Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a pandemic with millions of human infections. One limitation to the evaluation of potential therapies and vaccines to inhibit ...SARS-CoV-2 infection and ameliorate disease is the lack of susceptible small animals in large numbers. Commercially available laboratory strains of mice are not readily infected by SARS-CoV-2 because of species-specific differences in their angiotensin-converting enzyme 2 (ACE2) receptors. Here, we transduced replication-defective adenoviruses encoding human ACE2 via intranasal administration into BALB/c mice and established receptor expression in lung tissues. hACE2-transduced mice were productively infected with SARS-CoV-2, and this resulted in high viral titers in the lung, lung pathology, and weight loss. Passive transfer of a neutralizing monoclonal antibody reduced viral burden in the lung and mitigated inflammation and weight loss. The development of an accessible mouse model of SARS-CoV-2 infection and pathogenesis will expedite the testing and deployment of therapeutics and vaccines.
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•Adenovirus transduction of human ACE2 enables SARS-CoV-2 infection of BALB/c mice•High levels of viral RNA and infectious SARS-CoV-2 accumulate in lungs•Mice transduced with human ACE2 develop viral pneumonia after SARS-CoV-2 infection•Neutralizing mAbs protect from SARS-CoV-2-induced lung infection and inflammation
Laboratory mice transduced with adenoviruses encoding human ACE2 are permissive for SARS-CoV-2 and develop pneumonia. Passive transfer of a neutralizing monoclonal antibody reduces lung infection, inflammation, and disease.
Long-lived bone marrow plasma cells (BMPCs) are a persistent and essential source of protective antibodies
. Individuals who have recovered from COVID-19 have a substantially lower risk of ...reinfection with SARS-CoV-2
. Nonetheless, it has been reported that levels of anti-SARS-CoV-2 serum antibodies decrease rapidly in the first few months after infection, raising concerns that long-lived BMPCs may not be generated and humoral immunity against SARS-CoV-2 may be short-lived
. Here we show that in convalescent individuals who had experienced mild SARS-CoV-2 infections (n = 77), levels of serum anti-SARS-CoV-2 spike protein (S) antibodies declined rapidly in the first 4 months after infection and then more gradually over the following 7 months, remaining detectable at least 11 months after infection. Anti-S antibody titres correlated with the frequency of S-specific plasma cells in bone marrow aspirates from 18 individuals who had recovered from COVID-19 at 7 to 8 months after infection. S-specific BMPCs were not detected in aspirates from 11 healthy individuals with no history of SARS-CoV-2 infection. We show that S-binding BMPCs are quiescent, which suggests that they are part of a stable compartment. Consistently, circulating resting memory B cells directed against SARS-CoV-2 S were detected in the convalescent individuals. Overall, our results indicate that mild infection with SARS-CoV-2 induces robust antigen-specific, long-lived humoral immune memory in humans.
SARS-CoV-2 mRNA-based vaccines are about 95% effective in preventing COVID-19
. The dynamics of antibody-secreting plasmablasts and germinal centre B cells induced by these vaccines in humans remain ...unclear. Here we examined antigen-specific B cell responses in peripheral blood (n = 41) and draining lymph nodes in 14 individuals who had received 2 doses of BNT162b2, an mRNA-based vaccine that encodes the full-length SARS-CoV-2 spike (S) gene
. Circulating IgG- and IgA-secreting plasmablasts that target the S protein peaked one week after the second immunization and then declined, becoming undetectable three weeks later. These plasmablast responses preceded maximal levels of serum anti-S binding and neutralizing antibodies to an early circulating SARS-CoV-2 strain as well as emerging variants, especially in individuals who had previously been infected with SARS-CoV-2 (who produced the most robust serological responses). By examining fine needle aspirates of draining axillary lymph nodes, we identified germinal centre B cells that bound S protein in all participants who were sampled after primary immunization. High frequencies of S-binding germinal centre B cells and plasmablasts were sustained in these draining lymph nodes for at least 12 weeks after the booster immunization. S-binding monoclonal antibodies derived from germinal centre B cells predominantly targeted the receptor-binding domain of the S protein, and fewer clones bound to the N-terminal domain or to epitopes shared with the S proteins of the human betacoronaviruses OC43 and HKU1. These latter cross-reactive B cell clones had higher levels of somatic hypermutation as compared to those that recognized only the SARS-CoV-2 S protein, which suggests a memory B cell origin. Our studies demonstrate that SARS-CoV-2 mRNA-based vaccination of humans induces a persistent germinal centre B cell response, which enables the generation of robust humoral immunity.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the global COVID-19 pandemic. Rapidly spreading SARS-CoV-2 variants may jeopardize newly introduced antibody and vaccine ...countermeasures. Here, using monoclonal antibodies (mAbs), animal immune sera, human convalescent sera and human sera from recipients of the BNT162b2 mRNA vaccine, we report the impact on antibody neutralization of a panel of authentic SARS-CoV-2 variants including a B.1.1.7 isolate, chimeric strains with South African or Brazilian spike genes and isogenic recombinant viral variants. Many highly neutralizing mAbs engaging the receptor-binding domain or N-terminal domain and most convalescent sera and mRNA vaccine-induced immune sera showed reduced inhibitory activity against viruses containing an E484K spike mutation. As antibodies binding to spike receptor-binding domain and N-terminal domain demonstrate diminished neutralization potency in vitro against some emerging variants, updated mAb cocktails targeting highly conserved regions, enhancement of mAb potency or adjustments to the spike sequences of vaccines may be needed to prevent loss of protection in vivo.
Better vaccines against influenza virus are urgently needed to provide broader protection against diverse strains, subtypes, and types. Such efforts are assisted by the identification of novel ...broadly neutralizing epitopes targeted by protective antibodies. Influenza vaccine development has largely focused on the hemagglutinin, but the other major surface antigen, the neuraminidase, has reemerged as a potential target for universal vaccines. We describe three human monoclonal antibodies isolated from an H3N2-infected donor that bind with exceptional breadth to multiple different influenza A and B virus neuraminidases. These antibodies neutralize the virus, mediate effector functions, are broadly protective in vivo, and inhibit neuraminidase activity by directly binding to the active site. Structural and functional characterization of these antibodies will inform the development of neuraminidase-based universal vaccines against influenza virus.
The perspective that naive B-cell recognition of antigen in the absence of T-cell help causes cell death or anergy is supported by in vivo studies of B cells that are continuously exposed to ...self-antigens. However, intravital imaging suggests that early B-cell recognition of large foreign antigens may be transient. Whether B cells are tolerized or can be recruited into humoural immune responses following such encounters is not clear. Here we show that in the presence of T-cell help, single transient antigen acquisition is sufficient to recruit B cells into the germinal centre and induce memory and plasma cell responses. In the absence of T-cell help, transiently antigen-primed B cells do not undergo apoptosis in vivo; they return to quiescence and are recruited efficiently into humoural responses upon reacquisition of antigen and T-cell help.
Germinal centres (GC) are lymphoid structures in which B cells acquire affinity-enhancing somatic hypermutations (SHM), with surviving clones differentiating into memory B cells (MBCs) and long-lived ...bone marrow plasma cells
(BMPCs). SARS-CoV-2 mRNA vaccination induces a persistent GC response that lasts for at least six months in humans
. The fate of responding GC B cells as well as the functional consequences of such persistence remain unknown. Here, we detected SARS-CoV-2 spike protein-specific MBCs in 42 individuals who had received two doses of the SARS-CoV-2 mRNA vaccine BNT162b2 six month earlier. Spike-specific IgG-secreting BMPCs were detected in 9 out of 11 participants. Using a combined approach of sequencing the B cell receptors of responding blood plasmablasts and MBCs, lymph node GC B cells and plasma cells and BMPCs from eight individuals and expression of the corresponding monoclonal antibodies, we tracked the evolution of 1,540 spike-specific B cell clones. On average, early blood spike-specific plasmablasts exhibited the lowest SHM frequencies. By contrast, SHM frequencies of spike-specific GC B cells increased by 3.5-fold within six months after vaccination. Spike-specific MBCs and BMPCs accumulated high levels of SHM, which corresponded with enhanced anti-spike antibody avidity in blood and enhanced affinity as well as neutralization capacity of BMPC-derived monoclonal antibodies. We report how the notable persistence of the GC reaction induced by SARS-CoV-2 mRNA vaccination in humans culminates in affinity-matured long-term antibody responses that potently neutralize the virus.
Modern vaccines must be designed to generate long-lasting, high-affinity, and broadly neutralizing Ab responses against pathogens. The diversity of B cell clones recruited into germinal center (GC) ...responses is likely to be important for the Ag-neutralization potential of the Ab-secreting cells and memory cells generated upon immunization. However, the factors that influence the diversity of B cell clones recruited into GCs are unclear. As recirculating naive Ag-specific B cells arrive in Ag-draining secondary lymphoid organs, they may join the ongoing GC response. However, the factors that limit their entry are not well understood, and it is not known how that depends on the stage of the ongoing follicular T cell and GC B cell response. In this article, we show that, in mice, naive B cells have a limited window of time during which they can undergo Ag-driven activation and join ongoing immunization-induced GC responses. However, preloading naive B cells with even a threshold-activating amount of Ag is sufficient to rescue their entry into the GC response during its initiation, peak, and contraction. Based on these results, we suggest that productive acquisition of Ag may be one of the main factors limiting entry of new B cell clones into ongoing immunization-triggered GC responses.
Influenza B virus (IBV) infections can cause severe disease in children and the elderly. Commonly used antivirals have lower clinical effectiveness against IBV compared to influenza A viruses (IAV). ...Neuraminidase (NA), the second major surface protein on the influenza virus, is emerging as a target of broadly protective antibodies that recognize the NA active site of IAVs. However, similarly broadly protective antibodies against IBV NA have not been identified. Here, we isolated and characterized human monoclonal antibodies (mAbs) that target IBV NA from an IBV-infected patient. Two mAbs displayed broad and potent capacity to inhibit IBV NA enzymatic activity, neutralize the virus in vitro, and protect against lethal IBV infection in mice in prophylactic and therapeutic settings. These mAbs inserted long CDR-H3 loops into the NA active site, engaging residues highly conserved among IBV NAs. These mAbs provide a blueprint for the development of improved vaccines and therapeutics against IBVs.
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•Generation of seven human monoclonal antibodies to influenza B virus neuraminidase•Two antibodies, 1G05 and 2E01, are broadly cross-reactive•1G05 and 2E01 are potently protective against lethal Influenza B infection in mice•1G05 and 2E01 bind conserved residues in the Influenza B neuraminidase active site
Influenza B virus (IBV) infections cause severe disease. Madsen et al. develop and characterize human monoclonal antibodies that possess broad and potent capacities to inhibit IBV neuraminidase enzymatic activity, neutralize the virus in vitro, and protect against lethal IBV infection in mice in prophylactic and therapeutic settings.
In this study we profiled vaccine-induced polyclonal antibodies as well as plasmablast-derived mAbs from individuals who received SARS-CoV-2 spike mRNA vaccine. Polyclonal antibody responses in ...vaccinees were robust and comparable to or exceeded those seen after natural infection. However, the ratio of binding to neutralizing antibodies after vaccination was greater than that after natural infection and, at the monoclonal level, we found that the majority of vaccine-induced antibodies did not have neutralizing activity. We also found a co-dominance of mAbs targeting the NTD and RBD of SARS-CoV-2 spike and an original antigenic-sin like backboost to spikes of seasonal human coronaviruses OC43 and HKU1. Neutralizing activity of NTD mAbs but not RBD mAbs against a clinical viral isolate carrying E484K as well as extensive changes in the NTD was abolished, suggesting that a proportion of vaccine-induced RBD binding antibodies may provide substantial protection against viral variants carrying single E484K RBD mutations.
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•Antibody responses after SARS-CoV-2 mRNA vaccination target RBD, NTD, and S2•SARS-CoV-2 mRNA vaccination induces a high rate of non-neutralizing antibodies•Crossreactive antibodies to seasonal β-coronaviruses are induced by vaccination•Variant mutation N501Y enhances affinity to human ACE2 while E484K reduces it
An analysis of mRNA vaccine-induced polyclonal antibodies and plasmablast-derived monoclonal antibodies from individuals vaccinated against SARS-CoV-2 identifies a high proportion of non-neutralizing antibodies and the induction of cross-reactive antibodies to seasonal coronaviruses and also maps the regions in the spike protein that are targeted, even among viral variants.
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