Abstract 3644: Combination of OX40L fusion protein with an anti-tumor vaccine reduces lung metastasis and prolongs survival in a murine model of metastatic triple negative breast cancer
Authors: Malamas Anthony S. , Hammond Scott A. , Schlom Jeffrey , Hodge James W. 
Published: July 2017

Abstract
OX40 is a costimulatory receptor on activated T-cells that potentiates the proliferation, survival, and memory formation of the CD4+ and CD8+ immune populations upon its interaction with OX40L on antigen presenting cells. The engagement of OX40 on regulatory T-cells (Tregs) with its ligand has also been shown to inhibit their suppressive capabilities. The use of exogenous OX40L agonists for cancer immunotherapy is particularly attractive in combination with cancer vaccines in order to boost the immune activity of antigen specific T-cells and overcome self-tolerance and immunosuppressive mechanisms of the tumor. We investigated the efficacy of this strategy in the 4T1 murine mammary tumor model of metastatic triple-negative breast cancer by combining an OX40L fusion protein (OX40L-FP) with a poxvirus-based cancer vaccine (MVA-Twist-TRICOM) that induces T-cell responses specific to the tumor antigen Twist, a transcription factor highly expressed in lung metastases. OX40L-FP was administered 3 and 6 days after the prime and boost vaccinations to maximize its interaction with OX40 on activated T-cells. As single agents, OX40L-FP and MVA-Twist-TRICOM had minimal effect on the formation of lung metastases in 4T1 tumor-bearing mice. However, when combined, the two immunotherapies significantly decreased the number of metastatic colonies per lung, and prolonged survival after surgical resection of the primary tumor. Antibody depletion studies demonstrated that the observed anti-tumor effects were mediated by both CD4+ and CD8+ T-cells. Immune subset analysis revealed that the combination therapy increased the total number of CD4+Foxp3- and CD4+ effector memory T-cells in both the lung and periphery compared to the monotherapy controls. More importantly, the two agents synergistically induced greater CD4+ Twist-specific T-cell responses, as determined by ex vivo proliferation assays using T-cells isolated from the lung and spleen that were stimulated with Twist protein. Although the combination had no added effect on the number of total CD8+ and CD8+ effector memory T-cells in relation to the vaccine monotherapy, tetramer staining revealed a significant increase in CD8+ T-cells that were specific for Twist. We also observed a greater number of CD8+ T-cell memory precursors, as well as a greater number of IFNγ-producing CD8+ T-cells in both the lung and periphery. Tregs isolated from the lung and splenic tissue were found to be significantly less suppressive following the combination therapy, compared to those isolated from mice that received the OX40L-FP and MVA-Twist-TRICOM single agent treatments. This study provides the rationale for pairing OX40 agonists with cancer vaccines to stimulate CD4+ and CD8+ T-cell responses, while inhibiting Treg function, as a way to induce specific immunity and clearance of metastatic tumors.
Citation Format: Anthony S. Malamas, Scott A. Hammond, Jeffrey Schlom, James W. Hodge. Combination of OX40L fusion protein with an anti-tumor vaccine reduces lung metastasis and prolongs survival in a murine model of metastatic triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3644. doi:10.1158/1538-7445.AM2017-3644