UB-612, a Multitope Universal Vaccine Eliciting a Balanced B and T Cell Immunity against SARS-CoV-2 Variants of Concern

Abstract

ABSTRACTImportanceThe SARS-CoV-2 non-spike structural proteins of nucleocapsid (N), membrane (M) and envelope (E) are critical in the host cell interferon response and memory T-cell immunity and have been grossly overlooked in the development of COVID vaccines.ObjectiveTo determine the safety and immunogenicity of UB-612, a multitope vaccine containing S1-RBD-sFc protein and rationally-designed promiscuous peptides representing sequence-conserved Th and CTL epitopes on the Sarbecovirus nucleocapsid (N), membrane (M) and spike (S2) proteins.Design, setting and participantsUB-612 booster vaccination was conducted in Taiwan. A UB-612 booster dose was administered 6-8 months post-2nd dose in 1,478 vaccinees from 3,844 healthy participants (aged 18-85 years) who completed a prior placebo (saline)-controlled, randomized, observer-blind, multi-center Phase-2 primary 2-dose series (100-μg per dose; 28-day apart) of UB-612. The interim safety and immunogenicity were evaluated until 14 days post-booster.ExposureVaccination with a booster 3rd-dose (100-μg) of UB-612 vaccine.Main outcomes and measuresSolicited local and systemic AEs were recorded for seven days in the e-diaries of study participants, while skin allergic reactions were recorded for fourteen days. The primary immunogenicity endpoints included viral-neutralizing antibodies against live SARS-CoV-2 wild-type (WT, Wuhan strain) and live Delta variant (VNT50), and against pseudovirus WT and Omicron variant (pVNT50). The secondary immunogenicity endpoints included anti-S1-RBD IgG antibody, S1-RBD:ACE2 binding inhibition, and T-cell responses by ELISpot and Intracellular Staining.ResultsNo post-booster vaccine-related serious adverse events were recorded. The most common solicited adverse events were injection site pain and fatigue, mostly mild and transient. The UB-612 booster prompted a striking upsurge of neutralizing antibodies against live WT Wuhan strain (VNT50, 1,711) associated with unusually high cross-neutralization against Delta variant (VNT50, 1,282); and similarly with a strong effect against pseudovirus WT (pVNT50, 6,245) and Omicron variant (pVNT50, 1,196). Upon boosting, the lower VNT50 and pVNT50 titers of the elderly in the primary series were uplifted to the same levels as those of the young adults. The UB-612 also induced robust, durable VoC antigen-specific Th1-oriented (IFN-γ+-) responses along with CD8+ T-cell (CD107a+-Granzyme B+) cytotoxicity.Conclusions and relevanceWith a pronounced cross-reactive booster effect on B- and T-cell immunity, UB-612 may serve as a universal vaccine booster for comprehensive immunity enhancement against emergent VoCs.Trial registration[ClinicalTrials.gov: NCT04773067]KEY POINTSQuestionFacing ever-emergent SARS-CoV-2 variants and long-haul COVID, can composition-updated new vaccines be constructed capable of inducing striking, durable booster-recalled B/T-immunity to prevent infection by VoCs?FindingsIn a Phase-2 extension study, a booster dose of UB-612 multitope protein-peptide vaccine prompted high viral-neutralizing titers against live wild-type virus (VNT50, 1,711), Delta variant (VNT50, 1,282); pseudovirus wild-type (pVNT50, 6,245) and Omicron variant (pVNT50, 1,196). Robust, durable Th1-IFNγ+ responses and CD8+ T cell-(CD107a+-Granzyme B+) cytotoxic activity were both observed.MeaningUB-612 RBD-sFc vaccine armed with T cell immunity-promoting conserved N, M and S2 Th/CTL epitope peptides may serve as a universal vaccine to fend off new VoCs.