This result was confirmed using another MLV-defective mouse model (Supplementary information, Fig. S5a–c), in which Prox1-CreRT2+/– mice were bred with VEGFR3-flox+/+ mice (Prox1-CreRT2–/–;VEGFR3-flox+/+ mice as controls) as previously described.30 Consistent with a previous study,31 we observed that RT could increase the total CD8+ T cells in tumor in an MLV-dependent manner (Supplementary information, Fig. S4c, d). Here, FLT4 is linked to neoplasm.