Conditionally replicative adenovirus vectors (CRAds) are novel vectors with utility as virotherapy agents for alternative cancer therapies. These vectors already have established a broad safety record in humans. However, two confounding problems limit efficacy of these drug candidates, the paucity of the native Ad receptor on tumor tissues, and host humoral response due to pre-existing titers of neutralizing antibodies against the vector itself in humans. These problems have been highlighted in the clinical context. We have a well-characterized conditionally replicative adenovirus vector, Ad???-RGD, which is infectivity enhanced, thus overcoming the lack of coxsackievirus and adenovirus receptor (CAR), and this agent is already rapidly progressing towards clinical translation. However, the perceived host humoral response potentially will limit gains seen from the infectivity enhancement and therefore a strategy to blunt immunity against the vector is required. On the basis of this caveat we have a novel strategy, termed shielding, in which we have technology to genetically modify the virion capsid to provide uniformly shielded Ad vectors. We have identified the pIX capsid protein as an ideal locale for genetic incorporation of shielding ligands, in particular self-proteins such as albumin, to conceal the Ad vector from pre-existing neutralizing antibodies. In this SBIR proposal the basic feasibility of employing a shielding protein, albumin, in the Ad capsid in a defined manner utilizing a specific capsid protein of Ad?24-RGD, and the retention of the CRAd properties of the shielded Ad?24-RGD (Ad?24S- RGD) are established in appropriate monolayer cultures of human cancer cell lines. [In addition the immunogenic properties of the newly created shielded CRAd will be assessed in the C57BL/6 mouse model.] The data accrued from these studies will aid the development of a genetically incorporated shield around the capsid in which CRAd function in vivo is maintained, yet with reduced humoral immune reactions against the vector itself. We envision the creation of Ad?24S-RGD as a major progress in the development of clinically and commercially feasible shielded CRAds that can be dosed multiple times for maximum effectiveness against cancers in humans. ? ? ?
