Fetal Cell Transplantation

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Fetal Cell Transplantation

• Lisa McIlveried
• Sean Flynn

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What is fetal DA cell transplantation?

• Mechanisms of graft action
• Rewiring the pathway and integrating tissue into
  the host
• OR
• Providing DA and neurotrophic release from the
  graft itself or induced in the brain by the graft
• Replaces lost neurons rather than just increasing
  neurotransmitter

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Cell transplantion uses

• Parkinsons Disease (PD)
• Relatively well defined core pathology loss of
  dopaminergic nigrostriatal tract
• VM tissue working generally via nonspecific
  release of DA
• Huntington's Disease (HD)
• Core pathology loss of GABAergic striatal
  output neurons
• Grafting striatal tissue, greater facilitation of
  connectivity to host tissue (shown via EM)
• Alzheimer's Disease (AD)/Dementia
• Core pathology- decrease in cortical levels of
  cholinergic synthetic enzyme choline acetyl
  transferase
• Septal based grafts inducing some cholinergic
  reinnervation
• ALS
• Grafts from spinal cord of fetus
• Reinnervation of cholinergic motor neurons
• Temporal Lobe Epilepsy?
• Schizophrenia?

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PD (quick review)

• Symptomology
• Movement/neurodegenerative disorder
• Tremors, rigidity of limbs, poor balance,
  difficulty initiating movement, bradykinesia,
  frontal lobe dysfunction and dementia
• Associated Structures/Pathways
• Basal Ganglia (BG) striatum (caudate nucleus,
  putamen), globus pallidus, substantria nigra
  (SN)
• Nigrostriatal Pathway
• Frontal Cx (SN) ? putamen -- globus pallidus --
  VLo ? SMA
• Pathology
• Degeneration of DA SN inputs to the striatum
• Increase inhibition form BG induces hypokinesia

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Other Treatments

• Drug Therapy
• L-dopa
• MAO-B inhibitors
• Surgical Manipulations
• Pallidotomy
• Subthalamotomy
• Thalamotomy
• Electrical Stimulation
• Globus pallidus, thalamus, subthalamic nuclei

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PD is suitable for transplantation

• Relatively an easy neurodegenerative disease
• One pathway
• One neurotransmitter
• Well-defined core pathology
• Failure of drug treatment (L-dopa therapeutic
  window)
• Replaces lost neurons rather than symptomatic
  drug treatment

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Animal Studies

• Rat model
• 6-OHDA most widely used
• Excitotoxic lesion of SN
• Unilateral
• Creates behavioral deficits
• Rotational asymmetry
• Impaired contralateral forelimb use
• Procedure
• Harvest fetal ventral mesencephalic (VM) tissue
• Precursor neurons of SN
• Recreates host DA circuitry
• Grafted into caudate nucleus (striatum)
• Behavioral assessment

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Animal StudiesEfficacy of grafts is dependent on

• Allograft vs. xenograft
• Age of donor embryonic tissue
• 13-15 gestational days?
• Dissection of tissue
• Solid tissue vs. cell suspension?
• Placement in brain
• Caudate nucleus (striatum) and not SN
• Circumvents problem of long-distance neuritic
  growth in the CNS b/c functional recovery can be
  achieved with only a partial pattern repair
• Cell survivability

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Animal StudiesResults!

• Display many of the morphological and functional
  characteristics of intrinsic DA neurons
• Reinnervate the striatum and form synaptic
  contacts with host neurons
• Spontaneously active
• Release DA
• Receive afferent inputs from host
• Decrease behavioral deficits

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• Biosynthetic Pathway of DA
• Tyrosine is precursor molecule of DA

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Clinical EfficacyNeural Graft Survival

• About 350 clinical trials since 1987
• Age of embryonic donor (6-9 weeks)
• Dopaminergic cell survival (high variability)
• Proper tissue dissection
• Placement of graft in host (striatum not NAC)
• Allograft
• Rush to the clinic? little testing in rodent or
  non-human primate
• Comparative studies difficult given experimental
  procedure UPDRS (United Parkinsons Disease
  Rating Scale)

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Clinical EfficacyFunctional Recovery

• Fluorodopa maker labeling presynaptic DA
  terminals
• Indication of graft survival
• PET scan for in vivo analysis
• generally show fluorodopa uptake decreases in
  conjunction with progression of PD in caudate and
  putamen, significant reversal of decrease in VM
  grafted caudate and putamen
• Postmortem studies healthy grafts with abundant
  cells and fiber outgrowth into host striatum

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Functional Recovery

• Double-blind, placebo-control study
• Given VM graft or sham surgery
• Significant initial placebo effects
• Improved fluorodopa uptake only in patients under
  60 years of age
• Development of major dyskinesias in absence of
  L-dopa treatment

• Open-label trial
• Increased fluorodopa uptake in putamen
• UPDRS overall symptomatic relief in off state
  10-24 months postop 30-40

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Disclaimer

• Despite signs of improvement on a standardized
  clinical level ALL PATIENTS REMIAN PARKINSONIAN!

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Additional Problems with Transplantation

• Dyskinesias
• Cell death
• Necrosis
• Apoptosis

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Post-transplant Dyskinesias

• 15 show severe dyskinesias during off phase
• Study by Freed et al. 2002
• Patients with dyskinesia tested for fluorodopa
  uptake pre-transplantation, 12 and 24 months
  post-transplantation
• Increase in fluorodopa uptake in DYS localized
  to 2 regions of left putamen
• posterodorsal zone (decrease during baseline)
• ventrally
• Unbalanced increase in DA function complicate
  benefit of transplantation

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Cell Death

• Necrosis cell death via injury causing swelling
  and bursting and spilling of intracellular
  contents over neighboring cells
• Apoptosis programmed cell death
• 90 of DA neurons lost
• Greatest loss within 1st 24 hours

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Solutions?

• Growth factors
• Inhibiting MAP kinase pathway
• p38 inhibitors
• Suppression of Immune System and Inflammation
• Angiotensin II?

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Growth Factors

• In vitro (cultured DA neurons)
• Combination of IGF-I and bFGF reduced occurrence
  of apoptosis via proliferation of astrocytes
• GDNF improve DA neuron survival (1 year with
  astrocytes) and increase neurite outgrowth
• In vivo
• Pretreatment of VM tissue with GDNF, IGF-I, and
  bFGF transplanted into unilateral 6-OH-DPAT rat
• 49 increase in survival with in 24 hours

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Inhibitors of MAP kinase

• p38 stress-activated MAP (mitogen-activated
  protein) kinase
• Modulates cellular apoptosis
• Trophic factor withdrawal
• Excitotoxic stimuli
• Fas activation
• Insulin and Pyridinyl imidazole
• Inhibit p38 activity
• Effective both in vitro and in vivo
• Why? - Small organic molecules, orally active,
  cross BBB

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Suppression of immune system and inflammation

• Role of microglia
• Primary immune effector cells in the brain
• Activated ameboid forms are phagocytes
• Non-specific and can damage grafted tissue
• Clinical potential of minocycline
• Antibiotic used for decades
• Inhibits microglia
• Decreases inflammation and apoptosis

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Angiotensin II

• New animal model
• Rotenone plant derived pesticide
• More clinical similarities?
• In vitro
• VM cultures protected via action at AT2 receptor

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Neural Stem Cells?

• Stem cells
• Fetal tissue
• Discuss!