Viral vaccines and gene therapy Flashcards
(142 cards)
Gene therapy notes.
Uses of gene therapy
Production mechanism
Desirable qualities
Problems
Gene therapy - uses
Monogenic obvious.
Cancer and other chronic diseases to reverse symptoms.
Production mechanism - overview.
Separately generate structural proteins and vector genome in same cells. These will self-assemble to form viral vectors.
Gene therapy - desirable qualities.
Easy to produce. Safety. Targeted delivery. Transduction and transgene expression. Genome size.
Gene therapy - safety
Needs to be non-toxic and non-immunogenic.
Adeno vs adeno-associated viruses.
Problems - dysregulation of host function.
Uses of immunogenic viruses.
Gene therapy - safety. Adeno problems.
Adeno: most people have been challenged by at least one, so raise an immune response. Most immunogenic of vectors used. Prevents use of multi-dose regimens.
Jesse Gelsinger example.
Gene therapy - safety. Adeno getting around problems.
Adenovirus serotype 5 often used, with hexons expressed from a different serotype since Abs to those from Ad5 are common. Chimera is called rAd vector. BUT cross reactivity is common.
Elimination of all viral genes from genome helps.
Example: rAd-p53.
Gene therapy - safety. Adeno example.
rAd-p53
Chimera to avoid recognition
Administered directly to tumour for tissue specificity
Encodes p53: leads to massive overexpression in tumour cells with tumour cell death. May have effect on bystander tumour cells, may act synergistically with chemotherapies.
Gene therapy safety - adeno
Problems, solutions, example, Jesse Gelsinger example.
Targeted delivery
CF example - importance.
Limiting delivery
Targeting tissues
Targeted delivery - limiting delivery.
C- type, adeno and AAV.
Targeted delivery, targeting tissues.
Particle and genome expression.
Gene therapy - transduction and transgene expression.
Desired; minimal toxicity, easily detectable, quantifiable and consistent expression.
Persistent expression.
Integration.
Gene therapy - transduction and transgene expression. Persistent expression
Adeno and AAV.
Gene therapy - transduction and transgene expression. Integration.
Could be useful, but issues with safety/progeny. Consider example AAV serotype 2.
Gene therapy - genome size
Herpes
Increasing effective genome size in adeno-associated.
Hybrid vectors.
Wild-type AAV with efficient internalisation and nuclear targeting of adenovirus.
Production mechanism - details.
Delete coding region of virus, leaving sequences required in cis for packaging. Replace coding regions with cassette of choice. Express packaging proteins in same cell as synthesis of genome occurring in: self-packaging will cause genome with gene of choice to be packaged in viral proteins.
Purification is laborious, and difficult to scale up, but recent technological advances have dealt with this problem on the whole.
Gene therapy - desirable qualities.
Easy to produce. Safety. Targeted delivery. Transduction and transgene expression. Genome size.
Targeted delivery
CF example - importance.
Limiting delivery
Targeting tissues
Targeted delivery limiting usefulness - C type retroviruses.
Can only infect dividing cells – limits usefulness. Recent work lead to nuclear localisation signal engineered into SNV, which made it capable of transducing non-proliferating cells.
Targeted delivery limiting usefulness - AAV and adenoviruses.
Natural infections of AAV and adenoviruses are limited by transmission route, but this doesn’t occur with therapy.
Targeting specific tissues - particles.
Adeno-associated. Many available serotypes – varying tissue specificity, so greater understanding is meaning that therapies can be rationally designed using different capsids with more specific/targeted delivery.
Targeting specific tissues - transgene expression.
- Restricted to particular cell types or switched on and off by promoters, but dissemination of the virus particle itself can have harmful effects.
- Tumour specific transcriptional targeting: homologous recombination brought promoter in conjunction with reporter gene. This only occurs in tumour cells, as this is the only place that conditionally replicating adenovirus vector replicates.
- Transductional targeting by redirecting to specific cellular receptors.