Аttenuation мarkers of cold-adapted SARS-CoV-2 variants

BACKGROUND: Unprecedented anti-epidemic measures and the widespread use of vaccines against COVID-19 have reduced the rate of hospitalization and mortality from the disease, but have not stopped the SARS-CoV-2 pandemic spread. The development of live vaccines against COVID-19, capable of providing the formation of a long-term humoral and cellular immune response and cross-protection against new SARS-CoV-2 variants of concern, is relevant. Previously at the I.I. Mechnikov Research Institute of Vaccines and Sera SARS-CoV-2 cold-adapted (ca, cold-adapted) variants were obtained. This work is aimed to search for methodological approaches that allow in vitro screening studies to assess the attenuation (att) phenotype of ca SARS-CoV-2 variants. MATERIALS AND METHODS: The SARS-CoV-2 laboratory strain Dubrovka and its variants were cultured in Vero and Calu-3 cells. Quantitation of the virus was carried out by titration in Vero cells and by real-time RT-PCR. The attenuation (att) phenotype of SARS-CoV-2 variants was determined on an animal model of COVID-19 on Syrian hamsters. RESULTS: In experiments on Syrian hamsters, the presence of the att phenotype in the ca variants of the virus was established. Animals infected with virus ca variants had significantly less weight lost, had less viral load in the lungs and brain and less pronounced pathological changes in the lungs compared to infection with the virulent strain. In vitro experiments on Vero and Calu-3 cells revealed probable attenuation markers of the virus ca variants for syrian hamsters: (1) ability to reproduce at low temperature (ca phenotype); (2) inability to reproduce at 39 C (ts phenotype); (3) changes in the species and tissue specificity of the virus. CONCLUSIONS: The developed methodological approaches to the identification of SARS-CoV-2 attenuation markers are a valuable tool for monitoring the stability of the phenotype of candidate vaccine strains.