Immunogenic properties of SARS-CoV-2 inactivated by ultraviolet light

Abstract

Vaccination against COVID-19 is the most effective method of controlling the spread of SARS-CoV-2 and reducing mortality from this disease. The development of vaccines with high protective activity against a wide range of SARS-CoV-2 antigenic variants remains relevant. In this regard, evaluation of the effectiveness of physical methods of virus inactivation, such as ultraviolet irradiation (UV) of the virus stock, remains relevant. This study demonstrates that the UV treatment of SARS-CoV-2 completely inactivates its infectivity while preserving its morphology, antigenic properties, and ability to induce the production of virus-neutralizing antibodies in mice through immunization. Thus, the UV inactivation of SARS-CoV-2 makes it possible to obtain viral material similar in its antigenic and immunogenic properties to the native antigen, which can be used both for the development of diagnostic test systems and for the development of an inactivated vaccine against COVID-19.

Fig. 1

The ultraviolet (UV) light irradiation system. A UV wavelength of 253.7 nm was used. The length and diameter of the light tube were 295 ± 3 mm and 15.5 ± 0.5 mm, respectively. SARS-CoV-2 with a titer of 8.75 log10 TCID₅₀/ml was placed in a 177-cm² dish, 30 cm below the UV-C light tube, and irradiated using for 0.5, 1, 2, 4, 6, 8, and 12 min at a UV-C intensity of 290 μW/cm². The image was made using the online program BioRender [https://biorender.com/about/]

Fig. 2

Growth kinetics of SARS-CoV-2 (Dubrovka strain) in Vero cells. (A) Virus titer. (B) Viral RNA concentration. Cells were inoculated at an MOI of 0.001 and 0.00001. Supernatant samples were collected every 12 hours to titrate the virus and determine the concentration of viral RNA

Fig. 3

Survival of Vero cells on day 5 after inoculation with a UV-inactivated SARS-CoV-2 preparation. The virus preparation was irradiated for the indicated times at a UV-C intensity of 290 μW/cm². Inactivation of the virus was confirmed by blind passage in Vero cells. Vero cell survival was measured using an MTT test

Fig. 4

Electron micrograph of negatively stained UV-inactivated SARS-CoV-2 at 40 000× magnification. The arrow shows characteristic spikes (S-protein) on the surface of the coronavirus. Panels A and B represent different fields of view for the same preparation of the Dubrovka strain

Fig. 5

Detection of viral antigen in a UV-inactivated SARS-CoV-2 preparation by immunochromatography (IC). A SARS-CoV-2 Rapid Antigen Test kit was used to test sequential fivefold dilutions of UV-inactivated SARS-CoV-2 from 1:5 to 1:15,625 (1-6), a positive control (K+), and a negative control (K-)

Fig. 6

Mean antibody titers to SARS-CoV-2 in the sera of mice after the first and second immunization. (A) Antibody titer in ELISA. (B) Neutralizing antibody titer. 1, 14 days after the first immunization with UV-inactivated virus; 2, 14 days after the second immunization with UV-inactivated virus; LV, 14 days after immunization with live SARS-CoV-2; К, mice injected with PBS