Mesenchymal stem cells in neurological disorders: Insights from clinical trials

Abstract

Mesenchymal stem cells (MSCs) exhibit unique properties that make them promising candidates for cell therapy, particularly in neurological disorders. They can be derived from various tissues, with bone marrow, adipose tissue, umbilical cord, and placenta being the most common sources. Evidence suggests that the tissue of origin significantly influences MSC characteristics, including secretome composition, proliferation rate, and adhesion capacity.

Clinical trials have demonstrated the safety and therapeutic potential of MSCs in conditions such as spinal cord injury, multiple sclerosis, and stroke. MSC therapy has been associated with improvements in motor, sensory, and cognitive functions, as well as enhanced quality of life. Mechanistically, MSCs promote neuroprotection, reduce inflammation, and modulate immune responses. In spinal cord injury, intrathecal administration of adipose- and bone marrow-derived MSCs has led to significant functional recovery, with single high-dose treatments often yielding better outcomes than multiple lower doses. In amyotrophic lateral sclerosis, bone marrow-derived MSCs have shown potential in slowing disease progression, though higher doses do not always result in greater benefits. In multiple sclerosis, high doses of umbilical cord-derived MSCs improved quality of life and prevented disease progression, whereas lower doses of bone marrow-derived MSCs provided limited functional benefits.

While MSC therapy is considered safe, patient responses vary, and a definitive correlation between administered dose and therapeutic effects remains elusive. The small number of studies using comparable protocols impedes comparison of other relevant factor, limits the drawing of conclusions and underscore the importance of developing standardized protocols to optimize MSC-based treatments and maximize their clinical efficacy.

Abbreviations

MSCs –

Mesenchymal stem cells

BM- MSCs -

Bone marrow mesenchymal stem cells

UC-MSCs -

Umbilical cord mesenchymal stem cells

WJ-MSCs -

Wharton's jelly mesenchymal stem cells

AD-MSCs -

Adipose tissue mesenchymal stem cells

PMSCs -

Placenta-derived MSCs

A-MSCs -

Amniotic membrane

C-MSCs -

Chorionic membrane

D-MSCs -

Placenta decidua

IL -

Interleukin

TGF-β -

Transforming growth factor beta

PGE2 -

Prostaglandin E2

IDO -

Idoleamine-2,3-dioxygenase

BDNF -

Brain-derived neurotrophic factor

NGF -

Nerve growth factor

IGF-1 -

Insulin-like growth factor 1

GDNF -

Glial cell-line-derived neurotrophic factor

VEGF -

Vascular endothelial growth factor

βFGF -

Beta fibroblast growth factor

HGF -

Hepatocyte growth factor

PDGF -

Platelet-derived growth factor

TNF-α -

Tumor necrosis factor α

MMPs -

Matrix metalloproteinase

HLA-DR -

Human Leukocyte Antigen-DR isotype

IV –

Intravenous

IT

Intrathecal

ID

Intradiscal

IN

Intranasal

IM

Intramuscular

ITL-

Intralesional

IA

Intra-arterial

ITR –

Intraventricular

ITM –

Intramedullary

MCP-1

Monocyte chemoattractant protein 1

SDF-1 -

Stromal cell-derived factor 1

NCAM1 -

Neural Cell Adhesion Molecule 1

Treg –

Regulatory T cells

CSF -

Cerebrospinal fluid

MS –

Multiple Sclerosis

1. Mesenchymal stem cells

Mesenchymal stem cells (MSCs) are being intensively studied as a novel therapeutic strategy for diverse medical conditions. It is possible to isolate MSCs from adult tissues such as bone marrow and adipose tissue [1] but also from neonatal tissues such as the placenta and umbilical cord [2]. Although MSCs can be obtained from different sources, they all share common characteristics, they adhere to plastic under normal culture conditions, are able to differentiate into osteoblasts, adipocytes, and chondroblasts, and to self-renew [3]. MSCs are also characterized by the expression of several surface markers such as CD105, CD73, CD90, CD166, CD29 and CD44 and by not expressing CD45, CD34, CD14, CD11b, CD79α, CD19 and HLA-DR [4]. Since MSCs express low levels of MHC class I, MHC class II and co-stimulatory molecules such as CD40, CD40 ligand, CD80 and CD86, they are characterize by a low immunogenicity [3].

To modulate immune responses, MSCs can directly communicate with immune cells through cell-to-cell interactions or by secreting paracrine factors such as interleukin 10 (IL-10), transforming growth factor beta (TGF-β), prostaglandin E2 (PGE2), indoleamine-2,3-dioxygenase (IDO), Nitric Oxide (NO), and FAS/FASL [3]. Additionally, MSCs secrete growth factors like the brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), insulin-like growth factor 1 (IGF-1), glial cell-line-derived neurotrophic factor (GDNF), vascular endothelial growth factor (VEGF) [5], beta fibroblast growth factor (βFGF) and hepatocyte growth factor (HGF) [6]. These growth factors are known for their ability to promote the survival of damaged neurons and oligodendrocytes [7]. MSCs are chemoattracted to the injured sites by accumulated chemokines and cytokines, including platelet-derived growth factor (PDGF), tumor necrosis factor α (TNF-α), IL-1, IL-6, and IL-8. Once in the damaged tissue, the adherence of MSCs is facilitated by adhesion molecules such as selectins and integrins. Finally, matrix metalloproteinases (MMPs) and tissue inhibitors of these proteins promote the degradation of the extracellular matrix facilitating the infiltration of MSCs at the sites of injuries [3].

Like other stem cells, MSCs can be used for both autologous and allogeneic administration. While autologous administration avoids immunological responses, obtaining a sufficient number of cells can be challenging, requiring significant investment and potentially delaying treatment. And although allogenic MSCs have low immunogenicity, the risk of immune rejection still exists. Despite this risk, the allogeneic approach can address some of the limitations associated with the autologous use of cells. Furthermore, because the cells used for allogenic administration can be cryopreserved, they may be immediately available, thus offering advantages in terms of production time and cost [8,9]. While MSCs have characteristics that make them attractive for cell therapy, there are limitations and factors that can impact the therapeutic potential of MSCs and need to be considered, including the impact of tissue origin, effects of the cryopreservation process, culture time, medium supplementation, dose, or delivery route [8].

2. Sources of human mesenchymal stem cells

MSCs can be obtained from a variety of tissues (Fig. 1), however, the cells used in clinical trials are obtained mostly from bone marrow, umbilical cord, adipose tissue, and placenta [10].

Fig. 1.

Characteristics of MSCs. MSCs can be isolated from various tissue sources, including bone marrow, adipose tissue, umbilical cord, and placenta. These cells possess the ability to self-renew and differentiate into osteoblasts, chondroblasts, and adipocytes. MSCs are also characterized by the expression of specific surface markers, they are positive for CD105, CD73, CD90, CD166, CD29 and CD44 and negative for CD45, CD34, CD14, CD11b, CD79α, CD19 and HLA-DR. HLA-DR (Human Leukocyte Antigen-DR isotype). Illustration made with biorender.

2.1. Bone marrow-derived mesenchymal stem cells

The procedure for obtaining bone marrow mesenchymal stem cells (BM-MSCs) typically involves aspiration of bone marrow from the iliac crest [11]. This is by far the most commonly used source of MSCs, followed by cells from adipose tissue, umbilical cord, and placenta. Amable, P.R. et al. (2014) reported that BM-MSCs secrete lower concentrations of pro-inflammatory cytokines such as IL-6, IL-8, IL-7 and IL-12 compared to adipose tissue mesenchymal stem cells (AD-MSCs) and Wharton's jelly mesenchymal stem cells (WJ-MSCs) [12]. Additionally, BM-MSCs secrete lower levels of matrix metalloproteinases (MMP), such as collagenase 1 (MMP1) and stromelysin 1 (MMP3), and do not secrete collagenase 3 (MMP13). Since these enzymes are involved in the degradation of bone, cartilage and tendons, BM-MSCs are considered strong candidates for the regenerations of these tissues [12].

2.2. Umbilical cord-derived mesenchymal stem cells

MSCs from the umbilical cord can be extracted from the perivascular region, umbilical cord tissue, and Wharton's jelly. Since the umbilical cord is harvested after birth without the need for invasive method, this process raises fewer ethical concerns. Additionally, umbilical cord tissues provide a substantial number of cells, which is a major advantage [13].

When comparing the proliferative potential of MSCs from different sources, it was reported that umbilical cord mesenchymal stem cells (UC-MSCs) exhibit the highest proliferation potential, followed by adipose tissue mesenchymal stem cells (AD-MSCs), placenta-derived MSCs (PMSCs) and BM-MSCs [14]. Moreover, WJ-MSCs show a stronger anti-inflammatory profile compared to AD-MSCs and BM-MSCs, as they secrete higher levels of IL-1RA and IFN-α, as well as the highest levels of IL-6 and IL-8, TGF-β2, and PDGF-AA [12].

In a spinal cord injury model, UC-MSCs and BM-MSCs were reported to have a similar efficacy in inducing symptom relief, however, UC-MSCs demonstrated a higher survival rate after administration, suggesting that a lower number of cells might be required to achieve therapeutic effects [15].

2.3. Adipose tissue-derived mesenchymal stem cells

AD-MSCs are an attractive alternative source of MSCs, as they are easily accessible and can be obtained from waste tissues following surgical procedures such as liposuction and abdominoplasties [16]. MSCs isolated from adipose tissue share many similarities with those from bone marrow, yet they also exhibit distinct characteristics. Compared to BM-MSCs, AD-MSCs have a higher and faster proliferative capacity, and the proliferation is less influenced by the donor's age [1,17]. In a preclinical study on spinal cord injury comparing BM-MSCs and AD-MSCs, both cell types demonstrated survival and migration towards the injury site without significant differences. However, AD-MSCs shown greater potential in enhancing angiogenesis, likely due to their higher levels of BDNF and VEGF, which are known to promote cellular survival and angiogenesis. In terms of the outcomes in animal's models of spinal cord injury, both BM-MSCs and AD-MSCs improved locomotor function and reduced the size of the lesion cavity, although AD-MSCs led to superior results [17].

2.4. Placenta-derived mesenchymal stem cells

The placenta is composed of multiple layers, and PMSCs are a combination of MSCs derived from the amnion, chorion, and decidua. After childbirth, PMSCs can be collected non-invasively and in large quantities. Like UC-MSCs, these cells are younger and are likely less exposed to harmful substances such as reactive oxygen species, chemical and biological agents, and physical stressors, which may enhance their efficacy and safety in therapeutic applications [18].

A comparison between UC-MSCs and PMSCs revealed that PMSCs secrete higher levels of VEGF, IGF-1 and HGF. In terms of adhesive properties, PMSCs exhibit more dispersed microvilli-like structures, suggesting they may possess stronger adhesive qualities. However, a drawback of PMSCs is their lower proliferation capacity [19]. In a study comparing MSCs derived from amniotic membrane (A-MSCs), chorionic membrane (C-MSCs), placenta decidua (D-MSCs) and UC-MSCs, it was found that C-MSCs, D-MSCs and UC-MSCs were similar in most markers analyzed (CD105, CD73, CD90, CD45, CD34, CD11b, CD19, HLA-DR, CD14, CD3, HLA-G and CD56) and expressed higher levels of CD29 and CD44 compared to A-MSCs. The authors also reported that A-MSCs have the lowest proliferation potential [20].

3. Variability associated with mesenchymal stem cells

The variability observed in the secretome and characteristics of MSCs appears to be influenced not only by the tissue source, but also by the donors themselves. Factors such as age, gender, and medical history contribute to differences in MSCs derived from the same tissue of different donors [21,22]. Mohamed-Ahmed, S. et al. (2018) found that AD-MSCs and BM-MSCs exhibit varying proliferative, osteogenic, chondrogenic, and adipogenic differentiation capacities depending on the donor. Furthermore, the authors concluded that age alone does not account for variability in cell effects as their study involved MSCs from donors of similar ages (between 8 and 14 years) [11]. Siegel, G. et al. (2013) reported that BM-MSCs isolated from younger donors express higher levels of markers such as CD71, CD146^, and CD274, and female donors show higher levels of CD119 and CD130 [21]. However, Phinney, D.G. et al. (1999) found no correlation between the growth rate of BM-MSCs and donor age or gender [23]. These findings underscore the variability in MSCs, though it remains unclear whether these differences affect their therapeutic potential. In an animal model of spinal cord injury, Neuhuber, B. et al. (2005), observed differences in motor and sensorimotor recovery induced by BM-MSCs from different donors [24] supporting the assumption that the donor from which the MSCs are obtained impacts their therapeutic potential. The influence of donor variability on MSCs' therapeutic potential has also been reported in preclinical studies of other conditions, such as myocardial infarction. In one study, MSCs from two donors showed differences in modulating cardiac remodeling and activating the Akt-mTOR-GSK3β survival pathway [25]. However, so far, few studies have examined the impact of the donor-associated variability on MSCs’ therapeutic potential.

4. Clinical studies using mesenchymal stem cells

A search on the repository clinicaltrials.gov conducted on January 22, 2025, using the terms ((Neurological Disorders) OR (brain) OR (nervous system) OR (neurodegenerative) OR (ischemia) NOT (heart)) NOT (tumor OR cancer) and filtered for treatment with (“stem cells” OR “stromal cells” OR MSC), identified 781 clinical studies using MSCs-based strategies for neurological disorders. Of these, 287 are concluded, with only 44 having reported results. The therapeutic potential of MSCs has been demonstrated in several conditions including diabetic peripheral neuropathy [26], spinal cord injury [27,28], Alzheimer's disease [29], cerebral palsy [30,31], intervertebral disc degeneration [32], stroke [[33], [34], [35]], traumatic brain injury [36] and Parkinson's disease [37] (Table 1).

Table 1.

Overview of clinical trials reporting outcomes of mesenchymal stem cells (MSCs) in the treatment of neurological diseases, featured in the clinicaltrials.gov. The table provides data regarding the type of MSCs used, the target disease, administration route, number of patients included, serious adverse events, adverse events with a prevalence exceeding 20 % and the main clinical outcomes reported.

Source	Disease	Administration	N° patients	Gender	Serious Adverse events	Adverse events with prevalence >20 %	Outcomes	Clinical Trials.gov ID/Ref
AD-MSCs	Alzheimer's Disease	ND	21	Male/Female	Diarrhea; Oesophageal squamous cell carcinoma stage IV; pulmonary embolism	NR	Improvements in cognitive functions (Alzheimer's disease assessment scale and mini-mental status examination); Reduction of neuropsychiatric symptoms and depression (Neuropsychiatric inventory and geriatric depression scale); Slight Improvement in daily life activities	NCT03117738 [29]
AD-MSCs	Parkinson's Disease	IV	24	Male/Female	Dyspnea	Fatigue; Headache	Slight improvement in motor function;	NCT04928287 [37]
BM-MSCs	Diabetic Peripheral Neuropathy	IV	10	Male/Female	NR	NR	Transitory increase of β-FGF and VEGF 7 days after administration; Slight increase of nerve conduction velocities; Slight decrease of nerve conduction latency; Decrease of glycated hemoglobin 90 days after administration	NCT02387749 [26]
BM-MSCs	Intervertebral Disc Degeneration	ID	12	Male/Female	Device failure	Back Pain	Improvements in the level of pain and disability; Slight improvement in life quality	NCT01860417 [32]
BM-MSCs	Perinatal Arterial Stroke	IN	10	Male/Female	NR	Fever	Safety assessment only	NCT03356821 [33]
BM-MSCs	Spinal Cord Injury	IT	12	Male/Female	NR	Pain; Hyperthermia; Urinary tract infection; Back pain; Myalgia;	Increase sensitivity functions; Slight decrease of chronic pain; Increase somatosensory evoked potentials; Decrease volume and hyperintensity of intramedullary lesions in 7 patients; decrease voluntary micturition in flowmetry or in pressure/flow test	NCT01909154 [27]
BM-MSCs	Stroke	stereotactic	163	Male/Female	Hemorrhagic anemia; Leukocytosis; atrial fibrillation; pericardial effusion; ventricular tachycardia; vertigo; nausea; abdominal pain; vomiting; pyrexia; asthenia; chest pain; pneumonia; sepsis; pancreas infection; urinary tract infection; wound infection; subdural haematoma; contusion; incision site complication; hyponatremia; muscle hemorrhage; rhabdomyolysis; bladder cancer; seizure; basal ganglia hemorrhage; syncope; renal failure; hypotension	nausea; procedural pain; Headache	Improvements in motor function; Improvements in quality of life	NCT02448641 [35]
BM-MSCs	Traumatic Brain Injury	Stereotactic	61	Male/Female	Transient ischemic attack; Balance disorder; seizure; delirium	Nausea; pyrexia; wound complication; incision site pain; headache; dizziness; Upper respiratory tract infection; vomiting	Improvements in motor function (Fugl-Meyer Motor Scale); Improvements in disability and quality of life	NCT02416492 [36]
BM-MSCs or UC-MSCs	Cerebral Palsy	ND	20	Male/Female	Upper tract respiratory infection; Pneumonia; Febrile convulsion; osteotomy	Seizures; Nasal Congestion	Improvements in motor abilities were observed in both treatment groups (Gross Motor function Measure (GMFM-66 and GMFM-88)); Improvements in daily living, self-care and social functions; Improvements in memory and learning	NCT01988584 [31]
UC-MSCs	Cerebral Palsy	IV	91	Male/Female	Gastritis; Bronchitis viral; Respiratory syncytial virus infection; Rhinovirus infection; Dehydration; Seizure; Sleep disorder; Hospitalization; Surgery	Upper respiratory tract infection; Seizure	Improvements in Gross Motor Function Measure	NCT03473301 [30]
UC-MSCs	Spinal Cord Injury	IT	41	Male/Female	NR	Fever	Increase motor and sensory functions (American Spinal Injury Association score and spinal cord injury functional rating scale); No differences in muscle spasms; Increase muscle spasticity; Increase bladder and bowel function; Decrease residual urine volume	NCT02481440 [28]
UC-MSCs	Stroke	IV	79	Male/Female	Skin Infection; fracture; dehydration; cognitive disturbance; headache; intracranial hemorrhage; ischemia cerebrovascular; seizure; stroke; muscle weakness; confusion; acute kidney injury; bullous dermatitis; hypertension; hypotension; thromboembolic event	Pain in extremity	Improvements in disability and functional independence	NCT03004976 [34]

Among the various tissues from which MSCs can be derived, bone marrow is the most commonly used in clinical studies, followed by umbilical cord. Cox, C.S. (2022) administered BM-MSCs and UC-MSCs to children with cerebral palsy, and both cell types of resulted in functional improvements without significant differences between them NCT01988584 [31]. Similar promising results have been observed with autologous administration of MSCs in other neurological diseases, leading to beneficial effects in motor functions [28,30,31,[35], [36], [37]], sensory functions [27,28], urinary functions [27,28], cognitive functions [29,31], reduction in lesion volume [27] and enhancements in quality of life [29,31,32,[34], [35], [36]]. Baak, L.M. et al. (2022) showed that intranasally administered BM-MSCs in cases of perinatal arterial stroke are safe, with fever being the only reported adverse effect [33]. Other articles have also confirmed the safety of MSCs, with no serious adverse effects reported, though some studies have noted adverse effects such as headaches, pain, respiratory tract infections and seizures.

BM-MSCs – Bone marrow mesenchymal stem cells; UC-MSCs- Umbilical cord mesenchymal stem cells; AD-MSCs- Adipose tissue mesenchymal stem cells; IV – Intravenous; IT- Intrathecal; ID- Intradiscal; IN-Intranasal; ND- Non defined; NR- Not reported; β-FGF – Beta fibroblast growth factor; VEGF – Vascular endothelial growth factor.

Pubmed searches, conducted out on November 26, 2024, using the terms (“mesenchymal stem cells” OR “mesenchymal stromal cells” OR “MSCs”) AND (“neurologic*" or “brain")) AND (trial [Title/Abstract])) NOT (review)) NOT (“vesicles” OR “exosomes”), identified 54 clinical studies investigating MSCs as a potential therapy for various neurological diseases (Table 2; Fig. 2A). Most of these studies (96.3 %) reported that MSC use is safe, with no serious adverse effects. The studies differed in their protocols, including the source of the MSCs, route of administration, and cell dosage. Routes of administration included intravenous (IV), intrathecal (IT), intra-arterial (IA), and intramuscular (IM) (Fig. 3). Some studies utilized a single route of administration with a single dose [[38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53], [54], [55], [56], [57], [58], [59], [60], [61], [62]], while others employed repeated administrations [[63], [64], [65], [66], [67], [68], [69], [70], [71], [72], [73], [74], [75], [76], [77], [78], [79], [80], [81]]. Additionally, some studies combined two routes of administration, such as IV and IT administrations [[82], [83], [84], [85], [86]], IA and IV [87,88], or IT and IM [89].

Table 2.

Summary of the clinical trials using mesenchymal stem cells (MSCs) in neurological and neurodegenerative diseases. The table includes details on the MSCs source, target disease, administration route, number of administrations, total dose applied, number od patients enrolled, gender, age range, and the main clinical outcomes observed. All studies confirmed the safety of MSCs therapy.

Source	Disease	Administration	N° Administration	Total Dose	N° Patients	Gender	Age (Years)	Safe and Feasible	Outcomes	Ref.
AD-MSCs	Amyotrophic Lateral Sclerosis	IT	1 or 2	10–100 × 106 cells	27	Male/Female	39–73	✓	Safety assessment only	[78]
AD-MSCs	Multiple System Atrophy	IT	1 or 2	10–200 × 106 cells	24	Male/Female	57.3 ± 6.3	✓	Improvement in daily activities and motor functions (Unified multiple system atrophy rating scale); Increase NGF, BDNF and GDNF	[71]
AD-MSCs	Spinal Cord Injury	IT	3	90 × 106 cells	14	Male/Female	20–66	✓	Increase motor function (upper and lower extremity); Increase sensory Functions	[74]
AD-MSCs	Spinal Cord Injury	IT	1	100 × 106 cells	1	Female	53	✓	Increase motor function (upper and lower extremity); Increase sensitivity	[52]
AD-MSCs	Spinal Cord Injury	IT	1	100 × 106 cells	10	Male/Female	18–65	✓	Improvements in sensory and motor functions (Abbreviated Injury Scale); Increase VEGF; No differences in IL-16, IL-17, IL-1A, IL-5, IL-7 e TNF-β (evaluated by CSF samples)	[53]
AD-MSCs	Spinal Muscular Atrophy	IT	3	8 × 106 cells	10	Male/Female	<12 months	✓	Increase motor amplitude response of the tibial nerve; Slight improvement in mean life expectancy	[67]
AD-MSCs	Stroke	IV	1	1 × 106 cells/kg	13	Male/Female	60–80	✓	Trend to improvements in responsiveness, muscle strength, coordination, sensitivity, vision and speech (National Institutes of Health Stroke Scale); Decrease VEGF and BDNF	[39]
BM-MSCs	Neuromyelitis Optica Spectrum Disorder	IV	1	100 × 106 cells	15	Male/Female	19–63	✓	Improvements in pyramidal and sensory function; Visual acuity; Reduced serum levels of IL-21 and IL-6	[56]
BM-MSCs	Amyotrophic Lateral Sclerosis	IT	1	32 × 106 cells	9	Male/Female	23–75	✓	Significant slowing of the decline of the daily activity assessment (Amyotrophic lateral sclerosis functional rating scale) and respiratory functions (Forced vital capacity)	[45]
BM-MSCs	Amyotrophic Lateral Sclerosis	IT	2	96–172 × 106 cells	8	Male/Female	29–62	✓	No acceleration in the decline of the daily activity assessment (Amyotrophic lateral sclerosis functional rating scale) and respiratory functions (Forced vital capacity); Increase IL-10, TGF-β1, TGF-β2 AND IL-6; Decrease MCP-1	[68]
BM-MSCs	Amyotrophic Lateral Sclerosis	IV or IT	1	2 × 106 cells/kg	14	Male/Female	24–60	✓	Improvements in daily activities (Amyotrophic lateral sclerosis functional rating scale); Improvements in respiratory functions (Forced vital capacity)	[91]
BM-MSCs	Amyotrophic Lateral Sclerosis	IV + IT	2	2 × 106 cells/kg	15	Male/Female	23–60	✓	Improvements in daily activities (Amyotrophic lateral sclerosis functional rating scale); Improvements in respiratory functions (forced vital capacity)	[86]
BM-MSCs	Amyotrophic Lateral Sclerosis	ITM	1	11.4–120 × 106 cells	10	Male/Female	20–61	✓	No structural changes in the brain or the spinal cord	[62]
BM-MSCs	Hurler Syndrome and Metachromatic leukodystrophy	IV	1	2–10 × 106 cells/kg	12	Male/Female	5–25	✓	Improvements in bone mineral density and nerve conduction velocity	[43]
BM-MSCs	Multiple Sclerosis	IT	1	20 × 106 cells	7	Male/Female	30–50	✓	Increase Treg and the expression of FoxP3	[47]
BM-MSCs	Multiple Sclerosis	IT	1	2.26–18 × 106 cells	10	Male/Female	22–40	✓	Increase sensory, pyramidal, and cerebellar functions (6 patients) and (3 deteriorated) and (1 showed no differences); Improvement of functions affected by MS such as muscle weakness, balance, coordination and tremors, speech, and swallowing, unusual sensations or numbness, bowel and bladder, vision, thinking and memory (Expanded Disability Status Scale) (1 patient) and (4 showed no chances)	[48]
BM-MSCs	Multiple Sclerosis	IV	1	1.3–2 × 106 cells/kg	24	Male/Female	46.4 ± 5.2	✓	Safety assessment only	[55]
BM-MSCs	Multiple Sclerosis	IV	1	1–2 × 106 cells/kg	7	Male/Female	23–49	✓	Improvements in hand function stability, cognitive function, and quality of life; Increase Treg cells	[57]
BM-MSCs	Multiple Sclerosis	IV + IT	ND	ND	48	Male/Female	47.6 ± 9.7	✓	Improvement of functions affected by MS, such as muscle weakness, balance, coordination and tremors, speech and swallowing, unusual sensations or numbness, bowel and bladder, vision, thinking and memory (Expanded Disability Status Scale	[85]
BM-MSCs	Multiple Sclerosis	IV	1	1–2 × 106 cells/kg	25	Male/Female	35–55	✓	Safety assessment only	[61]
BM-MSCs	Multiple Sclerosis and Amyotrophic Lateral Sclerosis	IV + IT	2	MS -63.5–87.7 × 106ALS -54.7–78.1 × 106 cells	34	Male/Female	25–65	✓	Improvement of functions affected by MS, such as muscle weakness, balance, coordination and tremors, speech and swallowing, unusual sensations or numbness, bowel and bladder, vision, thinking and memory (Expanded Disability Status Scale); Induce immunomodulatory effects	[83]
BM-MSCs	Multiple System Atrophy	IV + IA	4	160 × 106 cells	29	Male/Female	ND	✓	Improvement in daily activities and motor functions (Unified multiple system atrophy rating scale); Increase cerebral glucose metabolism	[87]
BM-MSCs	Multiple System Atrophy	IV + IA	4	160 × 106 cells	33	Male/Female	ND	✓	Improvement in daily activities and motor functions (Unified multiple system atrophy rating scale); Increase cerebral glucose metabolism	[88]
BM-MSCs	Progressive Supranuclear Palsy	IA	1	1.2–2 × 106 cells/kg	5	Male/Female	60–68	✓	Some patients showed improvements in balance, gait and stability; 1 showed improvement in cognitive functions; 1 showed a worsening of these functions	[54]
BM-MSCs	Spinal Cord Injury	IT	1	20 × 106 cells	40	Male/Female	22–54	✓	Increase motor, sensory, and urinary functions; Decrease residual urine volume;	[38]
BM-MSCs	Spinal Cord Injury	IV	1	100–154 × 106 cells	13	Male/Female	21–66	✓	Increase motor and sensory functions; Increase respiratory function	[41]
BM-MSCs	Spinal Cord Injury	ITL	1	10 × 106 cells	14	Male/Female	23–61	✓	Increase motor functions (in 8 patients); Increase sensory and urinary functions	[46]
BM-MSCs	Spinal Cord Injury	IT	2	48 × 106 cells	16	Male/Female	18–65	✓	2 patients showed improvement in motor grade of the upper extremities; 4 patients showed somatosensory evoked potential improvement and 6 showed motor evoked potential improvement	[69]
BM-MSCs	Spinal Cord Injury	IT	3	300 × 106 cells	11	Male/Female	28–62	✓	Increase motor, sensitivity, spasms, pain, bladder and bowel functions and sexual functions	[72]
BM-MSCs	Spinal Cord Injury	IT	4	120 × 106 cells	10	Male/Female	34–59	✓	Increase sensitivity, motor, pain, spasms, bladder dysfunction	[73]
BM-MSCs	Spinal Cord Injury	IT	1	30 × 106 cells	3	Male/Female	26–66	✓	Slight increase of sensory function, trunk movements, stability, and standing positions; Increase urinary functions	[49]
BM-MSCs	Spinal Cord Injury	IT	1	100 × 106 cells	20	Male/Female	9–72	✓	Improvements in motor, sensory, urinary and intestinal functions; Increase muscle tone; Reduction of pain	[59]
BM-MSCs	Stroke	IV	2	100 × 106 cells	30	Male/Female	30–75	✓	Improvements in executing activities of daily living (Barthel index) and the degree of disability in daily activities (Modified Rankin Scale); less prominent improvement in responsiveness, muscle strength, coordination, sensitivity, vision and speech (National Institutes of Health Stroke Scale); Decrease prominent atrophy throughout the brain	[63]
BM-MSCs	Stroke	IV	1	60–160 × 106 cells	12	Male/Female	41–73	✓	Increase cerebral blood flow in one patient; Decrease lesion volume; Improvement in responsiveness, muscle strength, coordination, sensitivity, vision, and speech (National institutes of health stroke scale) were maintained for 1 year in all patients	[40]
BM-MSCs	Stroke	IV	ND	ND	12	Male/Female	20–60	✓	Improvements in executing activities of daily living (Barthel index)	[90]
BM-MSCs	Stroke	IV	1	50–60 × 106 cells	12	Male/Female	20–60	✓	Improvements in motor functions, balance and sensation (Fugl-Meyer scale); Improvements in executing activities of daily living (Barthel index)	[51]
BM-MSCs	Stroke	IV	1	100–300 × 106 cells	31	Male/Female	46–59	✓	Improvements in motor functions	[58]
BM-MSCs	Stroke	IV	2	0.265–1.45 × 106 cells/kg	9	Male/Female	41–59	✓	Improvements in motor and cognitive functions (Extended Glasgow Outcome Scale)	[80]
BM-MSCs	Subacute Middle Cerebral Artery Infarct	IV	1	2 × 106 cells/kg	17	Male/Female	30–75	✓	Decrease infarct volume; Although there was an initial difference in executing activities of daily living (Barthel index), this difference did not persist in the long term	[44]
BM-MSCs	Traumatic brain injury	IV + IT	2	678–20,000 × 106 cells	7	Male/Female	6–55	✓	Improvements in executing activities of daily living (Barthel index)	[84]
BM-MSCs (induced to secrete NTFs)	Amyotrophic Lateral Sclerosis	IT + IM	25	1270 × 106 cells	48	Male/Female	26–71	✓	Improvements in aspects such as speech, salivation, swallowing, handwriting, cutting food, climbing stairs, turning in bed, walking, dressing, and breathing (Revised amyotrophic lateral sclerosis functional rating scale); Decrease MCP-1, SDF-1, and caspase-3; Increase VEGF and HGF (evaluated by CSF samples	[89]
BM-MSCs (induced to secrete NTFs)	Multiple Sclerosis	IT	3	ND	18	Male/Female	18–65	✓	Slight improvement in manual agility; Increase CSF neuroprotective biomarkers (VEGF-A, HGF, NCAM1, Foollistatin and Fetuin-A); Decrease CSF inflammatory biomarkers (MCP-1, SDF-1, osteopontin and CD27)	[65]
PMSCs	Multiple Sclerosis	IV	2	150 × 106 cells OR 600 × 106 cells	16	Male/Female	36–58	✓	Safety assessment only	[77]
UC-MSCs	Cerebral Palsy	IV	4	45–55 × 106 cells	40	Male/Female	2–12	✓	Improvements in daily living; Improvements in comprehensive functional abilities and motor functions; Improvements in cerebral metabolic activity	[76]
UC-MSCs	Alzheimer	stereotactic	1	3–6 × 106 cells	9	Male/Female	54–74	✓	Safety assessment only	[60]
UC-MSCs	Autism Spectrum Disorder	IV	1, 2 or 3	1.79–6 × 106 cells/kg	12	Male/Female	4–9	✓	Increase social communication skills; Improvements in the severity of autism symptoms	[79]
UC-MSCs	Hypoxic-Ischemic Encephalopathy	IV	1 or 2	2 × 106 cells/kg	6	Male/Female	in birth	✓	Safety assessment only	[66]
UC-MSCs	Intraventricular Hemorrhage	ITR	1	5–10 × 106 cells/kg	9	Male/Female	Premature Infants	✓	Decrease IL-6; Tendency to decrease TGF- β1/2, TNF-α, IL-1β and VEGF (evaluated by CSF samples)	[50]
UC-MSCs	Multiple Sclerosis	IV	7	140 × 106 cells	20	Male/Female	24–55	✓	Improvement of functions affected by MS, such as muscle weakness, balance, coordination and tremors, speech, and swallowing, unusual sensations or numbness, bowel and bladder, vision, thinking and memory (Expanded Disability Status Scale	[70]
UC-MSCs	Spinal Cord Injury	IT	4	1 × 106 cell/kg	102	Male/Female	18–65	✓	Improvements in motor and sensory functions (American spinal injury association); Improvements in urinary functions; Improvements in spasticity (Ashworth scale-modified); Improvements in quality of life	[81]
UC-MSCs	Spinocerebellar Ataxias	IV + IT	4	80 × 106 cells	16	Male/Female	21–56	✓	Improvement in balance (Berg balance scale) and posture and walking, motor function, language disorder, and ocular motility disorder (International cooperative ataxia rating scale)	[82]
UC-MSCs	Stroke	IA	1	20 × 106 cells	4	Male	40–59	✓	Increase muscle strength (Except the hemorrhagic stroke patient); Two patients demonstrated improvements in the degree of disability in daily activities (Modified Rankin Scale)	[42]
UC-MSCs	Thoracolumbar Spinal Cord Injury	IT	2	40 × 106 cells	34	ND	19–57	✓	Increase sensation, motion, limb strength, strength of waist, abdomen, and lower limbs and urinary functions; Decrease muscle tension, residual urine volume and maximum detrusor pressure	[64]
UC-MSCs	Traumatic Brain Injury	IT	4	40 × 106 cells	40	Male/Female	5–48	✓	Increase motor function (upper and lower extremity), sensation, and balance	[75]

BM-MSCs – Bone Marrow Mesenchymal stem cells; UC-MSCs- Umbilical Cord Mesenchymal stem cells; AD-MSCs- Adipose Tissue Mesenchymal stem cells; IV – Intravenous; IM -Intramuscular; IT- Intrathecal; ITL- Intralesional; IA-Intra-arterial; ITR - Intraventricular; ITM – Intramedullary; MCP-1- Monocyte chemoattractant protein 1; SDF-1 - Stromal cell-derived factor 1; VEGF - Vascular endothelial growth factor; HGF - Hepatocyte growth factor; BDNF - Brain-derived neurotrophic factor; NGF - Nerve growth factor; GDNF - Glial cell line-derived growth factor; TGF-β - Transforming growth factor beta; TNF-α – Tumor necrosis factor alfa; NCAM1 - Neural Cell Adhesion Molecule 1; Treg – Regulatory T cells; CSF - Cerebrospinal fluid; MS – Multiple Sclerosis; IL – Interleukin; ND – Non define.

Fig. 2.

Summary of clinical studies using MSCs for neurological disorders, as presented in Table 2 (A) Distribution of clinical studies according to the neurological conditions. Spinal cord injury, multiple sclerosis, and stroke are the most commonly investigated using MSCs. (B) Tissue sources of MSCs used in clinical studies. Bone marrow was the most frequent (n = 35), followed by umbilical cord (n = 11).

Fig. 3.

Routes of stem cell administration used in clinical studies included in Table 2. The most common delivery method was intrathecal (IT), and intravenous (IV), followed by a combination of IV and IT. Less frequently used routes included intra-arterial (IA), IT combined with intramuscular (IM), intralesional (ITL), intramedullary (ITM), intraventricular (ITR), IV combined with IA and stereotactic injection. The variation in administration routes reflects ongoing efforts to optimize MSCs delivery for neurological disorders.

Bone marrow was the most commonly used source of MSCs being featured in thirty-four studies [38,40,41,[43], [44], [45], [46], [47], [48], [49],51,[54], [55], [56],58,59,[61], [62], [63],65,68,69,72,73,80,[83], [84], [85], [86], [87], [88], [89], [90], [91]], followed by umbilical cord in eleven studies [42,50,60,64,66,70,75,76,79,81,82], adipose tissue in six studies [39,52,67,71,74,78] and placenta in only one study [77] (see Fig. 2B). The number of patients enrolled in each study varied, ranging from one to one hundred two. There were also differences in the age of the participants, for example, only two studies focused on newborn babies, one on hypoxic-ischemic encephalopathy [66] and another on spinal muscular atrophy [67]. Even within studies of the same disease, the age range of the participants differed, with one study involving patients between forty to fifty nine years old [42] and another including patients aged sixty to eighty years [39]. Almost all studies included both male and female patients, except for two that included only male participants [42,52].

Published results indicate that MSCs led to improvements in sensory and motor functions [38,41,45,46,48,49,51,52,56,58,59,63,64,67,69,70,[72], [73], [74], [75], [76],80,81,84,87,89], strength [38,42,59,64,85], balance [51,54,75,82,85], urinary functions [38,46,49,59,63,64,70,72,73,81,84,85], cognitive functions [54,57,80,85], respiratory functions [87,91] and the ability to perform daily life activities [51,57,76,79,81,87,90,91]. Regarding targeted mechanisms, MSCs-therapy was reported to enhance neuroprotection [50,53,65,71,89], induced immunomodulatory effects [50,56,58,68,83], decreased inflammatory mediators [65,68,89], and reduced lesion volume [40,44].

In what concerns the efficacy of MSCs on the control of neurological diseases-associated deficits, promising results have been observed in the treatment of spinal cord injury with the intrathecal administration of AD-MSCs and BM-MSCs. In the case of AD-MSCs, a study involving 14 patients showed that the administration of 90 × 10⁶ cells divided into three doses of 30 × 10⁶ cells, resulted in a 36 % improvement in motor function and a 71 % recovery in sensory function [74]. On the other hand, a single dose of 100 × 10⁶ cells, administered to 10 patients, led to an improvement of 70 % in motor function and of 80 % in sensory function [53]. These results suggest that, despite the total number of cells being similar, the administration protocol plays a crucial role, indicating that a single administration of a higher dose may induce higher therapeutic effects of AD-MSCs in spinal cord injuries than multiple administrations. Similar effects were observed with BM-MSCs. Four administrations of 30 × 10⁶ cells promoted an 11.69 % recovery in motor function, 50 % in the pin prick test, which assesses pain sensitivity, and 15 % in the light touch test, which assesses light touch sensitivity. Bladder function and spasms were ameliorated by 80 % and 28.57 % respectively [73]. In contrast, three administrations of 100 × 10⁶ cells per dose resulted in a recovery of only 5.66 % in motor function, 30 % in the pin prick score and 20 % in light touch score, as well as a 66.6 % improvement in bladder function. No significant improvements were observed in sexual function or spasms [72]. These results indicate greater effects across most functions, except for the light touch score, when a lower number of cells was administered, suggesting that a higher number of cells does not necessarily correlate with better outcomes. Furthermore, a study administering a single dose of 20 × 10⁶ BM-MSCs led to a 15 % improvement in motor function and a 40 % improvement in sensory function [38]. Comparing these outcomes with the previously mentioned studies, it highlights that even lower doses of BM-MSCs can yield significant therapeutic effects.

In amyotrophic lateral sclerosis, the intrathecal administration of BM-MSCs at a dose of 32 × 10⁶ cells significantly slowed the decline in daily activities for approximately 50 % of patients [45]. Surprisingly, when a total of 96–172 × 10⁶ cells were administered over two intrathecal injections, the disease progression stabilized, however, no notable improvements were reported in daily functions [68].

In multiple sclerosis, outcomes also reflected the influence of dose and administration protocols. When UC-MSCs were administered at a relatively high doses (140 × 10⁶ through seven intravenous administrations), 55 % of patients reported improvements in quality of life after one year, and 83.3 % exhibited no disease progression [70]. In contrast, lower doses of BM-MSCs (2.26–18 × 10⁶ cells in a single intrathecal administration) resulted in 40 % of patients showing no visible improvements, and 10 % reporting enhancements in basic daily activities [48]. However, in this case, besides the cell dose, other factors such as cell source, route of administration and the number of administrations may contribute to the differences in the extent of recovery.

In conclusion, MSCs represent a promising therapeutic strategy for a diverse range of neurological disorders. Derived from both adult and neonatal tissues, MSCs exhibit characteristics, such as plastic adherence and multipotent differentiation, making them suitable candidates for cellular therapies. Among the various sources, BM-MSCs are the most widely used, with the IT route of administration being the most used, followed by IV administration (Fig. 3). This preference for BM-MSCs and the IT route may be related to the high prevalence of studies focused on spinal cord injury, followed by multiple sclerosis. Clinical trials have demonstrated the safety of MSCs, with no serious adverse effects associated with their administration. The majority of studies report beneficial effects, such as improvements in motor, sensory and cognitive functions, and quality-of-life outcomes. However, it is important to note that not all patients exhibit significant therapeutic improvements. Furthermore, it was not possible to establish a correlation between the observed effects and the administered doses, highlighting the need to establish standardized protocols to maximize the therapeutic potential of MSCs.

This variability in clinical outcomes underscores the importance of identifying biological determinants of MSCs potency. Preclinical and translational studies provide critical insights by linking specific surface markers and paracrine mediators with enhanced functional properties of MSCs. For instance, CD146 (MCAM) has been identified as a marker of MSCs subpopulations with superior migratory, proliferative, and immunomodulatory capacity. CD146⁺ MSCs secrete higher levels of trophic factors and show stronger inhibition of T-cell proliferation compared with CD146^- subsets and have been associated with improved cartilage and bone repair in vivo [[92], [93], [94]]. IGF-1 receptor (IGF-1R) expression supports MSC proliferation, survival, and regenerative activity. Activation of IGF-1/IGF-1R signaling enhances MSC engraftment, paracrine activity, and osteogenic potential [95,96]. IGF-1R⁺ MSCs have been shown to display greater self-renewal and improved regenerative responses in animal models. PDGF receptors (PDGFR-α and PDGFR-β) define MSC subpopulations involved in angiogenesis and tissue remodeling. PDGFR-positive MSCs demonstrate superior proliferation and migration, and promote vascular stabilization and osteogenic differentiation, thereby enhancing tissue repair [97,98].

Among soluble mediators, prostaglandin E₂ (PGE₂) is a central MSC-secreted factor that modulates immune responses. PGE₂ promotes expansion of regulatory T cells and induces anti-inflammatory cytokine production, including IL-10 [99,100]. Importantly, levels of PGE₂ correlate with the strength of T-cell suppression, making it a useful functional readout of MSC immunopotency. IL-10 is either secreted directly by MSCs or induced in host immune cells following MSC treatment. It is critical for MSC-mediated suppression of inflammation and neuroprotection, with studies demonstrating that MSC therapeutic effects in spinal cord injury and neuroinflammation are largely dependent on IL-10 induction [[101], [102], [103]].

Together, these findings provide mechanistic support for including CD146, IGF-1R, and PDGFR in extended phenotypic panels, and for systematically quantifying PGE₂ and IL-10 secretion in potency assays.

This review underscores the substantial heterogeneity observed across clinical studies employing MSC-based therapies, including differences in tissue of origin, culture passage number, cell viability, surface marker profiles, cryopreservation protocols, and potency assays. Such variability represents a major barrier to cross-study comparability and the development of clear clinical guidelines. To address this gap, we advocate for the adoption of a standardized quality control and potency testing framework for MSCs prior to their clinical use. At a minimum, trials should systematically report (i) tissue source and donor characteristics (age, sex, comorbidities); (ii) isolation and culture protocols, including supplements and expansion time; (iii) passage number at the time of administration; (iv) cell viability post-thaw; and (v) surface marker expression profiles. While adherence to ISCT (International Society for Cellular Therapy) minimal criteria (CD73⁺, CD90⁺, CD105⁺; CD45⁻, CD34⁻, HLA-DR^-) remains essential [4], extended profiling of markers such as CD146, CD71, PD-L1, and CD271 should be encouraged, given their potential links to immunomodulatory and neuroprotective potency. Furthermore, clinical studies should incorporate at least two standardized potency assays, for example, quantified tri-lineage differentiation, T-cell suppression assays, and secretion profiles of trophic and immunoregulatory factors (e.g., BDNF, GDNF, VEGF, HGF, IDO, PGE₂) [104].

Author contributions

Conceptualization: G.B., I·S., and B.A.; literature search: B.A..; writing—original draft preparation: B.A.; writing—review and editing: B.A., I·S., A.V.d.S., B.M.M. and G.B.; supervision and funding acquisition: G.B. All authors have read and agreed to the published version of the manuscript.

Funding

This work was developed within the scope of the projects UIDP/00709/2020 and UIDB/00709/2020 and was supported by a grant from the Portuguese Foundation for Science and Technology (2021.07854. BD) and by the “la Caixa” Foundation - within the scope of the Promove grant, held in collaboration with BPI and partnership with the Foundation for Science and Technology, REPAIR - PL23-00001.

Declaration of competing interest

The authors have no conflicts of interest to declare.