Masked IL-2 cytokines and methods of use thereof

The present invention provides, among other things, a masked cytokine comprising an interleukin 2 (IL-2) polypeptide, a VHH masking moiety, an anti-PD1 targeting moiety, and an engineered Fc domain comprising a tumor-associated protease cleavage site. In such masked cytokine, the IL-2 polypeptide is engineered to be activatable by a protease at a target site, such as in a tumor microenvironment. The VHH masking moiety blocks, occludes, inhibits (e.g., decreases) or otherwise prevents (e g masks) the activity or binding of the cytokine to its cognate receptor or protein. Upon proteolytic cleavage of the cleavage site in the Fc domain, the IL-2 polypeptide becomes activated, which renders it capable of binding to its cognate receptor or protein with increased affinity.