Inhibition of post-HSCT PBMC proliferation is improved by blockade of IDO activity with MDLT. The effect of the addition of 0.5 M MDLT on the proliferative responses of control PBMCs (□) and of post-HSCT PBMCs (▪) to PHA was assessed. Cells were stimulated with PHA and, in parallel, exposed to MDLT, either immediately after separation from whole blood (fresh) or after pre-exposure to M-CSF (20 ng/mL) for 4 days, and IFN-γ (100 U/mL) that was added for the last 18 hours of culture. Error bars indicate SEM.