The Italian biotech, headquartered in Rome, has developed its vaccine on a novel and proprietary replication-defective simian (gorilla) adenoviral vector (called GRAd) encoding the full-length coronavirus spike protein.
Preliminary Phase 2 data showed an antibody response against the SARS-CoV-2 spike protein in 93% of volunteers after the first dose; reaching 00% after the second dose. Five weeks after the first vaccination, the titer of both spike-binding and SARS-CoV-2 neutralizing antibodies was comparable to that of patients recovering from COVID-19 infection.
Conducted in 24 clinical centers across Italy, the study enrolled 917 volunteers. These either received a single vaccine dose (followed by placebo); two vaccine doses; or two placebo doses. Shots were administered three weeks apart.
The trial’s Independent Data Safety Monitoring Board and Steering Committee has recommended the continued clinical development of the vaccine.
Adenoviral vector vaccines: 'more potent and persistent cell-mediated responses than other vaccine platforms'
Simian adenoviral (SAd) vectors have been used as delivery agents for genetic vaccine candidates against multiple infectious diseases, including Ebola and RSV (Respiratory Syncytial Virus), in early and late stage clinical trials to date.
ReiThera's novel GRAd vector belongs to species C adenovirus that are considered the most potent vaccine carriers and has low seroprevalence in humans. This means that GRAd vaccine immunogenicity is not hampered by pre-existing anti-human adenovirus antibodies.
Roberto Camerini, MD Reithera Medical Director, said: "Our vaccine candidate confirmed its excellent safety and good immunogenicity profile in a large cohort.
"The Phase 3 program, based on a non-inferiority design with a primary immunological endpoint in comparison with a viral vectored vaccine already marketed, has received a positive opinion from the European Medicines Agency and other important regulatory agencies. We hope to be able to start Phase 3 trial as soon as possible."
Stefania Capone, Head of Preclinical and Clinical Immunology unit at ReiThera, added: "Adenoviral vector vaccines induce more potent and persistent cell-mediated responses than other vaccine platforms, due to the activation of T lymphocytes against the spike protein, as we confirmed in our Phase 1 study of our candidate vaccine GRAd-COV2. We and others have shown that, unlike antibody immunity, T lymphocyte responses do not lose potency against SARS-CoV-2 variants of concern. Therefore, in the context of current and future epidemics, vaccines with this property could prove to be important weapons in offering protection from COVID-19, alone or in heterologous combination with other vaccine platforms.”