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.

Cross-Protection against MERS-CoV by Prime-Boost Vaccination Using Viral Spike DNA and Protein.

Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe respiratory illness and has a high mortality of ∼34%. However, since its discovery in 2012, an effective vaccine has not been developed for it. To develop a vaccine against multiple strains of MERS-CoV, we targeted spike glycoprotein (S) using prime-boost vaccination with DNA and insect cell-expressed recombinant proteins for the receptor-binding domain (RBD), S1, S2, SΔTM, or SΔER. Our S subunits were generated using an S sequence derived from the MERS-CoV EMC/2012 strain. We examined humoral and cellular immune responses of various combinations with DNA plasmids and recombinant proteins in mice. Mouse sera immunized with SΔER DNA priming/SΔTM protein boosting showed cross-neutralization against 15 variants of S-pseudovirions and the wild-type KOR/KNIH/002 strain. In addition, these immunizations provided full protection against the KOR/KNIH/002 strain challenge in human DPP4 knock-in mice. These findings suggest that vaccination with the S subunits derived from one viral strain can provide cross-protection against variant MERS-CoV strains with mutations in S. DNA priming/protein boosting increased gamma interferon production, while protein-alone immunization did not. The RBD subunit alone was insufficient to induce neutralizing antibodies, suggesting the importance of structural conformation. In conclusion, heterologous DNA priming with protein boosting is an effective way to induce both neutralizing antibodies and cell-mediated immune responses for MERS-CoV vaccine development. This study suggests a strategy for selecting a suitable platform for developing vaccines against MERS-CoV or other emerging coronaviruses.IMPORTANCE Coronavirus is an RNA virus with a higher mutation rate than DNA viruses. Therefore, a mutation in S-protein, which mediates viral infection by binding to a human cellular receptor, is expected to cause difficulties in vaccine development. Given that DNA-protein vaccines promote stronger cell-mediated immune responses than protein-only vaccination, we immunized mice with various combinations of DNA priming and protein boosting using the S-subunit sequences of the MERS-CoV EMC/2012 strain. We demonstrated a cross-protective effect against wild-type KOR/KNIH/002, a strain with two mutations in the S amino acids, including one in its RBD. The vaccine also provided cross-neutralization against 15 different S-pseudotyped viruses. These suggested that a vaccine targeting one variant of S can provide cross-protection against multiple viral strains with mutations in S. The regimen of DNA priming/Protein boosting can be applied to the development of other coronavirus vaccines.

Safety and immunogenicity of a candidate Middle East respiratory syndrome coronavirus viral-vectored vaccine: a dose-escalation, open-label, non-randomised, uncontrolled, phase 1 trial.

BACKGROUND: Cases of Middle East respiratory syndrome coronavirus (MERS-CoV) infection continue to rise in the Arabian Peninsula 7 years after it was first described in Saudi Arabia. MERS-CoV poses a significant risk to public health security because of an absence of currently available effective countermeasures. We aimed to assess the safety and immunogenicity of the candidate simian adenovirus-vectored vaccine expressing the full-length spike surface glycoprotein, ChAdOx1 MERS, in humans. METHODS: This dose-escalation, open-label, non-randomised, uncontrolled, phase 1 trial was done at the Centre for Clinical Vaccinology and Tropical Medicine (Oxford, UK) and included healthy people aged 18-50 years with negative pre-vaccination tests for HIV antibodies, hepatitis B surface antigen, and hepatitis C antibodies (and a negative urinary pregnancy test for women). Participants received a single intramuscular injection of ChAdOx1 MERS at three different doses: the low-dose group received 5 × 109 viral particles, the intermediate-dose group received 2·5 × 1010 viral particles, and the high-dose group received 5 × 1010 viral particles. The primary objective was to assess safety and tolerability of ChAdOx1 MERS, measured by the occurrence of solicited, unsolicited, and serious adverse events after vaccination. The secondary objective was to assess the cellular and humoral immunogenicity of ChAdOx1 MERS, measured by interferon-γ-linked enzyme-linked immunospot, ELISA, and virus neutralising assays after vaccination. Participants were followed up for up to 12 months. This study is registered with ClinicalTrials.gov, NCT03399578. FINDINGS: Between March 14 and Aug 15, 2018, 24 participants were enrolled: six were assigned to the low-dose group, nine to the intermediate-dose group, and nine to the high-dose group. All participants were available for follow-up at 6 months, but five (one in the low-dose group, one in the intermediate-dose group, and three in the high-dose group) were lost to follow-up at 12 months. A single dose of ChAdOx1 MERS was safe at doses up to 5 × 1010 viral particles with no vaccine-related serious adverse events reported by 12 months. One serious adverse event reported was deemed to be not related to ChAdOx1 MERS. 92 (74% [95% CI 66-81]) of 124 solicited adverse events were mild, 31 (25% [18-33]) were moderate, and all were self-limiting. Unsolicited adverse events in the 28 days following vaccination considered to be possibly, probably, or definitely related to ChAdOx1 MERS were predominantly mild in nature and resolved within the follow-up period of 12 months. The proportion of moderate and severe adverse events was significantly higher in the high-dose group than in the intermediate-dose group (relative risk 5·83 [95% CI 2·11-17·42], p<0·0001) Laboratory adverse events considered to be at least possibly related to the study intervention were self-limiting and predominantly mild in severity. A significant increase from baseline in T-cell (p<0·003) and IgG (p<0·0001) responses to the MERS-CoV spike antigen was observed at all doses. Neutralising antibodies against live MERS-CoV were observed in four (44% [95% CI 19-73]) of nine participants in the high-dose group 28 days after vaccination, and 19 (79% [58-93]) of 24 participants had antibodies capable of neutralisation in a pseudotyped virus neutralisation assay. INTERPRETATION: ChAdOx1 MERS was safe and well tolerated at all tested doses. A single dose was able to elicit both humoral and cellular responses against MERS-CoV. The results of this first-in-human clinical trial support clinical development progression into field phase 1b and 2 trials. FUNDING: UK Department of Health and Social Care, using UK Aid funding, managed by the UK National Institute for Health Research.

Characterization of novel monoclonal antibodies against MERS-coronavirus spike protein.

Middle East Respiratory Syndrome coronavirus (MERS-CoV) causes severe pulmonary infection, with ∼35 % mortality. Spike glycoprotein (S) of MERS-CoV is a key target for vaccines and therapeutics because S mediates viral entry and membrane-fusion to host cells. Here, four different S subunit proteins, receptor-binding domain (RBD; 358-606 aa), S1 (1-751 aa), S2 (752-1296 aa), and SΔTM (1-1296 aa), were generated using the baculoviral system and immunized in mice to develop neutralizing antibodies. We developed 77 hybridomas and selected five neutralizing mAbs by immunization with SΔTM against MERS-CoV EMC/2012 strain S-pseudotyped lentivirus. However, all five monoclonal antibodies (mAb) did not neutralize the pseudotyped V534A mutation. Additionally, one mAb RBD-14F8 did not show neutralizing activity against pseudoviruses with amino acid substitution of L506 F or D509 G (England1 strain, EMC/2012 L506 F, and EMC/2012 D509 G), and RBD-43E4 mAb could not neutralize the pseudotyped I529 T mutation, while three other neutralizing mAbs showed broad neutralizing activity. This implies that the mutation in residue 506-509, 529, and 534 of S is critical to generate neutralization escape variants of MERS-CoV. Interestingly, all five neutralizing mAbs have binding affinity to RBD, although most mAbs generated by RBD did not have neutralizing activity. Additionally, chimeric antibodies of RBD-14F8 and RBD-43E4 with human Fc and light chain showed neutralizing effect against wild type MERS-CoV KOR/KNIH/002, similar to the original mouse mAbs. Thus, our mAbs can be utilized for the identification of specific mutations of MERS-CoV.