DEFINITION

• A cell that has the ability to continuously divide anddifferentiate (develop) into various other kind(s) ofcells/tissues.

• the body is made up of about 200 different kinds ofspecialised cells such as muscle cells, nerve cells, fat cellsand skin cells.

• all cells in the body come from stem cells.

• a stem cell is a cell that is not yet specialised.

• the process of specialisation is called differentiation.

• once the differentiation pathway of a stem cell has beendecided, it can no longer become another type of cell on itsown.

STEM CELL HISTORY

1998 - Researchers first extract stem cells from human embryos

1999 - First Successful human transplant of insulin-making cells

from cadavers

2001 - President Bush restricts federal funding for embryonic

stem-cell research

2002 - Juvenile Diabetes Research Foundation International

creates $20 million fund-raising effort to support stem-cell

research

2002 - California stem cell research

2004 - Harvard researchers grow stem cells from embryos using

private funding

2004 - Ballot measure for $3 Billion bond for stem cells

STEM CELL CHARACTERISTICS

‘Blank cells’ (unspecialized)

Capable of dividing and renewing themselves for long

periods of time (proliferation and renewal)

Have the potential to give rise to specialized cell types

(differentiation)

TYPES OF STEM CELL

Stem cell

type Description Examples

TotipotentEach cell can develop into

a new individual

Cells from early (1-3

days) embryos

PluripotentCells can form any (over

200) cell types

Some cells of

blastocyst (5 to 14

days)

Multipotent

Cells differentiated, but

can form a number of

other tissues

Fetal tissue, cord

blood, and adult

stem cells

KINDS OF STEM CELL

1. Embryonic stem cells come from a five to six-day-old embryo. Theyhave the ability to form virtually any type of cell found in thehuman body.

2. Embryonic germ cells are derived from the part of a humanembryo or foetus that will ultimately produce eggs or sperm(gametes).

3. Adult stem cells are undifferentiated cells found among specialisedor differentiated cells in a tissue or organ after birth. Based oncurrent research they appear to have a more restricted ability toproduce different cell types and to self-renew.

STEM CELL DIFFERENTIATION

WHY ARE STEM CELLS SPECIAL?

Stem cells can:

1. self-renew to make more stem cells.

2. differentiate into a specialised cell type.

Embryonic stem cells (pluripotent)

Stem cells that can become

many types of cells in the

body are called pluripotent

Tissue stem cells (multipotent)

Stem cells that can

become only a few types

of cells are called

multipotent

TISSUE STEM CELLS

• often known as adult stem cells

• also includes stem cells isolated from fetal and cord blood

• reside in most tissues of the body where they are involved in repair and replacement

• generally very difficult to isolate

• already used to treat patients (haematologicalmalignancies, diseases of the immune system)

Bone marrow Kidney Lung

8-cell blastocystfertilised egg

2-cellegg

Day 0 Day 1 Day 2 Day 3 Day 6

• Donated excess IVF embryos

Images from www.advancedfertility.com

Where do embryonic stem cells come from?

Inner cell mass

Embryonic stem cells

• derived from donated IVF

embryos

• can be grown indefinitely

in the laboratory in an

unspecialised state

• retain ability to specialise

into many different tissue

types – know as

pluripotent

• can restore function in

animal models following

transplantationHuman embryonic stem cells can become any

cell in the body including these beating heart

cells

human embryonic

stem cells

INDUCED PLURIPOTENT STEM CELLS

• derived from adult cells in2007 - very recent discovery!

• can be grown indefinitely in

culture in an undifferentiated

state

• similar properties to

embryonic stem cells as can

differentiate into many

different tissue types –

pluripotent

• can create stem cells directly

from a patient for research

Induced change in

gene expression

pluripotent

stem cells

Starting cells from

donor tissue

iPS Cells

WHAT MAKES STEM CELLS SO VALUABLE?

Cell Therapy

Research

New Drugs

Pluripotent

stem cells

Tissue stem

cells

No one stem cell type fits all applications.

Research must continue using all types of stem cells.

APPLICATIONS

Disease

• Diabetes, Spinal cord

injury, Parkinson’s

disease, heart

disease

Genetic based Disease

• Cystic fibrosis,

Huntington’s

CHALLENGES TO STEM CELL/CLONING

RESEARCH

1. Stem cells need to be differentiated to theappropriate cell type(s) before they can beused clinically.

2. Recently, abnormalities in chromosomenumber and structure were found in threehuman ESC lines.

3. Stem cell development or proliferation

must be controlled once placed into

patients.

4. Possibility of rejection of stem cell

transplants as foreign tissues is very high.

5. Contamination by viruses, bacteria, fungi, and

Mycoplasma possible.

6. The use of mouse “feeder” cells to grow ESC

could result in problems due to

xenotransplantation.

UNKNOWNS IN STEM CELL/CLONING RESEARCH

• It is uncertain that human embryonic stem cells in vitro can give rise to all the different cell types of the adult body.

• It is unknown if stem cells cultured in vitro(apart from the embryo) will function as the cells do when they are part of the developing embryo

REFERENCES

www.stemcellcentre.edu.au

www.stemcellchannel.com.au