Transcript Stem Cell Research Overview

Summer 2007 Workshop
 in Biology and Multimedia
 for High School Teachers

Stem Cell Research
Overview
Mountainous Path
Outline
What are Stem Cells?
 Potential Uses
 Claims Against Using Stem Cells
 Cultivation Process
 Stem Cells and Cloning
 Stem Cell Theory of Cancer
 Worldwide Status

What are stem cells?

Stem cells are undifferentiated cells that
have many potential scientific uses:
 Cell

based therapies
Often referred to as regenerative or reparative
medicine
 Therapeutic
cloning
 Gene therapy
 Cancer research
 Basic research
Two types of stem cells

Embryonic Stem Cells (ESC): received from:
 Embryos
created in vitro fertilization
 Aborted embryos

Adult Stem Cells (ASC): can be received
from:
 Limited

tissues (bone marrow, muscle, brain)
Discrete populations of adult stem cells generate
replacements for cells that are lost through normal
wear and tear, injury or disease
 Placental
cord
 Baby teeth
Source of ESC

Blastocyst
 “ball
of cells”
 3-5 day old embryo
 Stem cells give rise to multiple specialized cell
types that make up the heart, lung, skin, and
other tissues

Human ESC were only studied since 1998
 It
took scientists 20 years to learn how to grow
human ESC following studies with mouse ESC
How are embryonic stem cells
harvested?


Human ES cells are derived from 4-5 day old
blastocyst
Blastocyst structures include:
 Trophoblast:
outer layer of cells that surrounds the
blastocyst & forms the placenta
 Blastocoel: (“blastoseel”) the hollow cavity inside the
blastocyst that will form body cavity
 Inner cell mass: a group of approx. 30 cells at one end of
the blastocoel:

Forms 3 germ layers that form all embryonic tissues (endoderm,
mesoderm, ectoderm)
Blastocyst
http://www.ivf-infertility.com/infertility/infertility5.php
Unique characteristics of Stem
Cells

Stem cells can regenerate
 Unlimited

self renewal through cell division
Stem cells can specialize
 Under
certain physiologic or experimental
conditions
 Stem cells then become cells with special
functions such as:
Beating cells of the heart muscle
 Insulin-producing cells of the pancreas

Unspecialization

Stem Cells are unspecialized
 They
do not have any tissue-specific
structures that allow for specialized function
 Stem cells cannot work with its neighbors to
pump blood through the body (like heart
muscle cells)
 They cannot carry molecules of oxygen
through the bloodstream (like RBCs)
 They cannot fire electrochemical signals to
other cells that allow the body to move or
speak (like nerve cells)
Self - Renewal (Regeneration)

Stem cells are capable of dividing &
renewing themselves for long periods
is unlike muscle, blood or nerve cells –
which do not normally replicate themselves
 In the lab, a starting population of SCs that
proliferate for many months yields millions of
cells that continue to be unspecialized
 This

These cells are capable of long-term self-renewal
Specialization of Stem Cells:
Differentiation

Differentiation: unspecialized stem cells give
rise to specialized (differentiated) cells in
response to external and internal chemical
signals
 Internal
signals: turn on specific genes causing
differential gene expression
 External signals include:
Chemicals secreted by other cells such as growth
factors, cytokines, etc.
 Physical contact with neighboring cells

Differentiation
Why do your body cells look different
although they all carry the same DNA,
which was derived from one fertilized egg?
 Differentiation example

(http://learn.genetics.utah.edu/units/biotech/microarray/)
Potential of Stem Cells (vocab)

Totipotent (total):
 Total
potential to differentiate into any adult cell type
 Total potential to form specialized tissue needed for
embryonic development

Pluripotent (plural):
 Potential
to form most or all 210 differentiated adult
cell types

Multipotent (multiple):
 Limited
potential
 Forms only multiple adult cell types


Oligodendrocytes
Neurons
Adult Stem Cells

Adult or somatic stem cells have unknown
origin in mature tissues
 Unlike
embryonic stem cells, which are
defined by their origin (inner cell mass of the
blastocyst)
http://www.stemcellresearch.org/testimony/20040929prentice.htm Reprinted with permission of Do No Harm.
Adult stem cells continued

Adult stem cells typically generate the cell
types of the tissue in which they reside
 Stem
cells that reside in bone marrow give rise
to RBC, WBC and platelets
 Recent experiments have raised the possibility
that stem cells from one tissue can give rise to
other cell types

This is known as PLASTICITY
Adult Stem Cell Plasticity Examples




Blood cells becoming neurons
Liver cells stimulated to produce insulin
Hematopoietic (blood cell producing) stem cells
that become heart cells
CONCLUSION: Exploring the use of adult stem
cells for cell-based therapies has become a very
important (and rapidly increasing) area of
investigation by research scientists!
Adult stem cells: A brief history
Adult stem cell research began about 40
years ago
 Stem cell discoveries in 1960s:

 Bone
marrow contains 2 populations of stem
cells
Hematopoietic stem cells – forms all blood cell types
 Bone marrow stromal cells – mixed cell population that
generates bone, cartilage, fat and fibrous connective
tissue

 Rat
brain contains two regions of dividing cells,
which become nerve cells
History Cont.

Stem Cell Discoveries
in the 1990s
 Neural
stem cells in
brain are able to
generate the brain’s
three major cell types



Astrocytes
Oligodendroglial cells
Neurons
http://www.alsa.org/images/cms/Research/Topics/cell_targets.jpg
Adult Stem Cell Facts



Adult stem cells were found in many more
tissues than expected
Some may be able to differentiate into a number
of different cell types, given the right conditions
General consensus among scientist:
 Adult
stem cells DO NOT have as much potential as
embryonic stem cells

CLARIFICATION: not all new adult cells arise
from stem cells
 Most
arise by MITOSIS of differentiated cells
Potential Uses of Stem Cells

Basic research – clarification of complex
events that occur during human
development & understanding molecular
basis of cancer
 Molecular
mechanisms for gene control
 Role of signals in gene expression &
differentiation of the stem cell
 Stem cell theory of cancer
Potential uses cont.

Biotechnology(drug discovery &
development) – stem cells can provide
specific cell types to test new drugs
 Safety
testing of new drugs on differentiated
cell lines
 Screening of potential drugs
Cancer cell lines are already being used to screen
potential anti-tumor drugs
 Availability of pluripotent stem cells would allow
drug testing in a wider range of cell types & to
reduce animal testing

Potential uses cont.

Cell based therapies:
 Regenerative
therapy to treat Parkinson’s,
Alzheimer’s, ALS, spinal cord injury, stroke,
severe burns, heart disease, diabetes,
osteoarthritis, and rheumatoid arthritis
 Stem cells in gene therapy

Stem cells as vehicles after they have been
genetically manipulated
 Stem
cells in therapeutic cloning
 Stem cells in cancer
Embryonic vs Adult Stem Cells

Totipotent
 Differentiation

 Differentiation
into ANY
into some
cell types, limited
outcomes
cell type



Known Source
Large numbers can be
harvested from
embryos
May cause immune
rejection
 Rejection
of ES cells by
recipient has not been
shown yet
Multi or pluripotent



Unknown source
Limited numbers, more
difficult to isolate
Less likely to cause
immune rejection, since
the patient’s own cells
can be used
Claims against ESC
(unsubstantiated thus far!)








Difficult to establish and maintain *
Difficulty in obtaining pure cultures from dish*
Potential for tumor formation and tissue*
destruction
Questions regarding functional differentiation
Immune rejection
Genome instability
Few & modest results in animals, no clinical
treatments
* = same problem
Ethically contentious
with ASC
Cell Culture Techniques for ESC
Isolate & transfer of inner cell mass into
plastic culture dish that contains culture
medium
 Cells divide and spread over the dish
 Inner surface of culture dish is typically
coated with mouse embryonic skin cells
that have been treated so they will not
divide


This coating is called a FEEDER LAYER
 Feeder
cells provide ES cells with a sticky
surface for attachment
 Feeder cells release nutrients

Recent discovery: methods for growing
embryonic stem cells without mouse feeder
cells
– eliminate infection by viruses or
other mouse molecules
 Significance

ES cells are removed gently and plated into
several different culture plates before
crowding occurs
http://www.news.wisc.edu/packages/stemcells/illustration.html Images
depict stem cell research at the University of Wisconsin Madison.
Cloning of whole organisms

Purpose:
 Reproductive
cloning in animals
 Therapeutic cloning in animals
 Breeding animals or plants with favorable traits
 Producing TRANSGENIC animals that:
Make a therapeutic product (vaccine, human protein etc)
 Act as animal models for human disease
 Deliver organs that will not be rejected (cells lacking cell
surface markers that cause immune rejection)

 Vaccines
gene
in biotech industry: steps in cloning a
SCNT: Somatic Cell Nuclear
Transfer

SCNT is a method used for:
 Reproductive
cloning such as cloning an embryo
 Regenerative cloning to produce “customized”
stem cells & overcome immune rejection

Blastula stage cannot continue to develop in
vitro
 It
must be implanted into surrogate mom
 Surrogate mom is just a container that provides
protection & chemical signals necessary for
development
http://www.kumc.edu/stemcell/early.html Reprinted with permission from the University of Kansas Medical Center.
http://www.stemcellresearch.org/testimony/20040929prentice.htm Reprinted with permission of Do No Harm.
Challenges of Reproductive
Cloning

Many animals were cloned after Dolly
 Cats,

pigs, mice, goats, cattle, rabbits
Obstacles:
 Very
inefficient process
 Most clones have deleterious effects & die early
 Surviving clones show premature aging signs
 Signs of abnormal embryonic development:

Clones & their placentas grow much faster than
expected in surrogate mom
Therapeutic Cloning

3 goals of therapeutic cloning by SCNT in
humans:
 Use
embryo as source for ES cells
 Use ES cells to generate an organ

In this case the organ generated will carry cells with the
same genetic markers as the patient (recipient)
 Correct
genetic error in ESC in blastula stage
Pitfalls of therapeutic cloning (1)
Some immune rejection may occur- WHY?
 About
1% of the DNA in the clone will NOT be
identical to donor cell (patient)
 It will be identical to egg cell used in SCNT
 REASON: mitochonrial DNA in eggs

Human mitochondria carry about 13 genes, some
of which code for surface proteins
Pitfalls of therapeutic cloning (2)
Large number of eggs needed for SCNT
 To harvest large number of eggs:

 Excessive
hormone treatment of females to
induce high rate of ovulation
 Surgery to retrieve eggs
Both can be harmful to female human
 Cow/pig females may be used

 Cow/pig
eggs will carry species-specific
mitochondrial genes

Mixing species is reason for concern!
Common Opinions
Reproductive cloning is a criminal offense
(it is ILLEGAL worldwide!)
 Therapeutic cloning is acceptable,
however there is still significant
controversy over whether:

the clone is implanted into the uterus of
surrogate mom? OR
the clone is explanted into culture dish to
generate ES cells
Stem Cell Theory of Cancer

1855: Rudolf Virchow developed the
Embryonal- Rest Hypothesis
 Microscopic
examination of tumor samples
revealed many morphological (structural &
functional) resemblances to ESC in a developing
fetus

Isolation of teratoma: nonmalignant tumors
 Teratoma
represents a ball of almost all cell types
 This indicates that teratoma may originate from
unregulated stem cells that can give rise to almost
all tissues
Teratoma

Ovarian Teratoma
 You
can see teeth!
http://home.earthlink.net/~radiologist/tf/040802.htm Image courtesy of Leonard J. Tyminski, M.D., Radiologist at earthlink.net
Current Efforts with SC and Cancer



Tumor stem cell

Tumor cell
Drawn by Christine Rodriguez
Determine difference
between cancer & normal
stem cells
Identify potential points in
pathways critical for the
survival of cancer SCs
Develop therapies that
specifically target cancer
SC
Duke University
Explanation
Status of SC research in other
countries

Great Britain




France




Very liberal policies on research
Therapeutic cloning allowed, use of excess embryos & creation of
embryos allowed
Stem cell research allowed
Less liberal politics
Use of excess embryos from IVF allowed
Reproductive AND therapeutic cloning banned
Germany



Very strict policies
Use of excess embryos and creation of embryos banned
Scientists can IMPORT embryos
Debate in US

Federal funding available for research using the
Bush lines only:
 ES

cell lines that were already in existence by 8/9/01
Disadvantage of Bush stem cell lines:
 May
have lost regenerative ability
 May have accumulated mutations or infections

Private companies continue to pursue stem cell
research
 Use
of human embryos for IVF & therapeutic cloning is
legal in most states

No federal funding
 Some
states are considering banning both
Global Status

Ongoing debate regarding use of embryos

United Nations: proposal for a global
policy to ban reproductive cloning only
References

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Stem cells & Cloning Stem cells & Cloning; David A.
Prentice, Benjamin Cummings, 2003
http://www.pbs.org/wgbh/nova/sciencenow/3302/06.html
http://www.stemcellresearch.org
http://www.stemcells.nig.gov/info/nasics/nasics7.asp
http://www.stemcells.nig.gov/info/scireport/2006report.ht
m
http://www.whitehouse.gov/news/re;eases/2001/08/2001
0809-2.html
Stem cells in class; Badran, Shahira; Bunker Hill
Community College, 2007, Boston Museum of Science
Biotechnology Symposium
Harvard Stem Cell Institute