596. A Novel Replication Incompetent Human Subgroup D Adenoviral Vector Based on Type 49: Manufacture on PER.C6®, Cell Tropism and Immunogenicity

Recombinant adenoviral vectors based on type 5 (rAd5) show great promise as vaccine carrier. However, neutralizing activity against Ad5 is prevalent and high titered among human populations and significantly dampens Ad5-based vaccine modalities. The generation of alternative adenoviral vectors with low sero-prevalence thus receives much research interest. We have previously published that several members of human subgroup D adenoviruses display low sero-prevalence in Europe and here we demonstrate that one such member, i.e. Ad49, is immunologically distinct from Ad5. We next set out to construct a plasmid system that allows formation of replication incompetent adenovirus serotype 49 vaccine vectors (rAd49) and demonstrate that rAd49 can be successfully propagated to high titers on existing E1-complementing cell lines such as PER.C6|[reg]|. Using a rAd49 vector carrying the luciferase marker gene sero-prevalence studies were performed demonstrating that rAd49 has low sero-prevalence and neutralizing antibody titers worldwide. Also, we have initiated rAd49 vector receptor usage suggesting that rAd49 utilizes hCD46 as a cellular receptor. Next, we assessed the immunogenicity of the rAd49 vector and show that a rAd49.SIVGag vaccine induces strong anti-SIVGag CD8+T-lymphocytes in naive mice albeit approximately 1.5-fold less compared to a rAd5.SIVGag vaccine. However, in mice with high anti-Ad5 immunity the anti- SIVGag response was not statistically significant suppressed using the rAd49.SIVGag vaccine whereas the rAd5.SIVGag vaccine was severely blunted. Finally, rAd35.SIVGag prime-rAd49.SIVGag boost experiments in mice carrying high-level anti-Ad5 neutralizing activity demonstrated that the rAd49 based vaccine is not hampered by neither rAd5 nor rAd35 neutralizing activity. These data demonstrate the potential of a replication deficient human D-group adenoviral vector as stand-alone vaccine carrier or in prime-boost settings with other rare human adenoviral vectors.