PDCD1 and T-cell non-Hodgkin lymphoma: Binding assays demonstrated that high 89Zr-PD-1 IgG binding to EL4 T-cell lymphoma cells was abolished to 0.6 ± 0.2% of that of unblocked control cells in the presence of 500 nM of cold anti-PD-1 IgG (P < 0.001; Figure 1(c)).