In tumor-formation models, PD-1−/− mice completely suppressed the tumorigenesis of PD-L1+ myeloma cells (85); PD-1 deficiency also inhibited the hematogenous dissemination of poorly immunogenic tumors (which were PD-L1−in vitro) in PD-1−/− mice (10, 85). This evidence concerns the gene PDCD1 and plasma cell myeloma.