To investigate the specific impact of plasma arginine concentrations, we first identified in vitro that T cell expansion in response to allogeneic dendritic cells was profoundly inhibited by the addition of recombinant human arginase to mimic AML blast activity (Fig. 2a) with a corresponding reduction in activation‐induced IFN‐γ release (Fig. 2b). Here, IFNG is linked to acute myeloid leukemia.