Abstract 2353: Combination immunotherapy: T-cell costimulation (OX40L, TL1A, 4-1BBL and ICOSL) secreted locally by Gp96-Ig vaccines, elicits robust antigen-specific, memory T cell responses and tumor elimination
Authors: Fromm George J. , de Silva Suresh , Giffin Louise , Rose Jason , Goyal Aditi , Schreiber Taylor H. 
Published: July 2016

Abstract
Combination cancer immunotherapy incorporating T cell costimulation, vaccination, and checkpoint inhibition is anticipated to broaden clinical response compared to any single agent. Because T cell costimulation occurs at the site of immunization, we asked whether the delivery of a costimulator by a gp96-Ig secreting allogeneic vaccine would provide comparable costimulation to systemically administered agonist antibodies. As proof of concept, we engineered gp96-Ig vaccines that locally secrete Fc-OX40L and demonstrate that the priming of antigen-specific CD8+ T cells (peak of 13.3% of total CD8+) is significantly higher when compared to combinations with OX40 antibodies (8.4%) or vaccine alone (5.6%). Vaccine-expressed Fc-OX40L was associated with increased CD127+KLRG-1- memory precursor cells and antigen-specific CD4+ proliferation, with reduced off-target inflammation. Importantly, vaccine-expressed Fc-OX40L stimulated IFNγ+, TNFα+, granzyme-b+ and IL-2+ by antigen-specific CD8+ T cells, which enhanced rejection of established CT26 and B16.F10 tumors. We have subsequently expanded our repertoire of combination vaccines to secrete gp96-Ig along with either Fc-tagged TL1A, 4-1BBL or ICOSL. Each costimulator secreting vaccine cell line has a unique functionality, without the negative consequences of off-target inflammation associated with systemic administration of its agonist antibody counterpart. For example, costimulation with a TNFRSF25 (receptor for TL1A) agonist antibody synergized with gp96-Ig vaccination and generated a robust antigen-specific CD8+ T cell response. However, TNFRSF25 treatment also lead to a significant accumulation of FOXP3+ regulatory T cells (Treg). A gp96-Ig vaccine co-secreting Fc-TL1A resulted in similar antigen-specific CD8+ T cell production with no activation of the Treg compartment. Additionally, combining two separate gp96-Ig vaccines (one secreting Fc-OX40L and the other Fc-TL1A) leads to an additive increase in memory precursor production (CD127+KLRG1-), which may play a vital role in maintaining effective anti-tumor immunity. Together, we demonstrate that the magnitude and specificity of vaccination can be enhanced by locally secreted costimulatory molecules when delivered within a single product. This may simplify clinical translation and importantly, provide significant patient benefit by improving safety and lowering costs.
Citation Format: George J. Fromm, Suresh de Silva, Louise Giffin, Jason Rose, Aditi Goyal, Taylor H. Schreiber. Combination immunotherapy: T-cell costimulation (OX40L, TL1A, 4-1BBL and ICOSL) secreted locally by Gp96-Ig vaccines, elicits robust antigen-specific, memory T cell responses and tumor elimination. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2353.