Assessment of cell-mediated immune responses to SARS-CoV-2 in Syrian hamsters

BACKGROUND: The pandemic caused by the SARS-CoV-2 virus at the end of 2019 remains to be a serious healthcare problem. Constant antigenic drift of the pathogen led to a decrease of licensed COVID-19 vaccines effectiveness. And the development of broad-spectrum vaccines with high effectiveness rate against evolutionarily divergent SARS-CoV-2 variants remains an urgent issue. Unlike virus-specific antibodies with limited spectrum of action, T-cell immunity has a wider cross-protective potential. Syrian hamsters are the most appropriate model for preclinical evaluation of new vaccine candidates, since these animals are susceptible to SARS-CoV-2 infection and show clinical symptoms of the disease. However, study of T-cell vaccine response in hamsters is complicated by the lack of available reagents and test systems for adequate assessment of the virus-specific cellular immunity levels after vaccination. AIM: In this work, we report an optimized protocol of stimulation of Syrian hamsters immune cells with a live SARS-CoV-2 virus to assess virus-specific T-cell responses. MATERIALS AND METHODS: Intranasal infection of animals with SARS-CoV-2 virus followed by stimulation of immune cells with different doses of whole live coronavirus and counting of IFN-producing cells by ELISpot method. RESULTS: Stimulation of spleen and lung cells with SARS-CoV-2 at a dose 0.1 TCID50/cell is the most optimal viral concentration for detecting maximum of cytokine-producing cells in SARS-CoV-2-infected animals. Stimulation of cells with whole virus revealed greater number of virus-specific cells compared to a stimulation with pools of SARS-CoV-2 lyophilized peptides (S and N proteins). CONCLUSIONS: Overall, the new methodology allows assessment of the immunogenicity of COVID-19 T-cell vaccines more accurately in preclinical studies using the Syrian hamsters model.