Indeed, in a model of multiple myeloma, joint therapy with anti-PD-1 and anti-PD-L1 prevented MDSC-mediated cancer promotion to a greater extent than either alone.60 In contrast to cancers such as melanoma, head and neck squamous cell carcinoma (HNSCC) demonstrates reduced granulocytic MDSC infiltration post-PD-1/PD-L1 blockade.61 It is unclear whether this model involves different mechanisms of MDSC recruitment or whether the direct blockade of PD-1 is inhibiting MDSC proliferation. This evidence concerns the gene PDCD1 and melanoma.