One important goal in gene therapy is to develop adenovirus (Ad) vectors that are genetically de-targeted as well as re-targeted. Genetic re-targeting of Ad using complex cell-binding ligands has previously not been possible. We have previously demonstrated that ligands for genetic re-targeting of adenoviruses must be able to fold correctly in the cytoplasm of virus producing cells, a milieu that is not conducive to the formation of disulphide bonds.
Here, we describe functional Ad5 viruses with fibers and pIX capsid proteins genetically modified to contain two types of complex ligands. One is affibody® molecules, corresponding to small (6 kDa) binding proteins developed by combinatorial protein engineering using a single three-helix bundle staphylococcal protein A domain. The other type is hyperstable antibody scFv domains.
The affibody molecule used here (ZH2N) is directed against Her2/neu. Recombinant viruses were constructed with ZH2N in three different positions: (i) at the C-terminus of shaft repeat 7 of de-knobbed fibers; (ii) at the C-terminus of pIX; and (iii) in the HI-loop of the fiber knob. Each of the viruses exhibited a characteristic phenotype regarding fiber content, growth and ability to infect Her2/neu expressing cells.
In order to test the potentials of scFv liganded Ad vectors, a hyperstable antibody scFv against b-galactosidase was genetically incorporated into knobless fibers, in tandem with a mutated protein A domain reactive with IgG1 Fc that targeted the virus to Fc-expressing 293 cells. These fibers could be rescued into viable virions that retained the original antigen binding specificity of the scFv, demonstrating the basic potential of hyperstable scFvs for genetic re-targeting of Ad. Quite unexpectedly, the fiber content of Ad with knobless, scFv containing fibers was close to normal in contrast to other Ad with knobless fibers that generally has a much reduced fiber content. The hyperstable scFv was further fused to the C-terminus of the capsid protein pIX. The recombinant molecules could be rescued into viable viruses with wt fibers. The scFv retained its binding-specificity on the recombinant virions.
The results demonstrate that, contrary to current beliefs, it is possible to construct Ad that genetically incorporates functional scFvs and other complex ligands into the virus fiber and pIX. The feasibility is demonstrated by the creation of different viruses that are re-targeted to Her2/neu. These viruses are currently in pre-clinical development.
2004. Vol. 9, S250-S250 p.