Feb 21 (Reuters) - U.S. drugmaker Merck & Co Inc <MRK.N> said on Thursday it would buy immunotherapy developer Immune Design Corp <IMDZ.O> for nearly $300 million to gain access to new cancer treatments.

Merck will pay $5.85 in cash for each share of Immune Design. Shares of Immune Design closed at $1.42 on Wednesday.

 * MERCK TO ACQUIRE IMMUNE DESIGN
    * IMMUNE DESIGN CORP - DEAL FOR AN APPROXIMATE VALUE OF $300
MILLION
    * IMMUNE DESIGN CORP - DEAL FOR $5.85 PER SHARE IN CASH
    * IMMUNE DESIGN CORP - MERCK, THROUGH A SUBSIDIARY, WILL
INITIATE
A TENDER OFFER TO ACQUIRE ALL OUTSTANDING SHARES OF IMMUNE
DESIGN
    * IMMUNE DESIGN - UPON SUCCESSFUL COMPLETION OF TENDER
OFFER,
MERCK WILL ACQUIRE ALL SHARES OF CO NOT ACQUIRED IN TENDER
THROUGH A SECOND-STEP MERGER