SARS-CoV-2−Reactive Mucosal B Cells in the Upper Respiratory Tract of Uninfected Individuals

ABSTRACT

PURPOSE OF THE STUDY To investigate the role of the mucosal immune system of the upper respiratory tract in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection by exploration of the presence of pre-existing mucosal SARS-CoV-2-reactive B cells in tonsillar tissue specimens. STUDY POPULATION Tonsillar tissue from pediatric patients who underwent tonsillectomy at The Hospital for Sick Children in Toronto, Canada in 2015 to 2016, before the COVID-19 pandemic. METHODS: Using flow cytometry and fluorescently labeled tetramers to the SARS-CoV-2 Spike protein (S-protein), SARS-CoV-2-reactive B cells were isolated from tonsillar tissue. Monoclonal antibodies (mAbs) recognizing the SARS-CoV-2 S-protein were generated from these B-cells using single-cell real time-polymerase chain reaction and RNA sequencing. Human embryonic kidney derived cell lines expressing SARS-CoV-2 S protein were used for in vitro assays assessing the mAbs' SARS-CoV-2 recognition and Ag binding. RESULTS: Pre-existing SARS-CoV-2-reactive B cells were identified and isolated from prepandemic human tonsillar tissue. The mAbs generated from these B cells recognized the S-protein of the wild-type SARS-CoV-2 virus. Additionally, the mAbs originated from naïve B cells as well as Ag-experienced memory B cells, germinal center B cells, and plasma cells. These mAbs were able to partially block binding in vitro by consistently showing >20% inhibition of S-protein binding. The antibodies did not react to the S-proteins of endemic coronaviruses, human coronavirus-OC43 and human coronavirus-229E. The antibodies also demonstrated significantly reduced recognition of the SARS-CoV-2 B.1.1.7 and B1.315 variants. CONCLUSIONS: B cells contained in the lymphoid tissues of the upper respiratory tract can contain pre-existing SARS-CoV-2 reactive antibodies. Monoclonal antibodies generated by these B-cells demonstrated in vitro SARS-CoV-2 recognition and neutralizing potential. However, these mAbs had reduced binding to the Spike proteins of SARS-CoV-2 variants and did not recognize endemic coronaviruses. The existence of these antibodies may explain the variation in COVID-19 symptom severity since these pre-existing Abs may lead to rapid engagement of the SARS-CoV-2 pathogen as the mucosal surface of the respiratory tract is a main point of contact.