Single-vial filovirus glycoprotein vaccines: Biophysical characteristics and immunogenicity after co-lyophilization with adjuvant

Thermostable bivalent filovirus vaccine protects against severe and lethal Sudan ebolavirus and marburgvirus infection

Although two vaccines for Zaire ebolavirus (EBOV) have been licensed and deployed successfully to combat recurring outbreaks of Ebolavirus Disease in West Africa, there are no vaccines for two other highly pathogenic members of the Filoviridae, Sudan ebolavirus (SUDV) and Marburg marburgvirus (MARV). The results described herein document the immunogenicity and protective efficacy in cynomolgus macaques of a single-vial, thermostabilized (lyophilized) monovalent (SUDV) and bivalent (SUDV & MARV) protein vaccines consisting of recombinant glycoproteins (GP) formulated with a clinical-grade oil-in-water nanoemulsion adjuvant (CoVaccine HT™). Lyophilized formulations of the vaccines were reconstituted with Water for Injection and used to immunize groups of cynomolgus macaques before challenge with a lethal dose of a human SUDV or MARV isolate. Sera collected after each of the three immunizations showed near maximal GP-binding IgG concentrations starting as early as the second dose. Most importantly, the vaccine candidates (monovalent or bivalent) provided 100% protection against severe and lethal filovirus disease after either SUDV or MARV infection. Although mild, subclinical infection was observed in a few macaques, all vaccinated animals remained healthy and survived the filovirus challenge. These results demonstrate the value that thermostabilized protein vaccines could provide for addressing an important gap in preparedness for future filovirus outbreaks.

Maternal Immunization Using a Protein Subunit Vaccine Mediates Passive Immunity against Zaire ebolavirus in a Murine Model

The Ebola virus has caused outbreaks in Central and West Africa, with high rates of morbidity and mortality. Clinical trials of recombinant virally vectored vaccines did not explicitly include pregnant or nursing women, resulting in a gap in knowledge of vaccine-elicited maternal antibody and its potential transfer. The role of maternal antibody in Ebola virus disease and vaccination remains understudied. Here, we demonstrate that a protein subunit vaccine can elicit robust humoral responses in pregnant mice, which are transferred to pups in breastmilk. These findings indicate that an intramuscular protein subunit vaccine may elicit Ebola-specific IgG capable of being transferred across the placenta as well as into the breastmilk. We have previously shown protective efficacy with these vaccines in non-human primates, offering a potential safe and practical alternative to recombinant virally vectored vaccines for pregnant and nursing women in Ebola endemic regions.

Lyophilized Filovirus Glycoprotein Vaccines: Peroxides in a Vaccine Formulation with Polysorbate 80-Containing Adjuvant are Associated with Reduced Neutralizing Antibody Titers in Both Mice and Non-Human Primates

Zaire ebolavirus, Sudan ebolavirus, and Marburg marburgvirus are the filoviruses most commonly associated with human disease. Previously, we administered a three-dose regimen of trivalent vaccines comprising glycoprotein antigens from each virus in mice and non-human primates (NHPs). The vaccines, which contained a polysorbate 80-stabilized squalane-in-water emulsion adjuvant and were lyophilized from a solution containing trehalose, produced high antibody levels against all three filovirus antigens. Subsequently, single-vial formulations containing a higher concentration of adjuvant were generated for testing in NHPs, but these vaccines elicited lower neutralizing antibody titers in NHPs than previously tested formulations. In order to explain these results, in the current work we measured the size of adjuvant emulsion droplets and the peroxide levels present in the vaccines after lyophilization and reconstitution and tested the effects of these variables on the immune response in mice. Increases in squalane droplet sizes were observed when the ratio of adjuvant to trehalose was increased beyond a critical value, but antibody and neutralizing antibody titers in mice were independent of the droplet size. Higher levels of peroxides in the vaccines correlated with higher concentrations of adjuvant in the formulations, and higher peroxide levels were associated with increased levels of oxidative damage to glycoprotein antigens. Neutralizing titers in mice were inversely correlated with peroxide levels in the vaccines, but peroxide levels could be reduced by adding free methionine, resulting in retention of high neutralizing antibody titers. Overall, the results suggest that oxidation of glycoprotein antigens by peroxides in the polysorbate 80-stabilized squalane-in-water emulsion adjuvant, but not lyophilization-induced increases in adjuvant emulsion droplet size may have been responsible for the decreased neutralizing titers seen in formulations containing higher amounts of adjuvant.

A Recombinant Subunit Vaccine Induces a Potent, Broadly Neutralizing, and Durable Antibody Response in Macaques against the SARS-CoV-2 P.1 (Gamma) Variant

FDA-approved and emergency use-authorized vaccines using new mRNA and viral-vector technology are highly effective in preventing moderate to severe disease; however, information on their long-term efficacy and protective breadth against severe acute respiratory syndrome coronavirus 2 variants of concern (VOCs) is currently scarce. Here, we describe the durability and broad-spectrum VOC immunity of a prefusion-stabilized spike (S) protein adjuvanted with liquid or lyophilized CoVaccine HT in cynomolgus macaques. This recombinant subunit vaccine is highly immunogenic and induces robust spike-specific and broadly neutralizing antibody responses effective against circulating VOCs (B.1.351 [Beta], P.1 [Gamma], and B.1.617 [Delta]) for at least three months after the final boost. Protective efficacy and postexposure immunity were evaluated using a heterologous P.1 challenge nearly three months after the last immunization. Our results indicate that while immunization with both high and low S doses shorten and reduce viral loads in the upper and lower respiratory tract, a higher antigen dose is required to provide durable protection against disease as vaccine immunity wanes. Histologically, P.1 infection causes similar COVID-19-like lung pathology as seen with early pandemic isolates. Postchallenge IgG concentrations were restored to peak immunity levels, and vaccine-matched and cross-variant neutralizing antibodies were significantly elevated in immunized macaques indicating an efficient anamnestic response. Only low levels of P.1-specific neutralizing antibodies with limited breadth were observed in control (nonvaccinated but challenged) macaques, suggesting that natural infection may not prevent reinfection by other VOCs. Overall, these results demonstrate that a properly dosed and adjuvanted recombinant subunit vaccine can provide protective immunity against circulating VOCs for at least three months.

Pathogenicity and virulence of Marburg virus

Marburg virus (MARV) has been a major concern since 1967, with two major outbreaks occurring in 1998 and 2004. Infection from MARV results in severe hemorrhagic fever, causing organ dysfunction and death. Exposure to fruit bats in caves and mines, and human-to-human transmission had major roles in the amplification of MARV outbreaks in African countries. The high fatality rate of up to 90% demands the broad study of MARV diseases (MVD) that correspond with MARV infection. Since large outbreaks are rare for MARV, clinical investigations are often inadequate for providing the substantial data necessary to determine the treatment of MARV disease. Therefore, an overall review may contribute to minimizing the limitations associated with future medical research and improve the clinical management of MVD. In this review, we sought to analyze and amalgamate significant information regarding MARV disease epidemics, pathophysiology, and management approaches to provide a better understanding of this deadly virus and the associated infection.

Adjuvants Differentially Modulate the Immunogenicity of Lassa Virus Glycoprotein Subunits in Mice

Lassa Fever (LF) is an acute viral hemorrhagic fever caused by Lassa virus (LASV) that is primarily transmitted through contact with wild rodents in West Africa. Although several advanced vaccine candidates are progressing through clinical trials, some effective vaccines are virally vectored and thus require a stringent cold-chain, making distribution to rural and resource-poor areas difficult. Recombinant subunit vaccines are advantageous in this aspect as they can be thermostabilized and deployed with minimal storage and transportation requirements. However, antigen dose and adjuvant formulation must be carefully selected to ensure both the appropriate humoral and cell-mediated immune responses are elicited. In this study, we examine the immunogenicity of a two-step immunoaffinity-purified recombinant LASV glycoprotein (GP) with five clinical- and preclinical-grade adjuvants. Swiss Webster mice immunized intramuscularly with 2 or 3 doses of each vaccine formulation showed complete seroconversion and maximal GP-specific antibody response after two immunizations. Formulations with GPI-0100, LiteVax, Montanide™ ISA 51, and Montanide™ ISA 720 induced both IgG1 and IgG2 antibodies suggesting a balanced Th1/Th2 response, whereas formulation of LASV GP with Alhydrogel elicited a IgG1-dominant response. Splenocytes secreting both Th1 and Th2 cytokines i.e., IFN-γ, TNF-α, IL-2, IL-4 and IL-5, were observed from mice receiving both antigen doses formulated with ISA 720, LiteVax and GPI-0100. However, robust, multifunctional T-cells were only detected in mice receiving a higher dose of LASV GP formulated with GPI-0100. Our results emphasize the importance of careful adjuvant selection and lay the immunological basis for a recombinant subunit protein LF vaccine formulation.

Durable Immunity to Ricin Toxin Elicited by a Thermostable, Lyophilized Subunit Vaccine

The development of vaccines against biothreat toxins like ricin (RT) is considered an integral component of the U.S. national security efforts. RiVax is a thermostable, lyophilized RT subunit vaccine adsorbed to aluminum salt adjuvant intended for use by military personnel and first responders. Phase 1 studies indicated that RiVax is safe and immunogenic, while a three-dose intramuscular vaccination regimen in nonhuman primates elicited protection against lethal dose RT challenge by aerosol. Here, we investigated, in a mouse model, the durability of RiVax-induced antibody responses and corresponding immunity to lethal dose RT challenge. Groups of mice were subcutaneously administered 3 or 1 μg of RiVax on days 0 and 21 and challenged with 10× 50% lethal dose (LD50) RT by injection at six different intervals over the course of 12 months. Serum antibody titers and epitope-specific competition assays were determined prior to each challenge. We report that the two-dose, 3-μg regimen conferred near-complete protection against RT challenge on day 35 and complete protection thereafter (challenge days 65, 95, 125, 245, and 365). The two-dose, 3-μg regimen was superior to the 1-μg regimen as revealed by slight differences in survival and morbidity scores (e.g., hypoglycemia, weight loss) on challenge days 35 and 365. In separate experiments, a single 3-μg RiVax vaccination proved only marginally effective at eliciting protective immunity to RT, underscoring the necessity of a prime-boost regimen to achieve full and long-lasting protection against RT. IMPORTANCE Ricin toxin (RT) is a notorious biothreat, as exposure to even trace amounts via injection or inhalation can induce organ failure and death within a matter of hours. In this study, we advance the preclinical testing of a candidate RT vaccine known as RiVax. RiVax is a recombinant nontoxic derivative of RT's enzymatic subunit that has been evaluated for safety in phase I clinical trials and efficacy in a variety of animal models. We demonstrate that two doses of RiVax are sufficient to protect mice from lethal dose RT challenge for up to 1 year. We describe kinetics and other immune parameters of the antibody response to RiVax and discuss how these immune factors may translate to humans.

Recombinant protein subunit SARS-CoV-2 vaccines formulated with CoVaccine HT adjuvant induce broad, Th1 biased, humoral and cellular immune responses in mice

The speed at which several COVID-19 vaccines went from conception to receiving FDA and EMA approval for emergency use is an achievement unrivaled in the history of vaccine development. Mass vaccination efforts using the highly effective vaccines are currently underway to generate sufficient herd immunity and reduce transmission of the SARS-CoV-2 virus. Despite the most advanced vaccine technology, global recipient coverage, especially in resource-poor areas remains a challenge as genetic drift in naïve population pockets threatens overall vaccine efficacy. In this study, we described the production of insect-cell expressed SARS-CoV-2 spike protein ectodomain constructs and examined their immunogenicity in mice. We demonstrated that, when formulated with CoVaccine HTTM adjuvant, an oil-in-water nanoemulsion compatible with lyophilization, our vaccine candidates elicit a broad-spectrum IgG response, high neutralizing antibody (NtAb) titers against SARS-CoV-2 prototype and variants of concern, specifically B.1.351 (Beta) and P.1. (Gamma), and an antigen-specific IFN-γ secreting response in outbred mice. Of note, different ectodomain constructs yielded variations in NtAb titers against the prototype strain and some VOC. Dose response experiments indicated that NtAb titers increased with antigen dose, but not adjuvant dose, and may be higher with a lower adjuvant dose. Our findings lay the immunological foundation for the development of a dry-thermostabilized vaccine that is deployable without refrigeration.