ABSTRACT
The SARS-CoV-2 virus caused the most severe pandemic around the world, and vaccine development for urgent use became a crucial issue. Inactivated virus formulated vaccines such as Hepatitis A, oral polio vaccine, and smallpox proved to be reliable approaches for immunization for prolonged periods. During the pandemic, we produced an inactivated SARS-CoV-2 vaccine candidate, having the advantages of being manufactured rapidly and tested easily in comparison with recombinant vaccines. In this study, an inactivated virus vaccine that includes a gamma irradiation process for the inactivation as an alternative to classical chemical inactivation methods so that there is no extra purification required has been optimized. The vaccine candidate (OZG-38.61.3) was then applied in mice by employing the intradermal route, which decreased the requirement of a higher concentration of inactivated virus for proper immunization, unlike most of the classical inactivated vaccine treatments. Hence, the novelty of our vaccine candidate (OZG-38.61.3) is that it is a non-adjuvant added, gamma-irradiated, and intradermally applied inactive viral vaccine. Efficiency and safety dose (either 1013 or 1014 viral copy per dose) of OZG-38.61.3 was initially determined in Balb/c mice. This was followed by testing the immunogenicity and protective efficacy of OZG-38.61.3. Human ACE2-encoding transgenic mice were immunized and then infected with a dose of infective SARS-CoV-2 virus for the challenge test. Findings of this study show that vaccinated mice have lower SARS-CoV-2 viral copy number in oropharyngeal specimens along with humoral and cellular immune responses against the SARS-CoV-2, including the neutralizing antibodies similar to those shown in Balb/c mice without substantial toxicity. Subsequently, plans are being made for the commencement of Phase 1 clinical trial of the OZG-38.61.3 vaccine for the COVID-19 pandemic.
ABSTRACT
COVID-19 outbreak caused by SARS-CoV-2 created an unprecedented health crisis since there is no vaccine for this novel virus. Therefore, SARS-CoV-2 vaccines have become crucial for reducing morbidity and mortality. In this study, in vitro and in vivo safety and efficacy analyzes of lyophilized vaccine candidates inactivated by gamma-irradiation were performed. The candidate vaccines in this study were OZG-3861 version 1 (V1), an inactivated SARS-CoV-2 virus vaccine, and SK-01 version 1 (V1), a GM-CSF adjuvant added vaccine. The candidate vaccines were applied intradermally to BALB/c mice to assess toxicity and immunogenicity. Preliminary results in vaccinated mice are reported in this study. Especially, the vaccine models containing GM-CSF caused significant antibody production with neutralization capacity in absence of the antibody-dependent enhancement feature, when considered in terms of T and B cell responses. Another important finding was that the presence of adjuvant was more important in T cell in comparison with B cell response. Vaccinated mice showed T cell response upon restimulation with whole inactivated SARS-CoV-2 or peptide pool. This study shows that the vaccines are effective and leads us to start the challenge test to investigate the gamma-irradiated inactivated vaccine candidates for infective SARS-CoV-2 virus in humanized ACE2+ mice.
