Abstract A48: Interactions between lymphatic vessels and cancer-associated fibroblasts in tumor immunity
Authors: Mier Ingrid M. van , Munson Jennifer M. , Broggi Maria A.S. , Palma Michele De , Swartz Melody A.S. 
Published: October 2016

Abstract
Aggressive tumors often hijack the lymphatic vasculature in order to invade and metastasize to their draining lymph nodes (LNs) and ultimately to distant organs. The clinical relevance of lymphatic metastasis has been demonstrated for many cancers, most notably breast cancer, which has been observed to spread preferentially via the lymphogenous route, with the initial sites of metastasis frequently being the tumor-draining LN. Indeed, expression of vascular endothelial growth factor (VEGF)-C, the principal lymphangiogenic growth factor, by the tumor or recruited ancillary cells has been shown to correlate both with LN and distant metastasis, and shorter overall survival, and LN status represents an important prognostic factor for patients diagnosed with breast cancer. Although traditionally considered as passive conduits for tumor cell escape, it is becoming increasingly clear that lymphatic vessels play more active roles in facilitating tumor progression and metastasis. In addition to directly promoting tolerance upon VEGF-C-induced remodeling of the tumor-associated lymphatic vasculature, increased lymphatic density also leads to increased lymph flow from the tumor to the draining LN, causing mechanical stress-induced changes in the stroma surrounding the tumor that may synergize to further suppress anti-tumor immunity. We previously reported that heightened interstitial flow can drive myofibroblast differentiation, commonly identified by the expression of α-smooth muscle actin (α-SMA), and that such flow drives them to align and contract the extracellular matrix in a TGF-β1-dependent manner, leading to stromal stiffening, another feature that is strongly correlated with tumor progression, invasion, and poor prognosis in breast cancer. Here we show that lymphatic endothelial cells (LECs) may contribute directly to stromal stiffening through production of TGF-β1 upon stimulation with VEGF-C. To explore this hypothesis, we developed an orthotopic model of cells isolated from the spontaneous MMTV-PyMT model of breast cancer and stably transfected these cells to over-express VEGF-C, and found that increased VEGF-C secretion correlated with lymphangiogenesis as well as an increase in overall TGF-β1 within these tumors. Furthermore, VEGF-C induces TGF-β1 secretion by LECs in vitro, and in the spontaneous MMTV-PyMT model, inhibition of VEGF-C signaling upon administration of a VEGFR-3 blocking antibody yielded a reduction in overall TGF-β1 in the tumor, as well as specifically in the number of LECs producing TGF-β1 in vivo. Taken together, these results suggest a direct involvement of tumor-associated lymphatic vessels in stromal stiffening during tumor progression, linking tumor mechanobiology with tumor immunology.
Citation Format: Ingrid M. van Mier, Jennifer M. Munson, Maria A.S. Broggi, Michele De Palma, Melody A.S. Swartz. Interactions between lymphatic vessels and cancer-associated fibroblasts in tumor immunity. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr A48.