(Reuters) - Gritstone bio Inc said on Tuesday it had entered into a funding agreement of up to $20.6 million with the Coalition for Epidemic Preparedness Innovations (CEPI) to advance its vaccine program against COVID-19 variants, sending its shares up 2.6% before the bell. Gritstone’s vaccine is based on self-amplifying mRNA technology, which uses the body’s own machinery to make antigenic protein rather than injecting the antigen into the body. Under the agreement, CEPI, which co-leads the COVAX vaccine sharing facility, will fund an early stage study evaluating the program’s vaccine in convalescent, and HIV positive patients. The trial is expected to start before the end of 2021, Gritstone said. CEPI and Gritstone have agreed the vaccine candidate will be made available to the COVAX facility. Reporting by Dania Nadeem in Bengaluru; Editing by Vinay Dwivedi Our Standards: The Thomson Reuters Trust Principles.