Abstract B023: Regulatory T (Treg) cell contributes to tumor cell dissemination via extracellular matrix (ECM) remodeling, which is driven by TAMs in an IFNg-dependent manner
Authors: Garcia-Santillan Ailen D. , Lichtenberg Jessanne Y. , Shen He , Rodriguez Jasmine M , Barra Jonathan , Clark Nicholas M , Du Wei , Martinez Leandro M , Hadjis Ashley D , Calicchia Taylor , Dozmorov Mikhail G , Bravo-Cordero Jose J , Olex Amy L , Hwang Priscilla Y , Bos Paula D 
Published: November 2024

Abstract
Background: The extracellular matrix (ECM) is a highly organized non-cellular network consisting of structural proteins, growth factors, cytokines and other secreted molecules. The ECM is highly dynamic and is a critical player in the regulation of local invasion and metastasis. The ECM network is ever-changing and an important immunosuppressive component of the tumor microenvironment (TME). However, the reciprocal effects of the immune system on the tumor-associated ECM are elusive and largely unexplored. Regulatory T (Treg) cells function to enforce peripheral tolerance and are potent suppressors of tumor immunity. We have previously shown that Treg cells promote tumor growth in murine breast cancer models by favoring alternative activation of tumor-associated macrophages (TAMs) via suppression of IFN-g. Aims: In this work, we sought to assess whether Treg cell-mediated immune suppression is associated with changes in the ECM, and whether those ECM changes functionally impact metastatic dissemination. Further, we assessed the requirement of TAMs and IFN-g in the ECM remodeling. Design Methods: In this study, we used spontaneous and transplantable models of breast cancer susceptible to genetic ablation of Treg cells. We used a combination of histopathological analysis, tumor decellularization, bioengineering 3D-chip modeling, in vivo manipulations and bioinformatic analysis, to evaluate remodeling of the ECM, cancer cell invasive behavior and metastatic dissemination. Results Summary: Treg cell ablation resulted in significant ECM remodeling, with reduced amounts and organization of collagen fibers, and increased amounts of fibronectin and laminin. Tumor cells seeding on Treg cell ablated tumor- derived decellularized ECM matrices results in reduced epithelial-mesenchymal transition (EMT) transcription factors, and profound impairment of collective migration. In vivo, Treg cell ablation in a neo-adjuvant setting followed by primary tumor resection resulted in significant reduction of circulating tumor cells (CTC) and impairment of lung metastatic disease. Importantly, we demonstrated that Treg cell ablation-driven changes in the matrisome correlate with long-term improved survival in a cohort of breast cancer patient samples. Through genetic knock-out models and in-vivo neutralization, we observed that Treg cell-dependent changes in ECM-related phenotypes are dependent on IFN-g-signaling. Single-cell RNA-sequencing (scRNA-seq) of murine breast tumors revealed that the matrisome signature is highly upregulated among TAMs, compared to other TME cell types. Lastly, using conditional genetic knock-out models we show these IFN-g-dependent changes are mostly driven by TAMs. Conclusions: Altogether, we identified a novel metastasis-promoting effect of Treg cells in the breast cancer microenvironment through regulation of ECM dynamics beyond their described effects on primary tumor growth.
Citation Format: Ailen D. Garcia-Santillan, Jessanne Y. Lichtenberg, He Shen, Jasmine M Rodriguez, Jonathan Barra, Nicholas M Clark, Wei Du, Leandro M Martinez, Ashley D Hadjis, Taylor Calicchia, Mikhail G Dozmorov, Jose J Bravo-Cordero, Amy L Olex, Priscilla Y Hwang, Paula D Bos. Regulatory T (Treg) cell contributes to tumor cell dissemination via extracellular matrix (ECM) remodeling, which is driven by TAMs in an IFNg-dependent manner [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 B023.