Gene Therapy Flashcards
Gene therapy is designed to
Introduce genetic material into cells to compensate for abnormal genes or to make a beneficial protein
Gene therapy can be used to treat
Inherited genetic diseases, certain cancers, and viral infections such as HIV
Vectors are used to deliver the gene into the nuclei of cells. What is the most commonly used vector?
Adenovirus
Advantages of using the adenovirus as a vector?
- Only causes a mild immune response
- Infects both dividing and non-dividing cells
- Introduce their DNA into the nucleus of the cell without directly inserting into the host genome.
Disadvantage of using the adenovirus as a vector
Carrying capacity is limited (cannot insert large genes into the adenovirus)
How does the vector enter the cells of the pt’s?
(more often) A sample of the pt’s cells are removed and exposed to the vector in a lab setting and then returned to the patient. In this case, the virus travels through the cell membrane to the nucleus.
(less often) The virus is injected into the patients blood or tissue.
Risks of gene therapy
- Unwanted immune system reaction
- Immune system may think the virus is an intruder and attack. Could lead to inflammation and organ failure
- Jesse Gelsinger - Wrong cells targeted
- Viruses can affect more than one cell type. It is possible that the altered viruses may infect additional cells and damage healthy DNA - Infection by the virus
- It’s possible that once introduced into the body, the verses may recover their original ability to cause disease
There are 4 gene therapies approved by the FDA since 2017. What are they used to treat?
Diseases all result in mortality or morbidity.
- refractory leukemia in children and young adults
- Used to treat large B-cell lymphoma
- Used to threat an inherited retinal disease that causes mutations to both copies of RPE65, which is a protein involved in phototransduction.
- Used to treat spinal muscular atrophy that causes death by age 2.
Define refractory
Not responding to any other treatments. Stubborn.
Difference between mortality and morbidity
Mortality- Death
Morbidity- Loss of organ. Ex: eye morbidity is loss of vision.
Difference between gene therapy and gene editing
Gene therapy- Introducing a new gene
Gene editing- Removing an abnormal gene and possibly replacing with another gene
CRISPR- Cas system was discovered in
Bacteria. This system is used to help bacteria defend against attacking viruses.
What is CRISPR and what is Cas?
CRISPR- short stretches of DNA that bacteria have copied from invading viruses. When the virus invades again, the bacteria will transcribe the DNA into RNA.
Cas is a protein nuclease that cleaves the viral DNA sequence. Cas is guided to the viral DNA by the CRISPR RNA
How does the cell try to repair the DNA after CRISPR-Cas0 system has cleaved the DNA?
The cell will try to repair the DNA either by NHEJ (non-homologous end joining) or HR (homologous recombination).
- NHEJ. Errors are typically introduced in the form of small insertions or deletions which causes the gene to be disabled. This will signal to nucleus “hey, we can’t fix it. Just silence this gene”
- HR. DNA strand of interest can be inserted and used to be incorporated into the genome. More accurate. Used in genome editing to replace mutated gene with healthy gene.
Why do several clinical trials of gene therapy/gene editing involve the eye?
- Separate compartment from the body that is easily accessed.
- Immune privilege afforded by the blood-retinal barrier.
- Only need to deliver a microscopic quantity of the vector because it is such a small space
- The visual system has a very precise, quantifiable measures of function. Amsler, VA’s, VF’s
