Role of Th2 cytokines in progenitor-mediated formation of tumor lymphatics - PROJECT SUMMARY/ABSTRACT
Role of Th2 cytokines in progenitor-mediated formation of tumor lymphatics
Lymph node metastasis, a common event in breast cancer, is a strong indicator of poor outcome due to
spread of nodal metastatic cells to distant organs which leads to mortality of patients. Metastatic burden in lymph
nodes directly correlates with the density of tumor lymphatic vessels. Outgrowth of these vessels is promoted by
bone marrow (BM) derived progenitors that co-express specific markers of lymphatic endothelial cells and M2-
type macrophages. This subset dubbed Myeloid-derived Lymphatic Endothelial Cells Progenitors (M-LECP) is
present in mice and patients with metastatic breast tumors but not in cancer-free individuals. We previously
showed in clinical breast cancers that density of lymphatic progenitors significantly correlates with tumor
lymphatic formation and metastases in lymph nodes. These data underscore the clinical significance of M-LECP
and the need to define their properties and the mechanisms that induce tumor lymphatics formation.
We previously showed that M-LECP are M2-myeloid cells with lymphatic-specific markers whereas newly
formed lymphatic vessels express macrophage-specific markers. This misalignment between the markers and
their respective lymphatic/myeloid lineages is well-documented but unexplained. However, it can be explained
considering the traits of other BM progenitors known to adopt the phenotype of lineages targeted for repair, and
to employ fusion as the means to initiate the repair by inserting a trigger for cell proliferation. Fusion of BM
progenitors with targeted cells results in transfer of genomic material encoding for M2 myeloid markers which
explains their appearance in new structures. We reasoned that M-LECP, myeloid progenitors with partial
lymphatic identity, might similarly use BM-enabled fusogenic properties to expand lymphatic vessels. Our
preliminary data show that myeloid precursors treated with Th2 cytokines IL-4, IL-13 and IL-10 in vitro
differentiate into cells with combined M2-myeloid, lymphatic endothelial, and fusogenic phenotypes. This led to
the hypothesis that activation of Th2 pathways in M2-biased myeloid precursors co-regulates lymphatic
lineage-specific and fusogenic properties that collectively promote the ability of mature progenitors to
induce new lymphatic vessels. This hypothesis is supported by our data that demonstrate co-development of
M2, lymphatic, and fusogenic properties in differentiated M-LECP as well as multiple evidence for fusion of these
progenitors with lymphatic endothelial cells in vivo and in vitro. We will test this hypothesis through the following
Specific Aims: (1) Determine in vivo the significance of Th2 pathways in M-LECP driven tumor
lymphangiogenesis; and (2) Determine whether fusogenic properties induced by Th2 factors and its regulator
TLR4 enable M-LECP to trigger tumor lymphatic formation. Significance: Th2 factors could play a paramount
role in enabling the lymphangiogenic function of M-LECP through fusion, a concept that provides a novel
framework for delineating generation of tumor lymphatic vessels. Exploration of this concept can lead to new
therapeutic targets paving the way for suppression of tumor lymphatics and inhibition of lymph node metastasis.
