CD80 and plasma cell myeloma: While some PD-1+CD8+ T cells secreted IFN-γ in response to myeloma antigens (Fig. 1b), this number was significantly enhanced either by inclusion of anti-PD-L1 blocking antibody during the assay cell co-culture, or by antigen stimulation with 5T33 myeloma modified to express the co-stimulatory molecule CD80.