Celldex Therapeutics Inc. (NASDAQ:CLDX) has ridden a surge of investor interest in cancer immunotherapy to raise $300 million in a pair of follow-ons at successively higher valuations this year. The most recent deal was underwritten by a gaggle of banks, many of which had helped the biotech raise capital during its leaner years.

"Historically, it has been difficult for cancer immunotherapy companies to raise capital at high market rates, but we entered 2013 doing a lot of work