Stem Cells in Research

1
Stem Cells in Research

• Promises and Pitfalls

Denise Inman, PhD University of
Washington Department of Neurosurgery
2
(No Transcript)
3
Overview

• What are stem cells?
• How do embryonic and adult stem cells differ?
• How are different types of stem cell lines
  created?
• Stem cells in research and medicine
• Alternatives to the embryo

4
Early Development
Fertilized egg
5
Embryonic Stem Cell Characteristics

• Not committed to a specific fate
• Pluripotentcan differentiate into specialized
  cell types
• Self-renewing

6
Is that an Embryonic Stem Cell?
The true potential of stem cells can only be
assessed retrospectively
Embryonic stem cells injected into a SCID mouse
will grow into teratomas, tumors of the germ cell
layers. Individual ESCs under the correct
conditions will make many different cell types.
7
Stem Cells From Embryonic to Adult
Embryonic stem cells are those removed from the
blastocyst before the fate decision from
pluripotentiality to multipotentiality. Adult
stem cells are those multipotential cells that
persist in fully developed tissues. These cells
never differentiated into the mature cell types
of the tissues in which they reside.
8
Adult Stem Cells

• Multipotential
• Make cells within a specific lineage
• Not differentiated
• Rare
• Self-replicating

Neural stem cells in culture. One cell is
extending a process.
9
Adult Stem Cells Bone Marrow
Major repository of adult stem
cells -Hematopoeitic -Mesenchymal Give rise to
immune system cells Constant turnover
NIH stemcells.nih.gov/ info/basics/basics4.asp
10
Stem Cell Phenotype
Fate dictated by environment
Shihabuddin, et al., J. Neuroscience 20(23)
8727-8735, 2000
11
Re-cap What are stem cells?

• Embryonic and adult stem cells
• Obtained at different developmental stages
• Different potential
• Pluripotent versus Multipotent
• Sensitive to environment

12
Overview

• What are stem cells?
• How do embryonic and adult stem cells differ?
• How are different types of stem cell lines
  created?
• Stem cells in research and medicine
• How do scientists work with stem cells?
• In situ labeling
• Primary culture
• Cell lines
• Promises and perils of stem cells
• Alternatives to the embryo

13
Cell Lines

• Cells under propagation
• All cells are genetically identical
• Can be frozen and stored

14
Culturing Embryonic Stem Cells
Obtain stem cells from
Somatic Cell Nuclear Transfer
Oocyte without nucleus
Inject nucleus from adult somatic cell
Blastocyst
1. Remove inner cell mass 2. Put cells in dish
with feeder layer 3. Cells divide
15
Origins of ES Cell Lines

• Excess IVF embryos
• Therapeutic Cloning (somatic cell nuclear
  transfer)
• Donor oocytesomatic cell nucleus
• Cells have characteristics of nuclear donor
• Lines representing different diseases
• Individualized lines non-immunogenic to donor

New England Journal of Medicine, Wellcome Trust
16
Somatic Cell Nuclear Transfer
Challenging In cloned cell lines, about 4 of
genes function abnormally, owing to departures
from normal activation or expression of certain
genes -Imprinting, methylation state
Limited success 25 percent of nuclear transfers
led to a blastocyst 35 percent of blastocysts
led to establishment of cell lines
Patient-specific embryonic stem cells derived
from human SCNT blastocysts. Science
308(5729)1777-1783, 2005.
17
hES Cell Lines in the US

• Most, if not all, of the stem cell lines are
  contaminated with mouse feeder layer proteins.
• These cells will never be used in clinical
  application.
• Considerable biological variability across cell
  lines.
• Increased culturing can cause ES cells to
  accumulate epigenetic and genetic changes,
  altering their ability to form different types of
  cells.

18
Promises and Perils of Stem Cells
Whats at stake?

• Embryonic stem cells in therapy
• Cloning
• Adult stem cells in therapy
• Beyond cell replacement
• Beyond the embryo

19
What can ESCs do for you?

• Theoretically
• Replace damaged, diseased cells
• Gene therapy
• Genetically manipulated hES cells might serve as
  vectors to carry and express genes in target
  organs following transplantation in the course of
  gene therapy

20
Why Clone?
Therapeutic and Reproductive Cloning

• Human protein production
• Produce human protein-based medicine in milk from
  transgenic cows
• a-1-antitrypsin for cystic fibrosis
• Transplants without immune response
• Organ rejection or graft-vs-host disease

21
Therapeutic Cloning
22
How Promising are Adult Stem Cells?

• Bone marrow transplants
• Hematopoeitic stem cell transfer
• Difficulty maintaining control once in vivo
• Niche dictates phenotype
• Plasticity

23
Adult Stem Cell Clinical Trials

• Bone marrow stem cells from self or allogeneic
  (sibling) transplant
• after chemotherapy for myeloma, glioma, leukemia,
  lymphoma, neuroblastoma, lung cancer
• sickle cell anemia, liver disease, autoimmune
  disorders, vascular disease
• Mesenchymal stem cells for myocardial infarction

24
Potential Beyond Cell Replacement

• Exploring disease mechanisms
• study how basic cellular mechanisms are disrupted
  or changed by disease proteins
• Drug discovery
• High-throughput assays will identify targets. For
  example, using mouse ES cell-derived neural cells
  for an assay to screen Alzheimer's disease
• Genetic screening
• Toxicology testing

25
Overview

• What are stem cells?
• How do embryonic and adult stem cells differ?
• How are different types of stem cell lines
  created?
• Stem cells in research and medicine
• Alternatives to the embryo

26
Beyond the Embryo

• The Presidents Council for Bioethics
• White Paper published May 2005
• http//bioethics.gov/reports/white_paper/text.html

27
ESCs without the E

• De-differentiation
• Requires aid of special cytoplasmic factors
  obtained from oocytes (or from pluripotent
  embryonic stem cells)

• Obtainable from any adult
• Immunocompatible
• Some success with muscle, liver, blood

Issues How far back can dedifferentiation go?
28
ESCs without the E

• Remove single cell from 6-8 cell embryo
• Spin-off of preimplantation diagnosis

Issues Is there harm in removing a cell? Could a
cell line be established with one cell? Is cell
at this stage totipotent?
29
ESCs without the E

• Removal from dead embryo
• Early IVF embryos (roughly 4-8 cells) that have
  spontaneously died. Normal-appearing blastomeres
  in cleavage-arrested, mosaic embryos.

Issues Can markers of organismic death be
found? Can pluripotent stem cells be derived
from dead embryos? If so, will they be
chromosomally (and otherwise) normal?
30
Parthenogenesis

• Biochemically trick a human oocyte into thinking
  it has been fertilized.
• Treated eggs divide to the blastocyst stage
  (50-100 cells), at which point stem cells can
  presumably be derived.
• The parthenogenetic (that is, unfertilized but
  still developing) blastocyst-like entity is
  assumed by most to lack the potential for
  development as a human being.

31
ESCs without the E

• Bio-engineered embryo-like artifacts
• Embryos engineered to lack the essential elements
  of embryogenesis but still capable of some cell
  division and growth

Altered Nuclear Transfer
Embryo
32
ESCs without the E

• De-differentiation
• Single cell removal from embryo
• Removal from dead embryo
• Parthenogenesis
• Bio-engineered embryo-like artifact

Creative thinking, possible solutions to an
ethical dilemma. Research has yet to determine
if one or more of these proposals are possible.
33
Recent Research

• RNAi was used to change expression of a gene in a
  hESC line.
• Stem Cells 23(3)299305, 2005
• hESCs driven to develop into motor neurons.
• Nature Biotechnology 23215-221, 2005.

34
Recent Research

• Mesenchymal stem cells injected into rat heart
  increased pumping capacity and vessel growth
  after heart attack.
• Journal of Clinical Investigation 115326338,
  2005.
• Stembrids were made one ESC was enucleated and
  then given the nucleus from an adult somatic
  cell.
• Not shown that the resulting stembrid would be
  immunologically acceptable to the adult somatic
  cell donor.

35
Summary

• Stem cells
• Embryonic vs. Adult
• IVF, SCNT
• Therapeutic cloning and immune matching
• Much scientific progress, but therapies are not
  yet directly translated from research
• Greatest potential contribution from mechanistic
  studies in ESCs
• Embryonic alternatives need more development

36
Conclusion

• Stem cells are complicated scientifically,
  ethically, legally. The best way to approach them
  is with education.
• Working with stem cells is one of the most
  important opportunities of our time.