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Transcript of Gene Therapy
Somatic cells (most cells of the body)
Germline cells (eggs or sperm).
Both types of cells can be transformed. Ex Vivo Gene therapy using germ line cells results in permanent changes that are passed down to generations. It introduces the possibility of eliminating some diseases from a particular family, and ultimately from the population.
It is controversial because some people view this type of therapy as unnatural. Others worry that the genetic change may actually be harmful, with the potential for unforeseen negative effects on future generations.
All gene therapy to date on humans has been directed at somatic cells since germline engineering in humans remains controversial and prohibited in for instance the European Union. Viewed as a more conservative.
Safer approach because it affects only the targeted cells in the patient, and is not passed on to future generations meaning it ends with the individual receiving the therapy.
Usually, repeated treatments are necessary since somatic cell therapy is short lived because cell tissues die and are replaced by new cells.
Another problem is transporting the cells.
Despite the difficulties it is appropriate and acceptable for many disorders, including cystic fibrosis, muscular dystrophy, cancer, and other certain infectious diseases.
This therapy can be performed in utero, potentially correcting or treating a life-threatening disorder that may significantly impair a baby's health or development if not treated before birth. Most severe of the Primary Immune Deficiency diseases.
T-helpers direct and assist all other immune cells in attacking foreign antigens.
When a foreign antigen invades the body T-helper cells direct B-lymphocytes (or B-cells) to make antibodies against it. These antibodies bind to the foreign antigen, neutralize it and allow phagocytes to digest and eliminate it completely.
Defining characteristic of SCID is the absence of T cells and, as a result, lack of B cell function as well. Unless these defects are corrected the child will die of opportunistic infections before their first or second birthday. Gene therapy is a technique for correcting defective genes responsible for disease development. The following are different methods of gene therapy:
•An abnormal gene could be swapped for a normal gene through homologous recombination.
•The abnormal gene could be repaired through selective reverse mutation, which returns the gene to its normal function.
•The intensity of a particular gene could be altered.
•The most common approach is when a normal gene may be inserted into a nonspecific location within the genome to replace a nonfunctional gene. Viral vs. Non-viral Vectors Questions Somatic and Germ Line Cells Two categories of somatic cell therapy
This type of gene therapy is called ex vivo because the cells are treated outside the body.
The cells are modified outside the body and then transplanted back in again.
This can be done using either the patient's own cells, or stem cells. In Vivo This form of gene therapy is called in vivo, because the gene is transferred to cells inside the patient’s body. In 1980 Dr. Martin Cline conducted the first unapproved attempt at gene therapy. A rDNA transfer into the bone marrow cells of two patients with hereditary blood disorders.
It was a direct opposition to National Institute of Health gene therapy guidelines and he didn't have the approval of the Institutional Review Board at the University of California Los Angeles (UCLA), where his research was conducted.
The ethical concerns that were generated prompted a call for review by a number of organizations and Dr. Cline was forced to resign his department chairmanship at UCLA and lost several research grants.
The first approved experiments in gene therapy on humans began in 1990.
Two girls with ADA deficiency SCID were treated, several times, over a 2 year period, with T-cells carrying corrected DNA
Researchers corrected the DNA in a sample of the girls' T-cells and then returned the T-cells to them.
Success of these early trials is debated.
Periodic tests on both girls show that their re-engineered cells are surviving and producing the ADA enzyme, but both girls continue to receive replacement enzyme therapy. SCID or Severe Combine Immune Deficiency First Experiment in Gene Therapy Vectors – Methods of delivering genes to cells. These come in Viral and Non-viral types.
• Viruses are modified to deliver the desired genes.
• The most commonly used viruses are retroviruses, adenoviruses, adino-associated viruses, and herpes simplex viruses.
• Viruses are able to target and enter cells.
• These viruses are modified so that they can’t replicate.
• Risk of immune response to disease
• Sometimes better due to the size restrictions of viruses
• Wont generate a negative immune response
• Non-viral vectors are usually plasmids – these are used in nature to transfer DNA between bacteria
1. Give the name of the two types of cells and which is more commonly used for gene therapy?
2. Name two diseases that can be helped through gene therapy.
3. Explain the two broad categories gene therapy can be split into.
4. Explain one of the approaches of gene therapy?
5. What is the current status on gene therapy? Animation:
http://www.sumanasinc.com/scienceinfocus/sif_genetherapy.html Current Status on Gene Therapy The Food and Drug Administration (FDA) has not yet approved any human gene therapy product for sale.
Current gene therapy is experimental and has not proven too successful in clinical trials. Video: