The blood–brain barrier is a neurovascular unit that forms a tight barrier and highly regulates molecules entering the CNS.24 Other groups have hypothesized that permeation of T cells into brain is a critical hurdle to overcome in propagating antitumor immunity to the brain, with preclinical findings showing that cytotoxic CD8+ T cells are primed systemically prior to infiltrating melanoma brain metastases and do not proliferate at brain metastatic sites.22 Our data are compatible with this hypothesis. The gene discussed is CD8A; the disease is melanoma.