Some reasons come to my mind. Continual production. Cheap. Proof of principle for gene therapy. Methodology across in vitro -> animals is identical.
Having the 'drug' produced by its host means it costs pennies to administer the first virus. It means the drug is continually produced over the time period. And frankly, it's easier than having to purify the protein from another source, figure out injection conditions/strengths, etc. Further, if it works, it's a great demonstration of gene therapy in addition to HIV treatment.
And frankly, it's easier than having to purify the protein from another source, figure out injection conditions/strengths, etc
I see where you're going, but you don't avoid a lot of that work with gene therapy. You still need to produce and the test the virus, and then scale up product along with all the purification needed. The FDA will also ask you to test various doses to provide you're giving the right amount need for the desired efficacy.
In addition, gene therapy requires additional tests to prove that the inserted genes don't end up in some weird place that causes even more issues. Not a huge cost driver, but a concern that small molecules don't have (admitting they still need carcinogenicity testing).
Having the 'drug' produced by its host means it costs pennies to administer the first virus. It means the drug is continually produced over the time period. And frankly, it's easier than having to purify the protein from another source, figure out injection conditions/strengths, etc. Further, if it works, it's a great demonstration of gene therapy in addition to HIV treatment.