Question

7) Retroviruses are typically used for gene therapy approaches. The development of the retroviral packing cell lines was critical to the development of retroviruses as vectors for gene therapy. Explain how packing cell lines help to overcome the following problems. Note: Drawing pictures will be very helpful here (10) a) In order to fir therapeutic genes into retroviruses some of the viruses' essential genes must be replaced by the therapeutic genes. How then, is the viruses able to multiply to produce the viral particles necessary to infect targets? b) Wild-type retroviruses are often pathogenic-causing leukemia's, solid tumors, and AIDS for example. How do packing cell lines help prevent productive retroviral infections from occurring?

Answer 1

1. The retro virus contains 5' LTR, gag, pol, env genes and 3' LTR. These gag, pol, env genes are essential for the multiplication of the viruses. Initially the therapeutic genes are integrated in the place of gag, pol,env genes. Inorder to multiply and produce new viral particles gag,pol,env genes are expressed in a helper vector, so these genes acts from helper plasmid as trans acting elements.

2. The oncogenic genes which causes the diseases by insertional mutagenesis are removed in the retroviral vectors and are replaced by the genes which want to be inserted. The genomic region responsible for causing infections will be replaced by therapeutic genes ,thus help prevent infections.