Peptides can be selected off of huge bacterial peptide libraries and using in mammalian viruses for in vivo gene therapy vector targeting
This work began in the dim mists of history (1992) when Dr. Barry was a post-doctoral fellow with Stephen Johston. Part of his project was trying to retarget adenovirus (Ad) with Bob Gerard to get it to stop infecting the wrong cells and start infecting the right cells. The biggest problem was that there was no muscle targeting ligands known that you could add to Ad for this purpose. You had to be lucky to have a ligand like that and we were not lucky. Absent luck, we employed peptide-presenting phage libraries to find these missing ligands and reported this in 1996 in Nature Medicine.
Once Dr. Barry had his own lab, they tried inserting many of these into the proteins of Ad with little success. The insertions either blew apart the virus protein functions or the ligand quit working in this different structural “context”.
To get around this context problem, Rana Ghosh, a Rice University graduate student, built the Ad fiber protein context into phage libraries. He grafted the HI beta sheets from Ad into the phage and selected muscle-binding peptides from his library. He then showed that if you grafted one, 12.51, back into Ad, it increased muscle transduction.
While this was great, many of us in the targeting field have great success in targeting cells in a dish (shooting fish in a barrel), but our best vectors usually fail in vivo because the liver eats up our beautiful vectors and makes us sad. We spent the last 10 years figuring out (in part) how to detarget the liver.
Given some success with detargeting, we dusted off our old 12.51 and 12.52 peptides in this paper. Rather than insert them in the fiber, we inserted them in the Ad hexon for two reasons. The first reason is that most peptides selected from libraries will have low affinity. They may therefore not work when displayed in low numbers on the 36 fiber proteins on Ad. To avoid this problem, we instead displayed the peptides on the 720 copies of hexon on Ad to allow them to bind by avidity interactions. The second reason we used hexon was to disrupt liver infection by Ad based on work by Vigne et al. in 1999.
In this paper, we hoped for retargeting plus detargeting and have showed some success. Much of what we inject is still be gobbled up by immune cells, so more work is needed.
Introducing the authors
Counterclockwise from the upper left: Michael Barry, William Matchett, Stephanie Anguiano Zarate, Tien Nguyen, and Mary Barry
About the research
Retargeted and detargeted adenovirus for gene delivery to the muscle
Virology, Volume 514, 15 January 2018, Pages 118-123