PDCD1 and neoplasm: Rhodamine-labeled a-CTLA-4 and a-PD-1 or their combination could hardly be detected outside of the blood vessels positive for lectins (tomato and RCA120) in the intracranial tumors at 4 and 6 h after intravenous (I.V.)injection, indicating their inability to cross the BBB and reach the tumor parenchyma (Fig. 2a top; 2b top row).