Skip to 0 minutes and 14 seconds Properties of a viral vector. Since virus so frequently used as a vector, we need to know the properties of this or the viral vector. First, safety. They got to be safe. And they are usually modified to minimize the risk of handling the viruses. Low toxicity, goes without saying. Stability, and this is a significant problem.
Skip to 0 minutes and 49 seconds The viruses behave well in vitro, outside the system but once they get into the system, they can quickly rearrange and then become bad boys again. So they’re not as stable as we want them to be. Cell type specificity. Most viral vectors are designed to infect as many cell types as possible but I have to say that sometimes cell specificity is actually preferred. Identification marker. We need a marker gene to identify the cells that are successfully transferred the gene. And a common marker is the antibiotic resistant gene. Let’s look at an example of gene replacement therapy. This patient has an immune deficiency so-called “SCID” Severe combined immune deficiency.
Skip to 2 minutes and 7 seconds And that’s because his chromosome and the DNA in the chromosome has a defect. Now we have a therapeutic DNA and we use the retrovirus to unload the therapeutic DNA into the target cell. And now the cell is repaired. We grow the repaired cells in vitro and when we have a sufficient amount of it we infuse them back to the patient. And they grow and multiply again in the patient’s system so that the immune system function is restored. Now the guy is alive and kicking. Gene exchange is another kind of gene therapy. Essentially, it’s a recombinant gene technology, just like a recombinant DNA technology in which the nucleotide sequences are exchanged.
Skip to 3 minutes and 18 seconds For example, we have a sister chromatid with a defect section and we can make a complementary sister chromatid and those two segments would exchange.
In molecular biology, a vector is a virus or a plasmid that carries a piece of foreign (treatment) DNA to a host cell, to accomplish insertion, deletion, replacement, exchange or silencing of the host gene. Desirable vectors must be characterized with low toxicity, high stability and great specificity.
How vectors work? First, remove the genes in the virus that cause disease (e.g., SCID). Then, insert and replace the defective gene with therapeutic DNA encoded with desired effect. Keep the replacement genes in the host’s genome intact (e.g., not subject to mutation).