Fiber modifications enable fowl adenovirus 4 vectors to transduce human cells.

Background: Pre-existing immunities hamper the application of human adenovirus (HAdV) vectors in gene therapy or vaccine development. Fowl adenovirus (FAdV)-based vector might represent an alternative.

Methods: An intermediate plasmid containing FAdV-4 fiber genes, pMD-FAV4Fs, was separated from FAdV-4 adenoviral plasmid pKFAV4GFP. An overlap extension polymerase chain reaction (PCR) was employed for fiber modification in pMD-FAV4Fs, and the modified fibers were restored to generate new adenoviral plasmids through restriction-assembly. FAdV-4 vectors were rescued and amplified in chicken LMH cells. Fluorescence microscopy and flow cytometry were used to evaluate the gene transfer efficiency. The amount of viruses binding to cells was determined by a real-time PCR. A plaque-forming assay and one-step growth curve were used to evaluate virus growth.

Results: Four sites in the CD-, DE-, HI- and IJ-loop of fiber1 knob could tolerate the insertion of exogenous peptide. The insertion of RGD4C peptide in the fiber1 knob significantly promoted FAdV-4 transduction to human adherent cells such as 293, A549 and HEp-2, and the insertion to the IJ-loop demonstrated the best performance. The replacement of the fiber2 knob of FAdV-4 with that of HAdV-35 improved the gene transfer to human suspension cells such as Jurkat, K562 and U937. Fiber-modified FAdV-4 vectors could transduce approximately 80% human cells at an acceptable multiplicity of infection. Enhanced gene transfer mainly resulted from increased virus binding. Fiber modifications did not significantly influence the growth of recombinant FAdV-4 in packaging cells.

Conclusions: As a proof of principle, it was feasible to enhance gene transduction of FAdV-4 vectors to human cells by modifying the fibers.