NRP1 and neoplasm: Semaphorin 3A (Sema3A), a physiological ligand of Nrp1 (23, –, 25), inhibits in vitro dendritic cell (DC)-T cell interactions (26) and tumor-T cell interactions (27), and by blocking Sema3A, hence suppressing the downstream signaling involving Nrp1, T cell activation and proliferation were restored.