Gamma-irradiated SARS-CoV-2 vaccine candidate, OZG-38.61.3, confers protection from SARS-CoV-2 challenge in human ACEII-transgenic mice

Abstract

The SARS-CoV-2 virus caused one of the severest pandemic around the world. The vaccine development for urgent use became more of an issue during the pandemic. An inactivated virus formulated vaccines such as Hepatitis A, inactivated polio, and influenza has been proven to be a reliable approach for immunization for long years. In this pandemic, we produced an inactivated SARS-CoV-2 vaccine candidate by modification of the oldest but the most experienced method that can be produced quickly and tested easily rather than the recombinant vaccines. Here, we optimized an inactivated virus vaccine which includes the gamma irradiation process for the inactivation as an alternative to classical chemical inactivation methods so that there is no extra purification required. Also, we applied the vaccine candidate (OZG-38.61.3) using the intradermal route in mice which decreased the requirement of a higher concentration of inactivated virus for proper immunization unlike most of the classical inactivated vaccine treatments. Thus, the novelty of our vaccine candidate (OZG-38.61.3) is a non-adjuvant added, gamma-irradiated, and intradermally applied inactive viral vaccine. We first determined the efficiency and safety dose (either 1013 or 1014 viral copy per dose) of the OZG-38.61.3 in Balb/c mice. Next, to test the immunogenicity and protective efficacy of the OZG-38.61.3, we immunized human ACE2-encoding transgenic mice and infected them with a dose of infective SARS-CoV-2 virus for the challenge test. We showed that the vaccinated mice showed lowered 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. This study encouraged us towards a new promising strategy for inactivated vaccine development (OZG-38.61.3) and the Phase 1 clinical trial for the COVID-19 pandemic.

Preclinical efficacy and safety analysis of gamma-irradiated inactivated SARS-CoV-2 vaccine candidates

“…In the production of inactive vaccines in this study, both inactivation and sterilization steps were irradiation leads to less damage to the final product virus structure and allows the maximization of the preserved products. Besides, in our recently published pre-print 14 , we optimized an inactivated virus vaccine that includes the gamma irradiation process for the inactivation as an alternative to classical chemical inactivation methods so that there is no extra purification required. Also, we applied the third version of our vaccine candidate (OZG-38.61.3) using the intradermal route in mice which decreased the requirement of a higher concentration of inactivated virus for proper immunization unlike most of the classical inactivated vaccine treatments [14][15][16] .…”

“…Besides, in our recently published pre-print 14 , we optimized an inactivated virus vaccine that includes the gamma irradiation process for the inactivation as an alternative to classical chemical inactivation methods so that there is no extra purification required. Also, we applied the third version of our vaccine candidate (OZG-38.61.3) using the intradermal route in mice which decreased the requirement of a higher concentration of inactivated virus for proper immunization unlike most of the classical inactivated vaccine treatments [14][15][16] . In this study, we immunized human ACE2-encoding transgenic mice and infected them with a dose of infective SARS-CoV-2 virus for the challenge test.…”

“…This may explain the inability of GM-CSF in intradermally administered inactive virus vaccines. Therefore, it was decided to increase the SARS-CoV-2 effective viral copy dose (1x10 13 or 1x10 14 viral copies per dose) in version 2 of vaccine candidates.…”

“…With this study, it was seen that our gamma-irradiated inactivated vaccine candidates can effectively trigger the production of SARS-CoV-2 specific antibodies along with long-term T cell response. Hence, the findings of this study prompted us to plan a new in vivo experiment with the second version of SK-01 and OZG-3861 (1x10 13 or 1x10 14 viral copies per dose) in humanized ACE2+ mice 14 . In this report, we determined that GMCSF adjuvant positive vaccine administration should be removed in the newly designed version of the OZG-38.61 vaccine model due to the finding of inflammatory reaction in the skin, cerebellum, and kidney in toxicity analysis of vaccinated mice.…”

“…In this report, we determined that GMCSF adjuvant positive vaccine administration should be removed in the newly designed version of the OZG-38.61 vaccine model due to the finding of inflammatory reaction in the skin, cerebellum, and kidney in toxicity analysis of vaccinated mice. Therefore, it was decided to increase the SARS-CoV-2 effective viral copy dose (1x10 13 or 1x10 14 viral copies per dose) in the last version of vaccine candidates. In the challenge study, we produced the third and final version of the OZG-38.61 without an adjuvant 14 .…”