Immunomodulatory roles of lymphatic vessels in cancer progression.

Lymphatic vessels in the tumor microenvironment are known to foster tumor metastasis in many cancers, and they can undergo activation, hyperplasia, and lymphangiogenesis in the tumor microenvironment and in the tumor-draining lymph node. The mechanism underlying this correlation was originally considered as lymphatic vessels providing a physical route for tumor cell dissemination, but recent studies have highlighted new roles of the lymphatic endothelium in regulating host immunity. These include indirectly suppressing T-cell function by secreting immunosuppressive factors and inhibiting dendritic cell (DC) maturation, as well as directly driving T-cell tolerance by antigen presentation in the presence of inhibitory ligands. Furthermore, lymphatic endothelium scavenges and regulates transendothelial transport actively, controlling the sustained delivery of lymph-borne antigens from chronically inflamed tissues to draining lymph nodes where immature DCs, in the absence of danger signals, along with lymph node stromal cells present these antigens to T cells for maintenance of peripheral tolerance to self-antigens, a mechanism that may be hijacked by some tumors. This Masters of Immunology primer aims to present an overview of research in this area and highlight emerging evidence that suggests lymphatic vessels, and lymphangiogenesis, play important immunomodulatory roles in the tumor microenvironment. ©2014 American Association for Cancer Research.