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Virology Review 5

Exploiting Viruses as Gene Therapy & Vaccine Vectors

Gene Therapy Introduction of DNA sequences into the cell of a patient with the aim of achieving a clinical benefit (fix something that is wrong)
Gene Therapy in CA Does not aim to restore normal function, the objective is to kill the CA cells
Uses of Eukaryotic Virus Vectors Gene Therapy, Recombinant vaccines, Anticancer agents
Most common diseases addressed by gene therapy clinical trials Cancer, vascular, & Monogenic diseases
Most common gene types transferred in gene therapy clinical trials Cytokine, Antigen, Tumor suppressor
Most common vectors used in gene therapy clinical trials Adenovirus, Retrovirus, Naked/Plasmid DNA
2 Types of Gene Therapy 1. Somatic cell gene therapy -- 2.Germ line gene therapy
2 Methods of Delivery IN VIVO therapy: patient is injected with the modified gene therapy vector -- & -- EX VIVO therapy: cells are removed, genes introduced, cells transplanted back into patient
Chemical/Physical Methods of DNA Delivery Systems Electroporation, Calcium Phophatases, Liposomes, Naked DNA gene gun
Liposomes Gold labeled DNA complexed with lipid, taken up via endocytic process
liposomes advantage works great in vivo because high production & effects dividing and non-dividng cells
liposomes disadvantage plasmid liposome complex vector cant specifically target a cell, less efficient, requires large amounts to acheive gene transfer
Why use Viruses for Gene Therapy? Experts at delivering genetic info to cells, we can Construct viruses for gene delivery, & different viruses target different tissues
2 ways to prevent virus vectors from causing disease 1.Engineer a non-pathogenic virus that expresses therapeutic gene -- 2.Engineer virus that requires a helper virus to replicate
Technical Concerns Regenerate a replication competent recombinant; Loss of therapeutic gene expression; Inadvertently transferring a contaminating gene or genes along with the therapeutic ones
Technical Concerns: Loss of therapeutic gene expression Many viruses limit gene expression to avoid the immune system. This can be avoided by using an inducible promotor.
Gene therapy is difficult in differentiated/non-dividing cells Many viruses only infect dividing cells. Avoid this by using retrovirus vectors that encode HIV integrase, which allows them to effectively infect nondividing cells
Most popular Viral Vectors Adenoviruses, Adeno-associated virus, Retroviruses, HSV, & Vaccinia
Adenovirus Vectors Infect dividing & nondividing cells. E1 is replaced with gene of interest. No integration. Severe risk of immune response
AAV Vectors non-pathogenic, infects dividing & nondiving cells, always integrates into chromosome 19, long term expression. BUT very small
Retroviral Vectors long term expression, can be pakaged with G protein of VSV so can infect many cell types, less immunogenic than adenovirus, integrates genome
HSV Vectors potential for nuerologic delivery, accepts large inserts, easy to manipulate, episomal latent infection can lead to long-term expression
HSV & B-gal B-gal replaces an essential immediate-early gene (replication deficient virus); HSV delivers B-gal reporter gene to neurons; can visually check for infection (blue)
Vaccinia Virus Vectors Virus replicates in cytoplasm, so low efficincy of passage of gene into nucleus
Virotherpay a therapy that seeks to harness the natural properties of viruses to aid in the fight against cancer
Oncolytic Strategies Virus surface altered so binds to CA cells only; virus is "armed" with extra genes to enhance effect; virus altered so can replicate in CA cells only
Potential Oncolytic Viruses Reovirus, Adenovirus, VSV, HSV, Vaccinia
Adenovirall Vector CA Therapy Find surface protein specific to CA
Viruses, IFN, & CA Therapy Many CA cells lack functional IFN rsponse, so more susceptible to some viruses. Would stay local & not infect other good tissues that have IFN response
Created by: lbr9349