Abstract B015: Targeting CX3CL1 transforms a cold tumor microenvironment into a hot one by enhancing T cells and DCs locally and systemically
Authors: Chaudhary Piyush , Hughes Savannah , Tay Joshua , Letchworth Robert , Tanaka Miho , Reeves Melissa 
Published: November 2024

Abstract
Intratumoral heterogeneity (ITH) is associated with immunotherapy failure and a weaker anti- tumor immune response. Using a series of carcinogen-induced tumor (CIT) squamous cell skin carcinoma cell lines, our lab has sought to identify tumor-intrinsic factors—particularly chemokines and cytokines—which can have a “dominant negative” effect on the immune microenvironment when present within a heterogeneous tumor. We identified CX3CL1 as a one such critical mediator of a cold (T cell low) immune microenvironment and found that tumors containing as few as 10% CX3CL1high tumor cells exhibit a diminished T cell response compared to tumors which lack CX3CL1high tumor cells. We predicted that targeting CX3CL1 could therefore transform a cold tumor microenvironment (TME) into an inflammatory hot (T cell high) TME. Supporting this, we found that CRISPR-Cas9-mediated deletion of CX3CL1 in a tumor cell line that typically gives rise to cold tumors led to higher T cell infiltration and fewer immunosuppressive macrophages in the TME of CX3CL1-/- tumors. Building on this, we further explored T cell populations in the TME and found that CX3CL1-/- tumors had significantly increased activation and decreased exhaustion markers on T cells. Flow cytometry analysis showed higher expression of CD44 on effector CD4 T cells and an increase in the number of activated CD44+ PD1low CD4 T cells. By contrast, the frequency of CD4 T cells which were PD1High TIM3+ and PD1High TIM3+ TIGIT+ which represent a likely exhausted effector CD4 population was lower in CX3CL1-/- tumors than in counterpart control tumors. An interrogation of DC subsets in the TME further revealed a higher number of cDC1 and cDC2 populations in CX3CL1−/− tumors. To determine the effect of tumor-produced CX3CL1 on immune activity in lymphoid organs, we investigated T cell and DC markers in the spleen and tumor-draining lymph nodes during early tumor development. Spleens harvested 10 days after tumor injection showed higher infiltration of cDC1 CCR7+ and cDC2 CCR7+ mature DCs in CX3CL1-/- tumor-bearing mice. Thus, in the absence of tumor-produced CX3CL1, both cDC1 and cDC2 dendritic cell subsets attain more mature phenotypes in both the TME and the spleen. At the same time point, tumor-draining lymph nodes also exhibited a shift in immune cell composition characterized by an increased frequency of T cells, particularly CD4+ T cells, and a decreased frequency of B cells. Moreover, the percentage of PD1+ CD8 cells was also higher, indicating better priming and activation of CD8 T cells via DCs in tumor-draining lymph nodes. These findings indicate that tumor-produced CX3CL1 drives a cold immune microenvironment through both tumor-localized and systemic effects. These studies suggest therapeutically targeting CX3CL1 particularly in tumors where tumor cells produce high levels of CX3CL1 holds promise to transform a cold TME into a hot immune inflammatory TME and potentiate better anti-tumor immunity.
Citation Format: Piyush Chaudhary, Savannah Hughes, Joshua Tay, Robert Letchworth, Miho Tanaka, Melissa Reeves. Targeting CX3CL1 transforms a cold tumor microenvironment into a hot one by enhancing T cells and DCs locally and systemically [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr B015.