A safe and effective vaccine that can provide herd immunity against severe acute respiratory syndrome coronavirus (SARS-CoV-2) is urgently needed to stop the spread of this virus among humans. Many human viral vaccines are live, attenuated forms of viruses that elicit humoral and cellular immunity. Here, we describe a cold-adapted live-attenuated vaccine (SARS-CoV-2/human/Korea/CNUHV03-CA22 °C/2020) developed by gradually adapting the growth of SARS-CoV-2 from 37 °C to 22 °C in Vero cells. This vaccine can be potentially administered to humans as a nasal spray. Its single dose strongly induced neutralising antibodies (titre > 640), cellular immunity, and mucosal IgA antibodies in intranasally immunised K18-hACE2 mice, which are very susceptible to SARS-CoV-2 and SARS-CoV infections. The one-dose vaccinated mice were completely protected from SARS-CoV-2 infection and did not show body weight loss, death, or the presence of virus in tissues, such as the nasal turbinates, brain, lungs, and kidneys. These results demonstrate that the cold-adapted live attenuated SARS-CoV-2 vaccine we have developed may be a candidate SARS-CoV-2 vaccine for humans.

Severe acute respiratory syndrome coronavirus (SARS-CoV-2) has infected more than 16,000,000 people and has caused the death of more than 650,000 individuals since December 2019. A safe and effective vaccine that can provide herd immunity against SARS-CoV-2 is urgently needed to stop the spread of this virus among humans. Many human viral vaccines are live attenuated forms of viruses that elicit humoral and cellular immunity. Here, we describe the development of a cold-adapted live attenuated vaccine (SARS-CoV-2/human/Korea/CNUHV03-CA22 degree celsius/2020) by gradually adapting the growth of SARS-CoV-2 from 37 degree celsius to 22 degree celsius in Vero cells. This vaccine can be potentially administered to humans through nasal spray. Its single dose was observed to strongly induce the neutralising antibody (over 640), cellular immunity, and mucosal IgA antibody in intranasally immunised K18-hACE2 mice, which are very susceptible to SARS-CoV-2 and SARS-CoV infection. The one-dose vaccinated mice were completely protected from SARS-CoV-2 infection and did not show loss of body weight, death, and the presence of virus in tissues, such as the nasal turbinates, brain, lungs, and kidneys. Taken together, the cold-adapted live attenuated SARS-CoV-2 vaccine developed by us may contribute to saving of human lives from the threat of SARS-CoV-2.

Coronaviruses such as MERS-CoV and SARS-CoV-2 infect the human respiratory tract and can cause severe pneumonia. Disease severity and outcomes are different for these two infections: the human mortality rate for MERS-CoV and SARS-CoV-2 is over 30% and less than 10%, respectively. Here, using microarray assay, we analyzed the global alterations in gene expression induced by MERS-CoV or SARS-CoV-2 infections in primary human pulmonary epithelial cells. Overall, the number of differentially expressed genes was higher in human lung cells infected with MERS-CoV than in cells with SARS-CoV-2. Out of 44,556 genes analyzed, 127 and 50 were differentially expressed in cells infected with MERS-CoV and SARS-CoV-2, respectively (> 2-fold increase, compared to uninfected cells). Of these, only eight genes, including the one coding for CXCL8, were similarly modulated (upregulated or downregulated) by the two coronaviruses. Importantly, these results were virus-specific and not conditioned by differences in viral load, and viral growth curves were similar in human lung cells infected with both viruses. Our results suggest that these distinct gene expression profiles, detected early after infection by these two coronaviruses, may help us understand the differences in clinical outcomes of MERS-CoV and SARS-CoV-2 infections.

Background:The recently emerged variants of the severe acute respiratory coronavirus 2 (SARS-CoV-2) pose a threat to public health. Understanding the pathogenicity of these variants is a salient factor in the development of effective SARS-CoV-2 therapeutics. This study aimed to compare the expression patterns of genes involved in immune responses in K18-hACE2 mice infected with the wild-type, Delta, and Omicron SARS-CoV-2 variants. Methods: K18-hACE2 mice were intranasally infected with either wild-type (B.1), Delta (B.1.617.2), or Omicron (B.1.1.529) variants. On day 6 post-infection, lung, brain, and kidney tissues were collected from each variantinfected group. The mRNA expression levels of 39 immune response genes in all three groups were compared by RT-qPCR. Viral titers were measured using the median tissue culture infectious dose (TCID50) assay and expressed as Log10 TCID50/0.1 g. The statistical significance of the differences in gene expression was determined by one-way analysis of variance (ANOVA) (alpha = 0.05). Results: The expression of toll-like receptors (TLRs) was upregulated in the lung and brain tissues of the wild-type-and Delta-infected groups but not in those of the Omicron-infected group. The highest expression of cytokines, including interleukin (IL)-1α, IL-1β, IL-17α, interferon, and tumor necrosis factors, was observed in the lungs of mice infected with the wild-type variant. Additionally, CCL4, CCL11, CXCL9, and CXCL10 were upregulated (>3-fold) in wild-type-infected mice, with markedly higher expressions in the brain than in the lungs. Most of the apoptotic factors were mainly expressed in the brain tissues of Omicron-infected mice (caspase 8, caspase 9, p53, Bax, Bak, BCL-2, and Bcl-XL), whereas neither the lung nor kidney showed more than 3-fold upregulation of these apoptotic factors. Conclusions: Collectively, our findings revealed that the wild-type SARS-CoV-2 variant exhibited the highest pathogenicity, followed by the Delta variant, then the Omicron variant.