Eli Lilly and Co. said it will buy Armo Biosciences Inc. for about $1.6 billion, in an all-cash transaction intended to bolster its immuno-oncology program through the addition of Armo's lead candidate, pegilodecakin, a pegylated interleukin-10. The $50-per-share offer, coming just months after Armo's upsized January IPO, represents a 68 percent premium to Wednesday's close.