Circulating SARS-CoV-2+ Megakaryocytes Associate with Severe Viral Infection in COVID-19.

Several independent lines of evidence suggest that megakaryocytes are dysfunctional in severe COVID-19. Herein, we characterized peripheral circulating megakaryocytes in a large cohort of COVID-19 inpatients and correlated subpopulation frequencies with clinical outcomes. Using peripheral blood, we show that megakaryocytes are increased in the systemic circulation in COVID-19, and we identify and validate S100A8/A9 as a defining marker of megakaryocyte dysfunction. We further reveal a subpopulation of S100A8/A9+ megakaryocytes that contain SARS-CoV-2 protein and RNA. Using flow cytometry of peripheral blood and in vitro studies on SARS-CoV-2 infected primary human megakaryocytes, we demonstrate that megakaryocytes can transfer viral antigens to emerging platelets. Mechanistically, we show that SARS-CoV-2 containing megakaryocytes are NFκB-activated, via p65 and p52, express NFκB-mediated cytokines, IL-6 and IL-1β, and display high surface expression of TLR2 and TLR4, canonical drivers of NFκB. In a cohort of 218 COVID-19 inpatients, we correlate frequencies of megakaryocyte subpopulations with clinical outcomes and show that SARS-CoV-2 containing megakaryocytes are a strong risk factor for mortality and multi-organ injury, including respiratory failure, mechanical ventilation, acute kidney injury, thrombotic events, and ICU admission. Further, we show that SARS-CoV-2+ megakaryocytes are present in lung and brain autopsy tissues from deceased COVID-19 donors. This study offers the first evidence implicating SARS-CoV-2+ peripheral megakaryocytes in severe disease and suggests that circulating megakaryocytes warrant investigation in inflammatory disorders beyond COVID-19.