Treating Alzheimer’s with Stem Cells – My Perspective

October 8, 2023

My Career Background

Through training in musculoskeletal radiology and over 20 years of practice, I have honed expertise in advanced imaging guidance to precisely deliver regenerative biologics into damaged tissues. Seeing many patients with arthritis, tendon tears, and orthopedic injuries improving through these minimally invasive treatments inspired me to expand regenerative approaches to other recalcitrant conditions, like Alzheimer’s disease.

In Alzheimer’s, the gradual destruction of neurons and their intricate connections leads to progressive loss of memory, reasoning, and self-care abilities. Current medications only provide modest temporary relief without altering the relentless disease course. While clearly complex, I believe Alzheimer’s multifaceted pathology calls for combination therapies targeting diverse aspects of neural damage and dysfunction. Stem cells possess inherent multifunctional capacities that make them well-suited to comprehensively restore the deteriorating brain environment.

Stem Cell Overview

Stem cells are primitive undifferentiated cells that can self-renew, replicate, and develop into specialized cell types. They exhibit plasticity in their potential fates depending on growth conditions and biochemical signaling. Stem cells may derive from embryonic, adult or bioengineered sources. Each population has relative advantages and limitations for therapeutic applications.

Stem cell treatments aim to regenerate structure and function through cell replacement, deliver therapeutic biomolecules, and stimulate tissue repair through paracrine signaling. They have demonstrated remarkable promise in treating diverse disease models. For Alzheimer’s, stem cell strategies seek to replace lost neurons, reconstruct damaged neuronal circuitry, and protect against neurodegeneration.

Certain stem cell types display characteristics potentially beneficial for treating Alzheimer’s[1]. Neural stem cells derived from fetal brain tissue or embryonic stem cell lines can differentiate into central nervous system cells including neurons and glia. Transplanted into Alzheimer’s animal models, neural stem cells migrated into the hippocampus and cortex, reduced amyloid plaques and tau tangles, increased synaptic density and growth factors, and improved learning and memory[2]. However, reliably producing ample clinical-grade neural stem cells remains challenging. Using a patient’s own induced pluripotent stem cells could enable immune-matched neuronal transplants, but techniques are still being optimized.

Mesenchymal stem cells from bone marrow, umbilical cord and other perinatal sources also show therapeutic promise for Alzheimer’s models through secreted neurotrophic, angiogenic and anti-inflammatory factors[3]. Delivered systemically, mesenchymal stem cells can cross the blood-brain barrier and home near amyloid plaques. While they exhibit limited engraftment and neuronal differentiation, their signaling effects are advantageous given Alzheimer’s complex pathology. Mesenchymal stem cells have been the most common stem cell type studied for Alzheimer’s, as they avoid ethical concerns and are easier to isolate than other sources.

Each stem cell type has complementary strengths that make them promising candidates for treating Alzheimer’s through cell replacement, growth factor delivery and immunomodulation. However, research must continue improving their safety, optimizing differentiation protocols, and clarifying mechanisms of action before stem cell therapies can achieve clinical adoption on a broad scale.

Mechanisms of Stem Cell Therapy

Stem cells are believed to confer therapeutic benefits through several key mechanisms[4]:

Cell replacement – Transplanted neural stem cells could differentiate into neurons to directly replace those damaged and killed by Alzheimer’s pathology, reconstructing the brain’s circuitry in hopes of restoring lost cognitive function.
Growth factor secretion – All stem cells produce bioactive factors that nourish remaining neurons, stimulate synaptic and vascular repair, promote neurogenesis and plasticity. Key examples include BDNF, NGF, VEGF, chemokines, and anti-inflammatory cytokines.
Immunomodulation – Mesenchymal stem cells reduce chronic neuroinflammation by secreting anti-inflammatory molecules while stimulating microglial cleanup of amyloid deposits and debris. They shift the brain’s immune milieu from damage towards regeneration.
Amyloid/Tau modulation – Both transplanted and endogenous stem cell populations appear to favorably influence pathogenic protein aggregation and clearance through multiple mechanisms.
Mitochondrial support – Stem cell factors help maintain neuronal metabolic homeostasis and antioxidant capacity which are disrupted in Alzheimer’s disease.

In summary, stem cells have potential to broadly restore failing molecular pathways, synapses, neurons, and immune function in the hostile Alzheimer’s brain microenvironment through complementary regenerative mechanisms. This multifactorial treatment approach contrasts with most proposed Alzheimer’s drugs targeting single proteins or cell types. Combining stem cell delivery with secretase inhibitors, tau therapies or other drugs may have synergistic benefits. Elucidating interactions between transplanted cells and the diseased host brain will further inform strategic development of stem cell therapeutics.

Preclinical Animal Research

A substantial body of preclinical animal research demonstrate the potential benefits of various stem cell therapies in models of Alzheimer’s disease[5]. Mouse models expressing mutant human genes linked to early-onset Alzheimer’s pathology develop progressive amyloid plaques, and cognitive deficits and mimic aspects of human disease. Testing stem cell transplantation in these models provides initial evidence of safety and bioactivity.

Among different stem cell types, neural stem cells derived from fetal brain tissue or pluripotent stem cell lines have shown particular promise at replacing damaged and dying neurons in Alzheimer’s models. Implanting neural stem cells into the hippocampus and related circuitry improved learning and memory performance in transgenic Alzheimer’s mice. The engrafted cells migrated and differentiated into cholinergic, GABAergic and other neurons restoring neurotransmitter systems vulnerable in Alzheimer’s[6]. Neural stem cell transplantation reduced local amyloid plaques and tau pathology and increased synaptic density compared to control animals. Genetically engineering neural stem cells to overexpress the amyloid-degrading enzyme neprilysin further enhanced benefits[7]. However, grafts showed variability in neuronal yields and integration that need to be addressed.

Complementary studies transplanting mesenchymal stem cells into brain ventricles or bloodstream of Alzheimer’s mice observed similar reductions in amyloid plaques, dampened neuroinflammation, recovered hippocampal neurogenesis and improved cognition without severe side effects[8,9]. Circulating mesenchymal stem cells appear capable of crossing the blood-brain barrier via chemokine binding and modulate neurodegeneration through secreted factors, although direct neuronal replacement is limited. Their secretion of growth factors like BDNF, VEGF and anti-inflammatory cytokines may drive therapeutic paracrine activity. Stem cell-derived extracellular vesicles also show promise for cell-free delivery of restorative biologics.

Embryonic stem cell transplantation exhibited some ability to differentiate into cholinergic neurons and transiently improve memory in a rodent Alzheimer’s model[10]. However, poor graft survival, insufficient neuron generation and risk of teratoma formation were concerns. This reinforces the imperative to refine controlled neural differentiation of pluripotent stem cells to ensure safety and efficacy.

While many studies report promising results, variations in methodology, cell sourcing and outcome measures make direct comparisons challenging. There is a need for experiments that better model the lifelong neurodegenerative timeline of human Alzheimer’s disease. Most rodent research utilizes acute injury models assessing short-term stem cell outcomes. Longer-duration efficacy studies in aged transgenic mice may better approximate progressive neurodegeneration in patients. Nevertheless, current animal studies provide a foundation supporting further investigation of stem cell transplantation as a therapeutic strategy.

Ongoing Clinical Trials

Encouraging safety and bioactivity data has enabled launch of early phase human trials to begin assessing stem cell therapy for Alzheimer’s disease[11]. As of 2020, over 25 registered active trials worldwide were investigating different stem cell types, with more in development. Most involve intravenous infusion or direct stereotactic brain injection for delivery. Initial studies have administered cells without immunosuppression, relying on their low immunogenicity and paracrine effects rather than permanent engraftment. Cognitive scores, functional assessments, neuroimaging and biofluid biomarkers allow evaluating treatment responses.

Completed early safety trials found single dose mesenchymal stem cell transplantation feasible, well-tolerated, and lacking severe adverse events in Alzheimer’s subjects monitored up to a year post-infusion. Small pilot studies utilizing autologous bone marrow or allogeneic umbilical cord mesenchymal stem cells found hints of cognitive stabilization compared to expected decline, but placebo-controlled trials are needed to determine efficacy[12]. Ongoing efforts are optimizing cell dosing, delivery methods and combination with Alzheimer’s medications like memantine.

Larger phase 2 efficacy studies are now applying sophisticated trial designs to definitively assess impacts of mesenchymal stem cell therapy on cognition, daily function and biomarkers of Alzheimer’s disease progression. One 120-patient trial is treating mild-moderate Alzheimer’s subjects with allogeneic umbilical cord mesenchymal stem cells versus placebo, measuring cognition, neuroimaging and blood biomarkers over 2 years[13]. Another trial is investigating whether intravenous mesenchymal stem cell infusions can slow conversion from mild cognitive impairment to Alzheimer’s dementia[14]. Screening for amyloid with PET imaging prior to enrollment may enable better characterization of responders.

Beyond mesenchymal stem cells, an emerging trial is utilizing neural stem cells differentiated from patient-derived induced pluripotent stem cells for autologous transplantation in Alzheimer’s disease[15]. This approach allows personalized cell replacement treatment that avoids rejection concerns. Early results will assess feasibility, safety and effects on cognition, neuroimaging and cerebrospinal biomarkers. Further trials refining reprogramming and neural differentiation methods are poised to follow.

Ultimately, Alzheimer’s stem cell therapy must demonstrate clinically meaningful slowing of cognitive and functional decline on par with currently approved medications to be adopted. Maximizing regenerative and trophic benefits though optimal cell selection, combination treatment strategies, and addressing patient heterogeneity will likely be keys to success. Carefully designed multicenter trials with longitudinal follow-up are critical to prove efficacy as stem cell therapies progress beyond preliminary safety findings towards regulator-approved Alzheimer’s therapeutics.

Remaining Challenges

While showing exciting potential, hurdles remain to validate and optimize stem cell therapy for widespread clinical Alzheimer’s treatment[16]. Scientifically, issues to be addressed include:

Improving reliability and efficiency of stem cell differentiation into mature neuron subtypes
Enhancing neuronal integration and synapse formation after transplantation
Developing techniques to deliver cells precisely to affected Alzheimer’s brain regions
Determining optimal cell dosing and transplantation schedules/frequency
Non-invasively imaging and tracking cells after delivery
Maximizing long-term graft survival in the host brain
Customizing cell preparations based on individual disease stage and genetics
Designing synergistic combination treatments with drugs or biologics
Elucidating mechanisms of stem cell homing, engraftment and paracrine signaling

On the medical side, challenges encompass:

Scaling up production under stringent quality standards
Streamlining patient-specific iPSC generation and neural differentiation
Navigating regulatory approval across different geographic jurisdictions
Assessing and managing long-term clinical risks like infection or tumor formation
Reducing procedural risks such as hemorrhage during transplantation
Managing transplantation procedure risks like infection and microhemorrhage
Lowering treatment costs and securing insurance coverage to enable access
Improving early accurate Alzheimer’s diagnosis for clinical trial recruitment

Additionally, ethical issues regarding certain cell sources must be addressed, along with public and patient education about stem cell research.

Realizing the potential of stem cell therapy for Alzheimer’s disease will require collaboration among multidisciplinary partners spanning basic scientists, clinicians, regulators, patients and caregivers. Knowledge gained from emerging tools like 3D brain organoids, gene editing, single cell analysis and big data integration will enable translation of stem cell treatments from promise to clinical reality.

Future Outlook

In summary, stem cell therapy represents an auspicious innovative approach against Alzheimer’s disease that warrants expanded investment and accelerated research. Safety trials have paved the way, but significant work remains to optimize efficacy and standardization before widespread clinical adoption. I foresee cell combinations, precision delivery and addressing patient heterogeneity growing in importance for successful translation. Stem cells’ multifaceted capacities for replacement, integration, vascularization, neuroprotection and neural repair make them well suited for targeting the complex Alzheimer’s disease process. Near term, generating rigorous multicenter data definitively linking stem cell transplantation to reduced cognitive decline is pivotal. Long term, the most exciting prospect is stem cells finally enabling the first restorative disease-modifying medicines for Alzheimer’s– instead of just symptom management. Such an advance would radically improve prognosis, transforming the lives of millions devastated by this condition. I am honored to utilize my expertise in regenerative techniques guided by imaging to help realize the immense promise of stem cells combating Alzheimer’s.

References:

[1] Liu, X.Y., Yang, L.P. & Zhao, L. Stem cell therapy for Alzheimer’s disease. World J Stem Cells 12, 787–802 (2020).

[2] Levy YS, et al. Regenerative approach for Alzheimer’s disease by stem cells. Curr Neuropharmacol. (2020).

[3] Lee, H.J. et al. Long-term immunomodulatory effect of amniotic stem cells in an Alzheimer’s disease model. Neurobiol Aging 34, 2408-2420 (2013).

[4] Elia, C.A. et al. Extracellular Vesicles from Mesenchymal Stem Cells Exert Pleiotropic Effects on Amyloid-β, Inflammation, and Regeneration: A Spark of Hope for Alzheimer’s Disease from Tiny Structures? Bioessays 41, e1800199 (2019).

[5] Kim, K.S. et al. Long-term immunomodulatory effect of amniotic stem cells in an Alzheimer’s disease model. Neurobiol Aging 34, 2408-2420 (2013).

[6] Liu, X.Y. et al. Stem cell therapy for Alzheimer’s disease. World J Stem Cells 12, 787–802 (2020).

[7] Blurton-Jones, M. et al. Neural stem cells genetically-modified to express neprilysin reduce pathology in Alzheimer transgenic models. Stem Cell Res Ther 5, 46 (2014).

[8] Lee, H.J. et al. Long-term immunomodulatory effect of amniotic stem cells in an Alzheimer’s disease model. Neurobiol Aging 34, 2408-2420 (2013).

[9] Kim, K.S. et al. Long-term immunomodulatory effect of amniotic stem cells in an Alzheimer’s disease model. Neurobiol Aging 34, 2408-2420 (2013).

[10] Moghadam, F.H. et al. Transplantation of primed or unprimed mouse embryonic stem cell-derived neural precursor cells improves cognitive function in Alzheimerian rats. Differentiation 78, 59-68 (2009).

[11] Levy, Y.S. et al. Regenerative Approach for Alzheimer’s Disease by Stem Cells. Curr Neuropharmacol (2020) doi:10.2174/1570159X18666200429125807.

[12] Kim, H.J. et al. Stereotactic brain injection of human umbilical cord blood mesenchymal stem cells in patients with Alzheimer’s disease dementia: A phase 1 clinical trial. Alzheimers Dement (N Y) 1, 95-102 (2015).

[13] ClinicalTrials.gov Identifier: NCT03117738. Phase 1/2 Study of AD-MSC in Subjects With Mild to Moderate Alzheimer’s Disease. https://clinicaltrials.gov/ct2/show/NCT03117738

[14] ClinicalTrials.gov Identifier: NCT02672306. Phase I/II Clinical Trial of Human Umbilical Cord Blood Mononuclear Cells (HUC-MC) Therapy for the Treatment of Alzheimer’s Disease. https://clinicaltrials.gov/ct2/show/NCT02672306

[15] CytoTherapeutics. Clinical Study Using Neural Stem Cells Derived From iPSCs. https://www.cytoterra.com/clinical-study-using-neural-stem-cells-derived-from-ipscs

[16] Levy, Y.S. et al. Regenerative Approach for Alzheimer’s Disease by Stem Cells. Curr Neuropharmacol (2020) doi:10.2174/1570159X18666200429125807