Gene Therapy Flashcards
what is gene therapy? what are three general gene therapy strategies and what do they do?
gene therapy = transfer of genetic material to treat or prevent diseases
- gene replacemnt: not removing; healthy copy of a non-functional gene or gene with reduced function
- gene silencing: reduce expression/abundance of an aberrant toxic RNA/protein
- gene correction: isolation of cells, ex vivo correction of mutation and transplantation
For the following vectors, identifiy their immunogenic potential, tropism, limitation, major advantage, and if they’re integrating or episomal: retrovirus, lentivirus, AAV, HSV, adenovirus
- retrovirs: low immunogenicity, dividing cells only, potential oncogenicity, long term gene expression in dividing cells, integrating
- lentivirus: low immunogencity, dividing and non-dividing, potential oncogenicity, long term gene expression in most cells, integrating
- AAV: low immunogenicity, dividing and non-diving, small packaging capacity, non-inflammatory and non-pathogenic, episomal
- HSV: high immunogenicity, high in neurons, transient gene expression in neurons, large packaging capacity, episomal
- adenovirus: high immunogenicity, dividing and non-dividing (CAR receptor), viral capsid could induce immune response, efficient transduction of most cells, episomal
pros and cons of AAVs
pros
- low immunogenicity
- infect divinding and non-dividing cells –> use for broad range of diseases
- non pathogenic
- low frequency of genome integration
- diverse repertoire
- make in high batch quantities
- replication defective
cons
- some (10%) genome integration –> cancer?
- common virus - might already have immunity (BUT usually given to young people, not really immunogenic anyways)
- small genome –> fragile to change and can’t put big boy genes in it
challenges/unwanted consequences of virus-based gene therapy, why continue??
challenges
- integration –> cancer
- have to give to children and young people usually
- getting past the BBB
- need good animal model (they’re lacking)
- not a lot of incentive for pharm companies; rare disease + expense –> COST per demand (low profit)
- high titre –> toxicity (immune reaction to vector + non-immune)
- hard to reverse disease, easier to catch earlier
- now make foreign protein –> immunogenicity
- can’t reverse treatment, it’s very permament
- hard to work with secreted proteins
- need patience - takes a long time to get results from clinical trials
- academic challenge: clinical trial data takes years to publish
- management of expectations of patients/families and foundations
why continue
- risk-benefit is huge
- long term benefit – one dose
- severe diseases
- location/wide distribution of affected cells make conventional treatment difficult
what is a limitation of animal models?
they cannot always predict what happens in humans
why are the eye and liver most common primary targets for gene therapy?
eye – easy to access, closed compartment, small dose
liver – if it goes into the blood, it will go into the liver
what are challenges of delivering therapies to the CNS?
- mere size and distribution
- diversity of cell types
- BBB –> intrathecal injections into CSF
what are challenges of delivering therapies to the muscles?
over 600 muscles in the human body + different types (skeletal, cardiac, smooth)
Spinal muscular atropy (SMA): cause, describe the gene therapy
cause
- autosomal recessive disorder
- caused by reduced amounts of the SMN protein –> muscle atrophy
- normal: SMN1 gene –> all full length protein; SMN2 gene –> only 10% of full length protein; SMA is caused by missing SMN1 gene –> not enough SMN protein
gene therapy
- gene replacement therapy
- strongly extend lifespan – the earlier, the better
- single dose rescues survival of SMA type 1 patients
Why is SMA a good disease to treat with gene therapy?
- some function, already there – not foreign
- CNS: other drugs can’t reach it/no other treatment
- known single mutation – studied disease, single gene
- fits into AAV
- animal model
- can be diagnosed early
Childhood blindness: cause?
defects in the RPE56 gene
Duchenne Muscular Dystrophy: cause?
- deltaEx49-50 –> frameshift –> nonsense mutation in distrophin
- distrophin connects ECM
describe the nexus of symptom prevention vs reversal of disease
- will be disease mechanism dependent
- reduced cell survival vs reduced cellular function is a key aspect
- generally, the soooner the treatment occurs and/or the higher the strength/functionality of the patient, the better the outcome
- diagnosis and screening are very important
X-linked myotobular myoptahy (MTM): disease, gene involved, effect of gene therapy?
severe muscle disorder leading to death before 10 years of age
myotubularin gene - involved in muscle cell development and maintenance
one dose of gene therapy –> increased frowth of muscle fibers, some kisd were able to come off the ventilator permanently, 4 can now site, 3 can take steps by themselves
what are the many things could cause failure in a clinical trial?
- anything and everything is an adverse event
- can’t control what volunteers do when they go home
- hard to extrapolate dose mice –> humans (size, immunity, metabolism)
- criteria (what stage of disease) and/or endpoints (when do you stop) wrong and/or outcomes –> wrong design
- bad batch of virus
- toxicity
