T cells standing at the gates of brain metastasis.

Insufficient influx of T cells into the tumor microenvironment, including brain metastasis, dramatically limits efficacy of conventional immunotherapy. In this issue of Immunity, Messmer et al. interrogate spatiotemporal dependencies of melanoma brain metastasis T cell infiltration by intravital microscopy. They find that T cells enter these brain tumors through peritumoral venous vessels and can be stimulated with immunotherapy.