highlighted inter-individual variability in the effectiveness of autologous bone marrow-derived MSCs, which may be attributable to baseline patient characteristics such as age, comorbidities, and the etiology of heart failure (225). Notably, the POSEIDON trial found spatially specific effects of MSCs in improving regional contractile function within scarred myocardial zones, indicating that the local myocardial microenvironment may critically influence therapeutic efficacy (226).

Although the prevailing view is that MSCs exert their therapeutic benefits mainly through paracrine mechanisms, the precise molecular pathways involved remain poorly understood. The CONCERT-HF trial revealed cell-type-specific therapeutic effects: MSCs primarily improved patient-reported quality of life, whereas c-kit-positive cardiac progenitor cells (CPCs) demonstrated superiority in reducing major adverse cardiovascular events—a difference whose mechanism remains to be elucidated (227). While HGF is considered a key effector molecule, the downstream signaling pathways by which it orchestrates antifibrotic and proangiogenic responses require further clarification. Exosomes, as crucial paracrine mediators, pose additional challenges due to their compositional complexity, and current methodologies lack the sensitivity and specificity to reliably identify the key bioactive components responsible for therapeutic effects. These mechanistic uncertainties hamper the optimization and broader clinical application of MSCs-based therapies.

The clinical translation of MSCs therapy for HF faces numerous challenges, among which the standardization of cell preparation processes is particularly prominent. Significant variability exists in the cell culture systems used across clinical trials, directly impacting cell quality and therapeutic outcomes. For instance, in the MSC-HF trial, the average culture period was 46.9 ± 10.5 days (225), whereas the C-CURE trial required an additional 4–6 weeks of cardiopoietic preconditioning. Furthermore, only 75% of patients in C-CURE met the release criteria (>600 × 10⁶ cells) (221). In addition, there is no standardized method for exosome isolation; ultracentrifugation and commercial kits vary in yield, purity, and bioactivity. Optimal dosage and delivery routes (e.g., local injection vs. systemic administration) also remain controversial (228, 229). In the CONCERT-HF trial, 25% of MSCs and 16% of CPCs were excluded due to insufficient cell quantity or activity (227), highlighting the sensitivity of the manufacturing process and the critical importance of quality control.

In terms of delivery techniques, the demand for precision remains inadequately addressed. Intramyocardial injection methods, such as NOGA-guided endocardial delivery, are technically complex and operator-dependent. Approximately 20% of patients in the POSEIDON and CONCERT-HF trials were unable to receive the full injection protocol due to anatomical limitations (226, 227). Although the C-Cathez™ catheter used in the CHART-1 trial improved procedural efficiency, it still resulted in four cases of cardiac tamponade (222). Emerging technologies, such as real-time MRI-guided injections and robotic-assisted delivery systems, have shown promise in enhancing targeting accuracy; however, the associated costs are five to eight times higher than conventional approaches, limiting widespread adoption (230). Additionally, the application of exosomes in tissue repair is constrained by their low stability and short retention time. Studies have shown that exosomes are undetectable as early as 3 h post-myocardial injection (231). Moreover, systemic delivery faces targeting inefficiencies, with less than 1% of intravenously administered exosomes reaching the cardiac tissue (232, 233). Thus, future research should explore myocardial-specific modification strategies to improve delivery efficiency.

Another major barrier is the lack of consensus on endpoint measures, which limits comparability across clinical trials. Current studies use highly heterogeneous primary outcomes, including LVEF, left ventricular end-systolic volume (LVESV), scar size (assessed via MRI), and quality of life scores. However, some functional endpoints, such as the 6-min walk test, are susceptible to placebo effects—improvements of up to 30% have been observed in placebo groups in certain trials. Therefore, there is an urgent need to establish more objective and comprehensive composite endpoints that integrate imaging parameters (e.g., global longitudinal strain, GLS), biomarkers (e.g., NT-proBNP), and hard clinical outcomes (e.g., HF rehospitalization, cardiovascular mortality) to enhance the comparability and translational value of research findings.

The clinical translation of MSC therapy for HF is further hampered by long-term safety concerns and manufacturing limitations. Most current trials have relatively short follow-up durations (median 12–39 months), and potential risks such as tumorigenicity and immune rejection have yet to be fully elucidated. For example, in the RIMECARD trial, one patient treated with umbilical cord-derived MSCs was diagnosed with acute lymphoblastic leukemia 13 months later. Although trace-back analysis found no direct link to the treatment, the genomic instability that may result from replicative senescence during prolonged in vitro expansion of allogeneic MSCs remains a concern (224, 234, 235). While exosomes circumvent the risk of uncontrolled cell proliferation, their long-term immunomodulatory effects remain debatable. For instance, overexpression of programmed death-ligand 1 (PD-L1) may impair immune surveillance, a potential risk that warrants further validation through extended follow-up and larger sample sizes (236).

The scalability of the manufacturing process presents another critical bottleneck. Autologous MSCs therapies typically require 6–8 weeks from cell harvest to administration (as in the C-CURE trial), resulting in high costs and delayed treatment (223, 237). Donor-dependent variability in cell quality further complicates production. Compared with younger donors, MSCs from elderly patients show a 40%–60% reduction in proliferative capacity, leading to marked differences in therapeutic efficacy between batches (237–239). Although allogeneic umbilical cord-derived MSCs offer the advantage of cryopreserved “off-the-shelf” availability, post-thaw viability may decrease by 15%–30%, and the long-term effects of cryostorage on functional potency remain unclear (240). Exosome production faces its own set of technical limitations—fewer than 1 μg of exosomal protein can be harvested per milliliter of culture medium. Moreover, prolonged storage at −80 °C can compromise biological activity, hindering large-scale application (241–243).

The limitations of current quality control systems further exacerbate the complexity of clinical translation. Conventional assays (e.g., flow cytometry for phenotypic analysis) are time-consuming and insufficient for real-time clinical quality control. Although emerging technologies such as Raman spectroscopy offer real-time monitoring potential, they have not yet been standardized for clinical use (244–246). Exosome quality control is particularly challenging. Only a limited number of laboratories worldwide can simultaneously assess nanoparticle size distribution (via nanoparticle tracking analysis), purity markers (e.g., CD81/CD63), and functional potency (e.g., cell migration assays) (247, 248). Additionally, the absence of standardized functional evaluation systems—such as quantification of paracrine factors or assessments of tissue repair capacity—makes it difficult to ensure consistency between production batches (248, 249). These technical gaps not only compromise the predictability of therapeutic outcomes but also complicate regulatory approval processes. Moving forward, the development of automated quality control platforms and functional performance-based evaluation standards is crucial to overcoming current technological barriers and advancing stem cell therapies toward standardized and precise clinical application.

The personalized application of MSCs for heart failure remains hindered by multiple technical bottlenecks and translational challenges. Currently, patient stratification relies primarily on coarse indicators such as LVEF and the NYHA functional classification. However, post hoc analyses of the CHART-1 trial suggest that left ventricular end-diastolic volume (LVEDV) may serve as a more precise stratification marker (222).

The integration of multi-omics technologies offers promising avenues for precise stratification. Transcriptomic analysis has identified TNF-α as a key regulator of MSCs functionality; while TNF-α can activate the reparative and immunomodulatory capacities of MSCs via the inflammatory microenvironment, prolonged exposure or excessive concentrations may lead to functional exhaustion. Therefore, fine-tuning of TNF-α signaling is critical for optimizing MSC-based therapies (250). Proteomic profiling has revealed galectin-3 (Galectin-3) as a central mediator of the immunosuppressive and anti-inflammatory properties of MSCs, acting through regulation of macrophage polarization, T cell functionality, and fibrotic pathways (251–253). Future efforts are needed to delineate the dose-dependent effects and signaling networks of Galectin-3 to facilitate its targeted application in MSC therapy. Moreover, metabolomic data indicate that enhanced glycolysis and mitochondrial remodeling are tightly associated with the immunoregulatory function of MSCs. Targeting metabolic pathways may thus provide a novel strategy to modulate the immunosuppressive potential of MSCs (254). However, the clinical application of multi-omics technologies is limited by high per-test costs and the need for interdisciplinary expertise in data interpretation.

Dose optimization represents another critical challenge. Current preclinical studies demonstrate a non-linear, inverted U-shaped dose-response relationship, whereby both low and high doses result in inferior outcomes (255). The MSC-HF trial indicated that high doses (>100 × 10⁶ cells) significantly improved cardiac function (225), whereas the POSEIDON trial found that the 20 × 10⁶ cell group exhibited greater reduction in myocardial scar size compared to the 100 × 10⁶ cell group (226). Such discrepancies may reflect heterogeneity in the pathological microenvironment—advanced heart failure patients often experience severe myocardial hypoxia and elevated inflammatory cytokines, which may lead to increased cell apoptosis at higher doses due to intensified competition for nutrients, whereas lower doses may survive better and exert paracrine effects in less hostile environments.

The determination of optimal treatment windows poses an additional clinical challenge. Preclinical studies have demonstrated that the therapeutic window for preventing I/R injury is narrow and requires early intervention before full activation of apoptotic pathways (255). The timing of MSC administration significantly affects therapeutic efficacy, though results remain inconsistent. In large animal models, administration 30 min post-reperfusion yielded variable outcomes—some studies reported improvements in infarct size or ejection fraction, while others found no benefit (256–258). In contrast, intravenous delivery 15 min post-reperfusion or delayed injection at 3 days to 3 months post-infarction facilitated functional recovery or remodeling (165, 259), whereas administration at 30 days post-MI may expose MSCs to detrimental microenvironments that compromise cell viability (260). Clinical studies further underscore the importance of timing; meta-analyses suggest that administration within one week of myocardial infarction, particularly 5–7 days PCI, enhances ejection fraction and myocardial perfusion. In contrast, very early administration (within 24 h) may reduce infarct size without improving overall cardiac function (261).

In recent years, genetic engineering and preconditioning strategies have achieved substantial progress in enhancing the therapeutic efficacy of MSCs and their exosomes. In the domain of genetic regulation, the application of CRISPR-Cas9 and viral vector technologies has enabled precise genetic modifications of MSCs, thereby significantly improving their reparative capacity (262–265). Genetic modifications have been shown to augment MSC efficacy in heart failure by promoting cell survival, enhancing differentiation and integration, and strengthening paracrine signaling (266). For instance, overexpression of heat shock protein 27 (HSP27) and heme oxygenase-1 (HO-1) has been reported to increase MSCs survival, reduce apoptosis, and improve left ventricular function (267, 268). Furthermore, overexpression of stromal cell-derived factor 1 (SDF-1) and its receptor CXCR4 enhances MSCs homing ability, reduces ventricular remodeling, and restores cardiac function (269, 270). Similarly, upregulation of IGF-1, HGF, and Ang-1 has been shown to promote angiogenesis, attenuate infarct size, and improve cardiac performance (271–273).

Preconditioning under hypoxic conditions (0.5%–3% O₂) has also been demonstrated to activate the PI3K-Akt signaling pathway, enhance cellular survival, and upregulate key anti-apoptotic and pro-angiogenic factors including HIF-1α, VEGF, and Bcl-2, thereby reducing infarct size and improving cardiac outcomes (274). Exosome engineering represents another promising direction. For example, exosomes modified with ischemic myocardium-targeting peptides (IMTP-exosomes) have shown superior therapeutic efficacy compared to unmodified exosomes, significantly alleviating inflammation, reducing apoptosis and fibrosis, promoting angiogenesis, and enhancing cardiac function following myocardial infarction (275). Additionally, exosome microneedle patches loaded with microRNA-29b have been found to effectively prevent post-infarction cardiac fibrosis (276). Exosomes overexpressing CD47 have demonstrated improved targeting efficiency by evading immune clearance via the “don't eat me” signal (277, 278). These strategies provide powerful tools to optimize MSCs and exosome-based therapies, although further investigations are required to address challenges in clinical translation.

Although substantial progress has been made in applying MSCs and their exosomes for cardiac repair, conventional intramyocardial injection remains hindered by limited cell viability, uneven distribution, and difficulties in maintaining therapeutic function. To overcome these limitations, researchers have developed a range of biomaterial-based innovative delivery systems that improve local retention, enable controlled release, and enhance the stability of bioactive molecules, thereby significantly boosting the therapeutic potential of MSCs-based interventions.

Hydrogel scaffolds, owing to their superior biocompatibility and biomimetic properties, have emerged as one of the most promising delivery vehicles. These scaffolds mimic the native ECM microenvironment, thereby enhancing MSCs retention and functional expression (279, 280). Specifically, injectable peptide and alginate hydrogels loaded with EVs have demonstrated improved retention at the site of myocardial injury, facilitated angiogenesis, and mitigated fibrotic progression (281). The incorporation of 3D culture technologies has further potentiated the cardioprotective effects of these systems, offering new avenues for myocardial regeneration (282, 283).

Microsphere and encapsulation technologies also offer unique advantages in delivery system design. MSCs-derived microspheres formed via self-assembly into 3D structures have been shown to enhance anti-apoptotic capacity and optimize paracrine signaling (284). Spheroids cultured on chitosan membranes have exhibited enhanced myocardial contractility in animal models, potentially mediated by angiogenesis-related microRNAs (285, 286). Semipermeable encapsulation platforms provide physical protection from immune rejection while allowing the exchange of nutrients and signaling molecules, offering an ideal foundation for integrating gene editing technologies and achieving controlled release of therapeutic factors (266, 287–289).

Recently, the development of magnetically responsive delivery systems has opened new frontiers for precision therapy. MSCs labeled with superparamagnetic iron oxide nanoparticles (SPIONs) have demonstrated significantly enhanced myocardial engraftment under magnetic guidance (290). Moreover, magnetic navigation technologies have been shown to increase targeting accuracy and therapeutic efficacy of MSCs and their exosomes in heart failure models (291, 292). Future research should further investigate the interplay between biomaterials and cellular functions, aiming to develop intelligent delivery platforms with targeted homing and dynamic responsiveness. Additionally, standardization and large-scale production of these technologies will be crucial for their clinical translation, providing more effective solutions for cardiovascular therapy. These innovative strategies represent a major step toward overcoming the limitations of traditional cell therapies and highlight the vast potential of tissue engineering in regenerative medicine.

In recent years, combination strategies involving MSCs and their exosomes have achieved significant advances in the treatment of heart failure, primarily by leveraging synergistic mechanisms to amplify therapeutic efficacy. Among these, the co-administration of cells and pharmacological agents has emerged as a promising approach. Drug preconditioning with agents such as trimetazidine, melatonin, and statins has been shown to activate the Akt signaling pathway, reduce apoptosis, promote angiogenesis, and modulate immune responses—thereby significantly enhancing MSCs survival and tissue repair capacity (293–297). Currently, a clinical trial is underway investigating the combined application of atorvastatin and autologous BM-MSCs in patients undergoing PCI, aiming to improve cell survival through pharmacological dose optimization (298).

The therapeutic synergy of combination approaches is highly dependent on temporal coordination and vector design. As discussed in the previous section, combining MSCs with biomaterials (e.g., hydrogels or cell sheet technologies) enhances cell retention and facilitates myocardial repair. Notably, in a rat model of MI, sequential delivery of MSCs and their derived exosomes has demonstrated superior therapeutic effects (299). In this study, exosomes were administered 30 min post-MI to target the acute inflammatory phase, followed by MSC transplantation on day 3 to support regenerative processes (299). This precisely timed protocol significantly reduced infarct size and improved cardiac contractility, highlighting the potential advantages of temporally coordinated cell-exosome therapy.

More complex combination strategies involve co-transplantation of MSCs with CPCs. The CONCERT-HF trial has demonstrated that while CPCs primarily reduce clinical events and MSCs improve quality of life, their combined use yields additive benefits by targeting complementary aspects of cardiac repair (227). Additionally, the co-administration of MSCs with regulatory T cells (Tregs) has been shown to enhance MSC survival, proliferation, and pro-angiogenic potential, offering a novel avenue for cell-based combinatorial therapies (300).

Despite promising preclinical results, the clinical translation of combination therapies remains challenged by the need for optimized therapeutic regimens, thorough safety evaluations, and standardized manufacturing protocols. Future efforts should focus on developing intelligent delivery systems and conducting multicenter clinical trials to facilitate the adoption of combination strategies in clinical practice.