The efficacy of vaccine adjuvants such as Toll-like receptor agonists (TLRa) can be improved through formulation and delivery approaches. Here, we attached small molecule TLR-7/8a to polymer scaffolds (polymer-TLR-7/8a) and evaluated how varying physicochemical properties of the TLR-7/8a and polymer carrier influenced the location, magnitude and duration of innate immune activation in vivo. Particle formation by polymer-TLR-7/8a was critical for restricting adjuvant distribution and prolonging activity in draining lymph nodes. The improved pharmacokinetic profile by particulate polymer-TLR-7/8a was also associated with reduced morbidity and enhanced vaccine immunogenicity for inducing antibodies and T cell immunity. We extended these findings to the development of a modular platform in which protein antigens are site-specifically linked to temperature-responsive polymer-TLR-7/8a adjuvants that self-assemble into immunogenic particles at physiologic temperatures in vivo. Our findings provide a chemical and structural basis for optimizing adjuvant design to elicit broad-based antibody and T cell responses with protein antigens.

BackgroundViral-mediated oncolysis is a novel cancer therapeutic approach with the potential to be more effective and less toxic than current therapies due to the agents selective growth and amplification in tumor cells. To date, these agents have been highly safe in patients but have generally fallen short of their expected therapeutic value as monotherapies. Consequently, new approaches to generating highly potent oncolytic viruses are needed. To address this need, we developed a new method that we term “Directed Evolution” for creating highly potent oncolytic viruses.Methodology/Principal FindingsTaking the “Directed Evolution” approach, viral diversity was increased by pooling an array of serotypes, then passaging the pools under conditions that invite recombination between serotypes. These highly diverse viral pools were then placed under stringent directed selection to generate and identify highly potent agents. ColoAd1, a complex Ad3/Ad11p chimeric virus, was the initial oncolytic virus derived by this novel methodology. ColoAd1, the first described non-Ad5-based oncolytic Ad, is 2–3 logs more potent and selective than the parent serotypes or the most clinically advanced oncolytic Ad, ONYX-015, in vitro. ColoAd1's efficacy was further tested in vivo in a colon cancer liver metastasis xenograft model following intravenous injection and its ex vivo selectivity was demonstrated on surgically-derived human colorectal tumor tissues. Lastly, we demonstrated the ability to arm ColoAd1 with an exogenous gene establishing the potential to impact the treatment of cancer on multiple levels from a single agent.Conclusions/SignificanceUsing the “Directed Evolution” methodology, we have generated ColoAd1, a novel chimeric oncolytic virus. In vitro, this virus demonstrated a >2 log increase in both potency and selectivity when compared to ONYX-015 on colon cancer cells. These results were further supported by in vivo and ex vivo studies. Furthermore, these results have validated this methodology as a new general approach for deriving clinically-relevant, highly potent anti-cancer virotherapies.

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Type 5 adenovirus (Ad5) is a human pathogen that has been widely developed for therapeutic uses, with only limited success to date. We report here the novel finding that human erythrocytes present Coxsackie virus-adenovirus receptor (CAR) providing an Ad5 sequestration mechanism that protects against systemic infection. Interestingly, erythrocytes from neither mice nor rhesus macaques present CAR. Excess Ad5 fiber protein or anti-CAR antibody inhibits the binding of Ad5 to human erythrocytes and cryo-electron microscopy shows attachment via the fiber protein of Ad5, leading to close juxtaposition with the erythrocyte membrane. Human, but not murine, erythrocytes also present complement receptor (CR1), which binds Ad5 in the presence of antibodies and complement. Transplantation of human erythrocytes into nonobese diabetic/severe combined immunodeficiency mice extends blood circulation of intravenous Ad5 but decreases its extravasation into human xenograft tumors. Ad5 also shows extended circulation in transgenic mice presenting CAR on their erythrocytes, although it clears rapidly in transgenic mice presenting erythrocyte CR1. Hepatic infection is inhibited in both transgenic models. Erythrocytes may therefore restrict Ad5 infection (natural and therapeutic) in humans, independent of antibody status, presenting a formidable challenge to Ad5 therapeutics. “Stealthing” of Ad5 using hydrophilic polymers may enable circumvention of these natural virus traps.

In the recently halted HIV type 1 (HIV-1) vaccine STEP trial, individuals that were seropositive for adenovirus serotype 5 (Ad5) showed increased rates of HIV-1 infection on vaccination with an Ad5 vaccine. We propose that this was due to activation and expansion of Ad5-specific mucosal-homing memory CD4 T cells.