Specifically, they analyzed the features of tumor-infiltrating immune cell subsets; they also observed PD-1, PD-L1, and PD-L2 expression in tumor cells and immune cells through immunohistochemistry (IHC) in pretreatment samples from patients with advanced treatment-refractory solid tumors treated in phase I multi-institution trial of nivolumab in the Kimmel Cancer Center at Johns Hopkins University. Here, PDCD1 is linked to neoplasm.