A2A agonist and PDE inhibitor single-agent and combination activity in freshly isolated bone marrow plasma cells from patients with MM. Purified (CD138⁺) multiple myeloma cells from patients were treated with indicated concentrations of A2A agonist CGS-21680, PDE inhibitor trequinsin, or both agents. After 48 hours, cells were analyzed using the Cell Titer Glo assay and results plotted as a decrease in viability versus untreated control cells. The results for patients 1, 3, and 4 represent the mean and SD from 6 replicate measurements while with patient 2, N = 4.