Abstract 2403: Targeting 4-1BB in tumors enhances anti-tumor immune responses
Authors: Weber Amy Mackay , Innamarato Patrick , Morse Jennifer , Kidd Scott , Asby Sarah , Sarnaik Amod , Pilon-Thomas Shari 
Published: August 2019

Abstract
4-1BB (CD137) is a co-stimulatory receptor expressed on activated T cells and other immune cells and is associated with enhanced T cell proliferation, survival, and increased cytokine production upon engagement with its ligand (4-1BBL). We have previously shown that addition of agonistic 4-1BB antibody to tumor fragments increased tumor infiltrating lymphocyte (TIL) expansion in human melanoma and pancreatic tumors. Furthermore, agonistic 4-1BB antibody led to increased expression of maturation markers in resident dendritic cells (DCs) present within tumor fragments. While the role of 4-1BB in T cell biology is well described, little is known about 4-1BB signaling in tumor-resident DCs. We hypothesized that 4-1BB agonism in tumor-resident DCs would promote anti-tumor T cell immune responses. To evaluate the role of 4-1BB signaling on dendritic cells, murine bone marrow derived-DCs were cultured with agonistic 4-1BB antibody and loaded with OVA protein. Treatment with agonistic 4-1BB in vitro led to increased OVA-FITC uptake by DCs (32.6% compared to 15.9% in DCs treated with control antibody). DCs treated with agonistic 4-1BB antibody demonstrated increased T cell stimulatory capacity upon co-culture with OVA-specific OT-I and OT-II T cells. We next compared systemic and intralesional (IL) treatment with agonistic 4-1BB antibody. For the systemic model, mice were injected subcutaneously (SC) with B16 melanoma or Panc02 pancreatic tumor cells and treated by intraperitoneal injection of control or anti-4-1BB antibodies. Mice treated systemically with agonistic 4-1BB antibody exhibited a minimal reduction in tumor growth. In contrast, IL injection of agonistic 4-1BB antibody led to dramatic decreases in tumor growth. Next, we wanted to determine whether IL treatment with agonistic 4-1BB antibody would improve DC stimulatory capacity. Mice bearing B16 or Panc02 tumors were treated IL with normal control or anti-4-1BB antibody. After 7 days, tumor-resident CD11b+ DCs exhibited enhanced in vivo antigen uptake. In addition, an increased number of CD8+ T cells was measured within tumors treated with agonistic 4-1BB antibody (28.1% compared to 20% in NrIgG-treated Panc02OVA tumors and 19.45% compared to 7.3% in NrIgG treated B16-OVA tumors; p=0.0059). Together, these studies demonstrate that agonistic 4-1BB can enhance the ability of DCs to stimulate T cells and IL administration of agonistic 4-1BB antibody can significantly reduce tumor growth. This suggests that IL treatment of agonistic 4-1BB may yield greater efficacy than systemic therapy in patients with melanoma or pancreatic cancer.
Citation Format: Amy Mackay Weber, Patrick Innamarato, Jennifer Morse, Scott Kidd, Sarah Asby, Amod Sarnaik, Shari Pilon-Thomas. Targeting 4-1BB in tumors enhances anti-tumor immune responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2403.