CD80 and acute myeloid leukemia: One should finally emphasize that AML cell expression of co-stimulators or checkpoint molecules can be altered by therapeutic interventions, e.g., modulation by myeloid/monocytic differentiation induced by all-trans retinoic acid (ATRA) or vitamin D, increased PD-1L expression after IFN-γ exposure (e.g., released during local T-cell activation) [45], increased PD-1L expression after TLR2/4 ligation [46], decreased PD-1L after the inhibition of mitogen-activated protein kinase 7 (also known as MEK) [46] and increased CD80 during decitabine treatment [47].