Neutralizing antibody response in non-hospitalized SARS-CoV-2 patients
Natalia RuétaloRamona BusingerKarina AlthausSimon FinkFelix RuoffKlaus HamprechtBertram FlehmigTamam BakchoulMarkus F. TemplinMichael Schindler
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Abstract The majority of infections with SARS-CoV-2 are asymptomatic or mild without the necessity of hospitalization. It is of importance to reveal if these patients develop an antibody response against SARS-CoV-2 and to define which antibodies confer virus neutralization. We conducted a comprehensive serological survey of 49 patients with a mild course of disease and quantified neutralizing antibody responses against a clinical SARS-CoV-2 isolate employing human cells as targets. Four patients (8%), even though symptomatic, did not develop antibodies against SARS-CoV-2 and two other patients (4%) were only positive in one of the six serological assays employed. For the remainder, antibody response against the S-protein correlated with serum neutralization whereas antibodies against the nucleocapsid were poor predictors of virus neutralization. Regarding neutralization, only six patients (12%) could be classified as highly neutralizers. Furthermore, sera from several individuals with fairly high antibody levels had only poor neutralizing activity. In addition, employing a novel serological Western blot system to characterize antibody responses against seasonal coronaviruses, we found that antibodies against the seasonal coronavirus 229E might contribute to SARS-CoV-2 neutralization. Altogether, we show that there is a wide breadth of antibody responses against SARS-CoV-2 in patients that differentially correlate with virus neutralization. This highlights the difficulty to define reliable surrogate markers for immunity against SARS-CoV-2.Keywords:
Antibody response
Virus quantification
Plaque-forming unit
HSL and HSV
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SARS-CoV-2 variants raise concern because of their high transmissibility and their ability to evade neutralizing antibodies elicited by prior infection or by vaccination. Here, we compared the neutralizing abilities of sera from 70 unvaccinated COVID-19 patients infected before the emergence of variants of concern (VOCs) and of 16 vaccine breakthrough infection (BTI) cases infected with Gamma or Delta against the ancestral B.1 strain, the Gamma, Delta and Omicron BA.1 VOCs using live virus. We further determined antibody levels against the Nucleocapsid (N) and full Spike proteins, the receptor-binding domain (RBD) and the N-terminal domain (NTD) of the Spike protein. Convalescent sera featured considerable variability in the neutralization of B.1 and in the cross-neutralization of different strains. Their neutralizing capacity moderately correlated with antibody levels against the Spike protein and the RBD. All but one convalescent serum failed to neutralize Omicron BA.1. Overall, convalescent sera from patients with moderate disease had higher antibody levels and displayed a higher neutralizing ability against all strains than patients with mild or severe forms of the disease. The sera from BTI cases fell into one of two categories: half the sera had a high neutralizing activity against the ancestral B.1 strain as well as against the infecting strain, while the other half had no or a very low neutralizing activity against all strains. Although antibody levels against the spike protein and the RBD were lower in BTI sera than in unvaccinated convalescent sera, most neutralizing sera also retained partial neutralizing activity against Omicron BA.1, suggestive of a better cross-neutralization and higher affinity of vaccine-elicited antibodies over virus-induced antibodies. Accordingly, the IC50: antibody level ratios were comparable for BTI and convalescent sera, but remained lower in the neutralizing convalescent sera from patients with moderate disease than in BTI sera. The neutralizing activity of BTI sera was strongly correlated with antibodies against the Spike protein and the RBD. Together, these findings highlight qualitative differences in antibody responses elicited by infection in vaccinated and unvaccinated individuals. They further indicate that breakthrough infection with a pre-Omicron variant boosts immunity and induces cross-neutralizing antibodies against different strains, including Omicron BA.1.
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Abstract While there are various attempts to administer COVID-19-convalescent plasmas to SARS-CoV-2-infected patients, neither appropriate approach nor clinical utility has been established. We examined the presence and temporal changes of the neutralizing activity of IgG fractions from 43 COVID-19-convalescent plasmas using cell-based assays with multiple endpoints. IgG fractions from 27 cases (62.8%) had significant neutralizing activity and moderately to potently inhibited SARS-CoV-2 infection in cell-based assays; however, no detectable neutralizing activity was found in 16 cases (37.2%). Approximately half of the patients (~ 41%), who had significant neutralizing activity, lost the neutralization activity within ~ 1 month. Despite the rapid decline of neutralizing activity in plasmas, good amounts of SARS-CoV-2-S1-binding antibodies were persistently seen. The longer exposure of COVID-19 patients to greater amounts of SARS-CoV-2 elicits potent immune response to SARS-CoV-2, producing greater neutralization activity and SARS-CoV-2-S1-binding antibody amounts. The dilution of highly-neutralizing plasmas with poorly-neutralizing plasmas relatively readily reduced neutralizing activity. The presence of good amounts of SARS-CoV-2-S1-binding antibodies does not serve as a surrogate ensuring the presence of good neutralizing activity. In selecting good COVID-19-convalescent plasmas, quantification of neutralizing activity in each plasma sample before collection and use is required.
Convalescent plasma
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Infectivity
Antibody titer
Coxsackievirus
Cytopathic effect
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Studies of neutralizing antibodies in HIV-1 infected individuals provide insights into the quality of the response that should be possible to elicit with vaccines and ways to design effective immunogens. Some individuals make high titres of exceptional broadly reactive neutralizing antibodies that are of particular interest; however, more modest responses may be a reasonable goal for vaccines. We performed a large cross-sectional study to determine the spectrum of neutralization potency and breadth that is seen during chronic HIV-1 infection.Neutralization potency and breadth were assessed with genetically and geographically diverse panels of 205 chronic HIV-1 sera and 219 Env-pseudotyped viruses representing all major genetic subtypes of HIV-1.Neutralization was measured by using Tat-regulated luciferase reporter gene expression in TZM-bl cells. Serum-neutralizing activity was compared with a diverse set of human mAbs that are widely considered to be broadly neutralizing.We observed a uniform continuum of responses, with most sera displaying some level of cross-neutralization, and approximately 50% of sera neutralizing more than 50% of viruses. Titres of neutralization (potency) were highly correlated with breadth. Many sera had breadth comparable to several of the less potent broadly neutralizing human mAbs.These results help clarify the spectrum of serum-neutralizing activity induced by HIV-1 infection and that should be possible to elicit with vaccines. Importantly, most people appear capable of making low to moderate titres of broadly neutralizing antibodies. Additional studies of these relatively common responses might provide insights for practical and feasible vaccine designs.
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Neutralizing antibodies are a major correlate of protection for many viruses including the novel coronavirus SARS-CoV-2. Thus, vaccine candidates should potently induce neutralizing antibodies to render effective protection from infection. A variety of in vitro assays for the detection of SARS-CoV-2 neutralizing antibodies has been described. However, validation of the different assays against each other is important to allow comparison of different studies. Here, we compared four different SARS-CoV-2 neutralization assays using the same set of patient samples. Two assays used replication competent SARS-CoV-2, a focus forming assay and a TCID50-based assay, while the other two assays used replication defective lentiviral or vesicular stomatitis virus (VSV)-based particles pseudotyped with SARS-CoV-2 spike. All assays were robust and produced highly reproducible neutralization titers. Titers of neutralizing antibodies correlated well between the different assays and with the titers of SARS-CoV-2 S-protein binding antibodies detected in an ELISA. Our study showed that commonly used SARS-CoV-2 neutralization assays are robust and that results obtained with different assays are comparable.
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Coronavirus
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Summary The 7 S and 19 S rabbit antibodies to herpes simplex virus (HSV) from early and late (hyperimmune) sera differed in their ability to sensitize virus for subsequent neutralization by either complement (C′) or anti-γ-globulin (GAR). The early 7 S and 19 S antibodies showed low to negligible neutralizing activity in the absence of C′ or GAR. When C′ was added, however, both of these antibodies showed enhanced neutralizing activity. The early 7 S but not the early 19 S antibody was also capable of sensitizing virus for subsequent neutralization by GAR. The late 19 S antibody could neutralize virus in the absence of C′ or GAR, but its activity was enhanced in the presence of C′ or GAR. The late 7 S antibody showed high neutralizing activity in the absence of C′ or GAR. In the presence of C′, the neutralization rate constants (K) but not the neutralization titers of the late 7 S antibody were enhanced. In contrast, the neutralization titers of the late 7 S antibody were enhanced approximately threefold with GAR. The neutralizing activity of the early and late 19 S antibodies with C′ or GAR was sensitive to inactivation by 2-ME. Similarly, the neutralizing activity with C′ of the early 7 S antibody and the enhanced rate of neutralization with C′ of the late 7 S antibody were sensitive to inactivation by 2-ME. In contrast, 2-ME did not reduce the neutralization titers of the early and late 7 S antibodies in the presence of GAR.
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Convalescent plasma
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The experimental conditions most suitable for use in the assay of serum neutralizing antibody specific for bacteriophage ΦX174 by a 50 per cent neutralization method were investigated. Although assays conducted at 37° more readily revealed the presence of background neutralizing activity in the serum of non-immunized germ-free and conventionally reared mice, assays performed at 4° were more suitable for use in detecting the development of newly synthesized neutralizing antibody. In definitive experiments, the SD50 values obtained, i.e. the reciprocal of the serum dilution producing 50 per cent neutralization of added bacteriophage, were found to be directly proportional to the concentration of neutralizing antibody present in serum. The magnitude of the SD50 values obtained suggests that the procedure may be employed advantageously for the detection of very small amounts of antibody and in studies dealing with the kinetics of the antibody response.
Antibody response
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