Interim analysis from a phase 2 randomized trial of EuCorVac-19: a recombinant protein SARS-CoV-2 RBD nanoliposome vaccine.

BACKGROUND: Numerous vaccine strategies are being advanced to control SARS-CoV-2, the cause of the COVID-19 pandemic. EuCorVac-19 (ECV19) is a recombinant protein nanoparticle vaccine that displays the SARS-CoV-2 receptor-binding domain (RBD) on immunogenic nanoliposomes. METHODS: Initial study of a phase 2 randomized, observer-blind, placebo-controlled trial to assess the immunogenicity, safety, and tolerance of ECV19 was carried out between July and October 2021. Two hundred twenty-nine participants were enrolled at 5 hospital sites in South Korea. Healthy adults aged 19-75 without prior known exposure to COVID-19 were vaccinated intramuscularly on day 0 and day 21. Of the participants who received two vaccine doses according to protocol, 100 received high-dose ECV19 (20 µg RBD), 96 received low-dose ECV19 (10 µg RBD), and 27 received placebo. Local and systemic adverse events were monitored. Serum was assessed on days 0, 21, and 42 for immunogenicity analysis by ELISA and neutralizing antibody response by focus reduction neutralization test (FRNT). RESULTS: Low-grade injection site tenderness and pain were observed in most participants. Solicited systemic adverse events were less frequent, and mostly involved low-grade fatigue/malaise, myalgia, and headache. No clinical laboratory abnormalities were observed. Adverse events did not increase with the second injection and no serious adverse events were solicited by ECV19. On day 42, Spike IgG geometric mean ELISA titers were 0.8, 211, and 590 Spike binding antibody units (BAU/mL) for placebo, low-dose and high-dose ECV19, respectively (p < 0.001 between groups). Neutralizing antibodies levels of the low-dose and high-dose ECV19 groups had FRNT50 geometric mean values of 129 and 316, respectively. Boosting responses and dose responses were observed. Antibodies against the RBD correlated with antibodies against the Spike and with virus neutralization. CONCLUSIONS: ECV19 was generally well-tolerated and induced antibodies in a dose-dependent manner that neutralized SARS-CoV-2. The unique liposome display approach of ECV19, which lacks any immunogenic protein components besides the antigen itself, coupled with the lack of increased adverse events during boosting suggest the vaccine platform may be amenable to multiple boosting regimes in the future. Taken together, these findings motivate further investigation of ECV19 in larger scale clinical testing that is underway. TRIAL REGISTRATION: The trial was registered at ClinicalTrials.gov as # NCT04783311.

Intranasal Immunization with Liposome-Displayed Receptor-Binding Domain Induces Mucosal Immunity and Protection against SARS-CoV-2.

The global pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to efforts in developing effective vaccine approaches. Currently, approved coronavirus disease 2019 (COVID-19) vaccines are administered through an intramuscular (I.M.) route. Here, we show that the SARS-CoV-2 spike (S) glycoprotein receptor-binding domain (RBD), when displayed on immunogenic liposomes, can be intranasally (I.N.) administered, resulting in the production of antigen-specific IgA and antigen-specific cellular responses in the lungs. Following I.N. immunization, antigen-presenting cells of the lungs took up liposomes displaying the RBD. K18 human ACE2-transgenic mice that were immunized I.M or I.N with sub-microgram doses of RBD liposomes and that were then challenged with SARS-CoV-2 had a reduced viral load in the early course of infection, with I.M. achieving complete viral clearance. Nevertheless, both vaccine administration routes led to full protection against lethal viral infection, demonstrating the potential for the further exploration and optimization of I.N immunization with liposome-displayed antigen vaccines.

Advanced Materials for SARS-CoV-2 Vaccines.

The ongoing coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory coronavirus 2 (SARS-CoV-2), has killed untold millions worldwide and has hurtled vaccines into the spotlight as a go-to approach to mitigate it. Advances in virology, genomics, structural biology, and vaccine technologies have enabled a rapid and unprecedented rollout of COVID-19 vaccines, although much of the developing world remains unvaccinated. Several new vaccine platforms have been developed or deployed against SARS-CoV-2, with most targeting the large viral Spike immunogen. Those that safely induce strong and durable antibody responses at low dosages are advantageous, as well are those that can be rapidly produced at a large scale. Virtually all COVID-19 vaccines and adjuvants possess nanoscale or microscale dimensions and represent diverse and unique biomaterials. Viral vector vaccine platforms, lipid nanoparticle mRNA vaccines and multimeric display technologies for subunit vaccines have received much attention. Nanoscale vaccine adjuvants have also been used in combination with other vaccines. To deal with the ongoing pandemic, and to be ready for potential future ones, advanced vaccine technologies will continue to be developed in the near future. Herein, the recent use of advanced materials used for developing COVID-19 vaccines is summarized.

Vaccines: SARS-CoV-2 RBD Neutralizing Antibody Induction is Enhanced by Particulate Vaccination (Adv. Mater. 50/2020)

In article number 2005637, Jonathan F. Lovell and co-workers show that the SARS-CoV-2 RBD surface protein becomes a potent immunogen when presented in nanoparticle format. Using a vaccine adjuvant that spontaneously converts soluble recombinant antigens into stable particles, immunization studies in mice and rabbits shows that the particle-based RBD elicits strong immune responses and potent antibodies capable of neutralizing the virus.

SARS-CoV-2 RBD Neutralizing Antibody Induction is Enhanced by Particulate Vaccination.

The receptor-binding domain (RBD) of the SARS-CoV-2 spike protein is a candidate vaccine antigen that binds angiotensin-converting enzyme 2 (ACE2), leading to virus entry. Here, it is shown that rapid conversion of recombinant RBD into particulate form via admixing with liposomes containing cobalt-porphyrin-phospholipid (CoPoP) potently enhances the functional antibody response. Antigen binding via His-tag insertion into the CoPoP bilayer results in a serum-stable and conformationally intact display of the RBD on the liposome surface. Compared to other vaccine formulations, immunization using CoPoP liposomes admixed with recombinant RBD induces multiple orders of magnitude higher levels of antibody titers in mice that neutralize pseudovirus cell entry, block RBD interaction with ACE2, and inhibit live virus replication. Enhanced immunogenicity can be accounted for by greater RBD uptake into antigen-presenting cells in particulate form and improved immune cell infiltration in draining lymph nodes. QS-21 inclusion in the liposomes results in an enhanced antigen-specific polyfunctional T cell response. In mice, high dose immunization results in minimal local reactogenicity, is well-tolerated, and does not elevate serum cobalt levels. Taken together, these results confirm that particulate presentation strategies for the RBD immunogen should be considered for inducing strongly neutralizing antibody responses against SARS-CoV-2.

Inhibition of SARS-CoV-2 viral entry upon blocking N- and O-glycan elaboration.

The Spike protein of SARS-CoV-2, its receptor-binding domain (RBD), and its primary receptor ACE2 are extensively glycosylated. The impact of this post-translational modification on viral entry is yet unestablished. We expressed different glycoforms of the Spike-protein and ACE2 in CRISPR-Cas9 glycoengineered cells, and developed corresponding SARS-CoV-2 pseudovirus. We observed that N- and O-glycans had only minor contribution to Spike-ACE2 binding. However, these carbohydrates played a major role in regulating viral entry. Blocking N-glycan biosynthesis at the oligomannose stage using both genetic approaches and the small molecule kifunensine dramatically reduced viral entry into ACE2 expressing HEK293T cells. Blocking O-glycan elaboration also partially blocked viral entry. Mechanistic studies suggest multiple roles for glycans during viral entry. Among them, inhibition of N-glycan biosynthesis enhanced Spike-protein proteolysis. This could reduce RBD presentation on virus, lowering binding to host ACE2 and decreasing viral entry. Overall, chemical inhibitors of glycosylation may be evaluated for COVID-19.

COVID-19 is an infectious disease caused by the virus SARS-CoV-2. To access the internal machinery necessary for its replication, the virus needs to latch onto and then enter host cells. Such processes rely on specific 'glycoproteins' that carry complex sugar molecules (or glycans), and can be found at the surface of both viruses and host cells. In particular, the viral 'Spike' glycoprotein can attach to human proteins called ACE2, which coat the cells that line the inside of the lungs, heart, kidney and brain. Yet the roles played by glycans in these processes remains unclear. To investigate the role of Spike and ACE-2 glycans, Yang et al. designed a form of SARS-CoV-2 that could be handled safely in the laboratory. How these viruses infect human kidney cells that carry ACE2 was then examined, upon modifying the structures of the sugars on the viral Spike protein as well as the host ACE2 receptor. In particular, the sugar structures displayed by the virus were modified either genetically or chemically, using a small molecule that disrupts the formation of the glycans. Similar methods were also applied to modify the glycans of ACE2. Together, these experiments showed that the sugars present on the Spike protein play a minor role in helping the virus stick to human cells.However, they were critical for the virus to fuse and enter the host cells. These findings highlight the important role of Spike protein sugars in SARS-CoV-2 infection, potentially offering new paths to treat COVID-19 and other coronavirus-related illnesses. In particular, molecules designed to interfere with Spike-proteins and the viral entrance into cells could be less specific to SARS-CoV-2 compared to vaccines, allowing treatments to be efficient even if the virus changes.