Caitlin A. Williams

The emergence of COVID-19 necessitated the rapid development of vaccines. While highly effective at reducing severe disease and death, breakthrough infections remain a problem as the virus continues to mutate. To help address this issue, we show the utility of a multiplex immunoassay in measuring multiple aspects of the antibody response generated by SARS-CoV-2 vaccines. We use a multiplex immunoassay platform to measure spike-specific IgG concentration, avidity, and receptor-binding inhibition. In addition, we correlate results from an ACE-2 receptor-binding inhibition assay with corresponding data from a SARS-CoV-2 microneutralization assay to establish this inhibitory assay as a potential predictor of virus neutralization. We studied these antibody responses in SARS-CoV-2-naïve and -convalescent vaccinees. Our results showed increased IgG concentrations, avidity, and inhibition following vaccination in both groups. We were also able to differentiate the immune response between the two groups using the multiplex immunoassay platform to look at antibody diversity. The receptor-binding inhibition assay has strong correlations with a cell-based pseudovirus neutralization assay as well as with WT SARS-CoV-2 Washington and Delta variant PRNT₅₀ assays. This suggests that the inhibition assay may be able to simultaneously predict virus neutralization of different SARS-CoV-2 variants. Overall, we show that the developed custom multiplex immunoassay with several experimental variations is a powerful tool in assessing multiple aspects of the SARS-CoV-2 antibody response in vaccinated individuals.

The SARS-CoV-2 pandemic ignited global efforts to rapidly develop testing, therapeutics, and vaccines. However, the rewards of these efforts were slow to reach many low- to middle-income countries (LMIC) across the African continent and globally. Therefore, two bead-based multiplexed serological assays were developed to determine SARS-CoV-2 exposure across four counties in Liberia. This study was conducted during the summer of 2021 on 189 samples collected throughout Grand Bassa, Bong, Margibi, and Montserrado counties. Our multiplexed immunoassay (MIA) detected elevated exposure to SARS-CoV-2 and multiple variant antigens. Additionally, we detected evidence of exposure to Dengue virus serotype 2, Chikungunya virus, and the seasonal coronavirus NL63. Our multiplexed inhibition test (MINT) was developed from the MIA to observe antibody-mediated inhibition of SARS-CoV-2 spike protein binding to its cognate cellular receptor ACE-2. We detected inhibitory antibodies in the tested Liberian samples, which were collectively consistent with a convalescent serological profile. These complementary assays serve to supplement existing serological testing needs and may enhance the technical capacity of scientifically underrepresented regions globally.

Zaire ebolavirus (EBOV) poses a significant threat to public health due to its high case fatality rate and epidemic potential. This is further complicated by the lack of precise immune correlates of protection and difficulties in conducting in vivo animal studies due to species specificity of Ebola virus disease (EVD) and classification as a biosafety level 4 pathogen. Related ebolaviruses have also contributed to the public health threat; Uganda recently experienced an outbreak of Sudan ebolavirus, which also had a high case fatality rate. Vaccination targeting EBOV has demonstrated significant efficacy; however, the protective cellular and humoral responses at play are still poorly understood. Vaccination for vulnerable populations such as pregnant women, young children, and immunocompromised individuals is still limited. Understanding vaccine correlates of protection (vCOP) is key to developing alternative vaccination strategies for these groups. Components of immunity such as neutralizing antibody and cell-mediated immunity are likely responsible for protective responses; however, existing research fails to fully define their roles in protection. Here we investigated vaccine-elicited antibody avidity as a potential correlate of protection and to further characterize the contribution of antibody avidity in protective and nonprotective vaccine responses.

The U.S. Food and Drug Administration only gave emergency use authorization of the BNT162b2 and mRNA-1273 SARS-CoV-2 vaccines for infants 6 months and older in June 2022. Yet questions regarding the durability of vaccine efficacy, especially against emerging variants, in this age group remain. We demonstrated previously that a two-dose regimen of stabilized prefusion Washington SARS-CoV-2 S-2P spike (S) protein encoded by mRNA encapsulated in lipid nanoparticles (mRNA-LNP) or purified S-2P mixed with 3M-052, a synthetic Toll-like receptor (TLR) 7/8 agonist, in a squalene emulsion (Protein+3M-052-SE) was safe and immunogenic in infant rhesus macaques. Here, we demonstrate that broadly neutralizing and spike-binding antibodies against variants of concern (VOCs), as well as T cell responses, persisted for 12 months. At 1 year, corresponding to human toddler age, we challenged vaccinated rhesus macaques and age-matched nonvaccinated controls intranasally and intratracheally with a high dose of heterologous SARS-CoV-2 B.1.617.2 (Delta). Seven of eight control rhesus macaques exhibited severe interstitial pneumonia and high virus replication in the upper and lower respiratory tract. In contrast, vaccinated rhesus macaques had faster viral clearance with mild to no pneumonia. Neutralizing and binding antibody responses to the B.1.617.2 variant at the day of challenge correlated with lung pathology and reduced virus replication. Overall, the Protein+3M-052-SE vaccine provided superior protection to the mRNA-LNP vaccine, emphasizing opportunities for optimization of current vaccine platforms. The observed efficacy of both vaccines 1 year after vaccination supports the implementation of an early-life SARS-CoV-2 vaccine.

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.

The current COVID-19 pandemic has claimed hundreds of thousands of lives and its causative agent, SARS-CoV-2, has infected millions, globally. The highly contagious nature of this respiratory virus has spurred massive global efforts to develop vaccines at record speeds. In addition to enhanced immunogen delivery, adjuvants may greatly impact protective efficacy of a SARS-CoV-2 vaccine. To investigate adjuvant suitability, we formulated protein subunit vaccines consisting of the recombinant S1 domain of SARS-CoV-2 Spike protein alone or in combination with either CoVaccine HT™ or Alhydrogel. CoVaccine HT™ induced high titres of antigen-binding IgG after a single dose, facilitated affinity maturation and class switching to a greater extent than Alhydrogel and elicited potent cell-mediated immunity as well as virus neutralising antibody titres. Data presented here suggests that adjuvantation with CoVaccine HT™ can rapidly induce a comprehensive and protective immune response to SARS-CoV-2.