Leonard Firestone stepped down from his post as CEO and director of Hawaii Biotech Inc. on Thursday, according to an announcement from the company’s board of directors. Hawaii Biotech vice president and chief scientific officer Carolyn Weeks-Levy was named interim senior executive of the Aiea-based biotechnology company, the board said in a news release. She also will remain chief scientist of the company, which focuses on research and development of vaccines for infectious diseases such as West Nile virus.