IB Biology 1.1- Stem Cells Review

Therapeutic uses of stem cells- Stargardt's diesease:

- This is a genetic disease that develops in children between ages of 6-12. Most cases are due to a recessive mutation of a gene called 'ABCA4.' - This causes a membrane protein used for active transport in retina cells to malfunction, so photoreceptive cells degenerate and vision becomes progressively worse. Eventually leading to blindness. - Researchers have developed methods for making embryonic system cells develop into retina cells. In 2010 a woman in her 50s with Stargardt's disease was treated by having 50.,000 retina cells derived from embryonic stem cells injected into her eyes. - The cells attached to the retina and remained there during the 4-month trial. There was an improvement in the woman's vision- no side effects. Further trials with larger numbers of patients are needed, however we can be optimistic about the development of treatments for Stargadt's disease using embryonic stem cells.

Stem Cells- adult- pluripotent

- stem cells and are still present in the adult body, they are found in most human tissues- EG BONE MARROW, SKIN + LIVER - can differentiate into specialized cells of the body but not a complete organism

When a cell differentiates and becomes specialised, it loses its capacity to form alternative cell types Stem cells are unspecialised cells that have two key qualities:

1. Self Renewal - They can continuously divide and replicate 2. Potency - They have the capacity to differentiate into specialised cell types

Stargardt's Disease

An inherited form of juvenile macular degeneration that causes progressive vision loss to the point of blindness Caused by a gene mutation that impairs energy transport in retinal photoreceptor cells, causing them to degenerate Treated by replacing dead cells in the retina with functioning ones derived from stem cells

Stem cells can be derived from one of three sources:

Embryos (may be specially created by therapeutic cloning) Umbilical cord blood or placenta of a new-born baby Certain adult tissues like the bone marrow (cells are not pluripotent)

Other Therapeutic Examples

Leukemia: Bone marrow transplants for cancer patients who are immunocompromised as a result of chemotherapy Paraplegia: Repair damage caused by spinal injuries to enable paralysed victims to regain movement Diabetes: Replace non-functioning islet cells with those capable of producing insulin in type I diabetics Burn victims: Graft new skin cells to replace damaged tissue

ETHICS

Main argument: the health and quality of life of patients suffering from otherwise incurable diseases may be greatly improved AGAINST: - depends on source of stem cells - few objections to the use of an adult's own stem cells or cells from an adult volunteer - newborn babies cannot give consent for stem cells to be harvested from their umbilical cord, parental consent is given and the cells are store in case they are needed during the baby's subsequent life, unobjectionable Taken from embryos: - argue that embryo is human life, if dies as result of procedure it is immoral, and benefits from therapies using embryonic stem cells do not justify taking a life counter arguments: - early stage embryos are little more than balls of cells that have yet to develop the essential features of a human life - early stage embryos lack a nervous system, do not feel pain or suffer in other ways during stem cell procedures - if embryos are produced deliberately, no individual that would otherwise have had the chance of living is denied the chance of life - large numbers of embryos produced by IVF are never implanted and do not get the chance of life, rather to kill these embryos and use their stem cells to treat diesases and save lives

Stem cells- medical

Other tissues lack the stem cells and are needed for effective repair are BRAIN, KIDNEY HEART - great interest in therapeutic uses for stem cells with organs such as these - great potential for embryonic stem cells for tissue repair and for treating a variety of degenerative conditions

Uses of Stem Cells

Stem cells are necessary for embryonic development as they are an undifferentiated cell source from which all other cell types may be derived Cell types that are not capable of self-renewal (e.g. amitotic nerve tissues) are considered to be non-stem cells As these tissues cannot be regenerated or replaced, stem cells have become a viable therapeutic option when these tissues become damaged

Types of Stem Cells

There are four main types of stem cells present at various stages of human development: Totipotent - Can form any cell type, as well as extra-embryonic (placental) tissue (e.g. zygote) Pluripotent - Can form any cell type (e.g. embryonic stem cells) Multipotent - Can differentiate into a number of closely related cell types (e.g. haematopoeitic adult stem cells) Unipotent - Can not differentiate, but are capable of self renewal (e.g. progenitor cells, muscle stem cells)

Therapeutic uses of stem cells- Leukemia:

This is a type of cancer in which abnormally large numbers of white blood cells are produced in the bone marrow. White blood count cell rises above 30,000. Adult stem cells are used in the treatment of Leukemia: - A large needle inserted into a large bone, usually the pelvis and fluid is removed from the bone marrow. - Stem cells are extracted from this fluid, and stored by freeing them. They are adult stem cells and only have the potential for producing blood cells. - A high dose of chemotherapy drugs is given to the patient to kill the cancer cells in the bone marrow. The bone marrow loses its ability to produce blood cells. - The stem cells are then returned to the patient's body. They re-establish themselves into the bone marrow, multiply and start to produce red and white blood cells. In many cases this procedure cures leukemia completely.

Stem cells can be used to replace damaged or diseased cells with healthy, functioning ones

This process requires: The use of biochemical solutions to trigger the differentiation of stem cells into the desired cell type Surgical implantation of cells into the patient's own tissue Suppression of host immune system to prevent rejection of cells (if stem cells are from foreign source) Careful monitoring of new cells to ensure they do not become cancerous

The ethical considerations associated with the therapeutic use of stem cells will depend on the source

Using multipotent adult tissue may be effective for certain conditions, but is limited in its scope of application Stem cells derived from umbilical cord blood need to be stored and preserved at cost, raising issues of availability and access The greatest yield of pluripotent stem cells comes from embryos, but requires the destruction of a potential living organism

Stem Cells- totipotent

defined as cells that have the capacity to divide and differentiate along different pathways - human embryos consist entirely of stem cells in early stages, gradually the cells in the embryo commit themselves to a pattern of differentiation - once committed, a cell may still divide several more times, but all of the cells formed will differentiate in the same way and so they are no longer stem cells