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February 2023, Volume 73, Issue 2

Review Article

The promise of stem cells in amyotrophic lateral sclerosis: a review of clinical trials

Authors: Muhammad Usman Khalid  ( Department of Surgery, Aga Khan University Hospital, Karachi, Pakistan. )
Taleaa Masroor  ( Department of Surgery, Aga Khan University Hospital, Karachi, Pakistan. )


Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative condition with high cost of care, poor treatment outcomes, and a significant decrease in quality of life, eventually culminating in high mortality rates. Stem cells present an attractive alternative to conventional therapies as they can regenerate tissue and introduce growth factors to slow down the progression of disease. We conducted a comprehensive review of literature available in the MEDLINE (PUBMED), Scopus, and Cochrane Library databases, of current usage of stem cells and stem cell-based biomaterials for ALS treatment. Clinical trials, less than 10 years old, on human subjects were included in the study. Overall, stem cells, whether mesenchymal, non-lineage, or neural stem cells all seem safe for use in therapy for ALS. However, due to the chronic nature of the disease the efficacy of the treatment is not proven and warrants further investigation.


Keywords: Amyotrophic Lateral Sclerosis. Biocompatible Materials, Neural, Stem Cells.


DOI: 10.47391/JPMA.AKUS-22




Neurodegenerative diseases such as Amyotrophic Lateral Sclerosis (ALS), Alzheimer’s, Parkinson’s disease are debilitating conditions characterized by function and structural loss in neuronal tissues1. While treatment exists to slow down the rate of degeneration, it is often costly, with poor efficacy and significant side effects2. A major barrier to arresting the cell death and pathophysiological processes is the lack of regenerative capacity in the nervous system3. In the central nervous system (CNS) the blood brain barrier (BBB) is a major obstacle in the delivery of drugs that could potentially help slow down the disease process or potentially cure it4,5. Overall, neurodegenerative diseases lead to a loss of quality of life, increase the cost of care, and can spell a painful decline, particularly in resource limited areas where they are traditionally given lower priority6.

Amyotrophic lateral sclerosis (ALS) is an adult-onset, neurodegenerative condition that is characterized by progressive loss of upper and lower motor neurons7. Once the disease spreads to the diaphragm, it can cause severe respiratory distress, inevitably leading to death. Ninety percent of ALS patients are sporadically affected. Hereditary ALS cases have been linked to mutations in several different genes, with SOD1, FUS, and TARDBP mutations being the most frequent8. However, apart from a mean earlier onset, there is no difference between familial and sporadic ALS, with respect to disease severity and symptoms. Several theories have been proposed for the peculiar progression of the disease. It is speculated that like cancer, amyotrophic lateral sclerosis may involve a multi-process complex interaction between affected motor cells and the neuronal microenvironment9. The pathogenesis of ALS has also been linked to glutamate neurotoxicity. The only effective disease-modifying treatment for ALS that successfully slows disease progression and increases median patient survival by 3-6 months is the anti-glutamatergic drug Riluzole. However, even with its use symptoms persist and patients may develop non-cognitive impairments10.

Due to the elusiveness of the cause of neuronal death and the difficulty in making an early diagnosis in ALS, there are currently few effective therapeutic agents available. The neuroprotective and differentiation potential of stem cells makes them a possible therapeutic choice for interrupting the progression of disease11. We reviewed 19 clinical trials investigating approaches to stem cell therapy, type of stem cells used, safety and efficacy of the routes of administration and safety of multiple dosing.




We conducted a review of the available literature on clinical trials in stem cell therapy for the neurodegenerative disease. A bibliographic search was conducted through three major electronic databases. The MEDLINE (PUBMED), the Cochrane Library, and Scopus were the databases used with Medical Subject Headings (MeSH) terms (((neurodegenerative disease) OR (ALS) OR (Amyotrophic Lateral Sclerosis)) AND ((stem cells) OR (mesenchymal cells) OR (pluripotent stem cells) OR (IPSCs))). Most studies in the search originated from high income countries (HICs). The inclusion criteria were that studies needed to be less than 10 years old, clinical trials or outcome assessments, and on human populations. A total of 157 studies were initially screened from the databases on August 21st 2022 and imported into Rayyan software12. Duplicates were removed, studies were sorted by type, and 56 clinical trials were selected. From these title and abstract screening for relevance was done and 20 articles were selected for the final full text review which was completed by August 30 2022. These are summated in Table 1.





Stem cells can either be derived from an embryonic source (pluripotent stem cells), or from adult cell-lineage precursors i.e., haematopoietic stem cells, neural stem cells and olfactory ensheathing stem cells. Apart from the ability for neurodifferentiation, stem cells can secrete neurotrophic factors (NTFs) encased within exosomes that carry them past the blood brain barrier (BBB)13. Mesenchymal stem cells (MSCs) are multipotent progenitor cells that can differentiate into neural cells and neuroglia14. They have shown great therapeutic promise in the treatment of neurodegenerative diseases. The safety and efficacy of MSCs for the treatment of ALS has been established through several phase 1/ 2 trials conducted in the past decade15,16.


Safety and Efficacy of Bone-marrow MSC transplantation


Berry et al. conducted a phase 2 clinical trial where 48 ALS patients were randomized to receive either placebo or intramuscular and intrathecal doses of MSC-NTF cells17. No serious adverse events attributable to the intervention were noted. However, there was no difference in ALS progression within the two groups, except in a subgroup of rapid progressors, who showed significant improvement after 4 and 12 weeks of treatment (p< 0.05). To investigate the impact on survival time and ALS progression Barczewska et al. developed an approach comparing the impact of administering three doses of 30 x 10^6 MSCs derived from Wharton’s jelly on a two-monthly basis to a cohort of 134 patients18. There were 67 patients in the control and in the unexposed group. It showed a two-fold increase in survival time but no difference in ALS progression on the revised Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R)19. The intervention was deemed safe as no serious drug reactions were noted. The study also found that female gender and good therapeutic response to first dose of treatment were predictors of treatment efficacy. Similar safety profile and improvements were recorded in a phase 3 trial conducted by Cudkowicz et al, in which clinical response rates at 28 weeks were 35% MSC-NTF and 16% placebo20. They had pre-specified analysis of participants with baseline ALSFRS-R 35 (n = 58) (OR = 2.6, P =.29). Concerns regarding the viability and safety of infusing autologous bone-marrow mononuclear cells (ABMNC) via an intraspinal intramedullary injection, were investigated by Ruiz-Lopez et al. in an open phase 1 clinical trial21. The implementation was successful with no serious adverse events or changes in forced vital capacity compared to pre-intervention levels.

To compare efficacy of an intrathecal versus intramuscular approach to administration of bone marrow harvested MSCs, a phase 2a trial was conducted by Petrou et al.22. MSC-NTF cells were injected into the biceps and triceps at 24 different sites (1x 10^6 cells/site) or administered intravenously (1x 10^6/kg) during phase 1/2. In the second stage (phase 2a) of the study, three dosing cohorts of patients received both IT and IM treatment. Only the groups treated with IT showed systemic benefit with an improvement in the mean monthly rate of progression of the ALS-FRS-R score and FVC (from 1.56 to 0.28 and from 3.5% to 2.3%, respectively in phase 1/2; and from 1.4 to 0.6 and 2.6% to 0.86%, respectively in phase 2a). It is possible that a combined approach may exert a synergistic effect and improve outcome23.

Mouse models of ALS show that systemic or intraspinal dose of adipose-derived mesenchymal stem cell (MSC) transplantation slow motor neuron degeneration and enhance motor function24. Furthermore, harvesting MSCs via open biopsy of adipose tissue is simpler to execute compared to harvesting from bone marrow, however literature is unclear on efficacy of adipose derived MSCs25. A phase 1 trial aimed at determining impact of escalating doses of intrathecal autologous adipose-derived mesenchymal stromal cells showed that it had a good safety profile26. Participants were able to tolerate an intrathecal dose of 1 x 10^8 cells. However, there was no impact on ALS progression on ALSFRS-R scale and dose-dependent association with pain was noted. The most frequently reported side effects were transient low back and radicular leg pain at the highest dose level. These findings were linked to possible neuroinflammation, as there was a documented rise in nucleated cells and levels of CSF protein, with thickening of lumbosacral nerve roots on MRI.


CSF biomarkers and MSC transplantation


CSF biomarkers can help track treatment response at the level of the neural microenvironment. Vascular endothelial growth factor has been linked to neuroprotection in motor neurons, and reduced levels have been correlated with neurodegeneration27. Trials investigating VEGF levels show that patients receiving MSC-NTF reported significantly higher levels of VEGF expression compared to placebo20. They also saw significant reduction in cerebrospinal biomarkers of neuroinflammation, neurodegeneration, and support for neurotrophic factor. Berry et al. also noted similar findings with a significant increase in neurotrophic factors such as Leukaemia inhibitory factor and Basal hepatocyte growth factor post MSC transplantation17.




Lin cells or lineage-negative cells are a heterogenous group comprising of precursor, progenitor, and stem cells that lack mature morphotic blood components. They have demonstrated ability for self-renewal and paracrine release of different angiopoietic and neurotrophic factors. Paczkowska et al. showed that NTFs secreted by Lin cells increased expression of Ki-67 (antigen marker of cells in the active phases of the cell cycle) and anti-apoptotic Bcl-2 gene in a culture of serum-free SH-SY5Y line of human neuronal cells28. The safety of their use in ALS patients was established by a clinical trial conducted in Poland on 12 ALS patients that showed no transient or chronic adverse events related to intrathecal administration29. The trial simultaneously assessed the levels of neurotrophic factors and CSF inflammatory biomarkers after a single intrathecal dose of bone marrow derived Lin-cells and showed no sustained change in the CSF levels of BDNF and NGF at one-month follow-up. Reasons for the recorded findings could be a low baseline expression of BDNF in ALS patients with an undetectable rise post-transplantation. Furthermore, the study underlines the challenges of transplanting and monitoring the therapeutic potential of NTFs. Short half-life and inability to cross the blood-brain barrier (BBB), combined with an incompletely understood mechanism whereby they may exert effects by increasing expression of NTFs locally, makes them a challenging entity to assess30.


Neural Stem Cells


Neural stem cells or human spinal cord-derived stem cells (HSSCs) are progenitor cells that are isolated from an 8-week-old foetus's cervicothoracic spinal cord31. Animal studies have shown that injection of HSSCs in rats with ischaemic spinal cord injury caused survival of endogenous motor neurons and partial motor neuron recovery, prompting further inquiry into the novel approach32. Glass et al conducted a phase 1 clinical trial using HSSCs in 12 ALS patients, which showed promising outcomes33. The surgical intervention did not exacerbate disease presentation or cause treatment-associated morbidity. Mazzini et al. evaluated the feasibility of micro-transplanting hNSCs into the gray matter tracts of the lumbar or cervical spinal cord of 18 patients with spinal onset ALS34. The study utilized clinical grade hNSC lines that were isolated from miscarried foetus brain biopsies and reproducibly and steadily expanded ex vivo. The ALS FRS R, Ashworth Spasticity Scale, Medical Research Council (MRC) scale of 34 muscle groups in the upper and lower limbs, and FVC were used to assess clinical assessment and rate of disease progression19. Pre- and post-transplantation assessment was done based on clinical, psychological, neuroradiological, and neurophysiological data. None of the patients experienced severe side effects or accelerated disease progression for up to 60 months following surgery. The utility of Mazzini et al.’s findings lies in the description of a safe and uniform brain cell drug product that is readily available, can be used for larger and more uniform trials, and may even make it possible to implement global, multicentric clinical studies where patients receive the same care at every location37. Although the data for safety and efficacy looks promising, the small sample sizes make it difficult for any conclusions with regards to impact on disease progression to be drawn38.




Stem cells are a safe option for treatment of ALS and has shown a favourable side effect profile. It has shown improvement in the overall survival, although no significant improvement in rate of degeneration has been reported in these early phase trials. Late phase trials and longitudinal outcome studies are needed to investigate the efficacy of stem cell treatment for ALS.


Disclaimer: None to declare.


Conflict of Interest: None to declare.


Funding Disclosure: None to declare.




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