Abstract 756: Genetically enhanced DC vaccines for cancer: Bringing the ex vivo, in vivo
Authors: Kemnade Jan Ole , Collinson-Pautz Matthew , Narayanan Priyadharshini , Lapteva Natalia , Seethammagari Mamatha , Spencer David 
Published: June 2012

Abstract
Background and Objectives: Dendritic Cells (DCs) are potent antigen presenting cells, capable of activating naïve T-cells to recognize and kill tumor cells. Since DCs are also able to reverse the tumor-induced dormancy of killer and helper T-cells, DC vaccines have been developed to induce anti-tumor immune responses. To improve DC vaccine efficacy, we have focused on augmenting DC function using an inducible MyD88/CD40 signaling switch (iMC) capable of stimulating DC activation in a Th1-polarizing manner. iMC abrogates the need for more traditional, toxic DC activators such as LPS and allows for spatio-temporal control of DC activation, further increasing vaccine efficacy. In ex vivo pre-established tumor studies, DCs pulsed with tumor-specific antigen (TSA) and manipulated to express iMC significantly decreased tumor growth in mice relative to DCs pulsed with TSA alone.
While potentially efficacious, ex vivo modification and re-delivery of DCs requires specialized and expensive methods, which limit their utility as primary cancer-fighting agents. Therefore, we have focused on developing a strategy capable of TSA and iMC delivery to in vivo DCs using adenovectors. Treatment of tumor-bearing mice with adenovectors expressing only TSA was effective in significantly decreasing tumor growth. Combining this therapy with adenovectors expressing iMC resulted in only modest therapeutic enhancement.
We hypothesize that reliance on simultaneous transgene expression by two separate vectors in the same cell may prevent more potent immunogenicity. Our lab has shown that such double expression occurs in only about 20-50% of relevant cells. Therefore, we have developed a bicistronic adenovector (BAV), encoding both TSA and iMC.
Methods: To test dual transgene expression by BAV, DCs were transduced and both β-galactosidase activity (the TSA) and IL-12 secretion (by iMC) were assessed using X-gal staining and IL-12p70 ELISA, respectively. To evaluate anti-tumor response, mice bearing pre-established B16-LacZ tumors were treated via footpad injection of BAV followed by two days of dimerizer drug.
Results: DCs transduced with BAV were shown to express the TSA and secrete high levels of IL-12p70 when compared to empty vector or LPS-treated DCs. Treatment of B16-LacZ tumor-bearing mice with BAV resulted in significantly enhanced tumor reduction versus Ad-LacZ alone.
Conclusions: In order to further enhance BAV's ability to induce anti-tumor immune responses, we are adapting a method of targeting adenovectors to CD40+ DCs using bi-functional molecules (CFm40L), described by Pereboev et al. (Molecular Therapy, 2004). Our preliminary results have shown that adenoviral modification with CFm40L significantly increases DC transduction efficiency. This technology should further increase the therapeutic efficacy of BAV by specifically targeting it to DCs while at the same time reducing total viral dosage.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 756. doi:10.1158/1538-7445.AM2011-756