Phase 1 trial of a Candidate Recombinant Virus-Like Particle Vaccine for Covid-19 Disease Produced in Plants
Authors: Ward Brian J , Gobeil Philipe , Séguin Annie , Atkins Judith , Boulay Iohann , Charbonneau Pierre-Yves , Couture Manon , D’Aoust Marc-André , Dhaliwall Jiwanjeet , Finkle Carolyn , Hager Karen , Mahmood Asif , Makarkov Alexander , Cheng Matthew , Pillet Stéphane , Schimke Patricia , St-Martin Sylvie , Trépanier Sonia , Landry Nathalie 
Published: November 2020

Longer Abstract

Background

The stabilized prefusion form of the SARS-CoV-2 spike protein is produced by transient expression in Nicotiana benthamiana. The trimeric spike glycoproteins are displayed at the surface of self-assembling Virus-Like-Particles that mimic the shape and the size of the virus. The candidate vaccine (CoVLP) administered alone or with AS03 or CpG1018 adjuvants was evaluated in a Phase 1 trial in healthy adults. (ClinicalTrials.gov number NCT04450004)

Methods

The study was a randomized, partially-blinded, prime-boost 21 days apart, dose-escalation Phase 1 study intended to assess the safety, tolerability, and immunogenicity of CoVLP at three dose levels (3.75 µg, 7.5 µg, and 15 µg) unadjuvanted or adjuvanted with either CpG 1018 or AS03 in 180 SARS-CoV-2 seronegative healthy adults 18 to 55 years of age. Enrollment was staggered for dose-escalation. At each dose level, the vaccine was initially administered to a small number of subjects. Vaccination of the remaining subjects at the same dose level and the next higher vaccine dose level was administered with approval of an Independent Data Monitoring Committee (IDMC). The same procedure was followed for the second vaccine administration. Monitoring of safety signals was performed throughout the study with pre-determined pausing/stopping rules if there was clear evidence of harmful effects such as severe adverse events (AEs) related to the treatment. The primary endpoints were the safety and tolerability of the vaccine after each dose and the immunogenicity as assessed by neutralizing antibody responses assessed using a vesicular stomatitis virus (VSV) pseudovirion assay and interferon-gamma (IFN-γ) and interleukin-4 (IL-4) ELISpot assays at Days 0, 21 and 42. Secondary endpoints were anti-spike antibody responses by ELISA and neutralizing antibodies measured by live virus plaque reduction neutralization test (PRNT) assay at Days 0, 21 and 42 and immunogenicity with additional safety and immunogenicity endpoints planned for 6-months following the last vaccination. The anti-spike and neutralizing antibody responses were compared with 23 convalescent serum samples from symptomatic Covid-19 patients. We performed a primary analysis at day 42.

Results

A total of 180 subjects (102 females: 78 males: average 34.3 years) were recruited to the study and interim safety and immunogenicity data up to day 42 after the first dose are reported here. There was no obvious CoVLP dose effect in safety outcomes for any of the formulations tested and all formulations were generally well-tolerated. Most solicited local and systemic AEs were mild-moderate and transient. Reactogenicity was increased in all adjuvanted formulations and was generally highest in the CoVLP+AS03 groups. Local and systemic adverse events were reported with similar frequency after the first and second doses in subjects who received either CoVLP alone or CoVLP+CpG1018 but increased in both frequency and severity after the second dose in the CoVLP+AS03 groups. CoVLP alone only elicited a weak total anti-spike IgG response at the highest dose level and little-to-no neutralization antibody response, even after the second dose. Cellular responses in the CoVLP alone groups (IFNγ and IL-4) were detectable after the second dose but were still only marginally above background levels. The addition of either adjuvant substantially increased both antibody and cellular responses at most CoVLP dose levels and changes were most pronounced after the second dose. However, a substantial neutralizing antibody response after the first dose was only seen in all CoVLP+AS03 groups. After the second dose, both total anti-spike IgG and neutralizing antibody titers in the CoVLP+AS03 groups were higher than those in the CoVLP+CpG1018 groups. The antibody titers achieved were either similar to (CoVLP+CpG1018) or at least 10-times higher (CoVLP+AS03) than those seen in convalescent plasma. Administration of CoVLP with either adjuvant also significantly increased the cellular responses. After 2 doses, both IFN-γ and IL-4 responses were significantly increased in the CoVLP+CpG1018 groups. In the CoVLP+AS03 groups, significant increases in the cellular responses were observed after the first dose while IFN-γ and IL-4 increased further in both magnitude and number of subjects responding after the second dose. Again, the cellular responses in the CoVLP+AS03 groups were higher than those seen in the CoVLP+CpG1018 groups.

Conclusion

These data demonstrate that CoVLP administered with either CpG1018 or AS03 has a safety profile similar to other candidate vaccines for SARS-CoV-2. When administered with either AS03 or CpG1018, several of the CoVLP dose levels elicited strong humoral and T cell responses after the second dose. When administered with AS03, even the 3.75 μg CoVLP dose elicited neutralizing antibody titers that were ∼10-times higher than those observed in individuals recovering from Covid-19 as well as consistent and balanced IFN-γ and IL-4 responses. Although many CoVLP formulations were immunogenic, in the absence of established correlates of protection and given the advantages of dose-sparing in the context of the on-going pandemic, these findings suggest that CoVLP (3.75 μg)+AS03 has a good benefit/risk ratio and support the transition of this formulation to studies in expanded populations and to efficacy evaluations

Shorter Abstract

Background

Virus-like particles (VLP) displaying recombinant SARS-CoV-2 spike protein trimers were produced by transient expression in Nicotiana benthamiana. This candidate vaccine (CoVLP) was evaluated in healthy adults 18-55 years of age alone or with AS03 or CpG1018 (NCT04450004).

Methods

This randomized, partially-blinded, two-dose, dose-escalation study assessed CoVLP (3.75, 7.5 or 15 µg/dose) administered intramuscularly alone or with CpG1018 or AS03 in SARS-CoV-2 seronegative adults (18-55 years). Primary endpoints of safety and immunogenicity are reported to day 42. Neutralizing antibodies (NtAb) were assessed using a VSV pseudovirus assay and cellular responses by ELISpot (IFNγ, IL-4).

Results

180 subjects (avg.34.3yrs) were recruited. All formulations were well-tolerated but adjuvants increased reactogenicity. Adverse events were highest in the CoVLP+AS03 groups and increased in frequency/severity after dose two. CoVLP alone elicited weak humoral responses but modest cellular responses were detectable after dose two. Both adjuvants increased immunogenicity significantly, particularly after dose two. A significant NtAb response after dose one was only seen in CoVLP+AS03 groups. The vaccine dose had little impact on levels of NtAb responses achieved in the CoVLP+AS03 groups. Both adjuvants also increased IFNγ and IL-4 responses but these cellular responses also tended to be highest in the AS03-adjuvanted groups.

Conclusion

CoVLP ± adjuvants was well-tolerated. Several adjuvanted formulations elicited strong humoral and T cell responses after dose 2. Even at the lowest CoVLP+AS03 dose, NtAb titers were ∼10-times higher than in convalescent serum with a balanced IFNγ and IL-4 response. These findings support the transition of CoVLP (3.75μg+AS03) to further clinical evaluation.

Research In Context

Evidence before this study

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was recognized as the causative agent of COVID-19 in early 2020. Since that time, >150 candidate vaccines are reported to be under development of which 47 have entered clinical trials (https://www.who.int/publications/m/item/draft-landscape-of-covid-19-candidate-vaccines accessed Nov 4, 2020). No vaccine to prevent COVID-19 has been licensed yet for either emergency or general use in North America or Europe. We searched PubMed for research articles published between July 2019 and November 4, 2020, using the terms “SARS-CoV-2”, “vaccine”, “clinical trial” OR “human”, AND “phase”. The same terms were used to search ClinTrials.gov. No language restrictions were applied. We identified 10 peer-reviewed studies, describing phase 1 or 1/2 trials using a range of novel (eg: RNA, DNA, non-replicating virus vectored) and more traditional vaccine approaches (eg: inactivated virus or recombinant protein ± adjuvants). None of these candidate vaccines was produced in plants. These reports demonstrate that several different vaccination strategies (typically delivered in two doses 14-28 days apart) are capable of eliciting neutralizing antibody responses. In several cases, vaccine-induced cellular responses against SARS-COV-2 antigens - predominantly the spike (S) protein - can also be demonstrated. Although local and systemic adverse events following vaccination have varied between reports, the trials published to date suggest that each of these candidate vaccines is well-tolerated in the context of an evolving pandemic.

Added value of this study

We report the results of the first clinical study of CoVLP, a virus-like particle (VLP) vaccine that is produced by transient transfection of Nicotiana benthamiana plants. These VLPs spontaneously assemble at the plant cell membrane and display SARS-COV-2 trimers of stabilized pre-fusion S protein on their surface. The vaccine was administered as two intramuscular doses 21 days apart at three dose levels (S protein content 3.75, 7,5 or 15μg) alone or adjuvanted with either CpG1018 or AS03. All formulations were well-tolerated although both adjuvants increased reactogenicity. Humoral (anti-S IgG and neutralizing antibodies) as well as cellular responses (IFNg and IL4 ELISpots) were detectable in almost all subjects who received adjuvanted formulations 21 days after the second dose at all COVLP dose levels. Both antibody and cellular responses were highest in subjects who received AS03-adjuvanted formulations. Even at the lowest dose level (3.75μg), the neutralizing antibody titers 21 days after the second dose in subjects who received the AS03-afdjuvanted vaccine were 10-50-fold higher than those seen in subjects recovering from COVID-19 infection.

Implications of all the available evidence

Effective vaccines against SARS-CoV-2 are urgently needed to reduce the burden of disease and contribute to ending the global pandemic. Although no immune correlates for SARS-CoV-2 have been defined, it is likely that both arms of the immune system contribute to protection. After two doses of CoVLP (3.75μg+AS03), strong humoral and cellular responses were induced supporting the further clinical development of this vaccine.