Merck has struck a $1.9 billion deal to buy Pandion. The takeover will give Merck control of a pipeline of immune modulators led by a rival to IL-2 drugs in development at Amgen, Eli Lilly and Roche. Pandion went public last year, pulling in $135 million to fund the development of a pipeline led by an engineered IL-2 mutein fused to a protein backbone. The clinical-phase drug, PT101, is designed to selectively activate and expand regulatory T cells (Tregs) and, in doing so, treat autoimmune diseases including ulcerative colitis.