aAPC (IMAGE) Johns Hopkins Medicine Caption The effectiveness of killer T cells (pink) against tumor cells (brown) is damped by the interaction between PD-L1 (blue) and PD-1 (purple), but that can be somewhat overcome by artificial antigen presenting cells (orange), which encourage killer T cells to multiply. Credit Alyssa Kosmides and Randall Meyer, Johns Hopkins Medicine Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.