Influence of the CD200R signaling pathway on angiogenesis in the neoplastic microenvironment

The early stages of tumorigenesis as well as tumor progression and metastasis are strongly associated with the inflammatory response. After tumor formation, cancer cells contribute to the development of chronic inflammation by stimulating infiltration of pro-inflammatory cells of the immune system. The tumor-infiltrating immune cells stimulate angiogenesis, increase the permeability of blood vessels, as well as enhance tumor cell proliferation and colonization of distant organs. The formation of new blood vessels is crucial for tumor development, and the process is heavily regulated by inflammation developing in the tumor microenvironment. The interaction between the CD200 ligand and its CD200R receptor regulates the immune response and the inflammatory response in the course of infection, autoimmune diseases and cancer. The exact mechanism by which the CD200R-dependent signaling pathway works is not fully understood. We recently showed that the CD200R signaling pathway regulates arteriogenesis (the process of enlarging existing arteries), restoring normal blood flow, and increasing blood vessel lumen. Moreover, in preliminary studies, we were able to show that CD200R regulates angiogenesis in a mouse tumor model. CD200-deficient mice were characterized by a more intense blood supply to matrix implants containing melanoma cells, as well as an increased size of newly formed blood vessels. Importantly, vascular parameters correlated with an increased fraction of pro-inflammatory, undifferentiated macrophages and a sub-population of pro-angiogenic T lymphocytes. We hypothesize that the CD200R signaling pathway inhibits neoplastic angiogenesis. We will investigate the effect of CD200R modulation on the development of blood vessels in matrigel implants with B78 murine melanoma cells. This model has many advantages: it allows for a very reproducible examination of angiogenesis in relatively small tumors. Moreover, it enables the modification of the tumor microenvironment (e.g. the use of inhibitors, growth factors, cell transfer). We will use mice with a disabled CD200R pathway (Cd200 - / -) and wild-type mice. We will also study the effect of increasing CD200R stimulation (agonist antibody) and blockade of CD200R (soluble CD200R-Fc receptor). The use of flow cytometry, histological analysis, as well as depletion and adoptive transfer of selected immune cells iv vivo, will enable us to identify populations responsible for the regulation of tumor angiogenesis, dependent on CD200R. In addition, we will examine the profile of secreted inflammatory factors regulated by the CD200R. Immune cells expressing CD200R and possessing pro-angiogenic properties will be isolated and tested for the secretion of pro-inflammatory factors. The expression analysis of genes regulated by CD200R will also be performed. The results of these studies will be verified in the model of capillary formation by embryonic endothelial cells (in vitro) and in matrix implants with neoplastic cells (in vivo). Currently, the knowledge about the influence of immune cells on a developing neoplasm is used in the immunotherapy of neoplastic diseases. Modulation of the activity of individual populations of immune cells leads to a marked improvement in the cure rate. Yet a large proportion of these complex interactions remain unexplained. Understanding the mechanisms by which the CD200R regulates inflammation and angiogenesis in the tumor microenvironment may be of great importance in understanding the course of cancer formation and progression. It may also contribute to increasing the effectiveness of immunotherapy in neoplastic diseases.