Exhibit 4.1



ZQ|CERT#|COY|CLS|RGSTRY|ACCT#|TRANSTYPE|RUN#|TRANS#   . COMMON STOCK PAR VALUE $0.001 COMMON STOCK THIS CERTIFICATE IS TRANSFERABLE   IN CANTON, MA, JERSEY CITY, NJ AND COLLEGE STATION, TX Shares * * 000000 * *   * * * * * * * * * * * * * * * * * * * 000000 * * * * * * * * * * * * * * * *   * * * * * 000000 * * * * * * * * * * * * * * * * * * * * * 000000 * * * * * *   * * * * * * * * * * * * * * * 000000 * * * * * * * * * * * * * * Certificate   Number ZQ00000000 INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE ** Mr.   Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander   David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample   **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr.   Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander   David THIS CERTIFIES THAT Sample **** Mr. Alexander David Sample **** Mr.   Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander   David Sample **** Mr. Alexander Alexander David SamMple ***R* Mr.   A.lexaSnderADavidMSampPle ***L* MrE. Alexan&der DavMid SamRple **S** Mr..   AleSxandeAr DaMvid SamPple *L*** MEr. Alex&ander David Sample **** David   Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample ****   Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Mr.   Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander   David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample   Sample **** Mr. AlexandeMr DaviRd Sam.ple S**** MAr. AleMxandePr DavLid   SEample *&*** Mr. AMlexanRder DaSvid S.ampSle ***A* Mr.MAlexanPder   DLavidESample **** Mr. Alexander **** Mr. Alexander David Sample **** Mr.   Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander   David Sample **** Mr. Alexander David SEE REVERSE FOR CERTAIN DEFINITIONS   David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample   **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr.   Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander   David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample   **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr.   Alexander David Sample **** Mr. Alexander David Sample **** Mr. Sample ****   Mr. Sample is the owner of   **000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares***   *000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****   000000**Shar*es****0*000Z00**SEhareRs****00O0000**ShHares**U**0000N00**SDhares*R***000E000**DShares**T**000H000**SOhares*U***000S000**AShareNs****00D0000**Shares****0   00000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****00   0000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000   000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****0000   00**Shares****0Z0000E0**ShRares***O*000000*H*ShareUs****0N00000D**SharRes****0E0000D0**ShareAs****0N00000D**SharesZ****00E0000R**SharOes****0*000*00**Shares****00000   0**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000   **Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000*   *Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**   Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**S   FULLY PAID AND NON-ASSESSABLE SHARES OF THE COMMON STOCK, $0.001 PAR VALUE   PER SHARE, OF CELLDEX THERAPEUTICS, INC. transferable on the books of the   Corporation by the holder hereof in person or by duly authorized attorney,   upon surrender of this Certificate properly endorsed. This Certificate is not   valid unless countersigned by the Transfer Agent and registered by the   Registrar. WITNESS the facsimile seal of the Corporation and the facsimile   signatures of its duly authorized officers. DATED DD-MMM-YYYY COUNTERSIGNED   AND REGISTERED: COMPUTERSHARE TRUST COMPANY, N.A. TRANSFER AGENT AND   REGISTRAR, President and Chief Executive Officer By Senior Vice President and   Chief Financial Officer AUTHORIZED SIGNATURE CUSIP Holder ID Insurance Value   Number of Shares DTC Certificate Numbers 1234567890/1234567890   1234567890/1234567890 1234567890/1234567890 1234567890/1234567890   1234567890/1234567890 1234567890/1234567890 Total Transaction XXXXXX XX X   XXXXXXXXXX 1,000,000.00 123456 12345678 123456789012345 PO BOX 43004,   Providence, RI 02940-3004 Num/No. Denom. Total 1 2 3 4 5 6 7 1 2 3 4 5 6 1 2   3 4 5 6 MR A SAMPLE DESIGNATION (IF ANY) ADD 1 ADD 2 ADD 3 ADD 4 CUSIP 15117B   10 3 


    




 









 



. (Cust)   (Minor) (State) and not as tenants in common (Cust) (Minor) PLEASE INSERT   SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF ASSIGNEE For value received,   hereby sell, assign and transfer unto (PLEASE PRINT OR TYPEWRITE NAME AND   ADDRESS, INCLUDING POSTAL ZIP CODE, OF ASSIGNEE) Shares represented by the   within Certificate, and do hereby irrevocably constitute and appoint Attorney   to transfer the said shares on the books of the within-named Corporation with   full power of substitution in the premises. Dated: 20 Signature: Signature:   Notice: The signature to this assignment must correspond with the name as   written upon the face of the certificate, in every particular, without   alteration or enlargement, or any change whatever. Signature(s) Guaranteed: Medallion   Guarantee Stamp THE SIGNATURE(S) SHOULD BE GUARANTEED BY AN ELIGIBLE   GUARANTOR INSTITUTION (Banks, Stockbrokers, Savings and Loan Associations and   Credit Unions) WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION   PROGRAM, PURSUANT TO S.E.C. RULE 17Ad-15. The following abbreviations, when   used in the inscription on the face of this certificate, shall be construed   as though they were written out in full according to applicable laws or   regulations: TEN COM - as tenants in commonUNIF GIFT MIN ACT-. . . . . . . .   . .Custodian . . . . . . . . . . . . . . . TEN ENT - as tenants by the   entiretiesunder Uniform Gifts to Minors Act . . . . . . . . . . . . . JT   TEN-as joint tenants with right of survivorshipUNIF TRF MIN ACT . . . . . . .   . . . . . . . .Custodian (until age. . . ). . . . . . . . . . . under Uniform   Transfers to Minors Act. . . . . . . . . . (State) Additional abbreviations   may also be used though not in the above list.