PDCD1 and cancer: In three cancer patients who were each given an intravenous injection of the CD8-specific radiolabelled minibody, 89Zr-crefmirlimab, 14–28 days after initiation of anti-PD1 therapy, post-treatment CD8-PET/CT scans detected increased tumour uptake of 89Zr-crefmirlimab by 24–48 h post-injection, which suggested tumour infiltration of CD8+ lymphocytes, and was later followed by tumour stabilisation or shrinkage [49].