Particulate multivalent presentation of the receptor binding domain induces protective immune responses against MERS-CoV

Middle East respiratory syndrome coronavirus (MERS-CoV) is a WHO priority pathogen for which vaccines are urgently needed. Using an immune-focusing approach, we created self-assembling particles multivalently displaying critical regions of the MERS-CoV spike protein ─fusion peptide, heptad repeat 2, and receptor binding domain (RBD) ─ and tested their immunogenicity and protective capacity in rabbits. Using a "plug-and-display" SpyTag/SpyCatcher system, we coupled RBD to lumazine synthase (LS) particles producing multimeric RBD-presenting particles (RBD-LS). RBD-LS vaccination induced antibody responses of high magnitude and quality (avidity, MERS-CoV neutralizing capacity, and mucosal immunity) with cross-clade neutralization. The antibody responses were associated with blocking viral replication and upper and lower respiratory tract protection against MERS-CoV infection in rabbits. This arrayed multivalent presentation of the viral RBD using the antigen-SpyTag/LS-SpyCatcher is a promising MERS-CoV vaccine candidate and this platform may be applied for the rapid development of vaccines against other emerging vi

Characteristics of RSV-Specific Maternal Antibodies in Plasma of Hospitalized, Acute RSV Patients under Three Months of Age.

Respiratory syncytial virus (RSV) is the leading cause for respiratory illness that requires hospitalization in infancy. High levels of maternal antibodies can protect against RSV infection. However, RSV-infected infants can suffer from severe disease symptoms even in the presence of high levels of RSV-specific antibodies. This study analyzes several serological characteristics to explore potential deficiencies or surpluses of antibodies that could relate to severe disease symptoms. We compare serum antibodies from hospitalized patients who suffered severe symptoms as well as uninfected infants. Disease severity markers were oxygen therapy, tachypnea, oxygen saturation, admission to the intensive care unit and duration of hospitalization. Antibodies against RSV G protein and a prefusion F epitope correlated with in vitro neutralization. Avidity of RSV-specific IgG antibodies was lower in RSV-infected infants compared to uninfected controls. Severe disease symptoms were unrelated to RSV-specific IgG antibody titers, avidity of RSV-IgG, virus neutralization capacity or titers against pre- and postfusion F or G protein ectodomains and the prefusion F antigenic site Ø. In conclusion, the detailed serological characterization did not indicate dysfunctional or epitope-skewed composition of serum antibodies in hospitalized RSV-infected infants suffering from severe disease symptoms. It remains unclear, whether specific antibody fractions could diminish disease symptoms

Broad receptor engagement of an emerging global coronavirus may potentiate its diverse cross-species transmissibility

Porcine deltacoronavirus (PDCoV), identified in 2012, is a common enteropathogen of swine with worldwide distribution. The source and evolutionary history of this virus is, however, unknown. PDCoV belongs to the Deltacoronavirus genus that comprises predominantly avian CoV. Phylogenetic analysis suggests that PDCoV originated relatively recently from a host-switching event between birds and mammals. Insight into receptor engagement by PDCoV may shed light into such an exceptional phenomenon. Here we report that PDCoV employs host aminopeptidase N (APN) as an entry receptor and interacts with APN via domain B of its spike (S) protein. Infection of porcine cells with PDCoV was drastically reduced by APN knockout and rescued after reconstitution of APN expression. In addition, we observed that PDCoV efficiently infects cells of unusual broad species range, including human and chicken. Accordingly, PDCoV S was found to target the phylogenetically conserved catalytic domain of APN. Moreover, transient expression of porcine, feline, human, and chicken APN renders cells susceptible to PDCoV infection. Binding of PDCoV to an interspecies conserved site on APN may facilitate direct transmission of PDCoV to nonreservoir species, including humans, potentially reflecting the mechanism that enabled a virus, ancestral to PDCoV, to breach the species barrier between birds and mammals. The APN cell surface protein is also used by several members of the Alphacoronavirus genus. Hence, our data constitute the second identification of CoVs from different genera that use the same receptor, implying that CoV receptor selection is subjected to specific restrictions that are still poorly understood

Particulate multivalent presentation of the receptor binding domain induces protective immune responses against MERS-CoV

Middle East respiratory syndrome coronavirus (MERS-CoV) is a WHO priority pathogen for which vaccines are urgently needed. Using an immune-focusing approach, we created self-assembling particles multivalently displaying critical regions of the MERS-CoV spike protein ─fusion peptide, heptad repeat 2, and receptor binding domain (RBD) ─ and tested their immunogenicity and protective capacity in rabbits. Using a "plug-and-display" SpyTag/SpyCatcher system, we coupled RBD to lumazine synthase (LS) particles producing multimeric RBD-presenting particles (RBD-LS). RBD-LS vaccination induced antibody responses of high magnitude and quality (avidity, MERS-CoV neutralizing capacity, and mucosal immunity) with cross-clade neutralization. The antibody responses were associated with blocking viral replication and upper and lower respiratory tract protection against MERS-CoV infection in rabbits. This arrayed multivalent presentation of the viral RBD using the antigen-SpyTag/LS-SpyCatcher is a promising MERS-CoV vaccine candidate and this platform may be applied for the rapid development of vaccines against other emerging viruses such as SARS-CoV-2

RSV-specific IgG titer and RSV-IgG avidity do not correlate with disease severity.

<p>RSV-specific IgG levels in plasma of infants was determined by ELISA using virus particles. RSV-IgG avidity was assessed by supplementing NaSCN during ELISA. (A) RSV-specific IgG levels were displayed versus age. (B-C) Median RSV-specific IgG levels (± IQR) were compared between healthy and RSV-infected infants as well as between RSV patients with and without oxygen therapy. (D-E) Median (± IQR) avidity of RSV-IgG in healthy infants was compared to RSV-infected infants or between RSV patients with or without oxygen therapy. Associations were assessed by Spearman correlation test. Statistical analyses employed Mann Whitney U test. (**P<0.01).</p

RSV-specific IgG against individual RSV glycoproteins do not correlate with disease severity.

<p>RSV glycoprotein-specific antibody levels were determined by ELISA against recombinant, soluble ectodomains. Median IgG levels (± IQR) were compared between healthy and RSV-infected infants as well as between RSV patients with and without oxygen therapy. Glycoproteins used for ELISA coating were (A-B) RSV G protein, (C-D) prefusion F protein, and (E-F) postfusion F protein. (G-H) The relative abundance of antibodies against prefusion F compared to G protein as well as pre- compared to postfusion F protein were categorized assessed by subtracting their levels. The median (± IQR) difference was compared between plasma from healthy infants and RSV patients with or without oxygen therapy. No significant differences were observed by Mann Whitney <i>U</i> test for comparison between two groups and Kruskall-Wallis for comparison between more than two groups.</p

RSV-specific IgG against F protein antigenic sites Ø and I not correlate with disease severity.

<p>The abundance of antibodies in human infant plasma that bind to the prefusion F protein antigenic site Ø or the postfusion F protein antigenic site I was determined by competition with site-specific monoclonal antibodies in ELISA. (A-B) Median (± IQR) IgG titer that blocks 25% binding of D25 (site Ø) were compared between healthy and RSV-infected infants as well as between RSV patients with and without oxygen therapy. (C-D) Median (± IQR) IgG titer that blocks 15% binding of 131-2A (site I) were compared between healthy and RSV-infected infants as well as between RSV patients with and without oxygen therapy. No significant differences were observed by Mann Whitney <i>U</i> test.</p

Study population.

<p>Study population.</p

Antibody properties do not correlate with disease severity parameters.

<p>Antibody properties do not correlate with disease severity parameters.</p

RSV-specific IgG against prefusion F epitope and G protein correlate with neutralization.

<p>Neutralization titers against RSV-X (PRNT) were compared to IgG levels against (A) postfusion F protein, (B) site I (131-2A competition titer), (C) prefusion F protein, (D) site Ø (D25 competition titer) and (E) G protein. Testing for correlation was performed with Spearman correlation test.</p