Exhibit 31.1

CERTIFICATION

I, Anthony S. Marucci, certify that:

1.I have reviewed this Amendment No. 1 to Annual Report on Form 10-K/A of Celldex Therapeutics, Inc.; and

2.Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report.

/s/ ANTHONY S. MARUCCI

Anthony S. Marucci

President and Chief Executive Officer

Dated: March 31, 2010