The chronic autoimmune illness of the central nervous system (CNS), known as multiple sclerosis (MS), affects a sizable portion of the global population and has had a profound effect on public health globally (Kobelt et al., 2017; Sumowski et al., 2018; Bjornevik et al., 2022). This illness is typified by inflammation and myelin loss, which results in neurodegeneration. Clinical characteristics include exhaustion and mental/cognitive impairment, in addition to more unusual ones such as vision loss and sensorimotor complaints. It primarily affects female patients and younger people (Penesová et al., 2018). The illness is categorized into three clinical forms: primary progressive (PPMS), secondary progressive (SPMS), and relapsing-remitting (RRMS). Each type is distinguished by a different level of pathology, spanning acute/chronic inflammation and, or neurodegeneration (Stoiloudis et al., 2022). Numerous environmental, dietary, viral (such as the Epstein-Barr virus), genetic, and epigenetic factors may be causal in the onset and progression of MS. The pathophysiology and etiology of MS are complicated (Bjornevik et al., 2022; Ascherio, 2013; Miclea et al., 2020). The MS Atlas estimated in 2020 that one person with MS is diagnosed every 5 min throughout the world, with an average age of 32 years, adding to the 2.8 million people who already have the condition (Charabati et al., 2023). Its frequency varies by region, with Europe and North America having the highest rates (Thompson et al., 2018). Jean-Martin Charcot termed this condition sclérose en plaques in 1868, which was eventually shortened to MS. Charcot and colleagues (Charcot, 1868) discovered that pathological indicators of MS entail the identification of lesions in the regions of the CNS that involve both white and gray matter. These lesions exhibit different levels of demyelination, perivascular immune cell infiltration, reactive gliosis, and, or neurodegeneration. Subsequent research identified abnormalities of the blood-brain barrier (BBB) and axonal transection as additional characteristics of these lesions (Schreiner et al., 2022; Mey et al., 2023). Up till now, several treatment strategies, including fingolimod (FTY720), natalizumab, glatiramer acetate, and interferon-β (IFN-β), have been proposed to regulate aberrant immune responses in MS patients. These medications primarily work by inhibiting immunological responses, which lowers the frequency of relapses and slows the advancement of neurologic impairment. Nevertheless, they have not achieved consistent success (Yousefi et al., 2019; Bejargafshe et al., 2019). According to reports, these therapies are unable to stop the deterioration of nerve tissue in patients with a severe type of MS (Bejargafshe et al., 2019).

Stem cell-based therapies, among the various available methods, hold significant potential to effectively reduce neuronal damage in both in vivo and in vitro models of neurological disorders (Abdallah et al., 2019). The use of mesenchymal stem cells (MSCs) for treating MS has demonstrated encouraging results (ArefNezhad et al., 2023; Zolfaghari Baghbadorani et al., 2023; González et al., 2022; Zhang Y. et al., 2023). Friedenstein and associates identified MSCs as multipotent stem cells in the late 1960s (Friedenstein et al., 1966). Kaplan first used the term “MSCs” in 1991 following his study on human bone marrow (BM) (Caplan, 1991). The capacity of engineered stem cells to multiply (self-renew) and differentiate is well-known. Mammalian tissues such as BM, adipose tissue (AT), dental pulp, amniotic fluid (AF), umbilical cord (UC), etc., are practically all known to contain MSCs. When organs and tissues are damaged, they are in charge of tissue regeneration and repair (Andrzejewska et al., 2019; Yu et al., 2014; Shi et al., 2018). By producing co-stimulatory molecules, they exhibit immunomodulatory features that enable them to control immunological responses and cytokine release (Jiang and Xu, 2020). MSCs are readily extracted from BM, AT, peripheral blood, the placenta, and the UC (Figure 1) (Caplan and Correa, 2011; Laroye et al., 2020). Afterward, they can be grown into a massive population in a culture medium to facilitate cell-based treatment (Planchon et al., 2018). Recently, stem cell-based therapy has given MS patients hope and is currently seen as the most popular noninvasive way to treat many disorders (Xiao et al., 2015).

The primary aim of this review is to investigate and evaluate the valuable capacity of MSCs in managing MS. This includes examining their immunomodulatory and regenerative capacities, discussing findings from preclinical and clinical studies, and identifying challenges such as optimal delivery methods and therapeutic integration. By leveraging the latest advancements in MSC-based research, this review seeks to provide a comprehensive perspective on their clinical applications, limitations, and future directions in MS therapy.

MS, a condition characterized by the breakdown of myelin and loss of axons, is the most frequently encountered non-traumatic debilitating ailment (Hauser et al., 2020). Sclerotic plaques and lesion development in the CNS and cerebrospinal cord are common characteristics of MS (Oh et al., 2018; Kurtzke, 1983). Through controlling synaptic architecture, neurogenesis, and oligodendrogenesis, the immune system plays a crucial role in the evolution of the nervous system. As a result, immune cells may play a part in the cause and development of MS (Rahmati et al., 2021; Sedaghat et al., 2019). Environmental, genetic, and hormonal variables have a significant role in the etiology of MS. Changes in the expression and functionality of immunological agents, including T-cell receptor (TCR), immunoglobulin (Ig), major histocompatibility complex (MHC), and cytokines, have been linked to an elevated risk of MS. According to current MS research, the BBB breach and the start of an autoimmune cascade trigger autoreactive T-cell migration to the CNS, which destroys the myelin sheath and results in sclerotic lesions and plaques. One of the leading causes of MS is the destruction of the myelin sheath, which is essential for axon survival and integration (Khan et al., 2024; Kuhlmann et al., 2023).

MS primarily presents in three distinct clinical courses. RRMS, the most common form of the disease, is characterized by exacerbations followed by complete or partial remissions, affecting 85%–90% of MS patients. After several years, approximately 50%–60% of these individuals progress to SPMS, marked by a gradual worsening of symptoms without remission. Approximately 15% of individuals are diagnosed with PPMS, a condition characterized by a gradual decline in neurological function, with or without episodes of exacerbation (Oliveira et al., 2020).

The primary effector cells involved in the demyelination and destruction of the CNS are T helper 1 (Th1) and T helper 17 (Th17) cells. Specific pro-inflammatory cytokines, such as interferon-gamma (IFN-γ), interleukin-17 (IL-17), tumor necrosis factor-alpha (TNF-α), and IL-1, are produced by Th1 and Th17. Additionally, MS lesions contain CD8⁺ T lymphocytes, particularly in the vicinity of the blood vessels. Prior research has demonstrated that in MS patients, CD8⁺ T cells proliferate more than CD4⁺ T cells, which is mainly linked to axon damage (Khan et al., 2024; Dong et al., 2021; Dadfar et al., 2024). Other immune cells have significant involvement in the development of lesions and plaques in addition to T cells’ responsibilities in the pathogenesis of MS. More CNS antigens are exposed due to myelin being destroyed by Th1 cytokines, which activate macrophages. Although autoreactive T cells are the primary effector cells involved in the development of MS, there have been indications in some studies that autoreactive B cells also contribute significantly to the demyelination and axonal damage by presenting antigens, producing autoantibodies and secreting cytokines (Sedaghat, 2018). Autoantibodies are significant immune mediators present in MS plaques. Several reports suggest a potential correlation between immunoglobulin G (IgG) and the manifestation of symptoms related to MS. Additionally, it has been demonstrated that IgG, particularly IgG targeting myelin fundamental proteins (MBP) and proteolipid proteins (PLP), may be regarded as characteristic markers of the disease. However, their specific roles in the pathogenesis of MS have not been fully elucidated (Maroto-García, 2023; Amin and Hersh, 2023). Research has shown that the introduction of T-cell lines or clones targeting CND myelin antigens into genetically identical, naïve recipient mice has led to the development of experimental autoimmune encephalomyelitis (EAE) as a suitable animal model for MS (Ben-Nun and Lando, 1983; Ben‐Nun et al., 1981; Zamvil et al., 1985). Therefore, inflammation has been seen in MS due to damage to myelin along with axons and neurons, finally resulting in neurodegeneration. The primary means of diagnosis, in addition to clinical presentation, is the temporal and regional appearance of inflammatory lesions as shown by magnetic resonance imaging (Dadfar et al., 2024; Ananthavarathan et al., 2024).

MSCs are multipotent stromal cells that can undergo self-renewal and differentiate into various mesenchymal cell lineages (Dominici et al., 2006; Cesarz and Tamama, 2016; Afkhami et al., 2023; Mirshekar et al., 2023). They can also reduce excessive immune responses and hyperinflammatory processes by inducing the expression of Foxp3+ in CD4 T cells in a laboratory setting (English et al., 2009; Aliniay-Sharafshadehi et al., 2024). MSCs have various ways of regulating the immune system, such as promoting the production of regulatory T cells (Tregs) through direct interaction with T cells and releasing anti-inflammatory substances in a laboratory setting. These mechanisms enable MSCs to manage the development of autoimmune conditions like MS (Figure 1) (Yang et al., 2023; Andalib et al., 2023; Teymouri et al., 2024). When given the right triggers, MSCs can develop into various specialized cell types that originate from mesenchymal tissue, such as bone cells, muscle cells, ligament cells, cartilage cells, and tendon cells (Heldman et al., 2014; Liu et al., 2009; Fakouri et al., 2024). Various non-mesodermal cell lineages have been observed to undergo differentiation, including alveolar cells, hepatocytes, epithelial cells, astrocytes, mature neurons, and neural precursors. These findings indicate that MSCs may play a possible role in the inherent healing process of tissues (Liu et al., 2009; Weiss and Dahlke, 2019; Uccelli et al., 2008).

Previous studies have provided evidence that suggests these cells hold potential as viable treatment options for a range of neurological disorders, such as MS and amyotrophic lateral sclerosis (ALS) (Najafi et al., 2023; Vaheb, 2024). The immunomodulatory impacts of MSCs may be demonstrated through their direct engagement with immune cells or through the transmission of paracrine signals. Research has shown that MSCs can inhibit the differentiation of Th17 and Th1 cells. Research has indicated that MSCs expanded in a laboratory setting can hinder the growth of T lymphocytes, B lymphocytes, and natural killer (NK) cells, as well as impede the maturation and differentiation of dendritic cells (DCs) (Yang et al., 2023; Mei et al., 2024). In recent times, stem cell-based therapy has become a promising strategy for treating patients with MS. It is currently considered the most preferred and least intrusive treatment option for a range of medical conditions (Papaccio et al., 2017; Islam et al., 2023).

In RRMS, inflammation is dominant, driven by autoreactive T cells and a disrupted BBB. Several studies have demonstrated a reduction in relapse frequency and lesion formation in preclinical models of RRMS following MSC therapy (Vaheb, 2024; Gavasso et al., 2024). Applying MSCs in clinical research involving patients with RRMS has yielded promising results. The study observed a trend toward reduced levels of pathogenic inflammatory Th1 and Th17 cell subtypes, accompanied by a decrease in inflammation as indicated by MRI scans. Notably, there was also an increase in regulatory B cells (Llufriu et al., 2014a). In progressive forms of MS, such as PPMS and SPMS, the primary challenge lies in addressing neurodegeneration and promoting repair mechanisms. To treat PPMS and SPMS, MSC therapy has been investigated as a potential option for targeting various therapeutic targets (Gavasso et al., 2024; Ghareghani et al., 2024). The first placebo-controlled trial utilizing intrathecal administration of MSCs in patients with active progressive MS demonstrated a positive impact on disease outcomes. This included reduced neurofilament light chain levels (NfLs), stabilization or improvement of disability scores, and the achievement of status without evidence of disease activity (Roig-Carles et al., 2021; Colasanti et al., 2014). Despite showing signs of neuroprotection, MSC did not seem to influence humoral immunity to common antigens or peripheral T-cell subsets in the context of SPMS (Connick et al., 2012). This suggests that there may be significant differences in the mechanisms underlying the effects of MSCs in RRMS and progressive MS. It highlights the idea that, depending on the local environment, disease state, and phenotype, MSCs exhibit diverse immunomodulatory effects on various types of immune cells (Zhao, 2019).

MSCs have the potential to provide structural support to axons and improve the stability of neurons. Additionally, they are believed to possess antioxidant and anti-apoptotic properties and can release trophic factors. Additionally, they have the potential to facilitate the generation of fresh neurons and glial cells, such as oligodendrocytes (ODCs) (Guimarães-Camboa et al., 2017; Song et al., 2018). In individuals with MS, MSC has the potential to augment the differentiation of neural cells, reduce neuronal cell death, and stimulate the formation of new blood vessels, ultimately contributing to the repair of the CNS (Gavasso et al., 2024). According to recent research, it has been determined that MSCs can enhance peripheral tolerance by suppressing the differentiation and function of DCs, consequently diminishing antigen presentation and impeding the expansion of self-reactive T cells (Zhuo et al., 2023). In addition, MSCs can produce hepatocyte growth factor (HGF), which leads to an increase in tolerogenic DCs. Research has revealed that the administration of MSCs in combination with HGF results in a reduction of CNS inflammatory reactions and the infiltration of immune cells in mice with EAE. Consequently, MSCs derived from HGF demonstrate potential as a viable therapeutic approach for MS and other autoimmune disorders (Bai et al., 2012; Mansoor et al., 2019).

IL-6 and CD20 are key molecules intricately linked to the inflammasome and immune regulation, playing significant roles in the inflammatory cascade observed in MS (Margoni et al., 2022; Chmielewska and Szyndler, 2023). One of the most well-known pro-inflammatory cytokines is thought to be IL-6. More than 100 nations have approved using the neutralizing monoclonal antibody tocilizumab to treat autoimmune diseases by blocking IL-6 (Kishimoto, 2005; Tanaka, 2014). While circulating IL-6 levels are as low as 1–5 pg/mL under homeostatic settings, they may increase by over 1,000 times during inflammatory states, and in severe situations that result in sepsis, IL-6 levels as high as µg/mL have been seen (Waage et al., 1989). IL-6 is synthesized by myeloid cells in response to stimulation of Toll-like receptors, in conjunction with the cytokines IL-1β and TNF-α. This interaction initiates a feed-forward loop that significantly enhances the production of IL-6 in the context of inflammatory responses (Tanaka et al., 2014). IL-6 is a key mediator in the activation of the inflammasome, playing a significant role in chronic inflammation and tissue damage associated with MS. Elevated levels of IL-6 have been correlated with disease severity, underscoring its contribution to the persistence of neuroinflammation and the impairment of remyelination processes (Stampanoni Bassi et al., 2020; Vandebergh et al., 2022).

MSCs possess the ability to express and secrete various cytokines, including IL-6. However, they generally produce lower levels of IL-6 than immune cells such as T cells and macrophages. Under certain conditions, such as exposure to inflammatory stimuli or interaction with immune cells, MSCs can increase their production of IL-6 (Kerkis et al., 2024; Philipp et al., 2018; Huang et al., 2022). MSCs demonstrate potential in regulating IL-6 expression in the context of neuroinflammation. Both autocrine and paracrine signaling loops, along with feedback control from the immune system, contribute to the downregulation of IL-6 by MSCs (Hofer and Tuan, 2016; Lopez-Santalla et al., 2020; Molnar et al., 2022). The complex relationship between MSCs and endogenous IL-6 production depends on experimental conditions and cellular interactions (Dorronsoro et al., 2020). Gu et al. (2016) demonstrated that the release of endogenous IL-6 induced by MSCs led to an upregulation of IL-6 receptor (IL-6R) and phosphorylated signal transducer and activator of transcription 3 (p-STAT3) levels in astrocytes subjected to oxygen and glucose deprivation. Notably, a significant increase in the ratio of B-cell lymphoma 2 (Bcl-2) to Bcl-2-associated X protein (Bax), critical downstream components of the STAT3 signaling pathway, was observed. This study elucidated the neuroprotective effects of MSC transplantation in a rat model of neonatal hypoxic-ischemic brain injury, suggesting that these effects are partially mediated by IL-6, which enhances the anti-apoptotic properties of damaged astrocytes through the IL-6/STAT3 signaling pathway. Through paracrine signaling and immunomodulatory mechanisms, MSCs have demonstrated their ability to inhibit the production of IL-6 by immune cells such as T cells and macrophages. However, MSC-derived IL-6 has also been shown to stimulate or modulate the activity of other immune cells, which in turn affects endogenous IL-6 levels (Song et al., 2020; Toh, 2017; Glenn and Whartenby, 2014). MSCs have anti-inflammatory properties that influence IL-6 levels in a variety of settings. They can also reduce IL-6 synthesis by inhibiting immune cell activation (Dabrowska et al., 2021; Saadh et al., 2023).

CD20, a surface marker predominantly expressed in B cells, is another molecule associated with the pathogenesis of MS. It plays a crucial role in B cell activation, antigen presentation, and the production of pro-inflammatory cytokines (Margoni et al., 2022; de Sèze et al., 2023). In recent years, there has been a growing interest in CD20-targeting therapies, specifically anti-CD20 monoclonal antibodies that facilitate B-cell depletion, including ocrelizumab, rituximab, and ofatumumab. The therapeutic scenario for treating MS patients has significantly expanded due to the remarkable effectiveness and favorable safety profile of these selective B-cell-depleting treatments (Hauser et al., 2020; Hauser et al., 2008; Montalban et al., 2017). MSCs can complement this approach by further modulating B cell activity, promoting regulatory B cells, and inhibiting the production of autoantibodies that exacerbate disease progression (Yordanova et al., 2024; Veh et al., 2024). The negative regulatory influence of MSCs on B lymphocytes may result from direct contact with B cells, leading to the release of various soluble cytokines that impact B cell function. This, in turn, prevents B cells from proliferating and reduces the generation of memory B cells and plasma cells, which decreases the number of B cells that secrete cytokines, chemokines, and antibodies (Hoorweg et al., 2015). MSC can enhance the synthesis of granulocyte-macrophage colony-stimulating factor (GM-CSF) through the involvement of stem cell antigen 1/lymphocyte antigen 6AIE protein while simultaneously inhibiting the maturation of B lymphocytes. Transforming growth factor-beta (TGF-β) secreted by MSCs plays a crucial role in suppressing B lymphocytes by downregulating or inhibiting IL-7 produced by stromal cells (Hoorweg et al., 2015; Liu et al., 2015). The application of MSCs in MS, particularly concerning IL-6 and CD20, highlights their dual role in targeting innate and adaptive immune responses.

Autoinflammatory and autoimmune conditions are commonly managed with immunosuppressive medications, although their efficacy may vary among a diverse patient cohort. Consistent use of drugs may exacerbate adverse reactions, while prolonged suppression of the immune system heightens susceptibility to infections over time (Jung and Kim, 2022; Wigerblad and Kaplan, 2023). Recent studies have shown that MSCs are significantly involved in immune system regulation and tissue regeneration, suggesting their potential as a therapeutic approach for autoimmune conditions (Ding et al., 2015; Lv et al., 2014). Numerous recent clinical trials have been carried out using MSCs to manage MS. In the second phase of a randomized clinical trial, five patients with RRMS received MSC treatment for 6 months, leading to decreased brain MRI lesions (Llufriu et al., 2014b). Recently, Meng et al. (Meng et al., 2018) found that the systemic delivery of allogeneic UC-MSCs resulted in amelioration of the clinical manifestations in patients with MS. UC-MSCs therapy also reduced and Expanded Disability Status Scale (EDSS) and the frequency of foci, as determined with MRI. The most frequently reported adverse outcomes included elevated body temperature, head pain, and lightheadedness of feelings. The intervention also decreased levels of IL-2, CD86, HLADRB1, and CTLA-4 in peripheral blood (Meng et al., 2018). Other open-label prospective clinical trials (phase I/IIa) also revealed the clinical potentials of BM-MSCs in MS patients. Treatment reduced EDSS without altering lesion volume. Early-stage lesion reduction correlated with increased VEGF, IL-6, and IL-8 levels (Dahbour et al., 2017). Another study on 24 patients with active-progressive MS exhibited that the reduction in EDSS has an intimate association with increased FoxP3+CD4⁺CD25⁺ cells and decreased lymphocyte proliferation (Petrou et al., 2021a). Additional double-masked phase II clinical trials that were randomized and evaluated the effects of intrathecal (IT) or IV transplantation of MSC yielded comparable findings. The levels of NF-L CSF were notably reduced 6 months following the administration of MSC-IT treatment. Nine out of fifteen patients in the MSC-IT group experienced a reduction of more than 50% in their NF-L levels, as opposed to 33% in the MSC-IV group and 6.6% in the control group (Petrou et al., 2022). Llufriu et al. (2014b) found a non-significant decrease in the occurrence of Th1 (CD4⁺ IFN-γ+) cells in the bloodstream of patients who received autologous BMMSCs therapy. Of course, individuals who received MSC treatment demonstrated a reduced average total count of gadolinium-enhancing lesions (GEL). Finally, a shift from Th1 to Th2 immunity in hUCMSC-treated MS has been supported, according to reports (Li et al., 2014). On the other hand, Fernández et al. (2018) discovered that the IV administration of AT-MSCs did not lead to a statistically significant improvement in clinical outcome measures. These metrics encompassed the frequency of relapses, the EDSS score, the non-normalized cerebral volume on MRI scans, or the number of active lesions observed in gadolinium-enhanced T1 scans (Fernández et al., 2018). Yamout et al. (2010) administered autologous BM-derived MSCs via injection to nine with SPMS and one patient with RRMS. They documented improved clinical results in their patients following 3 months to 1 year. In this phase 2a clinical study, 10 individuals diagnosed with SPMS were administered MSCs intravascularly over 6 months. Following this intervention, the investigators examined to assess the impact of MSCs on the processes of remyelination and neuroprotection (Yamout et al., 2010). In a clinical study involving 15 patients with RRMS who had not responded to traditional disease-modifying therapies (DMTs), MSCs demonstrated systemic benefits for the immune system. The percentage of activated myeloid DCs and lymphocytes decreased while the number of regulatory T cells increased. Notably, these MSC-induced effects persisted in vitro, as immune cells from treated individuals demonstrated a reduction in lymphocyte proliferation. The effectiveness of MSC treatment was clinically supported by a reduction in the mean EDSS scores and the absence of new MRI lesions at the six-month follow-up (Karussis et al., 2010). Furthermore, in their 2007 study, M. Bonab and colleagues (MOHY et al., 2007) investigated the progression of the disease following the IT administration of MSC to 10 MS patients. Consequently, it has been observed that the advancement of the disease has progressively decelerated in 50% of the subjects being investigated (MOHY et al., 2007). Table 2 summarizes studies on the clinical application of stem cell therapy for MS and related adverse effects, along with observed results in patients.

There are presently specific disease-modifying treatments (DMTs) available to stop the accumulation of structural brain damage associated with MS and its adverse effects on MS patients (Filippi et al., 2022; Wiendl et al., 2021). The advent of more effective DMTs during the past several years has significantly changed the landscape of MS treatment (Comi et al., 2017; Giovannoni et al., 2020; Goldschmidt and McGinley, 2021). Currently, available DMTs are categorized based on their efficacy into two primary classifications: high-efficacy (HE) DMTs and moderate-efficacy (ME) DMTs. The HE DMTs include natalizumab, fingolimod, ozanimod, siponimod, alemtuzumab, cladribine, ocrelizumab, and ofatumumab. In contrast, the ME DMTs comprise glatiramer acetate, interferon-beta (IFN-β), teriflunomide, and dimethyl fumarate (Comi et al., 2017; Giovannoni et al., 2020; Simpson-Yap et al., 2021). Additionally, high-dose methylprednisolone is frequently used to manage acute relapses by suppressing inflammation (Sormani et al., 2021; Travers et al., 2022). Subcutaneous IFN-β1b, the first MS DMT ever created, was authorized by the Food and Drug Administration (FDA) in 1993 to treat progressive relapsing MS (PRMS) (Bayas and Gold, 2003).

DMTs have demonstrated effectiveness in managing MS; however, they are associated with several limitations. These limitations include heterogeneous responses among patients, the potential for long-term toxicity, and an incomplete capacity to halt disease progression, particularly in the later stages of the condition (Langer-Gould et al., 2023). In contrast, cell-based therapies, particularly those utilizing MSCs, have garnered attention due to their anti-apoptotic properties, paracrine signaling capabilities, and multidirectional differentiation potential. These characteristics have prompted their investigation in translational research and clinical trials aimed at addressing prevalent diseases, including neurological disorders that affect CNS structures, such as stroke, Huntington’s disease (HD), Parkinson’s disease (PD), MS, and SCI (Andrzejewska et al., 2021).

An essential component of MSC therapy involves monitoring the therapeutic outcomes and identifying potential complications through follow-up and evolutionary biomarkers. These biomarkers provide crucial insights into the dynamics of MSC behavior, their interaction with the host environment, and the overall therapeutic efficacy (Ghareghani et al., 2024; Iacobaeus et al., 2019; Granchi et al., 2019). MSCs exert immunomodulatory effects, which can be tracked using biomarkers such as IL-4, IL-10, IL-13, IL-16, and TGF-β, and reductions in pro-inflammatory cytokines like IL-6 and TNF-α. The normalization of these markers indicates the anti-inflammatory efficacy of MSCs, particularly in diseases like MS, where inflammation is a hallmark (Petrou et al., 2022; Li et al., 2014). Neurofilament proteins (NF), which are released into the CSF following axonal injury in the central nervous system, serve as reliable indicators of axonal damage and neuronal death. Among these, the neurofilament light chains (NF-L) are the most extensively studied subtype (Cairns et al., 2004). Since NF are essential parts of the neuron’s cytoskeleton, any neurological condition that damages neurons or axons may result in elevated CSF levels of these proteins. The CSF of patients with MS consistently contains elevated levels of NF-L, indicating that NF-L may function as a biomarker for MS disease activity, including subclinical activity, as well as for the responsiveness to various MS therapies. Additionally, studies have demonstrated that increased blood levels of NF-L in the early stages of MS may predict future increases in MS lesions and brain atrophy (Williams et al., 2021; Chitnis et al., 2018; Novakova et al., 2017; Håkansson et al., 2017). The most potent B-cell chemoattractant, the CXCR5 ligand CXCL13, is present in both active lesions of MS and the CSF of MS patients. Elevated levels of CXCL13 have been shown to predict the progression from clinically isolated syndrome (CIS) to MS. Furthermore, research indicates that CXCL13 is associated with disease exacerbations and a poorer prognosis in MS (Khademi et al., 2011). MSC-mediated healing processes can be identified by tissue regeneration markers such as matrix metalloproteinases (MMPs), VEGF, and fibroblast growth factor (FGF). Particularly in the context of MS, these indicators are valuable for assessing the recovery of vascular and neuronal structures in the central nervous system (Gavasso et al., 2024; Hofer and Tuan, 2016; Farooq et al., 2021).

Biomarkers like C-reactive protein (CRP) and systemic metabolic markers, such as changes in glucose and lipid profiles, provide insights into broader systemic responses to MSC administration (Yang et al., 2018; Weiss et al., 2021).

A class of micromolecules with potential as biomarkers for MS is microRNAs, which are small non-coding RNAs that regulate post-transcriptional gene expression (Raphael et al., 2015).

Research on specific metabolic pathways associated with the pathophysiology of MS provides an additional approach to identifying biomarkers. For example, studies have shown that the kynurenine pathway, the primary mechanism for tryptophan degradation, regulates immune activity. Evidence suggests that during relapses, the CSF of MS patients exhibits elevated levels of the neuroprotective metabolite kynurenine acid (Lim et al., 2010).

By integrating these biomarkers into the clinical evaluation framework, it becomes possible to optimize the therapeutic potential of MSCs while minimizing adverse effects.

In recent years, there has been a significant focus on stem cell therapy. MSC therapy in translational medicine has considerable expectations. However, various aspects of MSC treatment need to be well-defined. Given the variety of methods explored, the full extent of the potential impacts of MSC therapy remains uncertain (Lukomska et al., 2019). Moreover, due to their possible application in autologous transplantation, MSCs have gained significant clinical interest. Numerous clinical trials involving MSCs have been conducted, with many more currently under investigation. As the clinical use of MSCs continues to expand, particularly in the context of both autologous and allogeneic transplantation, long-term monitoring of patients is essential to assess the safety and efficacy of MSC therapy. According to recent studies, thousands of patients have received culture-expanded allogeneic or autologous MSCs to treat various diseases (Squillaro et al., 2016; Shandil et al., 2022). MSC treatment has proven highly effective in most cases; however, long-term monitoring remains crucial to assess the potential hazards associated with MSC transplantation. Numerous in vitro and in vivo investigations provided evidence for MSC differentiation into specific cell types (Nowakowski et al., 2016). While most in vivo studies have confirmed the safety of MSC therapy and demonstrated promising results, the therapeutic benefits of MSC-based treatments remain limited. Furthermore, there are potential risks associated with using MSCs in specific cellular niches that should be carefully evaluated in long-term follow-up studies (Lukomska et al., 2019).

Although MSC therapy holds significance in treating MS and other diseases, it is essential to acknowledge the potential adverse effects associated with its administration. One of the most notable challenges is the method of administration. The route of administration significantly influences the therapeutic outcome, and it has been shown that different routes can lead to varying levels of efficacy and safety (Mansoor et al., 2019; Lukomska et al., 2019). The approach to administering MSCs is greatly determined by the specific therapeutic objectives. For instance, IV administration, one of the most common routes, has been associated with limited success in MS models. Studies indicate that MSCs administered IV are often trapped in the lungs and liver, and their presence in the inflammatory lesions of the CNS is minimal. This inefficiency in homing to the target tissue is primarily due to the BBB, which prevents the passage of MSCs into the brain, thus limiting their therapeutic effects in MS patients (Abramowski et al., 2016; Cerri et al., 2015). Moreover, MSCs derived from BM have shown poor therapeutic efficacy when administered systemically. They fail to reach the damaged neurons, and in some cases, they are cleared from the system within a month post-administration (Neirinckx et al., 2021). The use of local administration techniques is restricted due to the associated risks of direct tissue injection or intraventricular infusion aimed at enhancing MSC homing. While local injections have the potential to deliver drugs precisely where they are needed, they also carry the risk of varying degrees of local inflammation, infection, or tissue damage at the injection site. The dosage and frequency of MSC therapy directly influence both safety and effectiveness. Excessive administration of MSCs may lead to abnormal tissue growth due to overuse, immune reactions or tumor formation resulting from improper dosing. It is crucial to understand how the doses are spatiotemporally related and to determine the optimal total number of doses to minimize cumulative adverse effects over time (Caplan et al., 2019; Galipeau and Sensébé, 2018; Kabat et al., 2020; Afkhami et al., 2024). Regarding broader systemic effects, adverse reactions can vary from transient symptoms, such as nausea, fever, and headache, to more serious complications. Several studies have documented these adverse effects, including the occurrence of transient symptoms like vomiting, nausea, and impaired visual acuity in 4.3% of individuals receiving MSC infusion for steroid-resistant graft-versus-host disease (GVHD) (Table 3) (Dotoli et al., 2017). These side effects underscore the importance of monitoring patients during and after MSC treatment, especially when high doses or repeated infusions are involved.

Lastly, the quality of the MSC product and its source play an essential role in determining safety outcomes. The donor’s age appears to be the most critical parameter to consider. MSCs derived from older donors or patients with comorbidities may exhibit compromised functionality, affecting their therapeutic potential and increasing the risk of adverse reactions. This challenge is especially relevant in autologous transplantation, where geriatric patients may struggle to obtain a sufficient number of viable MSCs for treatment (Dufrane, 2017; Liu et al., 2017; Kokai et al., 2017; Pachón-Peña et al., 2016).

In summary, while MSCs present a novel and promising approach to treating MS, it is crucial to recognize the potential adverse effects and complications that may arise from their application.

MSC therapy has demonstrated significant potential as an innovative approach for managing MS, addressing both the immunological and neurodegenerative aspects of the disease. MSCs exhibit robust immunomodulatory properties, promote remyelination, and support neuroregeneration, making them a promising candidate for comprehensive MS therapy. Preclinical and clinical studies have shown encouraging results, particularly in reducing inflammation and slowing disease progression. However, limitations such as optimal dosing, delivery methods, and long-term safety concerns remain critical challenges. Despite these challenges, MSC therapy represents a transformative step forward in personalized medicine for MS, offering hope for improved quality of life for patients. Future research should address the remaining challenges associated with MSC therapy, such as optimizing delivery routes and dosing regimens to enhance therapeutic efficacy and reduce potential adverse effects.