W10L2 Thues Gene therapy 2 Flashcards
The basis of genetic disease
- Cells contain information that is inherited (DNA/genes)
- Mutations in DNA cause genetic diseases
- Generally there is no cure for genetic diseases with normal medicine
- Gene therapy is a promising strategy to treat/cure genetic diseases
History of gene therapy
- Concept proposed in 1972 by Theodore Friedmann and Richard Robin
- Incorporating functional DNA into patient’s cells to treat genetic disorders
The first gene therapy
-4 year old girl have severe combined in 1990 immunodeficiency: lack of ADA and defective T, B cell
-retroviral vector carrying ADA gene into T cell
-10 infusion over 2 years
-restored immune fuction
Important consideration for gene therapy
- Efficient vector for gene delivery
- Gene expression & protein stability
- Precision is key, a serious concern is “off target” effect
-Avoide adverse immune respond
Type of gene therapy
- Gene augmentation: Introduce healthy copy of gene
- Gene editing: Correct genomic mutation(s)
Somatic vs germline gene therapy
- Somatic gene therapy: genome modification in somatic cells
- In vivo: the gene is transferred to cells inside the patient’s body
- Ex vivo: gene therapy on patient’s cells outside of body, then transplant back to patient
- Germline gene therapy: genome modification that will be carried to next generation
- E.g. CRISPR baby, mitochondrial replacement therapy
- Ethical considerations with manipulating the gene pool
Nuclear vs mitochondrial DNA
- Nucleus: 23 chromosome pairs, ~46000 nucleus genes
- Mitochondria: 37 mtDNA genes, multiple copies (homoplasmy, heteroplasmy)
Improving viral vector design
Better expression:
* Promoters: ubiquitous, cell-specific, truncated
* Kozak sequence
* other DNA regulatory elements: e.g. WPRE
Viral trophism:
* Modifying the viral capsid to improve specificity to target cells
inherited retinal degenerative disease LHON
- Characterized by loss of optic nerve cells – the retinal ganglion cells (RGCs)
- Most common mitochondrial DNA (mtDNA) disease, affecting ~ 1 in 30000 individuals, predominantly young males
- Homoplasmy mtDNA disease
- Central vision loss occurs usually around teenage to early twenties
- All LHON cases are caused by mutation in mtDNA encoding for mitochondria
Complex I subunits => Precise mechanism of how RGCs die is not known - Currently no effective treatment for LHON patients *
- No clinical relevant model to study LHON disease:
- Human primary RGCs are difficult to obtain and culture
- Species differences in rodent models
Using in vitro cell models to test gene therapy
-extract the patient skin cell and reprogram it into iPS (hard to obtain nerve sample from living patient)
-Allow it to differentiate into eyecell
-eye cell can be use for drug screening and disease modeling
-genetic correction of the eye cell, apply it to the paitient
Genetic correction of LHON
For LHON, the cybrid technology can be used to replace mutated mitochondria with healthy donor mitochondria
-correction of LHON mutation rescue optics nerve cell death in LHON
Current clinical trials for LHON gene therapy
Gene augmentation to deliver healthy copy of ND4 gene (most common LHON mutation)
* Neuropath
* NR082: AAV2 vector carrying ND4 gene
* Chinese clinical trial – 9 patients with 7 years follow-up (Yuan 2020 Ophthalmology)
* Safe and vision improvement in some patients
* USA phase I clinical trials
* AAV2 vector carrying ND4 gene
* Phase I with 14 patients, 12 month follow-up: Safe and vision improvement in some patients (Guy et al 2017 Ophthalmology)
* Phase I with 28 patients, 24 month follow-up: Good safety profile, limited efficacy (Lam et al. Am J Ophthalmol)
* GenSight Biologics (France) Phase III clinical trials with 90 patients:
* Lumevoq/GS010: AAV2 vector carrying ND4 gene
* Multi-centre, randomized, double-blind, placebo-controlled trial
* bilateral visual improvement in patients with unilateral gene therapy (Newman 2021 Ophthalmology, Yu-Wai-Man 2020 Sci Transl Med)
Leber’s congenital amaurosis (LCA)
- One of the most common causes of blindness in children affecting ~1 in 40000
- Severe visual loss at birth
- Other eye-related conditions such as abnormal sensitivity to light, roving eye movements
- RPE65 mutation => inability to process vitamin A => degeneration of photoreceptors
- There are other mutations that cause LCA: E.g. CEP290, CRB1, GUCY2D
Cure for LCA
-the first FDA approved gene therapy in the eye (2017)
-But extremely high cost 850K
-Approve in Australia in 2020
-2022, cost subsidize jointly by federal and Australia state goverment
Ethical consideration of gene therapy
-regulation of treatment
-consent
-risk and benefit
-cost
- germ line modification
-human modification/ enhancement
