Why do people need gene therapy every few months? Why does it only work for a short time?

[bobybob]

particularly SCID

[LazyGun]

1. The protocol is still in its infancy, and is developing an improving over time - But research, development and cinical trials takes time.
2. Essentially, gene therapy is inserting functional genes into an unspecified genomic location in order to replace a mutated gene - but this is, almost by definition, short lived, since you encounter problems trying to integrate the therapeutic DNA into a genome consisting of rapidly dividing cells. Gene therapy, at least as it is mostly practiced, is not the lifetime replacement of a defective or mutant gene.
3. Sometimes the carrier of the therapeutic DNA can provoke a severe immune response, curtailing the treatment.

By SCID,are you referring to Severe Combined Immunodeficiency? If memory serves, they did attempt such a treatment - but the replacement DNA was incorrectly integrated in the genome, in this case the tumour suppressor gene, and in at least some of the patients, a tumour developed. As a consequence, the research and gene therapy treatment were immediately shut down - but it is an area that probably should be looked at again.

http://scienceblogs.c...and_x-linked_scid.php

[theprof]

LazyGun is correct but if I could add that another problem is that the presence of different genetic changes in different tumours results in the inability to use the same target. Regularly spaced therapy is the only means to counteract this problem.

In addition, the transfection efficiency of most genes is so very low that regular therapy is the only answer. There are also issues over specificity and autoimmunity that are relevant but I'm afraid are too complex to discuss in detail on AB.

SCID is very problematical but there are encouraging research projects being undertaken right now that I'm confident will provide an answer during the next few years.