Neutralizing antibody-independent immunity to SARS-CoV-2 in hamsters and hACE-2 transgenic mice immunized with a RBD/Nucleocapsid fusion protein

Castro, Julia T.; Fumagalli, Marcílio J.; Hojo-Souza, Natalia S.; Azevedo, Patrick; Salazar, Natalia; Rattis, Bruna; Ramos, Simone G.; Faustino, Lídia; Almeida, Gregório G.; Oliveira, Livia I.; Marçal, Tomas G.; Augusto, Marconi; Magalhães, Rubens; Cassaro, Bruno; Burle, Gabriela; Doro, Daniel; Kalil, Jorge; Durigon, Edson; Salazar, Andrés; Caballero, Otávia; Machado, Alexandre; Silva, João S.; da Fonseca, Flávio; Fernandes, Ana Paula; Teixeira, Santuza R.; Gazzinelli, Ricardo T.

The nucleocapsid (N) and the receptor binding domain (RBD) of the Spike (S) proteins elicit robust antibody and T cell responses either in vaccinated or COVID-19 convalescent individuals. We generated a chimeric protein that comprises the sequences of RBD from S and N antigens (SpiN). SpiN was highly immunogenic and elicited a strong IFNγ response from T cells and high levels of antibodies to the inactivated virus, but no neutralizing antibodies. Importantly, hamsters and the human Angiotensin Convertase Enzyme-2-transgenic mice immunized with SpiN were highly resistant to challenge with the wild type SARS-CoV-2, as indicated by viral load, clinical outcome, lung inflammation and lethality. Thus, the N protein should be considered to induce T-cell-based immunity to improve SARS-CoV-2 vaccines, and eventually to circumvent the immune scape by variants.