GZMB and neoplasm: Recombinant GrB and chimeric GrB fusion proteins that harbor peptide ligands or antibody domains for tumor-specific cell recognition have been successfully produced in bacterial, yeast and mammalian expression systems [12], [13], [14], [15], [16], [17], and have been shown to retain potent cytotoxicity upon targeted delivery into tumor cells [12], [13], [15], [18], [19], [20].