ABSTRACT
As new variants of SARS-CoV-2 continue to emerge, it is important to assess the neutralizing capabilities of naturally elicited antibodies against SARS-CoV-2. In the present study, we evaluated the activity of nine anti-SARS-CoV-2 monoclonal antibodies (mAbs), previously isolated from convalescent donors infected with the Wuhan-Hu-1 strain, against the SARS-CoV-2 variants of concern (VOC) Alpha, Beta, Gamma, Delta and Omicron. By testing an array of mutated spike receptor binding domain (RBD) proteins, cell-expressed spike proteins from VOCs, and neutralization of SARS-CoV-2 VOCs as pseudoviuses, or as the authentic viruses in culture, we show that mAbs directed against the ACE2 binding site (ACE2bs) are far more sensitive to viral evolution compared to anti-RBD non-ACE2bs mAbs, two of which kept their potency against all VOCs tested. At the second part of our study, we reveal the neutralization mechanisms at high molecular resolution of two anti-SARS-CoV-2 neutralizing mAbs by structural characterization. We solved the structures of the Delta-neutralizing ACE2bs mAb TAU-2303 with the SARS-CoV-2 spike trimer and RBD at 4.5 [A] and 2.42 [A], respectively, revealing a similar mode of binding to that between the RBD and the ACE2 receptor. Furthermore, we provide five additional structures (at resolutions of 5.54 [A], 7.76 [A], 6.47 [A], 3.45 [A], and 7.32 [A]) of a second antibody, non-ACE2bs mAb TAU-2212, complexed with the SARS-CoV-2 spike trimer. TAU-2212 binds an exclusively quaternary epitope, and exhibits a unique, flexible mode of neutralization that involves transitioning between five different conformations, with both arms of the antibody recruited for cross linking intra- and inter-spike RBD subunits. Our study provides new mechanistic insights about how antibodies neutralize SARS-CoV-2 and its emerging variants and provides insight about the likelihood of reinfections.
ABSTRACT
BackgroundPatients with inflammatory bowel diseases (IBD), specifically those treated with anti-tumor necrosis factor (TNF) biologics are at high risk for vaccine preventable infections. Their ability to mount adequate vaccine responses is unclear. Aimto assess immune responses to mRNA-COVID-19 vaccine, and safety profile, in patients with IBD stratified according to therapy, compared to healthy controls (HC). MethodsProspective, controlled, multi-center Israeli study. Subjects enrolled received two BNT162b2 (Pfizer/BioNTech) doses. Anti-spike (S) antibodies levels and functional activity, anti-TNF levels and adverse events (AEs) were detected longitudinaly. ResultsOverall 258 subjects: 185 IBD (67 treated with anti-TNF), and 73 HC. After the first vaccine dose all HC were seropositive, while some patients with IBD, regardless of treatment, remained seronegative. After the second dose all subjects were seropositive, however anti-S levels were significantly lower in anti-TNF treated compared to untreated patients, and HC (p<0.001; p<0.001, respectively). Neutralizing and inhibitory functions were both lower in anti-TNF treated compared to untreated patients, and HC (p<0.03; p<0.0001, respectively). Anti-TNF drug levels and vaccine responses did not affect anti-S levels. Infection rate ([~]2%) and AEs were comparable in all groups. IBD activity did not change in response to BNT162b2. ConclusionsIn this prospective study in patients with IBD stratified according to treatment all patients mounted an immune response to two doses of BNT162b2. However, its magnitude was significantly lower in patients treated with anti-TNF, regardless of administration timing and drug levels. Vaccine was safe. As vaccine immune response longevity in this group may be limited, vaccine booster dose should be considered.
ABSTRACT
The interactions between antibodies, SARS-CoV-2 and immune cells contribute to the pathogenesis of COVID-19 and protective immunity. To understand the differences between antibody responses in mild versus severe cases of COVID-19, we analyzed the B cell responses in patients 1.5 months post SARS-CoV-2 infection. Severe and not mild infection correlated with high titers of IgG against Spike receptor binding domain (RBD) that were capable of viral inhibition. B cell receptor (BCR) sequencing revealed two VH genes, VH3-38 and VH3-53, that were enriched during severe infection. Of the 22 antibodies cloned from two severe donors, six exhibited potent neutralization against live SARS-CoV-2, and inhibited syncytia formation. Using peptide libraries, competition ELISA and RBD mutagenesis, we mapped the epitopes of the neutralizing antibodies (nAbs) to three different sites on the Spike. Finally, we used combinations of nAbs targeting different immune-sites to efficiently block SARS-CoV-2 infection. Analysis of 49 healthy BCR repertoires revealed that the nAbs germline VHJH precursors comprise up to 2.7% of all VHJHs. We demonstrate that severe COVID-19 is associated with unique BCR signatures and multi-clonal neutralizing responses that are relatively frequent in the population. Moreover, our data support the use of combination antibody therapy to prevent and treat COVID-19.
