A Single Dose of COVID-19 mRNA Vaccine Induces Airway Immunity in COVID-19 Convalescent Patients

Background: Mucosal antibodies can prevent virus entry and replication in mucosal epithelial cells and hence virus shedding. Preclinical and clinical studies have shown that a parenteral booster injection of a vaccine against a mucosal pathogen promotes stronger mucosal immune responses following prior infection compared to two injections of a parenteral vaccine. We investigated whether this was also the case for a COVID-19 mRNA vaccine. Methods: Twenty-three COVID-19 convalescent patients and 20 SARS-CoV-2-naive subjects were vaccinated with respectively one and two doses of the Pfizer-BioNTech COVID-19 RNA vaccine. Nasal Epithelial Lining Fluid (NELF) and plasma were collected before and after vaccination and assessed for Immunoglobulin (Ig)G and IgA to Spike and for their ability to inhibit the binding of Spike to its ACE-2 receptor. Blood was analyzed one week after vaccination for the number of Spike-specific Antibody Secreting Cells (ASCs) with a mucosal tropism. Results: In COVID-19 convalescent patients, a single dose of vaccine amplified pre-existing Spike-specific IgG and IgA antibody responses in both NELF and blood against both vaccine homologous and variant strains, including delta. These responses were associated with Spike-specific IgG and IgA ASCs with a mucosal tropism in blood. Nasal IgA and IgG antibody responses were lower in magnitude in SARS-CoV-2-naive subjects after two vaccine doses Conclusion: This study showed that a parenteral booster injection of a COVID-19 RNA vaccine promoted stronger mucosal immune responses in COVID-19 convalescent patients compared to SARS-CoV-2 naive subjects who had received a first vaccine dose.

Antibody in Lymphocyte Supernatant (ALS) responses after oral vaccination with live Shigella sonnei vaccine candidates WRSs2 and WRSs3 and correlation with serum antibodies, ASCs, fecal IgA and shedding

The levels of antigen-specific Antibodies in Lymphocyte Supernatant (ALS) using an ELISA are being used to evaluate mucosal immune responses as an alternate to measuring the number of Antibody Secreting Cells (ASCs) using an ELISpot assay. A recently completed trial of two novel S. sonnei live oral vaccine candidates WRSs2 and WRSs3 established that both candidates were safe, well tolerated and immunogenic in a vaccine dose-dependent manner. Previously, mucosal immune responses were measured by assaying IgA- and IgG-ASC in peripheral blood mononuclear cells (PBMCs). In this report, the magnitude of the S. sonnei antigen-specific IgA- and IgG-ALS responses was measured and correlated with previously described ASCs, serum antibodies, fecal IgA and vaccine shedding. Overall, the magnitude of S. sonnei anti-Invaplex50 ALS was higher than that of LPS or IpaB, and both vaccines demonstrated a more robust IgA-ALS response than IgG; however, compared to WRSs3, the magnitude and percentage of responders were higher among WRSs2 recipients for IgA- or IgG-ALS. All WRSs2 vaccinees at the two highest doses responded for LPS and Invaplex50-specific IgA-ALS and 63–100% for WRSs3 vaccinees responded. Regardless of the vaccine candidate, vaccine dose or detecting antigen, the kinetics of ALS responses were similar peaking on days 7 to 9 and returning to baseline by day 14. The ALS responses were vaccine-specific since no responses were detected among placebo recipients at any time. A strong correlation and agreement between responders/non-responders were noted between ALS and other mucosal (ASC and fecal IgA) and systemic (serum antibody) immune responses. These data indicate that the ALS assay can be a useful tool to evaluate mucosal responses to oral vaccination, an observation noted with trials of other bacterial diarrheal pathogens. Furthermore, this data will guide the list of immunological assays to be conducted for efficacy trials in different populations. It is hoped that an antigen-specific-ALS titer may be a key mucosal correlate of protection, a feature not currently available for any Shigella vaccines candidates. https://clinicaltrials.gov/show/NCT01336699.

Sublingual Immunization with Chimeric C1q/CD40 Ligand/HIV Virus-like Particles Induces Strong Mucosal Immune Responses against HIV

Development of a vaccine that can elicit robust HIV specific antibody responses in the mucosal compartments is desired for effective prevention of HIV via sexual transmission. However, the current mucosal vaccines have either poor immunogenicity when administered orally or invite safety concerns when administered intranasally. Sublingual immunization has received more attention in recent years based on its efficiency in inducing systemic and mucosal immune responses in both mucosal and extra-mucosal tissues. To facilitate the transport of the immunogen across the sub-mucosal epithelial barrier, we found that CD91, the receptor of C1q, is prevalently expressed in the sublingual mucosal lining, and thus, a modified chimeric C1q surface conjugated CD40L/HIV VLP was generated. The ability of this chimeric C1q/CD40L/HIV VLP to bind, cross the epithelial layer, access and activate the sub-mucosal layer dendritic cells (DCs), and ultimately induce enhanced mucosal and systemic immune responses against HIV is evaluated in this study. We found that C1q/CD40L/HIV VLPs have enhanced binding, increased transport across the epithelial layer, and upregulate DC activation markers as compared to CD40L/HIV VLPs alone. Mice immunized with C1q/ CD40L/HIV VLPs by sublingual administration showed higher levels of IgA salivary antibodies against both HIV Gag and Env than mice immunized with CD40L/HIV VLPs. Moreover, sublingual immunization with C1q/CD40L/HIV VLPs induced more Env- and Gag-specific IFN-γ producing T cells than the CD40L/HIV VLPs group. Interestingly, C1q/CD40L/HIV VLP immunization can also induce more mucosal homing T cells than that in CD40L/HIV VLP group. Our data suggest that incorporation of C1q to CD40L/HIV VLPs is a promising novel strategy and that the sublingual immunization can be a favorite immunization route for HIV mucosal vaccines.

Mucosal immune responses against an oral ETEC vaccine evaluated in clinical trials

Enterotoxigenic Escherichia coli, ETEC, is a leading cause of mortality and morbidity in children in low-income countries. We have tested an oral ETEC vaccine, ETVAX, consisting of inactivated E. coli over-expressing the most prevalent colonization factors and a toxoid, LCTBA, administered together with a mucosal adjuvant, dmLT, for capacity to induce mucosal immune responses and immunological memory against the primary vaccine antigens, i.e. colonization factors, LTB and O antigen. The studies show that ETVAX could induce strong intestine-derived and/or fecal immune responses in a majority of vaccinated Swedish adults and in different age groups, including infants, in Bangladesh.

Molecular Characterization and Expression Analysis of Intercellular Adhesion Molecule-1 (ICAM-1) Genes in Rainbow Trout (Oncorhynchus mykiss) in Response to Viral, Bacterial and Parasitic Challenge

The intercellular adhesion molecule-1 (ICAM-1), known as CD54, is a transmembrane cell surface glycoprotein that interacts with two integrins (i.e., LFA-1 and Mac-l) important for trans-endothelial migration of leukocytes. The level of ICAM-1 expression is upregulated in response to some inflammatory stimulations, including pathogen infection and proinflammatory cytokines. Yet, to date, our knowledge regarding the functional role of ICAM-1 in teleost fish remains largely unknown. In this study, we cloned and characterized the sequence of ICAM-1 in rainbow trout (Oncorhynchus mykiss) for the first time, which exhibited that the molecular features of ICAM-1 in fishes were relatively conserved compared with human ICAM-1. The transcriptional level of ICAM-1 was detected in 12 different tissues, and we found high expression of this gene in the head kidney, spleen, gills, skin, nose, and pharynx. Moreover, upon stimulation with infectious hematopoietic necrosis virus (IHNV), Flavobacterium columnare G4 (F. columnare), and Ichthyophthirius multifiliis (Ich) in rainbow trout, the morphological changes were observed in the skin and gills, and enhanced expression of ICAM-1 mRNA was detected both in the systemic and mucosal tissues. These results indicate that ICAM-1 may be implicated in the mucosal immune responses to viral, bacterial, and parasitic infections in teleost fish, meaning that ICAM-1 emerges as a master regulator of mucosal immune responses against pathogen infections in teleost fish.

DCLK1 isoforms and aberrant Notch signaling in the regulation of human and murine colitis

Alternative promoter usage generates long and short isoforms (DCLK1-L and DCLK1-S) of doublecortin-like kinase-1 (DCLK1). Tight control of Notch signaling is important to prevent and restitute inflammation in the intestine. Our aim was to investigate whether Notch1–DCLK1 axis regulates the mucosal immune responses to infection and whether this is phenocopied in human models of colitis. In the FFPE (formalin-fixed paraffin-embedded) sections prepared from the colons of ulcerative colitis (UC) and immune-mediated colitis (IRAEC) patients, expression of DCLK1 isoforms correlated positively with Notch1 and negatively with a transcriptional repressor, FoxD3 (Forkhead Box D3). DCLK1 protein staining in these sections was predominantly sub-epithelial (stromal) wherein DCLK1 co-localized with NICD, CD68, CD11c, and neutrophil elastase (NE). NE also co-stained with Citrullinated-H3 indicating the presence of neutrophil extracellular traps. In human neutrophils, elevated levels of DCLK1-S, CXCL-10, Ly6G, MPO, NE, and Notch1/2 in LPS-treated cells were inhibited when LPS was added in conjunction with Notch blocker dibenzazepine (DBZ; LPS + DBZ group). In CR-infected Rag1−/− mice, higher levels of DCLK1 in the colonic crypts were inhibited when mice received DBZ for 10 days coincident with significant dysbiosis, barrier disruption, and colitis. Concurrently, DCLK1 immunoreactivity shifted toward the stroma in CR + DBZ mice with predominance of DCLK1-S that coincided with higher Notch1 levels. Upon antibiotic treatment, partial restoration of crypt DCLK1, reduction in MPO activity, and increased survival followed. When intestinal epithelial cell-specific Dclk1-knockout (Dclk1ΔIEC) or Dclk1ΔIEC;Rag1−/− double knockout (DKO) mice were infected with CR and given a single dose of DBZ, they developed barrier defect and severe colitis with higher levels of stromal DCLK1-S, Ly6G, NE, and Notch1. We therefore propose that, by regulating the mucosal immune responses, the Notch–DCLK1 axis may be integral to the development of murine or human colitis.