Proteomic analysis of circulating immune cells identifies cellular phenotypes associated with COVID-19 severity

Certain serum proteins, including C-reactive protein (CRP) and D-dimer, have prognostic value in patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Nonetheless, these factors are non-specific, providing limited mechanistic insight into the peripheral blood mononuclear cell (PBMC) populations that drive the pathogenesis of severe COVID-19. To identify cellular phenotypes associated with disease, we per-formed a comprehensive, unbiased analysis of total and plasma-membrane PBMC proteomes from 40 unvac-cinated individuals with SARS-CoV-2, spanning the whole disease spectrum. Combined with RNA sequencing (RNA-seq) and flow cytometry from the same donors, we define a comprehensive multi-omic profile for each severity level, revealing that immune-cell dysregulation progresses with increasing disease. The cell-surface proteins CEACAMs1, 6, and 8, CD177, CD63, and CD89 are strongly associated with severe COVID-19, corre-sponding to the emergence of atypical CD3+CD4+CEACAM1/6/8+CD177+CD63+CD89+ and CD16+CEACAM1/ 6/8+ mononuclear cells. Utilization of these markers may facilitate real-time patient assessment by flow cy-tometry and identify immune populations that could be targeted to ameliorate immunopathology.