Immune response to SARS-CoV-2 variants of concern in vaccinated individuals

The SARS-CoV-2 pandemic virus is consistently evolving with mutations within the receptor binding domain (RBD)1 being of particular concern2-4. To date, there is little research into protection offered following vaccination or infection against RBD mutants in emerging variants of concern (UK3, South African5, Mink6 and Southern California7). To investigate this, serum and saliva samples were obtained from groups of vaccinated (Pfizer BNT-162b28), infected and uninfected individuals. Antibody responses among groups, including salivary antibody response and antibody binding to RBD mutant strains were examined. The neutralization capacity of the antibody response against a patient-isolated South African variant was tested by viral neutralization tests and further verified by an ACE2 competition assay. We found that humoral responses in vaccinated individuals showed a robust response after the second dose. Interestingly, IgG antibodies were detected in large titers in the saliva of vaccinated subjects. Antibody responses showed considerable differences in binding to RBD mutants in emerging variants of concern. A substantial reduction in RBD binding and neutralization was detected for the South African variant. Taken together our data reinforces the importance of administering the second dose of Pfizer BNT-162b2 to acquire high levels of neutralizing antibodies. High antibody titers in saliva suggest that vaccinated individuals may have reduced transmission potential. Substantially reduced neutralization for the South African variant highlights importance of surveillance strategies to detect new variants and targeting these in future vaccines.

Severe COVID-19 infection is associated with increased antibody-mediated platelet apoptosis

The pathophysiology of COVID-19 associated thrombosis seems to be multifactorial, involving interplay between cellular and plasmatic elements of the hemostasis. We hypothesized that COVID-19 is accompanied by platelet apoptosis with subsequent alteration of the coagulation system. We investigated depolarization of mitochondrial inner transmembrane potential ({Delta}{Psi}m), cytosolic calcium (Ca2+) concentration, and phosphatidylserine (PS) externalization by flow cytometry. Platelets from intensive care unit (ICU) COVID-19 patients (n=21) showed higher {Delta}{Psi}m depolarization, cytosolic Ca2+ concentration and PS externalization, compared to healthy controls (n=18) and COVID-19 non-ICU patients (n=4). Moreover significant higher cytosolic Ca2+ concentration and PS was observed compared to septic ICU control group (ICU control). In ICU control group (n=5; ICU non-COVID-19) cytosolic Ca2+ concentration and PS externalization was comparable to healthy control, with an increase {Delta}{Psi}m depolarization. Sera from ICU COVID-19 13 patients induced significant increase in apoptosis markers ({Delta}{Psi}m depolarization, cytosolic Ca2+ concentration and PS externalization). compared to healthy volunteer and septic ICU control. Interestingly, immunoglobulin G (IgG) fractions from COVID-19 patients induced an Fc gamma receptor IIA dependent platelet apoptosis ({Delta}{Psi}m depolarization, cytosolic Ca2+ concentration and PS externalization). Enhanced PS externalization in platelets from ICU COVID-19 patients was associated with increased sequential organ failure assessment (SOFA) score (r=0.5635) and DDimer (r=0.4473). Most importantly, patients with thrombosis had significantly higher PS externalization compared to those without. The strong correlations between apoptosis markers and increased D-Dimer levels as well as the incidence of thrombosis may indicate that antibody-mediated platelet apoptosis potentially contributes to sustained increased thromboembolic risk in ICU COVID-19 patients. Key pointsO_LISevere COVID-19 is associated with increased antibody-mediated platelet apoptosis. C_LIO_LIPlatelet apoptosis in severe COVID-19 is correlated with D-Dimer and higher incidence of thromboembolisms. C_LI