Abstract 714: Bioengineering of the adeno-associated virus (AAV) vectors for dendritic cell (DC)-based immunotherapy

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Dendritic cell (DC) based immunotherapy has recently demonstrated great potential for clinical application. However, additional progress in methods of tumor specific antigen delivery to DC is necessary for the further development of the anti-tumor vaccine. In our studies of the adeno-associated virus (AAV) crystal structure combined with data from various mutagenesis experiments on the capsid genes, we have identified specific residues which play a critical role in intracellular trafficking of these vectors. Genetic modifications of these regions increase transduction efficiency of AAV vectors most likely by preventing phosphorylation of serine (S) and threonine (T) residues by cellular kinases and subsequent degradation of vectors by host proteosomes. These studies led to development of several vectors such as AAV6-S663V, AAV6-T492V and AAV6-T492+S663V which can increase transduction efficiency of the monocytes-derived DCs (moDCs) by up to 5-fold compared to AAV6-WT. This significant improvement in infectivity of capsid-optimized over AAV6-WT vectors was associated with advanced nuclear translocation rather than facilitated viral entry into cells, which was confirmed by qPCR analysis on viral genome distribution in cytoplasmic and nuclear fractions. Our data indicate that approximately 85% of viral genomes of mutant AAV vectors accumulated in the nucleus 24 hrs post-infection compared with approximately 50% of AAV6-WT vectors at the same time-point. Considering the relatively short period of time between the initiation of maturation and cytopathic changes in DCs, rapid expression of antigen is critical to provide appropriate signals for T-cell activation. Another important advantage of the employment of such capsid-modified AAV6 vectors for vaccination is that efficient nuclear translocation in DCs will provide less material for potential presentation, and might prevent induction of immuno-competition in immune responses against vector-derived and antigen-derived epitopes. We next evaluated the possibility of whether high transduction efficiency of the new vectors will be associated with better antigen presentation and generating antigen-specific cytotoxic T-cells (CTLs). Our data show that DCs loaded with AAV6-T492+S663V carrying human prostate specific antigen (hPSA) resulted specific T-cell clone proliferation and generation of superior CTLs with higher killing capability of human prostate adenocarcinoma cells, LNCaP, compare CTLs stimulated by AAV6-WT vectors. In summary, our studies lead to the development of effective novel AAV vectors by manipulating viral capsid structure for the potential use in DC-based immunotherapy. Citation Format: Pandya Jheel, Kellee Britt, George Aslanidi. Bioengineering of the adeno-associated virus (AAV) vectors for dendritic cell (DC)-based immunotherapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 714. doi:10.1158/1538-7445.AM2014-714