Tetravalent SARS-CoV-2 S1 subunit protein vaccination elicits robust humoral and cellular immune responses in SIV-infected rhesus macaque controllers

The coronavirus disease 2019 (COVID-19) pandemic has highlighted the need for safe and effective vaccines to be rapidly developed and distributed worldwide, especially considering the emergence of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. Protein subunit vaccines have emerged as a promising approach due to their proven safety record and ability to elicit robust immune responses. In this study, we evaluated the immunogenicity and efficacy of an adjuvanted tetravalent S1 subunit protein COVID-19 vaccine candidate composed of the Wuhan, B.1.1.7 variant, B.1.351 variant, and P.1 variant spike proteins in a nonhuman primate model with controlled SIVsab infection. The vaccine candidate induced both humoral and cellular immune responses, with T and B cell responses mainly peaking post boost immunization. The vaccine also elicited neutralizing and cross-reactive antibodies, angiotensin-converting enzyme 2 (ACE2)-blocking antibodies, and T cell responses, including spike-specific CD4(+) T cells. Importantly, the vaccine candidate was able to generate Omicron variant spike-binding and ACE2-blocking antibodies without specifically vaccinating with Omicron, suggesting potential broad protection against emerging variants. The tetravalent composition of the vaccine candidate has significant implications for COVID-19 vaccine development and implementation, providing broad antibody responses against numerous SARS-CoV-2 variants.