Angiogenesis is increasingly recognized as an important prognosticator associated with the progression of lymphoma and as an attractive target for novel modalities. We report a previously unrecognized mechanism by which lymphoma endothelium facilitates the growth and dissemination of lymphoma by interacting with circulated T cells and suppresses the activation of CD4⁺ T cells. Global gene expression profiles of microdissected endothelium from lymphoma and reactive lymph nodes revealed that T cell immunoglobulin and mucin domain–containing molecule 3 (Tim-3) was preferentially expressed in lymphoma-derived endothelial cells (ECs). Clinically, the level of Tim-3 in B cell lymphoma endothelium was closely correlated to both dissemination and poor prognosis. In vitro, Tim-3⁺ ECs modulated T cell response to lymphoma surrogate antigens by suppressing activation of CD4⁺ T lymphocytes through the activation of the interleukin-6–STAT3 pathway, inhibiting Th1 polarization, and providing protective immunity. In a lymphoma mouse model, Tim-3–expressing ECs promoted the onset, growth, and dissemination of lymphoma by inhibiting activation of CD4⁺ T cells and Th1 polarization. Our findings strongly argue that the lymphoma endothelium is not only a vessel system but also a functional barrier facilitating the establishment of lymphoma immune tolerance. These findings highlight a novel molecular mechanism that is a potential target for enhancing the efficacy of tumor immunotherapy and controlling metastatic diseases.