Nevertheless, different studies have shown that some Wuhan-Hu-1-based COVID-19 vaccines can protect against SARS-CoV-2 VoC morbidity and mortality in different animal models, although with different degrees of infection protection (2332). (with also 3P substitutions), demonstrated that two intramuscular doses of both vaccine candidates fully protected transgenic K18-hACE2 mice from a lethal challenge with SARS-CoV-2 beta variant, reducing mRNA and infectious viral loads in the lungs and in bronchoalveolar lavages, decreasing lung histopathological lesions and levels of proinflammatory cytokines in the lungs. Vaccination also elicited high titers of anti-S Th1-biased IgGs and neutralizing antibodies against ancestral SARS-CoV-2 Wuhan strain and VoCs alpha, beta, gamma, delta, and omicron. In addition, similar systemic and local SARS-CoV-2 S-specific CD4+and CD8+T-cell immune responses were elicited by both vaccine candidates after a single intranasal immunization in C57BL/6 mice. These preclinical data support clinical evaluation of MVA-S(3Pbeta) and MVA-S(3P), to explore whether they can diversify and potentially increase recognition and protection of SARS-CoV-2 VoCs. Keywords:COVID-19, SARS-CoV-2, MVA-based vaccine, variants of concern, S protein, immunogenicity, efficacy, mice == Introduction == SARS-CoV-2 virus has spread worldwide since 2019, causing as of July 2023 more than 700 million cases and close to 7 million deaths. The fast development of vaccines has made it possible to prevent severe illness and minimize the risk of death. However, immediately after the outbreak, several variants of concern (VoCs) emerged, each containing numerous mutations within the viral genome (1). SARS-CoV-2 VoCs, with mutations in the spike (S) protein, specifically in the receptor-binding domain (RBD), spread more efficiently and escape to neutralization by antibodies induced by vaccination or infection (18). Among the VoCs, SARS-CoV-2 beta (B.1.351) AGN-242428 variant is of special interest for this work. SARS-CoV-2 B.1.351 was first identified in October 2020 in South Africa and contains 10 amino acid substitutions in the S protein, with three of them in the RBD that are reported to increase binding between S and its cell receptor angiotensin converting enzyme 2 (ACE2), and also results in a reduced level of neutralization by natural and vaccine-induced antibodies (8,9). Moreover, recently the European Medicines Agency (EMA) recently approved for human use a protein-based COVID-19 vaccine, termed Bimervax, consisting of a fusion RBD heterodimer of Wuhan and beta (B.1.351) variant strains administered with an adjuvant (https://www.ema.europa.eu/en/medicines/human/EPAR/bimervax) (1012). The continued emergence of SARS-CoV-2 VoCs has led to imminent challenges in establishing protective immunity by using approved first-generation COVID-19 vaccines (based in the ancestral Wuhan strain), as two or three doses of approved COVID-19 vaccines confer variable efficacy against various SARS-CoV-2 VoCs (1322). AGN-242428 Following the same line of results, different Wuhan-based COVID-19 vaccines have been reported to protect against morbidity and mortality due to SARS-CoV-2 VoCs in several animal models, although with distinct degrees of protection against infection (2332). Although Wuhan-based COVID-19 vaccines have proven useful in decreasing the number of hospitalizations and deaths caused by VoCs, new variant-specific vaccines capable of increasing protection capacity against disease and viral transmission are desirable. We have previously described that modified vaccinia virus Ankara (MVA) vectors expressing full-length native (MVA-S) or prefusion-stabilized Wuhan-derived SARS-CoV-2 S proteins (MVA-S(3P)) were highly immunogenic and effective in mice (3338), hamsters (39) and rhesus macaques (40). In particular, MVA-S(3P) was more immunogenic than MVA-S, and a single dose induced antibodies that neutralized several VoCs and protected K18-hACE2 mice from a lethal challenge with the ancestral Wuhan SARS-CoV-2 (isolate MAD6, containing the mutation D614G in the S protein) (36,37). Moreover, we have recently reported that MVA-S(3P) fully protects against SARS-CoV-2 infection in hamsters (41). Here, to extend our previous studies on the capacity of MVA-based vaccine candidates to prevent SARS-CoV-2 infections, we describe the generation and characterization of an optimized MVA-based vaccine candidate expressing a human codon optimized full-length prefusion-stabilized S protein derived from SARS-CoV-2 beta (B.1.351). Head-to-head comparison of the immunogenicity and efficacy of MVA-S(3Pbeta) and MVA-S(3P) in C57BL/6 and transgenic K18-hACE2 mice, respectively, revealed that both vaccine candidates elicited potent and similar T-cellular and humoral immune responses against ancestral SARS-CoV-2 Wuhan strain and beta (B.1.351) variant and cross-neutralizing antibodies against other VoCs of human health relevance. Importantly, both AGN-242428 vaccine candidates similarly protected K18-hACE2 mice from a lethal challenge with beta (B.1.351) variant, significantly reducing mRNA and infectious viral loads in the lungs and broncoalveolar lavages (BAL), pulmonary histopathological lesions, and levels of proinflammatory cytokines in the lungs. These findings highlight the importance of defining the preclinical immune efficacy Rabbit Polyclonal to FPR1 against emerging VoCs of Wuhan- and VoC-based vaccines, to assure activation of markers of protection. == Materials and methods == == Animals and ethics statement == Female C57BL/6OlaHsd mice (68 weeks old) used for immunogenicity experiments were purchased from Envigo Laboratories and stored in the animal facility of the Centro Nacional.