**Exhibit 31.1**

 

CERTIFICATION

 

I,Anthony S. Marucci, certify that:

 
| 1.     | I  have reviewed this report on Form 10-Q of Celldex Therapeutics, Inc.;                                                                                                                                                                                                                                                                                 |
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| 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;                                                     |
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| 3.     | Based  on my knowledge, the financial statements, and other financial information  included in this report, fairly present in all material respects the  financial condition, results of operations and cash flows of the registrant  as of, and for, the periods presented in this report;                                                                        |
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| 4.     | The  registrant’s other certifying officer and I are responsible for establishing  and maintaining disclosure controls and procedures (as defined in Exchange  Act Rules 13a-15(e) and 15d-15(e)) and internal control over  financial reporting (as defined in Exchange Act Rules 13a-15(f) and  15d-15(f)) for the registrant and have: |
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|   | (a)                                                                                                                                                                                                                                                                                                                                                                | Designed  such disclosure controls and procedures, or caused such disclosure controls  and procedures to be designed under our supervision, to ensure that material  information relating to the registrant, including its consolidated  subsidiaries, is made known to us by others within those entities,  particularly during the period in which this report is being prepared; |
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|   | (b)                                                                                                                                                                                                                                                                                                                                                                | Designed  such internal control over financial reporting, or caused such internal control  over financial reporting to be designed under our supervision, to provide  reasonable assurance regarding the reliability of financial reporting and the  preparation of financial statements for external purposes in accordance with  generally accepted accounting principles; |
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|   | (c)                                                                                                                                                                                                                                                                                                                                                                | Evaluated  the effectiveness of the registrant’s disclosure controls and procedures and  presented in this report our conclusions about the effectiveness of the  disclosure controls and procedures, as of the end of the period covered by  this report based on such evaluation; and |
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|   | (d)                                                                                                                                                                                                                                                                                                                                                                | Disclosed  in this report any change in the registrant’s internal control over financial  reporting that occurred during the registrant’s most recent fiscal quarter  (the registrant’s fourth fiscal quarter in the case of an annual report) that  has materially affected, or is reasonably likely to materially affect, the  registrant’s internal control over financial reporting; and |
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| 5.     | The  registrant’s other certifying officer and I have disclosed, based on our most  recent evaluation of internal control over financial reporting, to the  registrant’s auditors and the audit committee of the registrant’s board of  directors (or persons performing the equivalent functions):                                                 |
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|   | (a)                                                                                                                                                                                                                                                                                                                                                                | All  significant deficiencies and material weaknesses in the design or operation  of internal control over financial reporting which are reasonably likely to  adversely affect the registrant’s ability to record, process, summarize and  report financial information; and |
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|   | (b)                                                                                                                                                                                                                                                                                                                                                                | Any fraud, whether or not material, that involves  management or other employees who have a significant role in the registrant’s  internal control over financial reporting. |

 
| Date:  August 7, 2009 |   | By     | /s/  ANTHONY S. MARUCCI                |
|----------------------------|--------|--------|----------------------------------------|
|                       |   | Name:  | Anthony  S. Marucci                    |
|                       |   | Title: | President  and Chief Executive Officer |

 

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