Abstract A119: CCL3 in the tumor microenvironment augments antitumor immune priming in the lymph node

Any therapeutic approach toward the eradication of metastatic tumor cells must involve targeting both the tumor9s primary site of origin and those seeding in secondary tissues where metastasis has occurred. Lymph nodes represent an area of interest for targeting metastatic tumors because they play an essential role in tumor survival in non-native tissues. Interrogation of early cellular events in the draining lymph nodes (DLNs) during the initial priming of the adaptive T cell response can reveal new insights into how LN cells respond to a metastasizing tumor. The inflammatory chemokine CCL3 is important in orchestrating cellular contacts in vaccinated lymph nodes (LNs) and enhancing memory T cell generation. CCL3 has also been implicated in the modification and recruitment of natural killer (NK) cells and dendritic cells (DCs) to sites of epithelial insult and are important in establishing whether tumors will be tolerated or rejected. We hypothesize that by introducing a continuous supply of CCL3 into the microenvironment of a metastatic tumor, we can redirect a lymph node destined for tumor-tolerance toward the production of greater antitumor cellular responses. To interrogate our hypothesis, we subcutaneously inoculated naive murine recipients with a Balb/c colon metastatic tumor (CT26) that is either the wild-type (WTTUs) or WTTUs transfected to secrete CCL3 (L3TUs). Immunocompetent mice injected with L3TUs resulted in a suppression of tumor growth compared to the WTTU group in a CD8 + T cell dependent manner. 1, 3, and 5-days after injection with WTTUs or L3TUs, there was an enhanced accumulation of endogenous DCs, NKs, and T cells in the DLNs and non-draining LNs (NDLNs). In vivo analysis of DCs in the DLN of L3TUs showed increased numbers of CD11c + cells that upregulated the T cell costimulatory molecule, CD86 + , while in vitro , SIINFEKL-pulsed BMDCs cultured with CCL3, showed an enhance capacity to induce proliferation of OT-I (CD8 + ) T cells. Examination of the day-5 DLN for direct signs of adaptive antitumor responses revealed an enhanced production of the antitumor cytokine, IFNγ, in the L3TU group, while the WTTU group showed a greater accumulation of CD4 + T-regulatory cells (Treg) over convention CD4 + T cells. Together these data suggest that CCL3 may enhance the overall immune response in the DLN in three ways. First, CCL3 attracts key cell-types such as NK cells to the DLN in larger quantities that can directly interact with DCs or T cells to enhance the development of IFNγ producing immune cells. Second, CCL3 directly influences DC maturation and indirectly enhances T cell proliferation. Third, CCL3 directly enhances the overall systemic accumulation of lymphocyte and myeloid cells in the DLN and NDLNs. Citation Format: Frederick Allen, Joseph M. Nthale, Saada K. Eid, Peter Rauhe, David Askew, Jay Myers, Alexander Tong, Alex Y. Huang. CCL3 in the tumor microenvironment augments antitumor immune priming in the lymph node [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A119.