Tumor lymphangiogenesis, which involves both the activation and growth induction of surrounding lymphatic vessels, is well-known to correlate with tumor progression and metastasis in many solid tumors. While it is typically assumed that lymphangiogenesis supports an ‘escape route’ for cells to leave the primary tumor, the tumor-draining lymph node serves as the key site of immune surveillance. Our lab has been exploring how lymphatic involvement affects the tumor immune microenvironment and anti-tumor immunity while promoting metastasis at the same time. In doing so, we have discovered new fundamental roles for lymphatic endothelial cells (LECs) as direct modulators of immunity. This is important because LECs are constantly bathed with peripheral antigens, cytokines, danger signals and immune cells travelling from peripheral tissues to lymph nodes. In terms of promoting metastasis, we have learned that tumor-activated lymphatics alter the tumor microenvironment in multiple ways, including (i) increasing immune suppressive cell types and factors in the tumor microenvironment both directly and indirectly, (ii) inhibiting maturation of antigen-presenting cells and T cell activation, and (iii) driving changes in the stromal microenvironment that promote both cancer invasion and immune suppression.  However, lymphatic activation also enhances communication with cells in the draining lymph node by antigen and cell transport, and leads to increased immune cell infiltration within the tumor. As a consequence, lymphangiogenic tumors can be exceptionally responsive to immunotherapy, paradoxically. This ‘lymphangiogenic potentiation’ of immunotherapy depends on tumor cell infiltration of both cross-presenting dendritic cells and naïve T cells, driving local T cell education post-immunotherapy and antigen spreading.  On the translational side, we are engineering novel strategies to exploit lymphangiogenesis for cancer immunotherapy.  Beyond cancer, our findings suggest that LECs may be potential targets for immunomodulation in vaccination, autoimmunity, and allergy.