Investigating extensive SARS-CoV-2 neutralizing immunoglobulins from COVID-19 recovered subjects
A recent study posted to the bioRxiv* preprint server discovered immunoglobulins (Igs) with powerful broad-acting neutralizing capacity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from SARS-CoV-2 convalescents. The Igs also neutralized SARS-CoV-2 Omicron BA.2 and BA.1 sublineages.
Background
SARS-CoV-2 emerged at the end of 2019 and has caused over 489 million cases and six million mortalities around the globe to date. SARS-CoV-2 gains entry into the host primarily through its spike (S) protein and host angiotensin-converting enzyme 2 (ACE2) receptor contacts.
Antibody (Ab) and memory B cell responses towards SARS-CoV-2 S protein facilitate long-lasting immune protection from the severe form of coronavirus disease 2019 (COVID-19). Moreover, therapeutic interventions based on Abs could also impart this effect.
About the study
In the current work, the scientists performed a broad immunoprofiling of SARS-CoV-2 among COVID-19-recovered individuals by coupling monoclonal Ab (mAb), cellular, and serological analyses. The team characterized 102 SARS-CoV-2 S protein mAbs derived from the memory B cell IgGs/IGAs of 10 COVID-19 recovered volunteers in an in-depth functional and molecular manner.
Blood samples from SARS-CoV-2 convalescent volunteers were gathered on behalf of the cohorts from the REACTing French COVID-19 and CORSER studies. The participants submitted written informed consent before enrolling in the present study. Subject coding was used to procure data in pseudo-anonymized settings. The collected sera samples were inactivated at 56°C using heat for an hour. Human IgA and IgG Abs were purified from the donor serum employing affinity chromatography.
SARS-CoV-2 D614G mutant strain, Beta, Delta, Gamma, Omicron (BA.2 and BA.1 subtypes), and Alpha variants were used in this work. In addition, SARS-CoV-1, Middle East respiratory syndrome CoV (MERS-CoV), HKU1-CoV, NL63-CoV, 229E-CoV, and OC43-CoV viruses were also used in the study.
Results
The study results depicted that the mAbs derived from convalescent COVID-19 individuals were expressed by a distinct set of immunoglobulin genes. These Abs recognize diverse conformational SARS-CoV-2 S protein epitopes and significantly adhere to the viral S2 subunit.
The COVID-19 recovered volunteers had high anti-trimeric (anti-tri)-S IgG titers, particularly IgG1, consisting of MERS-CoV tri-S protein cross-reactive Abs. The serum anti-receptor-binding domain (RBD) IgG levels were also high. Even though the SARS-CoV-2 seroreactivity of IgG Abs was globally stronger than IgAs, both were linked.
None of the anti-S2 mAbs were neutralizing, but the majority exhibited crystallizable fragment (Fc)-dependent effector activities. A third of the mAbs targeting RBD neutralized SARS-CoV-2 in vitro. The highly powerful mAbs, Cv2.3194 derived from IgG and Cv2.1169 derived from IgA, were completely active against SARS-CoV-2 Delta, Gamma, Beta, and Alpha variants of concern (VOC). In addition, they also substantially hindered the SARS-CoV-2 Omicron BA.2 and BA.1 sublineages infection in vitro.
The Omicron BA.2 and BA.1 VOCs neutralization capacity of Cv2.1169 IgA was considerably enriched by its J-chain dimerization. Cv2.1169 IgA demonstrated therapeutic effects in hamster and mouse COVID-19 models. Structural explorations by X-ray crystallography and cryo-electron microscopy (cryo-EM) depicted the atomic-level mechanism of Cv2.1169 binding and its interaction with the SARS-CoV-2 RBD. The neutralizing titers of IgAs in convalescent COVID-19 patients were associated with the S protein memory IgA B cell frequencies and anti-RBD/-S1 Ab levels, indicating coordinated humoral and cellular immune responses in these individuals in line with previous reports. The authors found a link between T helper 2 (Th2)-like circulating T follicular helper (cTfh) cells and S-reactive resting memory IgG B cells, probably including S-specific cTfh2 cells.
Conclusions
The study findings indicated that COVID-19-convalescent individuals had coordinated humoral immune responses against SARS-CoV-2. The in-depth analyses of SARS-CoV-2 S protein memory B cell mAbs from the COVID-19-recovered subjects revealed the variations in these Abs’ antiviral activities and repertoire. In addition, the B cell-derived mAbs’ antiviral functions were impacted by their directed S protein region containing robust Fc-dependent effectors to the SARS-CoV-2 S2 subunit. Further, strong neutralizers to the SARS-CoV-2 RBD in the B cell-derived Abs also influenced the B cell-derived mAbs antiviral activities.
Among the mAbs, Cv2.3194 and Cv2.1169 cross-neutralized SARS-CoV-2 VOCs such as Omicron BA.2 and BA.1. An IgA memory B cell derived from the mucosa, Cv2.1169, exhibited potency enhancement comparable to IgA dimers and therapeutic effects similar to IgG Abs in animal models. Structural findings imparted mechanistic hints on Cv2.1169 breadth and potency.
Overall, the present work shows key elements of SARS-CoV-2-specific humoral responses and discovered broad and potent SARS-CoV-2 neutralizers with COVID-19 prevention and therapeutic capacities. The study depicts that the powerful broadly neutralizing IgA Abs generated in mucosal tissue of convalescent COVID-19 patients could halt SARS-CoV-2 infection.
Furthermore, this investigation illustrates that Cv2.3194 and Cv2.1169 Abs are good candidates for SARS-CoV-2 treatment and prevention. Moreover, Cv2.3194 and Cv2.1169 Abs with prolonged half-life might impart SARS-CoV-2 protective immunity in immunocompromised people.
*Important notice
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
