Module 3- Gene Therapy Flashcards
The Magnitude of The Human Genome
Each somatic cell in the human body (except for mature red blood cells and platelets, which do not contain a nucleus) contains a complete copy of the human genome:
● Approximately 3.2 billion base pairs
● Organized into 23 pairs of
chromosomes
● An estimated total of 30,000 genes
The Human Genome Project mapped and sequenced all of the genes of the human genome — and one of the lead contributors to this effort was esteemed Brown Professor Sorin Istrail! While Director of Celera Genomics, his group co-authored the 2001 Science paper, “The Sequence of the Human Genome.”
What are gene therapies?
- The FDA defines gene therapies as products that harness the Central Dogma — the principles of transcription and translation — to modify genetic information and integrate it to a patient as nucleic acids, viruses, or genetically engineered microorganisms.
-The products may be used to modify cells in vivo or transferred to cells ex vivo prior to administration to the recipient
Gene therapies are regarded as a potential revolution in the health sciences and pharmaceutical fields
The number of clinical trials investigating gene therapies is increasing worldwide, despite the limited number of products that have successfully reached the market.
While the majority of these have been centered in the United States, the development of gene therapies is a global effort
To treat a genetic disease, we must first identify the ___
Causing gene
Monogenic diseases
Monogenic diseases result from changes to a single gene — occurring in all cells of the body. Examples include:
● Thalassaemia
● Sickle cell anemia
● Hemophilia
● Cystic Fibrosis
● Tay sachs disease
● Spinal muscular atrophy
● Huntington’s disease
Scientists estimate that over 10,000 human diseases are monogenic disorders
Indications addressed by gene therapy clinical trials
Somatic vs Germ Cell Gene Therapy
For a gene therapy to be approved, two important criteria must be met:
- There must be effective therapeutic genes that can be expressed at specific target sites
● Specificity
● Effective transfer to target cell and target cell nucleus - There must be an efficient and safe delivery system
● Protection against premature degradation in blood and
intracellular (endosomal) degradation
● Entry through cytoplasmic and nuclear membranes
Vectors and Delivery Vehicles
Gene therapies can’t be administered as a simple, over-the-counter pill — special vectors must be used
Adenovirus vectors
Adenovirus vectors release the gene freely into the nucleus — the gene is not incorporated and readministration is often required
Retrovirus vectors
Retrovirus vectors insert RNA and enzymes — which incorporate randomly into genome (integrase)
Comparison of commonly used viral vectors in gene therapy
In Vivo v. Ex Vivo
In Vivo v. Ex Vivo
There are benefits and drawbacks to both methods — which is used ultimately depends on the specific therapy
The process of immunotherapy
CAR-T cell therapy
- Chimeric Antigen Receptor - T cell therapy (CAR-T) is a type of treatment in which a patient’s T cells are genetically modified to attack cancer cells.
- Think back to the vaccines lecture — T cells focus on recognizing and attacking specific foreign antigens or particles.
Introducing CD-19
CD-19 is a molecule exclusive to B-cells — lymphocytes that produce antibodies. Since B-cells are a common marker for certain cancers and are also not necessary for survival, CAR-T can target B-cells for patients with CD19+ lymphoma and leukemia.
CD19-targeted CAR-T cell therapy
Market Case: Kymriah
Kymriah is the first gene therapy treatment approved (2017) for the treatment of patients up to 25 years of age with B-cell precursor acute lymphoblastic lymphoma that is refractory or in second or later relapse.
There is a life threatening risk of cytokine release syndrome and neurological effects.
Understanding the Retina
- The retina is the layer in the back of the eye containing cells that are sensitive to light and trigger nerve impulses that pass via the optic nerve to the brain — where a visual image is formed.
- The retinal pigment epithelium is a single layer of cells that acts as a barrier to the retina as well as providing protection and stability.
RPE65 and rhodopsin
- RPE65 is critical to resetting the visual cycle and responsible for rhodopsin production — the most abundant protein in the rod cells that is the primary photoreceptor molecule of vision
- When RPE65 is mutated, photoreceptor cells (rods and cones) die.
Normal vs. degenerated retina
The proposed gene therapy —
RPE65-Leber Congenital Amaurosis: AA
- The FDA advisory committee voted unanimously to approve this therapy in 2017.
- 90% of study participants report increased sight within days.
Epidermolysis Bullosa
- Epidermolysis Bullosa patients have skin as delicate as butterfly wings — it falls apart with the slightest touch
- Several forms of this disease result from different genes — all of which affect either cell adhesion molecules, basement membrane proteins, or matrix proteins.
- Patients often have “mitten hands” due to frequent wound healing and the formation of scar tissue.
Epidermolysis Bullosa treatment
Genetically modified cells for an unmutatedLAMB3 regenerate the skin —a gene responsible for a majority of epidermolysis bullosa cases. Lamin is the protein network foundation for most cells and organs.
