PharmAthene, Inc. (NYSE MKT: PIP) and Altimmune, Inc., a privately-held immunotherapeutics company targeting infectious diseases, announced today the signing of a definitive agreement for the merger of PharmAthene and Altimmune in an all-stock transaction. Altimmune's current investors include Novartis Venture Fund, HealthCap, Truffle Capital and Redmont Capital. The combined company will be a fully-integrated and diversified immunotherapeutics company with four clinical stage and one preclinical stage programs. The proposed transaction does not affect PharmAthene's previously announced special one-time cash dividend of $2.91 per share of common stock.