Stem cell therapy in neurological diseases

Dr. Parag MoonSenior resident

Dept. of Neurology

Stem Cell- cell which can make exact copies of itself indefinitely, can differentiate, and produce specialized cells for various tissues of body

Self-renewal and multipotentiality

Terminology

Totipotent- can become any kind of cellEarly Embryonic SC

Pluripotent- almost any kind of cellBlastocyst Embryonic SC

Multipotent- limited range of cell typesAdult SC: nerve cells, blood cells,

muscle cells, bone and skin cells.

1. EMBRYONIC STEM CELL- from embryos that develop eggs that have been fertilized in vitro.- not derived from eggs fertilized in a woman’s body.

2. ADULT STEM CELL- undifferentiated cell types in a tissue or organ.- multipotent (limited range of cell type)

Two Major Types of Stem Cell

(a) capacity to proliferate in culture and large numbers of cells can be derived from a limited source;

(b) potential to be harvested from the patients themselves;

(c) ability to migrate and disseminate following implantation within the adult CNS;

Why are stem cell important and receiving so attention??

(d) possible tropism for areas of pathology;(e) ease of manipulation using viral and non-

viral gene transfer methods;(f) ability to better integrate into normal brain

cytoarchitecture with the potential for physiologically regulated release of substances.

Derived from the inner cell mass of the embryonic blastula

Pluripotent with great proliferative potential Risk of teratomas. Majority of research done on mouse derived

embryonic stem cell Showed promising results in animal studies.

Embryonic stem cell

Human embryonic stem cells been isolated, grown in culture with enrichment for neuronal lineages with help of growth factors and mitogens.

When placed in the developing rat brain, can migrate widely and differentiate in a site specific fashion without the formation of teratomas.

The safety of these cells needs further investigation

Issue of therapeutic cloning is a major concern.

Derived from the neuroepithelium of the developing embryo.

Respond in vitro to mitogens such as epidermal growth factor (EGF) and fibroblast growth factor (FGF2)

EMBRYONIC NEURAL STEM CELLS(NSCs)

Primarily found in the subependymal layer of the ventricular zone and the dentate gyrus of the hippocampus and other sites

Potential for autologous grafts is possible, assuming that the NPCs are not themselves involved in the disease process

Tried in one pt. with parkinsonism

ADULT NEURAL PRECURSOR CELLS

It is theoretically possible that stem cells derived from non-neural system through a transdifferentiation process can be used for nerve cell therapy.

Haematopoietic stem cell transplanted into irradiated recipients can differentiate into microglia, astrocytes, and possibly neurons

BONE MARROW ANDNON-NEURAL STEM CELLS

Some functional benefit in a rodent model of Parkinson’s disease when transfected with the dopamine synthetic enzyme tyrosine hydroxylase

Limitation-robustness and efficiency of this system to produce neural cells is still poor.

Reversal of the terminally differentiated cells to totipotent or pluripotent cells

Achieved using nuclear transplantation, or nuclear transfer (NT), procedures (often called "cloning").

Error-prone procedure with a very low success rate

Used to produce patient-specific ES cells carrying a genome identical to that of the patient

Nuclear Reprogramming

The capacity to differentiate into cell types outside their lineage restrictions.

HS cells may be converted into neurons as well as germ cells

May provide a means to use tissue stem cells derived directly from a patient for therapeutic purposes

Stem Cell Plasticity or Transdifferentiation

Proliferation of ENPs in culture is not indefinite.

“Hayflick limit”-equivalent to approximately 50 population doublings after which non-transformed cells enter replicative senescence and stop dividing.

Seems to be species dependent,and although greater for human than rodent ENPs

Hayflick limit

Capable of clonal propagation in vitro to ensure homogeneity

Genetic stability at high passage Integration within the host brain following

transplantation Connectivity within host circuits Migration and engraftment at sites of damage Correct differentiation into appropriate neural

cell types Functional benefits Lack of side effects

Essential properties of stem cellsfor use in clinical transplantation

Investigations confirmed the immunomodulatory properties of NPCs in EAE in mice.

NPCs promote apoptosis of type 1 T-helper cells, shifting the inflammatory process in the brain toward a more favorable climate of dominant type 2 T-helper cells

Significant suppression of proinflammatory cytokines

IMMUNOSUPPRESSIVE EFFECTSOF TRANSPLANTED Nscs

The primary goal of NSC therapy is to replace missing cells and tissue.

Best targets for stem cell–based therapies-> those that would be improved by the transplant or induced replacement of a limited number of cell types.

Aim to replace the lost motor neurons with those that express normal levels of SMN1.

Neural progenitors are not particularly migratory and would not be expected to spread much from the injection site

Multiple injection needed

Spinomuscular atrophy

ALS- or SMA-specific ESC lines can be generated either

1. engineering 2. therapeutic cloning

Dopaminergic fetal cells delivered to brains of Parkinson’s patients.

Transfer of fetal midbrain progenitors to the striatum

Two recent double-blind placebo-controlled clinical trials -limited efficacy for the procedure

Limitations- availability limited, the transplanted cells are heterogeneous

Parkinson’s disease

Embryonic stem-derived dopaminergic neural progenitors

Can be produced in great abundance Can be engineered to express additional

proteins that might assist with survival, differentiation, or pathfinding of the new neural cells

Limitation-In vitro, NPCs derived from the developing ventral mesencephalon lose the ability to spontaneously differentiate into dopaminergic cells after only a few divisions

Solution-employ ex vivo genetic techniques to modify cells prior to implantation to express tyrosine hydroxylase

Transplanting neural stem cells to an injury site leads to increased behavioral improvement in rats

Side effects seen due to the addition of inappropriate circuitry

Difficulty of preventing scar tissue from forming at the site of the transplant which hinders growth of neural projection.

Spinal cord injuries

Blindness-stem cells of a particular stage when placed into the subretinal space can incorporate into the adult retina and form functional circuits.

Hearing-stem cells with the ability to differentiate into new hair cells exist in the adult inner ear.

Sensory system disorders

Oligodendrocytes can develop from adult or fetal neural stem cells and from ESCs

Oligodendrocyte precursors delivered to the nervous system migrate readily and myelinate neuronal projections in several disease models.

Useful in demyelinating disorders. Transplanting the cells intrathecally and

intraventricularly is a promising approach for cell delivery

Glial disorders

Studies using NSCs limited but some evidence of appropriate neuronal differentiation with human NSCs.

Functional efficacy and connectivity of these cells in repairing the brain has not been demonstrated.

Huntington’s chorea

Transplantation of the MHP36 line (ReNeuron holdings) has been reported to ameliorate cognitive deficits in rodent models of ischaemia.

hNT neurons derived from a human teratocarcinoma cell line

No evidence for tumorigenesis or other adverse effects in the 12 patients in the phase I study

Cerebral ischaemia

The associated neurodegeneration is too widespread and diffuse.

Therefore unlikely to be ameliorated by adding more cells to the system.

Disease-specific ESC lines could be used to study the degeneration of neurons in vitro.

Alzheimer’s disease

Role as efficient and flexible vectors for the sustained, local delivery of neuroactive compounds to the brain

1. Neurotrophic factors for neuroprotection2. To replace proteins lost because of single

gene defects

Vectors For The Delivery OfBiologically Active Substances

Inherited neurological conditions attributed to the loss of function of a single gene that encodes for a metabolically or developmentally critical enzyme

Tried in mucopolysaccharidosis type VII (MPS VII, Morquio).

Treatment of genetic disorders

NSC’s delivery strategy is attractive compared to a viral vector based delivery system because

1. Host brain is not genetically manipulated, preventing insertional mutagenesis

2. Preserving the function of neurons in the host.

Can be incorporated with “suicide cassette”, allowing elimination of cells

Neurotrophins and cytokines forneuroprotection

Certain ENPs may show a tropism for areas of pathology and can be used for chemotherapy

C17.2 NSC line which is highly migratory in the adult brain when retrovirally transfected to express the anti-mitotic compound cytosine Deaminase.

Appeared to migrate preferentially towards the tumours, which decreased in size

Delivery of Chemotherapeutic agents

Stem cells are an attractive option in drug discovery process.

Drug discovery and therapeutics

Stem cells and neurological disease:R A Barker, M Jain, R J E Armstrong et al; J Neurol Neurosurg Psychiatry 2003 74: 553-557

The Changing Face of Neural Stem Cell Therapy in Neurologic Diseases:Ofira Einstein,Tamir Ben-Hur:Arch Neurol. 2008;65(4):452-456

Cell replacement therapy in neurological disease:Philos Trans R Soc Lond B Biol Sci. 2006, 361(1473):1463-1475.

Harrisons principle of internal medicine.

References