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.

Phenotypes of disease severity in a cohort of hospitalized COVID-19 patients: Results from the IMPACC study

BACKGROUND

Better understanding of the association between characteristics of patients hospitalized with coronavirus disease 2019 (COVID-19) and outcome is needed to further improve upon patient management.

METHODS

Immunophenotyping Assessment in a COVID-19 Cohort (IMPACC) is a prospective, observational study of 1164 patients from 20 hospitals across the United States. Disease severity was assessed using a 7-point ordinal scale based on degree of respiratory illness. Patients were prospectively surveyed for 1 year after discharge for post-acute sequalae of COVID-19 (PASC) through quarterly surveys. Demographics, comorbidities, radiographic findings, clinical laboratory values, SARS-CoV-2 PCR and serology were captured over a 28-day period. Multivariable logistic regression was performed.

FINDINGS

The median age was 59 years (interquartile range [IQR] 20); 711 (61%) were men; overall mortality was 14%, and 228 (20%) required invasive mechanical ventilation. Unsupervised clustering of ordinal score over time revealed distinct disease course trajectories. Risk factors associated with prolonged hospitalization or death by day 28 included age ≥ 65 years (odds ratio [OR], 2.01; 95% CI 1.28-3.17), Hispanic ethnicity (OR, 1.71; 95% CI 1.13-2.57), elevated baseline creatinine (OR 2.80; 95% CI 1.63- 4.80) or troponin (OR 1.89; 95% 1.03-3.47), baseline lymphopenia (OR 2.19; 95% CI 1.61-2.97), presence of infiltrate by chest imaging (OR 3.16; 95% CI 1.96-5.10), and high SARS-CoV2 viral load (OR 1.53; 95% CI 1.17-2.00). Fatal cases had the lowest ratio of SARS-CoV-2 antibody to viral load levels compared to other trajectories over time (p=0.001). 589 survivors (51%) completed at least one survey at follow-up with 305 (52%) having at least one symptom consistent with PASC, most commonly dyspnea (56% among symptomatic patients). Female sex was the only associated risk factor for PASC.

INTERPRETATION

Integration of PCR cycle threshold, and antibody values with demographics, comorbidities, and laboratory/radiographic findings identified risk factors for 28-day outcome severity, though only female sex was associated with PASC. Longitudinal clinical phenotyping offers important insights, and provides a framework for immunophenotyping for acute and long COVID-19.

FUNDING

NIH.

Anti‐S2 Protection in COVID‐19 Infection and SARS‐CoV‐2 Spike Vaccination

The overall goal of this project is to define the magnitude, quality, and duration of the primary immune response elicited against SARS‐CoV‐2 Spike by measuring domain‐specific antibody abundance and binding characteristics in plasmas after infection and vaccination. This investigation has enabled initiation of the screening of convalescent plasma polyclonal antibody (pAb) abundance and specificity through the IMPACC (Immunophenotyping Assessment in a COVID‐19 Cohort) at Drexel U College of Medicine (DUCOM) in collaboration with Tower Health Hospitals. We measured the active concentration of pAbs specific for RBD, S1 and S2 domains using SPR (surface plasmon resonance) molecular interaction analysis. By adopting a kinetic format, a complementary SPR analysis step was optimized to determine the binding rates and affinities of elicited antibodies targeting each domain of the Spike using the same plasma dilution aliquot. Most importantly, we found that the abundance of S2 reactive antibodies was comparable to that of anti‐S1 and RBD in convalescent plasmas. Plasmas obtained up to 6 months post‐vaccination are also becoming available through the TTC (Vaccination TetraCore cohort) assessment at DUCOM, and screening for these has demonstrated that anti‐S2 pAbs are also elicited, though intriguingly in lower abundance than after infection. To assess the importance anti‐S2 antibodies from convalescent plasmas, we purified anti‐S2 fractions by an SPR‐based microaffinity method and used the recovered antibodies in pseudovirus infection inhibition assays of ACE2 expressing cells to measure neutralization activity. Evidence for sustained generation of S2 antibodies up to 6 months post‐infection and occurrence of neutralizing anti‐S2 pAbs has begun to emerge with the possibility that antibodies targeting the S2 domain of the SARS‐CoV‐2 spike protein complex could provide pan‐coronavirus protection against COVID‐19, emerging variants, and other coronaviruses with conserved spike structures. Targeting the more conserved fusion machinery in the virus spike ultimately can lead to therapeutic antibodies or small molecule inhibitors effective on escape variants that occur mainly in S1 as well as other coronaviruses.

The novel adjuvant, ADA-1, restores age-associated defects in the adaptive immune response to Clostridioides difficile infection and vaccination in an aging mouse model

Clostridioides difficile is the leading cause of healthcare-associated infection in the United States. The elderly (≥65) have the greatest risk of C. difficile infection (CDI), severe morbidity, and mortality due to CDI. Though antibody responses against C. difficile Toxin A/B (TcdA/B) following primary infection or vaccination are protective against symptomatic disease, the elderly have impaired humoral responses. Using an aging mouse model, we show that there is significantly greater morbidity and mortality in aged mice during primary CDI compared to young adult mice, as seen in elderly CDI patients. Additionally, during both primary CDI and vaccination against TcdA/B, aged mice have significantly lower anti-TcdA/B antibody titers. This impaired humoral response is the result of poor Tfh and B cell responses following infection and vaccination as aged mice have a significantly lower frequency of Tfh cells and number of anti-TcdA/B B cells compared to young adult mice. While these age-associated defects in the humoral response allow for increased vulnerability to CDI, we show that these defects can be restored with the addition of the novel adjuvant ADA-1 during vaccination of aged mice with TcdA/B-encoding DNA. With ADA-1, the anti-TcdA/B antibody response in aged mice is restored to levels seen in young adult mice. ADA-1 also boosts the frequency of Tfh cells in aged mice following vaccination, suggesting that ADA-1 can restore the development of the aged germinal center reaction following vaccination. As such, this work highlights both the need for the development of a C. difficile vaccine with the elderly in mind and presents ADA-1 as a solution to overcoming age-associated defects in the vaccine response of the elderly.

Supported by Department of Defense Grant: W81XWH0910382 Pennsylvania Department of Health CURE Grant

Comprehensive analysis of the durability and the quality of humoral and T cell responses in SARS-CoV-2 vaccinated and infected subjects

Understanding adaptive immune memory to SARS-CoV-2 is relevant for the development of vaccines and new immunotherapies. Specifically, understanding the interactions between memory B cells and T-cell subsets can shed light on persistent immune memory and its effects on antibody durability and antibody affinity. Studying the frequencies of SARS-CoV-2 memory B cells and antigen-specific T-cells 3–6 months following natural infection or vaccination would aid us in vaccine development and vaccination in infected subjects. In this study, we analyzed these responses in individuals who were hospitalized with COVID-19 (n=20), individuals who were vaccinated after COVID hospitalization (n=20), and uninfected individuals (n=40) with two doses of the Pfizer or Moderna SARS-CoV-2 vaccine. We hypothesize individuals who were vaccinated after hospitalization will have the highest frequency of memory T follicular helper cells, memory B cells and antibody durability. To accomplish this, we will analyze anti-SARS-CoV-2 antibodies, including 7 RBD variants as well as 65-cytokines in all patients via Luminex and examine frequencies of memory T follicular helper cells, persistent memory B-cells specific to SARS-CoV-2 using flow cytometry. All immune responses will be analyzed 3–6 months after hospitalization or after a second vaccination. These results show the differences in durability and quality of humoral and T cell responses between vaccinated and infected subjects.

Supported by grants from NIH supplement #U19AI128910-04S1 

Age-associated defects in the adaptive immune response to Clostridium difficile infection impair the development of a protective immune response in the elderly

Clostridium difficile is the number one cause of healthcare-associated infection in the United States and the most lethal acute enteric pathogen. The elderly (≥65) have the greatest risk of C. difficile infection (CDI) and severe morbidity and mortality due to CDI. Additionally, most recurrent CDIs occur within the elderly. To better understand why the elderly are at greater risk of severe and recurrent CDI, our lab has conducted a longitudinal study of the aging immune response to primary and recurrent CDI in patients at Hahnemann University Hospital. Both elderly and young CDI patients were enrolled in the study, and stool and blood samples were collected at enrollment and 12 days after diagnosis of CDI. Analysis of the samples looking at the humoral response in elderly versus young CDI patients shows that the early humoral response in elderly patients is impaired when compared to young CDI patients. In addition, recurrent CDI patients have similarly defective humoral responses. Finally, preliminary work in an aging mouse model of CDI further supports that age-related defects within the adaptive immune response impair the development of a protective immune response. Since the adaptive immune response to CDI plays an important role in neutralizing toxins produced by C. difficile, an impaired humoral response in both aged and recurrent CDI patients may contribute to the increased risk of infection, morbidity, and mortality observed in elderly patients. Future studies will seek to further characterize the aging immune response using patient samples as well as aging mouse models of CDI.

Using molecular chemokine adjuvants to target the germinal center reaction and enhance HIV-specific humoral responses to DNA immunogens in the mucosa or the periphery

The germinal center (GC) is a dynamic cellular substructure found in lymphoid organs where follicular helper T cells (TFH) provide the necessary proliferation stimuli and cytokine signaling that promote antibody classs-witching and affinity maturation of B cell receptors. DNA vaccines have demonstrated great potential as vaccine immunogens and in vivo electroporation (EP) has enhanced this immunogenicity. The ability to deliver plasmid encoded molecular adjuvants to direct immune responses is an advantage of the DNA platform. Mucosa-associated epithelial chemokine (MEC, or CCL28) is secreted by epithelial cells that line mucosal surfaces, it signals through CC-chemokine receptors 10 and 3 (CCR10 and CCR3) which are expressed on IgA+ plasma cells, TH17 cells, and mucosa-resident antigen presenting cells. IL-12 is a T cell stimulating cytokine that promotes a helper-T cell phenotype. Mice were vaccinated twice intramuscularly with either consensus HIV-1 env DNA alone or DNA plus molecular MEC or IL-12 delivered by in vivo EP. Fourteen days post vaccination, animals were sacrificed and spleens and draining lymph nodes were harvested for flow cytometric analysis. Both MEC and IL-12 significantly increased antigen-specific GC B cells (B220+CD138−Igm−IgD−PNA+CXCR5+gp120+) (11.1% and 8.91% respectively, compared to 6% with DNA alone). Antigen specific isotype- ELISA confirmed that MEC increases IgA in serum (900ng/ml compare to 600ng/ml with DNA alone) and fecal extracts (27ng/ml compared to 22ng/ml), while IL-12 increases IgG in serum alone (2200ng/ml compared to 1300ng/ml with DNA alone). These data indicate that molecular adjuvants can be used to specifically direct immune responses to the mucosa or the periphery.

Characterizing the germinal center response to electroporated DNA immunogens

Most licensed vaccines rely on the production of antibodies that mediate protection from disease. The germinal center (GC) is a dynamic cellular substructure found in lymphoid organs where follicular helper T cells (TFH) provide the necessary proliferation stimuli and cytokine signaling that promote antibody class-switching, somatic hypermutation, and affinity maturation of B cell receptors. Here, mature B cells differentiate into long-lived antibody-secreting cells and memory B cells, instituting the characteristic humoral memory response to vaccination. Although HIV-1 DNA vaccines have been shown to be highly immunogenic, leading to enhanced HIV-1 env epitope breadth and titers in pre-clinical and clinical studies, many questions remain regarding the quality of the humoral immune response and the ability of the DNA antigen/molecular adjuvant to induce long-lived anti-viral antibody that seeds mucosal secondary immune tissues. However, the magnitude and kinetics of the GC response to EP DNA has not been elucidated. Our results indicate that DNA antigens induce a GC response. Antigen-specific GC B cells (B220+CD138−IgM−IgD−PNA+CXCR5+gp120+) are successfully detected by flow cytometry using fluorophore-conjugated HIV-1 gp120 protein after two immunizations in the spleens and draining lymph nodes of vaccinated animals and by antigen-specific ELISpot assay. The presence of antigen-specific antibodies of multiple isotypes is successfully detected in the serum of vaccinated animals via ELISA. These results represent, to our knowledge, the first reports on the magnitude and kinetics of the germinal center response to EP DNA. This work is funded by a W.W. Smith Charitable Foundation grant to MK.

Increase in Incidence of Clostridium Difficile infection in aged models and the need for novel vaccines for the prevention of disease

Clostridium difficile associated disease (CDAD) constitutes a large majority of nosocomial diarrhea cases and is mediated by the effects of two secreted toxins, toxin A (TcdA) and toxin B (TcdB). Key toxin-neutralizing epitopes have been discovered within the carboxy-terminal receptor-binding domain (RBD) of the toxins, which has generated interest in developing the RBD as a vaccine target. The elderly mount an impaired humoral response to C. difficile toxins leading to more severe and recurrent disease; however, it has yet to be determined what underlying mechanisms lead to lower anti-toxin titers, thus higher incidence of severe and recurrent disease. While numerous platforms have been studied, very few data describe the potential of DNA vaccination against CDAD. We created highly optimized plasmids encoding the RBD from TcdA and TcdB and immunized C57BL/6 mice and rhesus macaques intramuscularly followed by in vivo electroporation. In these animal models, vaccination induced significant levels of anti-RBD antibodies within the serum and feces that could neutralize toxins in an in vitro cytotoxicity assay. Moreover, mice that were actively immunized with the DNA vaccine or given passive transfer of immunized non-human primate sera were protected from a lethal intraperitoneal challenge of purified C. difficile toxins. Finally, immunized mice were significantly protected following orogastric challenge with strains of C. difficile spores that were homologous (VPI 10463; n=10/10) and heterologous (hypervirulent UK1; n=4/8) strains to our vaccine antigens. These data demonstrate the robust immunogenicity and efficacy of a TcdA/B RBD-based DNA vaccine in preclinical models of acute toxin-associated disease.

Immunogenicity of Clostridium difficult DNA-based vaccine in an aging mouse model (VAC7P.959)

Clostridium difficile infection (CDI) is a major source of morbidity and mortality, costing our healthcare system ~ $1 billion/year. Over 90% of CDI-related deaths occur in individuals >85yrs. Protection against severe C. difficile-associated disease and recurrent CDI is mediated by host antibody responses against C. difficile toxins. Our goal is to determine the immunogenicity of a DNA based anti-toxin vaccine in an aging mouse model. Young (4 mo.) and old (>18mo.) mice were immunized with our optimized DNA vaccine encoding toxin A and toxin B receptor-binding domain of C. difficile (A-RBD; B-RBD). Day 12 after the first immunization the younger mice had significantly higher IgG titers against A-RBD than older mice (25 ug/ul vs. 5 ug/ul anti-toxin serum IgG). However 10 days post second immunization the both groups had comparable IgG titers (~500 ug/ul IgG) against A-RBD. Anti toxin B-RBD IgG responses in older mice remained lower when compared to young following the second immunization. This suggests our DNA vaccine platform can generate an antibody response against C. difficile toxin in older mice but defects in vaccine priming may be occurring leading to lower titers. Day 14 post second immunization, mice cellular responses were analyzed. Higher frequencies of CD4+/CD44+ (activated) T cells and toxin-specific CD4+ T cells secreting pro-inflammatory cytokines (IFN-gamma, IL2) and Th2 cytokines (IL4, IL10) were generated in older mice.

Immunity to secondary bacterial pneumonia caused by Streptococcus pneumoniae following Influenza A infection (108.10)

IAV is highly contagious and responsible for both seasonal and pandemic flu. However, mortality associated with IAV is mainly due to secondary bacterial infections. The bacterial and host factors that mediate lethality, as well as the protective immune mechanisms against co-infections, are largely unknown. By sequentially infecting mice with IAV and Sp (IAV/Sp), we show that IAV-infected mice are highly susceptible to secondary Sp infections (<10 CFU). Mice lacking IL-12, Type 1 IFN receptors, or both were just as susceptible to an IAV/Sp infection, suggesting these inflammatory cytokines are not involved in lethality. IAV-specific CD8 T cells from IAV/Sp co-infected mice had increased PD-1 expression, a marker associated with dysfunctional/exhausted CD8 T cells. When we immunized mice with different strains of IAV or Sp and challenged them with IAV/Sp co-infection, IAV-immunized mice were fully protected against an IAV/Sp infection. Immunization with one IAV strain provided cross-protection against a co-infection challenge with a different serotype strain of IAV. Immunization with Sp prolonged survival of co-infected mice, and was IL-12 dependent. We conclude that 1) Early inflammatory cytokines are not responsible for death caused by IAV/Sp co-infections, 2) Secondary Sp infections do not affect the magnitude but the quality of IAV-specific CD8 T cell responses, and 3) cross-protective immunity against IAV/Sp co-infections can be induced by immunization with IAV or Sp.