IgM N-glycosylation correlates with COVID-19 severity and rate of complement deposition

The glycosylation of IgG plays a critical role during human severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, activating immune cells and inducing cytokine production. However, the role of IgM N-glycosylation has not been studied during human acute viral infection. The analysis of IgM N-glycosylation from healthy controls and hospitalized coronavirus disease 2019 (COVID-19) patients reveals increased high-mannose and sialylation that correlates with COVID-19 severity. These trends are confirmed within SARS-CoV-2-specific immunoglobulin N-glycan profiles. Moreover, the degree of total IgM mannosylation and sialylation correlate significantly with markers of disease severity. We link the changes of IgM N-glycosylation with the expression of Golgi glycosyltransferases. Lastly, we observe antigen-specific IgM antibody-dependent complement deposition is elevated in severe COVID-19 patients and modulated by exoglycosidase digestion. Taken together, this work links the IgM N-glycosylation with COVID-19 severity and highlights the need to understand IgM glycosylation and downstream immune function during human disease.

IgM N-glycosylation correlates with COVID-19 severity and rate of complement deposition

The glycosylation of IgG plays a critical role during human SARS-CoV-2, activating immune cells and inducing cytokine production. However, the role of IgM N-glycosylation has not been studied during acute viral infection in humans. In vitro evidence suggests that the glycosylation of IgM inhibits T cell proliferation and alters complement activation rates. The analysis of IgM N-glycosylation from healthy controls and hospitalized COVID-19 patients reveals that mannosylation and sialyation levels associate with COVID-19 severity. Specifically, we find increased di- and tri-sialylated glycans and altered mannose glycans in total serum IgM in severe COVID-19 patients when compared to moderate COVID-19 patients. This is in direct contrast with the decrease of sialic acid found on the serum IgG from the same cohorts. Moreover, the degree of mannosylation and sialylation correlated significantly with markers of disease severity: D-dimer, BUN, creatinine, potassium, and early anti-COVID-19 amounts of IgG, IgA, and IgM. Further, IL-16 and IL-18 cytokines showed similar trends with the amount of mannose and sialic acid present on IgM, implicating these cytokines' potential to impact glycosyltransferase expression during IgM production. When examining PBMC mRNA transcripts, we observe a decrease in the expression of Golgi mannosidases that correlates with the overall reduction in mannose processing we detect in the IgM N-glycosylation profile. Importantly, we found that IgM contains alpha-2,3 linked sialic acids in addition to the previously reported alpha-2,6 linkage. We also report that antigen-specific IgM antibody-dependent complement deposition is elevated in severe COVID-19 patients. Taken together, this work links the immunoglobulin M N-glycosylation with COVID-19 severity and highlights the need to understand the connection between IgM glycosylation and downstream immune function during human disease.

Lipid nanoparticles (LNP) induce activation and maturation of antigen presenting cells in young and aged individuals

Herein, we studied the impact of empty LNP (eLNP), component of mRNA-based vaccine, on anti-viral pathways and immune function of cells from young and aged individuals. eLNP induced maturation of monocyte derived dendritic cells (MDDCs). We further show that eLNP upregulated CD40 and induced cytokine production in multiple DC subsets and monocytes. This coincided with phosphorylation of TANK binding kinase 1 (pTBK1) and interferon response factor 7 (pIRF7). In response to eLNP, healthy older adults (>65 yrs) have decreased CD40 expression, and IFN-γ output compared to young adults (<65 yrs). Additionally, cells from older adults have a dysregulated anti-viral signaling response to eLNP stimulation, measured by the defect in type I IFN production, and phagocytosis. Overall, our data show function of eLNP in eliciting DC maturation and innate immune signaling pathways that is impaired in older adults resulting in lower immune responses to SARS-CoV-2 mRNA-based vaccines.

Lipid nanoparticles (LNP) induce activation and maturation of antigen presenting cells in young and aged individuals

Despite the overwhelming success of mRNA-based vaccine in protecting against SARS-CoV-2 infection and reducing disease severity and hospitalization, little is known about the role lipid nanoparticles (LNP) play in initiating immune response. In this report we studied the adjuvantive impact of empty LNP with no mRNA cargo (eLNP) on anti-viral pathways and immune function of cells from young and aged individuals. We found that eLNP induced maturation of monocyte derived dendritic cells by measuring the expression of CD40, CD80, HLA-DR and production of cytokines including IFN-α,IL-6, IFN-γ, IL-12, and IL-21. Flow cytometry analysis of specific dendritic cell subsets showed that eLNP can induce CD40 expression and cytokine production in cDC1, cDC2 and monocytes. Empty LNP (eLNP) effects on dendritic cells and monocytes coincided with induction pIRF7 and pTBK1, which are both important in mitigating innate immune signaling. Interestingly our data show that in response to eLNP stimulus at 6 and 24 hrs, aged individuals have decreased CD40 expression and reduced IFN- γ output compared to young adults. Furthermore, we show that cDC1, cDC2, and CD14 ^dim CD16 ⁺ monocytes from healthy aged individuals have dysregulated anti-viral signaling response to eLNP stimulation as measured by the defect in type I IFN production, phosphorylation of IRF7, TBK-1, and immune function like phagocytosis. These data showed a novel function of eLNP in eliciting DC maturation and innate immune signaling pathways and that some of these functions are impaired in older individuals providing some suggestion of why older individuals (> 65 yrs of age) respond display lower immune responses and adverse events to SARS-CoV-2 mRNA-based vaccines.

Aging alters antiviral signaling pathways resulting in functional impairment in innate immunity in response to pattern recognition receptor agonists

The progressive impairment of immunity to pathogens and vaccines with aging is a significant public health problem as the world population shifts to an increased percentage of older adults (> 65). We have previously demonstrated that cells obtained from older volunteers have delayed and defective induction of type I interferons and T cell and B cell helper cytokines in response to TLR ligands when compared to those from adult subjects. However, the underlying intracellular mechanisms are not well described. Herein, we studied two critical pathways important in the production of type I interferon (IFN), the interferon response factor 7 (pIRF7), and TANK-binding kinase (pTBK-1). We show a decrease in pIRF7 and pTBK-1 in cross-priming dendritic cells (cDC1s), CD4⁺ T cell priming DCs (cDC2s), and CD14^dimCD16⁺ vascular patrolling monocytes from older adults (n = 11) following stimulation with pathway-specific agonists in comparison with young individuals (n = 11). The decrease in these key antiviral pathway proteins correlates with decreased phagocytosis, suggesting impaired function in Overall, our findings describe molecular mechanisms which explain the innate functional impairment in older adults and thus could inform us of novel approaches to restore these defects.

Improved Durability to SARS-CoV-2 Vaccine Immunity following Coimmunization with Molecular Adjuvant Adenosine Deaminase-1

Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines have demonstrated strong immunogenicity and protection against severe disease, concerns about the duration and breadth of these responses remain. In this study, we show that codelivery of plasmid-encoded adenosine deaminase-1 (pADA) with SARS-CoV-2 spike glycoprotein DNA enhances immune memory and durability in vivo. Coimmunized mice displayed increased spike-specific IgG of higher affinity and neutralizing capacity as compared with plasmid-encoded spike-only-immunized animals. Importantly, pADA significantly improved the longevity of these enhanced responses in vivo. This coincided with durable increases in frequencies of plasmablasts, receptor-binding domain-specific memory B cells, and SARS-CoV-2-specific T follicular helper cells. Increased spike-specific T cell polyfunctionality was also observed. Notably, animals coimmunized with pADA had significantly reduced viral loads compared with their nonadjuvanted counterparts in a SARS-CoV-2 infection model. These data suggest that pADA enhances immune memory and durability and supports further translational studies.

Adenosine deaminase-1 (ADA-1) induces maturation and skewing of cytokine and chemokine production in dendritic cells to improve adaptive immune responses

Dendritic cells (DCs) are critical mediators of antigen-specific immunity through their ability to present antigen and drive T cell differentiation into different effector subsets such as follicular helper T cells (TFH). TFH cells provide both physical and cytokine-mediated stimuli to B cells resulting in somatic hypermutation and class-switching of B cell receptors. Molecules that target TFH cells, such as adenosine deaminase-1 (ADA-1), would improve humoral immunity. We have previously demonstrated that co-delivery of plasmid-encoded adenosine deaminase with an HIV-1 envelope and SARS-CoV-2 DNA vaccines in vivo, enhanced both humoral and cellular responses. However, the mechanism by which ADA-1 is acting as an adjuvant remains to be elucidated. To this end, we treated monocyte-derived DCs from healthy human donors in vitro with recombinant ADA-1 protein and evaluated the expression of maturation markers, cytokines and chemokines. ADA-1-treated DCs had a significantly increased expression of CD40 and CD86 as well as HLA-DR compared to their unstimulated, immature counterparts. The level of co-stimulatory marker and HLA-DR expression on ADA-1-treated DCs was similar to that on LPS/IFN-γ-treated DCs, indicating ADA-1-mediated DC maturation. ADA-1-treated DCs also exhibited a significant increase in IL-6, IL-1β and CXCL13 expression. IL-6 is a key pro-TFH cytokine and IL-1β and CXCL13 may play a role in TFH cell differentiation, function, and proliferation. Ongoing studies are aimed to drive ADA-1 overexpression in DCs and evaluate effects on antigen presentation. Overall, elucidating the mechanism of ADA-1’s adjuvanticity will allow for its progression as a clinical adjuvant.

This work was supported by funding to Dr. Elias Haddad from NIH 5RO1AI106482-01A and 1U19 AI128910-01.

Pre-vaccination frequency of circulatory Tfh is associated with robust immune response to TV003 dengue vaccine

It has been estimated that more than 390 million people are infected with Dengue virus every year; around 96 millions of these infections result in clinical pathologies. To date, there is only one licensed viral vector-based Dengue virus vaccine CYD-TDV approved for use in dengue endemic areas. While initially approved for administration independent of serostatus, the current guidance only recommends the use of this vaccine for seropositive individuals. Therefore, there is a critical need for investigating the influence of Dengue virus serostatus and immunological mechanisms that influence vaccine outcome. Here, we provide comprehensive evaluation of sero-status and host immune factors that correlate with robust immune responses to a Dengue virus vector based tetravalent vaccine (TV003) in a Phase II clinical cohort of human participants. We observed that sero-positive individuals demonstrate a much stronger immune response to the TV003 vaccine. Our multi-layered immune profiling revealed that sero-positive subjects have increased baseline/pre-vaccination frequencies of circulating T follicular helper (cTfh) cells and the Tfh related chemokine CXCL13/BLC. Importantly, this baseline/pre-vaccination cTfh profile correlated with the vaccinees' ability to launch neutralizing antibody response against all four sero-types of Dengue virus, an important endpoint for Dengue vaccine clinical trials. Overall, we provide novel insights into the favorable cTfh related immune status that persists in Dengue virus sero-positive individuals that correlate with their ability to mount robust vaccine specific immune responses. Such detailed interrogation of cTfh cell biology in the context of clinical vaccinology will help uncover mechanisms and targets for favorable immuno-modulatory agents.

Co-immunization with adenosine deaminase rescues age-associated impairment of SARS-COV-2 synDNA vaccine-induced responses

SARS-CoV-2 is responsible for a global pandemic claiming over 2 million lives and infecting over 100 million people. Elderly patients display increased COVID-19 morbidity and mortality. Vaccine candidates have been studied and deployed in the clinic. However, age-associated immune deficits are known to cause sub-optimal responses, and the longevity of vaccine-induced responses is under investigation. Germinal center follicular helper T cells (TFH) promote affinity maturation of B cell receptors and memory B cell differentiation and are defined by expression of adenosine deaminase-1 (ADA-1). We investigated the adjuvant properties of plasmid-encoded adenosine deaminase (pADA) in the context of a SARS-CoV-2 spike synDNA antigens. Young and aged mice were immunized with plasmid-encoded spike (pS) alone or co-immunized with pS and pADA and cellular and humoral responses were evaluated. When immunized with pS alone, aged mice had decreased spike-binding IgG and neutralization titers. However, young and aged animals co-immunized with pADA had similar humoral responses. We observed similar trends in serum antibody affinity as measured by SPR. pADA co-immunization also rescued age-associated decreases in spike-specific IFNy secretion in the spleens and lungs of co-immunized aged mice as measured by ELISpot. Finally, preliminary data analysis indicates that co-immunization with pADA significantly impacts viral load in a model of SARS-CoV-2 infection. These data suggest that pADA enhances antigen-specific cellular and humoral immunity in aged mice and supports further study of this molecule as an immunoadjuvant for vaccines targeting elderly populations.

Determining Adenosine Deaminase 1 (ADA-1) Impact on Immune Memory and Durability as a Molecular Adjuvant in a SARS-CoV-2 DNA Vaccine Formulation

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for coronavirus disease of 2019 (COVID-19), has infected millions of people causing a global pandemic. SARS-CoV-2 vaccines candidates have demonstrated acute immunogenicity and protection however, it has yet to be demonstrated whether natural or vaccine induced immunity against SARS-CoV-2 induces long term, protective immunity. In this study we sought to understand if adenosine deaminase (ADA), as a molecular adjuvant, can enhance immune memory and durability in the context of a SARS-CoV-2 DNA vaccine. Mice were immunized with a plasmid encoding for SARS-CoV-2 spike alone or in combination with plasmid encoded ADA. Subsequent B and T cell responses were measured until d60pi. In mice co-immunized with ADA, there were increased concentrations of spike receptor binding domain (RBD)-specific IgG in the sera which were found to bind RBD at an increased affinity as well as exhibit increased neutralization capability against SARS-CoV-2 pseudotyped viruses. Additionally, ADA co-immunized mice exhibited increased frequency of RBD specific memory B cells. In regard to T cell responses, mice co-immunized with ADA exhibited increased spike-specific IFN-γ, TNF-a and IL-2 as measured by flow cytometry and ELISpot. The ADA-enhanced anti-spike antibody durability over time was associated with increased frequencies of T follicular helper cells (TFH). Preliminary analysis supports that co-immunization with pADA impacts viral load in a SARS-CoV-2 infection model. These data suggest that ADA enhances immune memory and durability and supports further study with translational focus for enhancement of vaccines.