 Stem Cells

Definition  The capacity of cells to divide and differentiate along different pathways is necessary in embryonic development. It also makes stem cells suitable for therapeutic uses.

Egg and Sperm  A new animal life  2 gametes = 1 zygote  1 cell divided into 2 = embryo  Further division  But cells have not differintiated

Stem Cell Properties Can divide repeatedly  Produce copious quantities of new cells.  Useful for the growth of tissues or the replacement of cells that have been lost or damaged. Not fully differentiated  They can differentiate in different ways, to produce different cell types.

Embryonic Stem Cells – Therapeutic  Potentially very useful to:  Regenerate tissue  Means of healing disease  Grow whole replacement organs

Embryonic Stem Cells – Non-therapeutic  Produce large quantities of striated muscle fiberes (meat)  In the future – might not need to slaughter cattle

Differentiation  During embryo development cells commit to a pattern.  Eventually each cell becomes committed to develop into one specific cell types.  They are no longer stem cells.

Some remain  A few remain as stem cells  Present in tissue: bone marrow, skin and liver  Powers of regeneration & repair

 Therapeutic Uses

Stargardt’s disease  Stargardt’s Macular Dystrophy  Genetic disease  Appears in children ages 6-12  Recessive mutation of gene ABCA4  Membrane protein used for active transport in retina cells malfunctions  Photoreceptive cells in the retina degenerate  These cells detect light so vision worsens  May cause blindness

Stargardt’s Disease  Researchers have developed methods for making embryonic stem cells develop into retina cells.  Originally done in mice  Injected cells not rejected  Did not form tumours  Cells moved to the retina, attached and remained  Caused vision improvement  Video Video  November FDA approved stem cell research November FDA approved stem cell research  Research in England Research in England

Trial  Woman in her 50’s  50,000 retina cells derived from embryonic stem cells injected into her eyes  Cells attached to retina  Improvement in vision with no side effects

 Another use in disease: Leukemia

 Cancer – mutation of genes  Begins to make abnormally large numbers of white blood cells  No tumour forms  Normal range = 4,000 – 11,000 per mm 3 of blood  With leukemia = 30,000 or above

Cure Leukemia  Must kill cells in bone marro  Chemotherapy  Destroys stem cells in the bone marrow

Stem cells & Leukemia  A large needle inserted into a large bone (pelvis) – fluid removed  Stem cells extracted from the fluid & frozen (adult stem cells therefore can only make blood cells)  High dose of chemotherapy drugs – bone marrow loses its ability to produce blood cells  Stem cells are returned to the patient’s body and re-establish themselves

Stem Cell Ethics  Stem cell research is controversial  Old research would be considered unethical today  Patients without their consent  People do not understand the sources of stem cells

Sources of Stem Cells Embryos can be deliberately created by fertilizing egg cells (4 – 16 cells) Blood can be extracted from the umbilical cord of newborns (frozen) Stem cells can come from some adult tissues (bone marrow)

Embryonic stem cells  Almost unlimited growth potential.  Can differentiate into any type in body.  More risk of becoming tumour cells than adult stem cells  Less chance of genetic damage due to the accumulation of mutations than with adult stem cells  Likely to be genetically different from an adult patient  Kills the embryo

Cord Blood Stem Cells  Easily obtained and stored.  Commercial collection & storage services already available.  Fully compatible with the tissues of the adult that grow – no rejection problems occur.  Limited capacity to differentiate into different cell types – only naturally develop into blood  Limited quantities of stem cells from one baby’s cord.  The umbilical cord is discarded whether or not stem cells are taken from it.

Adult Stem Cells  Difficult to obtain because there are few and buried deep.  Less growth potential than embryonic stem cells.  Less chance of malignant tumours developing than from embryonic stem cells.  Limited capacity t differentiate into different cell types.  Fully compatible with the adult’s tissues; rejection not a problem.  Removal of stem cells does not kill the adult from which the cells are taken.

Final Thoughts  When does human life begin?  in vitro fertilization required hormone treatment to women  Should women be paid for supplying eggs