Recombinant protein HR212 targeting heptad repeat 2 domain in spike protein S2 subunit elicits broad-spectrum neutralizing antibodies against SARS-CoV-2 and its variants.

SARS-CoV-2 variants are under continuous emergence carry numerous mutations within S1 subunit in spike protein and have escaped neutralization through many currently used vaccines and antibodies. The development of next-generation vaccines is a continuing and long-term need. In our prior research, the recombinant protein vaccine HR121 targeting the heptad repeat (HR) 1 domain of S2 subunit was constructed, which could evoke highly broad-spectrum neutralizing antibodies in vivo and confer efficient protective effect on several SARS-CoV-2 variants within multiple animal models. Compared with HR1, HR2 domain shows a more conservative degree within SARS-CoV-2 and related coronaviruses. Here, we designed a recombinant protein HR212 consisting of HR2-linker1-HR1-linker2-HR2. HR212 showed a high affinity with HR1 and was functionally analogous to HR2 within fusion intermediate in S2 subunit. Immunizing rabbits using HR212-mediated high nAbs for 28 pseudotyped SARS-CoV-2 variants, like currently circulating variants, such as BA.2.86 and JN.1. Transfer of rabbit anti-HR212 sera or immunization with HR212 offered efficient protective effect on SARS-CoV-2 ancestral strain and Omicron BA.2 variant infections of Syrian golden hamsters. According to our results, HR2 domain of S2 subunit is the novel target that can be used to develop broad-spectrum vaccines to resist SARS-CoV-2 variants.