Combining CRISPR/Cas mediated terminal resolution with a novel genetic workflow to achieve high-diversity adenoviral libraries

While recombinant Adenoviruses are widely used in both laboratory and medical gene transfer, library-based applications using this vector platform are not readily available. Recently, we developed a new method, the CRISPR/Cas9 mediated in vivo terminal resolution aiding high-efficiency rescue of recombinant Adenoviruses from recombinant DNA. Here we report on a genetic workflow that allows construction of BAC-based recombinant Adenoviruses libraries reconstituted using highly efficient terminal resolution. We utilized frequent, pre-existing genomic sequences to allow the insertion of a selection marker, complementing two selected target sites into novel endonuclease recognition sites. In the second step, this selection marker is replaced with a transgene or mutation of interest via Gibson assembly. Our approach does not cause unwanted genomic off-target mutations while providing substantial flexibility for the site and nature of the genetic modification. This new genetic workflow, which we termed half-site directed fragment replacement allows the introduction of >10ˆ6 unique modifications into rAd encoding BACs using laboratory scale methodology. To demonstrate the power of HFR, we rescued barcoded viral vector libraries yielding a diversity of ∼2.5x10ˆ4 unique recombinant Adenoviruses per cmˆ2 of transfected cell culture.