Following the initial screening experiments to elucidate possible apoptosis effects, we focused our studies on cystatins C and D. These inhibitors evidently affect the overall rate of leukemia cell growth dose‐dependently under conditions of oxidative stress leading to apoptosis (Fig. 5A), but also when cells were not subject to oxidative stress induction (Figs 5B and 9). Here, CST3 is linked to leukemia.