Incorporation of Sars-Cov-2 Spike Ntd to Rbd-Based Vaccine Improves Immunity and Protection Against Viral Variants

Emerging SARS-CoV-2 variants pose a threat to human health worldwide. SARS-CoV-2 receptor binding domain (RBD)-based vaccines are suitable candidates for booster vaccines, eliciting a focused antibody response enriched for virus neutralizing activity. Although RBD proteins are manufactured easily, and have excellent stability and safety properties, they are poorly immunogenic compared to the full-length spike protein. We have overcome this limitation by engineering a subunit vaccine composed of an RBD tandem dimer fused to the N-terminal domain (NTD) of the spike protein. We found that inclusion of the NTD (i) improved the magnitude and breadth of the T cell and anti-RBD response, and (ii) enhanced T follicular helper cell and memory B cell generation, antibody potency, and cross-reactive neutralization activity against multiple SARS-CoV-2 variants, including B.1.1.529 (Omicron BA.1). In summary, our uniquely engineered RBD-NTD-subunit protein vaccine provides a promising booster vaccination strategy capable of protecting against known SARS-CoV-2 variants of concern.Funding Information: COVID-19 Innovation Acceleration Fund, Ministry of Business, Innovation & Employment (MBIE), New Zealand, and the Addressing Security of Supply for a SARS-COV-2 Prophylactic Vaccine for New Zealanders, New Zealand (MALA2001) Intramural Program of NIAID, NIH, United States.Declaration of Interests: The authors declare no conflict of interests, other than the filing of patent application number AU2021902667 entitled “Fusion Polypeptide”.Ethics Approval Statement: Mouse studies - All experimental protocols were approved by the Victoria University of Wellington Animal Ethics Committee and experiments were carried out in accordance with their guidelines (28569). Human studies - Written informed consent was received for ten participants who had received two doses of Pfizer (BNT162b) vaccine, as part of the VAANZ Vaccine Study (sub study of Healthy Donor Tissue for Immune System Research) with approval from the Health and Disability Ethics Committee (Ref # 21/CEN/227).All challenge studies were performed in accordance with institutional guidelines approved by the Animal Care and Use Committee and were conducted in Assessment and Accreditation of Laboratory Animal Care-accredited Biosafety Level 2 and 3 facilities at the NIAID/National Institutes of Health. The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the University of Otago Human Ethics Committee (protocol H21/134) All experiments involving replication-competent (authentic) SARS-CoV-2 were performed under the auspices of the Institutional Biological Safety Committee (IBSC) at University of Otago, in an approved BSL-3 facility. Protocols for virus inactivation were approved by the IBSC. Work with inactivated SARS-CoV-2 and SARS-CoV-2 spike pseudotyped viruses was performed in a BSL-2 laboratory.