Understanding the role of memory re-activation and cross-reactivity in the defense against SARS-CoV-2

Abstract

Recent efforts in understanding the course and severity of SARS-CoV-2 infections have highlighted both potential beneficial as well as detrimental effects of cross-reactive antibodies derived from memory immunity. Specifically, due to a significant degree of sequence similarity between SARS-CoV-2 and other members of the coronavirus family, memory B-cells that emerged from previous infections with endemic human coronaviruses (HCoVs) could be re-activated upon encountering the newly emerged SARS-CoV-2, thus prompting the production of cross-reactive antibodies. Understanding the affinity and concentration of these potentially cross-reactive antibodies to the new SARS-CoV-2 antigens is therefore particularly important when assessing both existing immunity against common HCoVs and adverse effects like antibody-dependent enhancement (ADE) in COVID-19. However, these two fundamental parameters cannot easily be deconvoluted by surface-based assays like enzyme-linked immunosorbent assays (ELISAs) which are routinely used to assess cross-reactivity. Here, we have used microfluidic antibody-affinity profiling (MAAP) to quantitatively evaluate the humoral immune response in COVID-19 convalescent patients by determining both antibody affinity and concentration against spike antigens of SARS-CoV-2 directly in nine convalescent COVID-19 patient and three pre-pandemic sera that were seropositive for common HCoVs. All 12 sera contained low concentrations of high affinity antibodies against spike antigens of HCoV-NL63 and HCoV-HKU1, indicative of past exposure to these pathogens, while the affinity against the SARS-CoV-2 spike protein was lower. These results suggest that cross-reactivity as a consequence of memory re-activation upon an acute SARS-CoV-2 infection may not be a significant factor in generating immunity against SARS CoV-2.

Serological fingerprints link antiviral activity of therapeutic antibodies to affinity and concentration

“…At the lowest antibody concentrations, in the absence of binding, all three types of RBD (wild type, Delta, and Omicron) displayed R h of approx. 3.4 nm, as observed previously 17,19,20 . The complex sizes with both antibodies were as observed previously for the binding of monoclonal antibodies to spike RBD 17 .…”

“…At the lowest antibody concentrations, in the absence of binding, wild type, Delta, and Omicron spike RBDs displayed R h values of 3.40 nm (SD = 0.27 nm), as observed previously 18,20,21 .…”

“…To address this issue, we recently introduced microfluidic affinity profiling (MAAP) which utilizes MDS to provide a fingerprint of the antibodies able to bind an antigen probe. Specifically, the fingerprint consists of the in-solution K D and the concentration of antibody binding sites in any complex biological background [17][18][19][20] . To assess the functional immune response against SARS-CoV-2, MAAP is used as a new type of serological assay that allows simultaneous determination of antibody affinity against a fluorescently labeled antigen probe as well as the concentration of the binding antibodies directly in biological samples.…”

“…Generally, affinities of serum antibodies and their specific concentrations are difficult to measure. To address this issue, we recently introduced microfluidic affinity profiling (MAAP) 18,20,21,32 as an advanced serological assay which utilizes MDS to provide a fingerprint of the antibodies able to bind an antigen probe. Specifically, the fingerprint consists of the in-solution K D and the concentration of antibody binding sites in any complex biological background.…”

“…Here, we use microfluidic diffusional sizing (MDS) [17][18][19][20] to measure the in-solution binding affinities of the Omicron spike RBD to casirivimab (REGN10933) and imdevimab (REGN10987) which constitute a therapeutic antibody-drug cocktail administered to reduce SARS-CoV-2 viral load and alleviate COVID-19 symptoms. Both antibodies bind wild type and Delta SARS-CoV-2 spike with high affinities and are potent virus neutralizing agents 21 .…”