Northwest Biotherapeutics, Inc. said it made additional sales of its series B preferred stock and class D-2 warrants to certain investors from May 4 to May 17.

The Bethesda, Md.-based biotechnology company issued 487,117 series B preferred stock at $2.30 apiece for about $1.1 million.

Each share of series B preferred stock is convertible into 10 common shares.

The company also issued class D-2 warrants to acquire up to 4,871,170 common shares at an exercise price of 30 cents per share.

Northwest said that since May 4, about 111,765 series A preferred stock and 271,955 series B preferred stock were converted into 3,837,200 common shares.