Abstract 718: Nanoparticle-based tumor cell lysate vaccine for cancer immunotherapy

Introduction Combination of tumor-associated antigen (TAA) and toll-like receptor (TLR) agonists can facilitate a potent anticancer immune response. Synthetic peptides, which are derived from antigens that are highly elevated or only expressed in tumor tissue, have been investigated as a source of TAA. However, these peptides are not available for all tumor types and often poorly immunogenic. Whole tumor cell lysate is a promising alternate antigen source that seeks to overcome some of the limitations associated with peptide-based vaccines. In this study, we utilized whole tumor cell lysate as antigen source and a novel TLR 7/8 agonist encapsulating nanoparticles as adjuvant to formulate the cancer vaccine and examined its efficacy against subcutaneous (S.C.) tumor models. Methods A new imidazaquinoline-based TLR 7/8 agonist (termed ‘5229) was encapsulated in poly(lactide-co-glycolide) (PLGA) nanoparticles using emulsion solvent evaporation method to formulate the vaccine adjuvant. The adjuvant (522NP) was used in combination with whole tumor cell lysate (CL) prepared from murine bladder carcinoma (MB49) cells. Immunocompetent C57BL/6 mice were immunized subcutaneously with 5 doses of cell-lysate vaccine or various control treatments. Two days after the final vaccination dose, mice were sacrificed and organs were harvested. Splenocytes were analyzed using flow cytometry to measure antigen (Ag)-specific CD8 T cell response. We investigated whether prophylactic and therapeutic CL+522NP immunization can delay tumor growth and improve survival in MB49 S.C. tumor models. Results CD11ahighCD8low CD8 T cells were examined as they represent Ag-experienced CD8 T cells that can respond to Ag. Frequency of CD11ahigh CD8low CD8 T cells increased in mice vaccinated with CL+522NP. In the prophylactic model, CL+522NP significantly delayed tumor growth compared to that in other control groups. On d 30, average tumor volumes reached ~1000 mm3 in untreated mice compared to ~500 mm3 in CL alone and CL+Soluble522 treated groups. However, CL+522NP vaccinated mice showed remarkably very little tumor growth (~122 mm3) over the same time period. In the therapeutic model, only CL+522NP treatment was effective in delaying tumor growth. Unlike in the prophylactic study, where CL alone had a moderate effect, therapeutic effects were not observed from CL alone or CL+Soluble522 groups. Conclusion CL+522NPs vaccination triggered a robust anti-cancer immune response that resulted in the expansion of CD11ahigh CD8low CD8 T cells, which suggests that 522NPs enhance the immunogenicity of cell lysate and elicit Ag-specific CD8 T cell response. Furthermore, CD8 T cells generated by CL+522NPs vaccination appeared to be effective in killing tumors in both prophylactic and therapeutic tumor models. These results suggest that 522NPs are effective vaccine adjuvants capable of improving the outcome of cancer immunotherapy. Citation Format: Hyunjoon Kim, Peter Larson, Tamara A. Kucaba, Katherine A. Murphy, David M. Ferguson, Thomas S. Griffith, Jayanth Panyam. Nanoparticle-based tumor cell lysate vaccine for cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 718.