Just months after hitting an all-time low, shares of Immune Design Corp. (NASDAQ:IMDZ) rocketed 310 percent higher Thursday to $5.82 as Merck & Co. Inc. moved to buy the immunotherapy developer for $5.85 cash per share, or about $300 million. The deal focuses on a portfolio of approaches to cancer immunization, adjuvant systems and technologies designed to enhance the ability of a vaccine to protect against infection, said Roger Perlmutter, president of Merck Research Laboratories.