High titre neutralizing antibodies in response to SARS-CoV-2 infection require RBD-specific CD4 T cells that include proliferative memory cells. (preprint)

Long-term immunity to SARS-CoV-2 infection, including neutralizing antibodies and T cell-mediated immunity, is required in a very large majority of the population in order to reduce ongoing disease burden. We have investigated the association between memory CD4 and CD8 T cells and levels of neutralizing antibodies in convalescent COVID-19 subjects. Higher titres of convalescent neutralizing antibodies were associated with significantly higher levels of RBD-specific CD4 T cells, including specific memory cells that proliferated vigorously in vitro. Conversely, up to half of convalescent individuals had low neutralizing antibody titres together with a lack of receptor binding domain (RBD)-specific memory CD4 T cells. These low antibody subjects had other, non-RBD, spike-specific CD4 T cells, but with more of an inhibitory Foxp3+ and CTLA-4+ cell phenotype, rather than the effector T-bet+, cytotoxic granzymes+ and perforin+ cells seen in high antibody subjects. Single cell transcriptomics of antigen-specific CD4+ T cells from high antibody subjects revealed heterogenous RBD-specific CD4+ T cells that comprised central memory, transitional memory and Tregs, as well as cytotoxic clusters containing diverse TCR repertoires, that were absent in individuals with low antibody levels. However, vaccination in low antibody convalescent individuals led to a slight but significant improvement in RBD-specific memory CD4 T cells and increased neutralizing antibody titres. Our results suggest that targeting CD4 T cell epitopes proximal to and within the RBD-region should be prioritized in booster vaccines.

SARS-CoV-2 neutralizing antibodies; longevity, breadth, and evasion by emerging viral variants (preprint)

The SARS-CoV-2 antibody neutralization response and its evasion by emerging viral variants are unknown. Antibody immunoreactivity against SARS-CoV-2 antigens and Spike variants, inhibition of Spike-driven virus-cell fusion, and infectious SARS-CoV-2 neutralization were characterized in 807 serial samples from 233 RT-PCR-confirmed COVID-19 individuals with detailed demographics and followed up to seven months. A broad and sustained polyantigenic immunoreactivity against SARS-CoV-2 Spike, Membrane, and Nucleocapsid proteins, along with high viral neutralization were associated with COVID-19 severity. A subgroup of high responders maintained high neutralizing responses over time, representing ideal convalescent plasma therapy donors. Antibodies generated against SARS-CoV-2 during the first COVID-19 wave had reduced immunoreactivity and neutralization potency to emerging Spike variants. Accurate monitoring of SARS-CoV-2 antibody responses would be essential for selection of optimal plasma donors and vaccine monitoring and design.