Merck entered into a definitive agreement to acquire Harpoon Therapeutics, Inc. for an approximate total equity value of $680 million.   Harpoon has a portfolio of novel T-cell engagers that employ the company’s Tri-specific T cell Activating Construct (TriTAC) platform, an engineered protein technology designed to direct a patient’s own immune cells to kill tumor cells, and ProTriTAC platform, applying a prodrug concept to its TriTAC platform to create a therapeutic T-cell engager that’s desi...