(323d) Controlling M1/M2 Macrophage Ratio through Differential Abilities to Migrate Upstream to Tumor Sites.

All blood cells must exit the vasculature to distal sites to perform their end effector functions by actively migrating along the endothelial surface. We have previously demonstrated a pervasive mode of ameboid motility wherein cells actively migrate against the direction of shear flow, to transmigrate significantly faster, through an LFA-1-ICAM-1 interactions. To this end, both macrophages and their blood borne precursors, monocytes, migrate out of the vasculature into tissues to perform their anti or pro-inflammatory functions. Previous work has shown innate immune cells, such as macrophages, which express the LFA-1 and Mac-1 integrins are able to migrate upstream when Mac-1 is blocked. To see if this observation held in macrophages, we utilized blocking antibodies to neutralize and genetic engineering to delete Mac-1 on the PMA differentiated U937 and M-CSF differentiated human peripheral blood monocytes (PMBCs). While the WT macrophages migrated primarily downstream, both the Mac-1 blocked and deleted Macrophages migrated efficiently against the direction of shear flow. Interestingly, our Mac-1 deficient macrophages lost the ability to crawl upstream upon polarization into M1 (anti-tumor) but retained the ability when polarized into M2 (pro-tumor). This is of critical importance as: the higher the ratio of M2 to M1 tumor associated macrophages (TAMs) recruited to the tumor microenvironment is, the worse the prognosis is due to recruitment of CTCs. In sum, we are differentially able to direct M1 and M2 macrophages from the vasculature to tumor sites with the hope of increasing the M1 to M2 ratio and creating a more anti-tumor microenvironment.