TIE-2-expressing monocytes are lymphangiogenic and associate specifically with lymphatics of human breast cancer

Abstract

In experimental mouse models of cancer, increasingly compelling evidence point toward a contribution of tumor associated macrophages (TAM) to tumor lymphangiogenesis. Corresponding experimental observations in human cancer remain scarce although lymphatic metastasis is widely recognized as a predominant route for tumor spread. We previously showed that, in malignant tumors of untreated breast cancer (BC) patients, TIE-2-expressing monocytes (TEM) are highly proangiogenic immunosuppressive cells and that TIE-2 and VEGFR signaling pathways drive TEM immunosuppressive function. We report here that, in human BC, TEM express the canonical lymphatic markers LYVE-1, Podoplanin, VEGFR-3 and PROX-1. Critically, both TEM acquisition of lymphatic markers and insertion into lymphatic vessels were observed in tumors but not in adjacent non-neoplastic tissues, suggesting that the tumor microenvironment shapes both TEM phenotype and spatial distribution. We assessed the lymphangiogenic activity of TEM isolated from dissociated primary breast tumors in vitro and in vivo using endothelial cells (EC) sprouting assay and corneal vascularization assay, respectively. We show that, in addition to their known hemangiogenic function, TEM isolated from breast tumor display a lymphangiogenic activity. Importantly, TIE-2 and VEGFR pathways display variable contributions to TEM angiogenic and lymphangiogenic activities across BC patients; however, combination of TIE-2 and VEGFR kinase inhibitors abrogated these activities and overcame inter-patient variability. These results highlight the direct contribution of tumor TEM to the breast tumor lymphatic network and suggest a combined use of TIE-2 and VEGFR kinase inhibitors as a therapeutic approach to block hem- and lymphangiogenesis in BC.

Extended Adjuvant Chemotherapy in Triple-Negative Breast Cancer

“…Lehmann et al. [5] have proposed one of the most frequently used subclassifications, which includes 4 subtypes: 2 basal-like (BL1 and BL2), a mesenchymal, and a luminal androgen receptor subtype.Approximately 70% of TNBCs contain 20% or more tumor-infiltrating lymphocytes (TILs) in the tumor stroma [6]. The generally higher level of TILs and the higher expression of immune checkpoint molecules in TNBC compared with ER-positive (ER+) BCs also makes TNBC an attractive target for immunotherapy.…”

TIE-2 expressing monocytes in human cancers

“…detected TEM in human tumors, including those of the kidney, colon, pancreas and lung as well as soft tissue carcinomas, while they were excluded from surrounding healthy tissues 15 . We made similar observation in human breast cancer (BC) and reported that TEM are also highly pro-angiogenic 16 and pro-lymphangiogenic cells 17 . Further, TEM display an immune suppressive activity evidenced by their ability to secrete IL-10 and VEGF in large amounts and to dampen in vitro tumor-specific T-cell proliferation mediated by tumor dendritic cells (DC) 18 .…”

“…and further work is required to establish whether mouse and human TMEM have parallel functions and share similar mechanisms of tumor cell intravasation. Along these lines, we show that a fraction of TEM were found inserted into tumor lymphatics, but not with lymphatics of adjacent non-neoplastic tissue, where TEM show drastically reduced expression of TIE-2 and LEC markers 17 . Interestingly, we observed that all BC patients with metastasis to the lymph node (LN) show TEM inserted into their tumor lymphatics, whereas this was only the case for 57% of the patients without LN metastasis.…”

“…To address these issues, pre-clinical models of TEM truly reflecting the functions and phenotypes of patient TEM are required. In human BC, we report that more than 95% of tumor TEM co-expressed TIE-2 and VEGFR-1 in a co-regulated manner 17 and synergistically control TEM proangiogenic, 16 immune suppressive, 18 and lymphangiogenic 17 activities. By contrast, we observed that in 4T1, FARN168, and MMTV-PyMT, currently held as the closest model to human BC model, a much lower fraction of TEM co-express TIE-2 and VEGFR-1 (28%, 45% and 5% of monocytes, respectively) and this co-expression was not co-regulated.…”

“…Interestingly, we observed that all BC patients with metastasis to the lymph node (LN) show TEM inserted into their tumor lymphatics, whereas this was only the case for 57% of the patients without LN metastasis. 17 Thus, given the lymphangiogenic activity of TEM and the correlation between tumor lymphatics with sentinel and non-sentinel LN metastasis in BC, 69,70 it is reasonable to suggest that TEM insertion into lymphatics may contribute to the spreading of tumor cells to the proximal LN. The underlying mechanisms of TEM pro-metastatic activity and insertion into tumor LV are currently under investigation in our group.…”