Normally biotechs crash and burn on poor trial results and/or weak catalysts and pipeline. CLDX has a strong and potentially very lucrative pipeline -- with really nothing that negative to cause the decline in the price of the stock. Its never easy to pick a bottom, but I would have to think this one has some big upside in coming months, and the time to buy may be right here.
If you compare intraday and daily charts of many biotech stocks for the past four weeks, you'll see that most of them have very similar intraday and daily graphs. Computers have been trading the sector down. The drop has had NOTHING whatsoever to do with Celldex's promise, potential, value, science, catalysts, or news. It's been purely a computer-driven herd-mentality movement in the biotech sector.