Several examples of such inhibitor-based molecular probes have been described in immuno-oncology studies to predict response to checkpoint inhibitors in mouse preclinical models of cancer.98–100 For instance, Craik and colleagues designed a smart PET probe based on a restricted interaction peptide in which a radiolabeled antimicrobial peptide was connected to a caged sequence by means of a GzmB cleavable linker.101 Upon cleavage of the sequence mediated by GzmB, the radiolabeled antimicrobial peptide was liberated and able to accumulate in adjacent cell membranes. This evidence concerns the gene GZMB and cancer.