What does this study add to the field?Using latent class analysis (LCA), we identified two subgroups among a cohort of 483 patients with COVID-19-related ARDS. Class 2 patients had higher inflammatory markers and lactate and corresponded with the previously identified hyperinflammatory subphenotype, whereas Class 1 corresponded with the hypoinflammatory subphenotype. Class 2 had significantly higher 90-day mortality compared with Class 1 (75% vs 48%; p<0•0001). Differential response to corticosteroid treatment was observed, with decreased mortality in steroid-treated patients in Class 2 but not Class 1. SARS-CoV-2 polymerase chain reaction cycle threshold was a predictor of mortality in Class 1, but not Class 2, suggesting distinct drivers of mortality among classes.

A body of evidence has shown that the control of E2F transcription factor activity is critical for determining cell cycle entry and cell proliferation. However, an understanding of the precise determinants of this control, including the role of other cell-cycle regulatory activities, has not been clearly defined. Here, recognizing that the contributions of individual regulatory components could be masked by heterogeneity in populations of cells, we model the potential roles of individual components together with the use of an integrated system to follow E2F dynamics at the single-cell level and in real time. These analyses reveal that crossing a threshold amplitude of E2F accumulation determines cell cycle commitment. Importantly, we find that Myc is critical in modulating the amplitude, whereas cyclin D/E activities have little effect on amplitude but do contribute to the modulation of duration of E2F activation, thereby affecting the pace of cell cycle progression.

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