S1PR1 and neoplasm: Sequestration of lymphocytes in secondary lymphoid organs with FTY720 (a sphingosine-1-phosphate receptor modulator) and or pharmacologic depletion of CD8 + T cells both blocked the tumor response to treatment, suggesting the critical role of lymphatic trafficking in mediating the antitumor effects of tdRT→αPD-1 (Fig. 4I, Supplementary Fig. 6C).