Comparison of mouse species in an in vivo sars-cov-2 challenge model

The K18-hACE2 transgenic mice, a model animal having human ACE receptors, is employed in studies against the SARS-CoV-2 virus all over the world. Aged Balb/C mice utilized during the SARS-CoV outbreak were compared to non-T-cell, immunosuppressive Nude mice often employed in cancer research and K18-hACE2 transgenic mice used as a model animal against the SARS-CoV-2 virus challenge assay. At the same time, the role of the model animal K18-hACE2 transgenic mice in organs other than the lung was studied. The BSL3 facility was used for the challenge experiment in this study. In three groups, 105 TCID50 SARS-CoV-2 virus B.1.1.7 (the alpha variant was gavaged and intranasally administered to mice under anesthesia. The experiment was ended on the tenth day, and gross pathology was done. The viral load of SARSCoV- 2 was determined by RT-PCR after collecting the target organ lungs from all mice as well as the spleen, liver, heart, and kidneys from the K18-hACE2 transgenic mouse group. In comparison to Balb/C and Nude mice, the K18-hACE2 transgenic mouse model animal has been shown to be a suitable model against the SARS-CoV-2 virus in our study. At the same time, when the organs of K18-hACE2 transgenic mice were compared, viral load retention occurred in the target organ, the lung, with no significant retention in other organs

Process development for an effective COVID-19 vaccine candidate harboring recombinant SARS-CoV-2 delta plus receptor binding domain produced by Pichia pastoris

Abstract Recombinant protein-based SARS-CoV-2 vaccines are needed to fill the vaccine equity gap. Because protein-subunit based vaccines are easier and cheaper to produce and do not require special storage/transportation conditions, they are suitable for low-/middle-income countries. Here, we report our vaccine development studies with the receptor binding domain of the SARS-CoV-2 Delta Plus strain (RBD-DP) which caused increased hospitalizations compared to other variants. First, we expressed RBD-DP in the Pichia pastoris yeast system and upscaled it to a 5-L fermenter for production. After three-step purification, we obtained RBD-DP with > 95% purity from a protein yield of > 1 g/L of supernatant. Several biophysical and biochemical characterizations were performed to confirm its identity, stability, and functionality. Then, it was formulated in different contents with Alum and CpG for mice immunization. After three doses of immunization, IgG titers from sera reached to > 106 and most importantly it showed high T-cell responses which are required for an effective vaccine to prevent severe COVID-19 disease. A live neutralization test was performed with both the Wuhan strain (B.1.1.7) and Delta strain (B.1.617.2) and it showed high neutralization antibody content for both strains. A challenge study with SARS-CoV-2 infected K18-hACE2 transgenic mice showed good immunoprotective activity with no viruses in the lungs and no lung inflammation for all immunized mice