UB-612 Multitope Vaccine Targeting SARS-CoV-2 Spike and Non-Spike Proteins Provides Broad and Durable Immune Responses

The SARS-CoV-2 non-Spike (S) structural protein targets of nucleocapsid (N), membrane (M) and envelope (E), critical in the host cell interferon response and memory T-cell immunity, have been grossly overlooked since the inception of COVID vaccine development. To pursue a universal (pan-sarbecovirus) vaccine against ever-emergent future mutants, we explored booster immunogenicity of UB-612, a multitope-vaccine that contains S1-RBD-sFc protein and sequence-conserved rationally designed promiscuous Th and CTL epitope peptides on the Sarbecovirus N, M and S2 proteins. To a subpopulation of infection-free participants (aged 18-85 years) involved in a two-dose Phase-2 trial, a UB-612 booster (third dose) was administered 6-8 months after the second dose. The immunogenicity was evaluated at 14 days post-booster with overall safety monitored until the end of study. The booster induced high viral-neutralizing antibodies against live Wuhan WT (VNT50, 1,711) and Delta (VNT50, 1,282); and against pseudovirus WT (pVNT50, 11,167) vs. Omicron BA.1/BA.2/BA.5 variants (pVNT50, 2,314/1,890/854), respectively. The lower primary neutralizing antibodies in the elderly were uplifted upon boosting to approximately the same high level in young adults. UB-612 also induced potent, durable Th1-oriented (IFN-{gamma}+-) responses (peak/pre-boost/post-boost SFU/106 PBMCs, 374/261/444) along with robust presence of cytotoxic CD8+ T cells (peak/pre-boost/post-boost CD107a+-Granzyme B+, 3.6%/1.8%/1.8%). Booster vaccination is safe and well tolerated without SAEs. By recognition against epitopes on Spike (S1-RBD and S2) and non-Spike (N and M) structure proteins, UB-612 provides potent, broad and long-lasting B-cell and T-cell memory immunity and offers a potential as a universal vaccine to fend off Omicrons and new VoCs. SIGNIFICANCE STATEMENTThe Omicron has swept the globe with a rapid succession of dominating sublineages from BA.1, BA.2, to the current BA.5 with increasing infectivity and antibody evasion. Concerningly, the non-Spike structure proteins that promote T-cell immunity are grossly overlooked in vaccine development. Looking beyond short-interval booster jabs and omicron-updated vaccines, a pragmatic approach to curbing ever-emergent new mutants would be "universal (pan-Sarbecovirus) vaccines" targeting conserved nonmutable epitopes on coronavirus. UB-612, a multitope-vaccine armed with Spike (S1-RBD and S2) and non-Spike targets (Nucleocapsid N and Membrane M), allows booster vaccination to elicit potent, broadly-recognizing, durable B- and T-cell memory immunity. Sequence-conserved epitope peptides were rationally-designed from S2, N and M proteins to synergistically enhance memory helper and cytotoxic T-cell immunity and B-cell immunity.