The use of interleukin-2 (IL-2)-directed therapies has been associated with systemic toxicities, regulatory T cell (Treg) activation and limited efficacy so far. Researchers from Regeneron Pharmaceuticals Inc. have described REGN-10597 (PD1-IL2Ra-IL2), a programmed cell death protein 1 (PD-1)-targeted, receptor-masked IL-2 immunocytokine.