Abstract 2416: SA-4-1BBL costimulatory ligand as an immune modulator and effective vehicle to deliver antigens into dendritic cells for the generation of robust therapeutic antitumor immune responses

The success of therapeutic TAAs-based subunit vaccines may not only depend on their ability to activate new and/or boost existing immune responses, but also on their potential to overcome tumor-induced immunosuppressive mechanisms. This will require the use of adjuvants with pleiotropic effects on the cells of innate, adaptive, and regulatory immunity as the immunomodulatory component of subunit vaccines. Additionally, the adjuvant efficacy can further be enhanced if it can also serve as a vehicle to deliver TAAs to DCs for uptake, processing, and cross-presentation to T cells. We have recently hypothesized that costimulatory ligands of the TNFR family may serve as effective immunomodulatory component of subunit therapeutic vaccines against cancer. We therefore generated a chimeric 4-1BBL with streptavidin (SA-4-1BBL) that exists as tetramers/oligomers with potent activity on cells of innate, adaptive, and regulatory immunity. In this study, we tested if SA-4-1BBL can be used as a vehicle to deliver TAAs into dendritic cells constitutively expressing 4-1BB receptor for the generation of effective immune responses against tumors. We demonstrated that SA-4-1BBL can be effectively conjugated to biotinylated ovalbumin (Ova) as a model antigen. Immunization with Ova conjugated to SA-4-1BBL resulted in increased Ova uptake and cross-presentation by DCs, most notably lymphoid subpopulation, that resulted in potent Ova specific proliferation of CD4 + (OT-II) and CD8 + (OT-I) T cells. These effects were superior to the nonconjugate (Ova mixed with SA-4-1BBL) vaccine. The conjugate vaccine also generated significantly higher in vivo specific CTL responses to Ova and HPV E7 oncoprotein than nonconjugate vaccine. Importantly, a single vaccination with HPV E7 oncoprotein conjugated to SA-4-1BBL resulted in robust and superior efficacy than nonconjugate vaccine in the eradication of established E7 expressing TC-1 tumors. Similar results were found in the 3LL lung carcinoma model using survivin as a bona fide self TAA. Therapeutic efficacies of the vaccines were achieved in the absence of detectable toxicity and associated with increased CD4 + T and CD8 + T cell effector and memory responses and higher intratumoral CD8 + Teff/CD4 + CD25 + Foxp3 + Treg ratio. In conclusion, potent immunomodulatory activities of SA-4-1BBL combined with its ability to serve as a vehicle to deliver TAAs to DCs further rationalizes the extensive evaluation of this novel molecule as a platform for the development of therapeutic vaccines against cancer. Funded in parts by NIH 2R44 AI071618-02, R43 AI074176, R41 CA121665, KLCP, the W.M. Keck Foundation, and the Commonwealth of Kentucky Research Challenge Trust Fund. *Equal contribution. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2416.