Science Bite (3 minute oral presentation with PPT in live session with pre-recorded e-poster) - Students and ECR's only Lorne Infection and Immunity 2022

DURABILITY OF B-CELL MEMORY TO SARS-CoV-2 INFECTION AND VACCINATION (#56)

Gemma E Hartley 1 , Emily S J Edwards 1 , Pei M Aui 1 , Nirupama Varese 1 2 , Stephanie Stojanovic 2 , James McMahon 1 3 , P.Mark Hogarth 1 4 , Robyn E O'Hehir 1 2 , Menno C van Zelm 1 2
  1. Immunology and Pathology, Monash University, Melbourne, VIC, Australia
  2. Allergy, Asthma and Clinical Immunology, Alfred Health, and Department of Allergy, Immunology & Respiratory Medicine, Central Clinical School, Monash University, Melbourne, VIC, Australia
  3. Department of Infectious Diseases, Alfred Health and Monash University, Melbourne, VIC, Australia
  4. Centre for Biomedical Research, Burnet Institute, Melbourne, VIC, Australia

Background: Lasting immunity following SARS-CoV-2 infection or vaccination is questioned because serum antibodies decline in convalescence. However, functional immunity is mediated by long-lived memory T and B (Bmem) cells, which we hypothesise are more accurate markers of long-term immunity.

Objective: To determine the immunophenotype and durability of SARS-CoV-2-specific Bmem cells in individuals after infection or vaccination for SARS-CoV-2.

Methods: Recombinant Spike receptor binding domain (RBD) and Nucleocapsid (NCP) proteins were produced for ELISA-based serology, and biotinylated for fluorescent tetramer formation to identify SARS-CoV-2-specific Bmem cells by flow cytometry. Cells were obtained from 29 convalescent patients and repeat samples were taken from individuals up to one-year post-infection. In addition, samples were collected from healthy adults immunised with the Pfizer mRNA (n=30) and AstraZeneca vector (n=35) SARS-CoV-2 vaccines at three time points: pre-vaccination, 3-4 weeks post-dose 1 and 4-weeks post-dose 2.

Results: All recovered COVID-19 patients had serum IgG that specifically recognised RBD and NCP proteins, with levels declining beyond 20 days post-infection. Vaccination induced anti-RBD antibodies, which were increased after dose 2, whereas no anti-NCP antibodies were formed. In recovered COVID-19 patients, RBD- and NCP-specific Bmem cell numbers remained stable at 1.25-170 cells/ml of blood in all patients for >240 days post-infection and predominantly expressed IgM or IgG1. Individuals immunized with the Pfizer mRNA vaccination generated RBD-specific Bmem cells at 16-85.4 cells/ml blood 1-month post-dose 2 and also predominantly expressed IgM or IgG1.

Conclusion: Detailed immune profiling revealed durable RBD- and NCP-specific Bmem cells in COVID-19 convalescent individuals, and RBD-specific Bmem cells upon Pfizer vaccination. We will now quantify the serological and antigen-specific Bmem cell response in AstraZeneca vaccinated individuals. This will allow us to compare the generation of durable immunological memory between natural infection and vaccination, as well as between mRNA and vector-based SARS-CoV-2 vaccinations. This could inform on the need for future booster vaccinations and levels of protection to emerging variants of concern.