**4. Materials and Methods**

#### *4.1. Viral Preparations*

SARS-CoV-2/human/RUS/Nsk-FRCFTM-1/2020 strain was isolated from a clinical sample of a nasopharyngeal swab from the patient in Novosibirsk. The virus was purified and concentrated, as described [12]. Both SARS-CoV-2/human/RUS/Nsk-FRCFTM-1/2020 and an antigen of the SARS-CoV strain Frankfurt 1 (2002) [23] were stored at the Federal Research Center of Fundamental and Translational Medicine SB RAS at −80 ◦C. Viral preparations with an infectious titer of 6 lg tissue cytopathic doses (TCPD50/mL) were inactivated (in a 1:1 ratio) in a lysis buffer used for electrophoresis (composition for 2 mL: 1 M Tris-HCl with pH 6.8–0.5 mL; 10% sodium dodecyl sulfate (SDS) solution—0.8 mL; glycerin—0.2 mL; mercaptoethanol—0.2 mL; 0.4% Bromphenol Blue Na-sulf—0.1 mL).
