Alex Denner, the top health care deputy for Carl Icahn, confirmed on Monday that he had resigned from the billionaire investor's firm.

Denner, who had joined Icahn Enterprises LP in 2006 as senior managing director, had been integral in a number of successful activist campaigns alongside the billionaire investor. He pushed for the eventual sale of at least three biotechnology companies, including Genzyme Corp, MedImmune LLC and ImClone Systems.

Denner declined to elaborate on his next plans although an earlier report by Bloomberg, citing people familiar with Denner's situation, had said he was expected to start his own hedge fund this year. Bloomberg was also first to report Denner's resignation.

The departure marks the latest major blow for Icahn, who last year announced the departure of Keith Meister, who left to start his own event-driven hedge fund called Corvex Capital.

Denner is chairman of New Jersey-based Enzon Pharmaceuticals Inc and sits on the boards of several high-profile pharmaceutical and biotechnology companies including Massachusetts-based Biogen Idec Inc and San Diego-based Amylin Pharmaceuticals Inc .

Prior to joining Icahn, Denner served as a portfolio manager specializing in healthcare investments for Viking Global Investors. Previously, Denner served in a variety of roles at Morgan Stanley , beginning in 1996, including as portfolio manager of healthcare and biotechnology mutual funds.

Carl Icahn was not immediately available for comment.

(Reporting by Toni Clarke in Boston and Nadia Damouni in New York)