Treatment with anti-PD-1 antibodies resulted in increased cytotoxicity and IFN-γ production of peripheral NK cells from multiple myeloma patients carrying high proportions of PD-1+ NK cells, suggesting that PD-1 could be a target for an immunotherapeutic strategy in EBV-positive PTLD patients [52]. This evidence concerns the gene PDCD1 and post-transplant lymphoproliferative disease.