US immunotherapy company Inovio Pharmaceuticals Inc said on Wednesday its experimental vaccine to prevent coronavirus infection produced protective antibodies and immune system responses in mice and guinea pigs.

Dr. David Weiner, director of the vaccine and immunotherapy center at the Wistar Institute, which has collaborated with Inovio said, "We saw antibody responses that do many of the things we would want to see in an eventual vaccine and we are able to target things that would prevent the virus from having a safe harbor in the body."

Inovio, which began human testing of its vaccine in April, said preliminary results from that trial are expected in June.  The 40 healthy participants in the Phase 1 trial are given 2 shots, 4 weeks apart, of the vaccine, called INO-4800, and then followed for 2 weeks.

Inovio said the latest animal study results, published in the journal Nature Communications, validate its DNA medicines platform and build on previous positive clinical trial data for its experimental vaccine against a different, but related, the coronavirus that causes Middle East Respiratory Syndrome.

Inovio also said that the newly published data demonstrate virus-neutralizing activity using 3 separate testing procedures. Study authors also said they detected the antibodies in the lungs of the vaccinated animals.

Inovio's next plans to test the vaccine in larger animals including rabbits and monkeys, and to undertake "challenge" studies in mice, ferrets, and monkeys, Broderick said. 

Challenge studies involve intentionally giving the virus to an animal and then seeing if the vaccine prevents infection.

There are currently no approved treatments or vaccines for COVID-19, the disease caused by the new coronavirus, with governments, drugmakers, and researchers working on around 100 vaccine programs.