Evaluation of Oropharyngeal responses to SARS-CoV-2

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications & trials

Abstract

Peripheral blood, tonsil tissues, and adenoid tissues were obtained from 110 children who underwent tonsillectomy at Children's National Hospital from late 2020 to 2021 with the goal of: 1) evaluating the prevalence of prior COVID-19 and epidemiologic risk factors for infection; 2) evaluating the nature of SARS-CoV-2-specific immune responses in the oropharyngeal tissue; and 3)comparing the immune profile in the mucosal tissue and blood of COVID-19-convalescent children and children without prior COVID-19. All patients had to be PCR negative for SARS-CoV-2 prior to surgery. We identified 24 participants with evidence of prior COVID-19 through serologic testing and identification of B cells that recognize the RBD region of the SARS-CoV-2 spike protein by flow cytometry. Only 11 of these participants had a prior positive PCR test for SARS-CoV-2 (25-303 days prior to surgery) and were aware of their prior infection. Participants found to be COVID-19-convalescent during this early period of the pandemic were more likely to be Hispanic and to live in a zip code with a poverty level >10% (Mudd et al. Laryngoscope, 2022). With high dimensional flow cytometry and CITE-seq, we identified SARS-CoV-2-specific memory B cells in the tissue derived from robust geminal center (GC) responses, with evidence of somatic hypermutation and class switching; we also noted overlapping clones in the tonsil and adenoid suggesting migration of cells between these two oropharyngeal tissues. We also found persistent expansion of B and T cell populations involved in the GC and anti-viral response including GC B cells, CD57+PD-1hi GC-Tfh, and CD57+PD1+ CD8 TRM cells, as well as CXCR3+ (IFN-gamma-associated) Tfh populations in COVID-19-convalescent subjects. These changes were most notable in the adenoids, with fewer changes observed in peripheral blood. With CITE-seq, we found more expanded CD8+ and CD4+ T cell clones in convalescent samples, some of which had CDR3 sequences that have been reported to be SARS-CoV-2 specific. Lastly, we found persistent viral RNA by ddPCR as long as 10 months after acute infection. In summary, our results indicate persistent SARS-CoV-2-specific immunity in the upper respiratory tract weeks to months after infection (Xu et al Nat. Immunol. 2023). However, whether intramuscular vaccination elicits similar tissue immunity in the oropharyngeal lymphoid tissue remained an important question. In the last year, we characterized SARS-CoV-2-specific B cell responses in tonsils, adenoids, and peripheral blood of children who had been immunized with a SARS-CoV-2 mRNA vaccine and compared these samples with those from children infected with SARS-CoV-2 or both infected and immunized. Notably, we found SARS-CoV-2-specific B cells in the tonsils and adenoids of children both post-infection and post-vaccination. These were primarily memory B cells but also a small portion of GC B cells, indicating that immune memory can be found and maintained in the upper respiratory tract after intramuscular vaccination as well as after infection. Nonetheless, vaccination and infection generated different quantities and qualities of responses in both the mucosal tissues and blood, with memory B cells expressing different markers associated with distinct functional responses. Our work provides evidence for tissue-specific immunity post-vaccination, but also highlights differences between SARS-CoV-2 specific B cells generated post-infection and post-vaccination, which will provide important insight for evaluating mucosal vaccines (Xu et al, under revision).