CD4 and neoplasm: Seven mouse tumor models (4T1, CT26, B16F10, P815, MC38, Renca, Sa1N) were established for 89Zr-DFO-CD4 and 89Zr-DFO-CD8a PET/CT imaging to assess the effect of Sym021 (a humanized PD1 antibody cross-reactive with mouse PD1) treatment (Fig. 4A).