The immune system is a complex network of cells that regulates one’s response against any kind of pathogen. Once an antigen is detected, an immune response is mounted through the collaboration of antigen presenting cells (APCs), such as dendritic cells (DCs) and T cells. The focus of this thesis was to investigate whether lymphatic endothelial cells (LECs) ,which line the afferent and efferent lymphatics of the LN, could function as major histocompatibility complex class II (MHCII) APCs in the tumor microenvironment. Using murine lymphangiogenic tumor cell lines, we show that tumor associated LECs (TA-LECs) contribute to the generation of an immunosuppressive tumor microenvironment and highlight a new role for them, as MHC-II restricted APCs, that favor tumor growth and are essential for the suppressive functions of intratumoral TREGS.