An example is the use of systemic high‐dose IL‐2 to boost Tregs in autoimmune disease: while IL‐2 can expand Tregs, effector T cells and NK cells can also be activated, leading to paradoxical inflammation or capillary leak syndrome at high doses.[164] NP delivery might mitigate some of these issues by improving localization and dose control, but extensive in vivo testing is needed to find a safe therapeutic window. Here, IL2 is linked to capillary leak syndrome.