Circulating proteomes provide a snapshot of the physiological state of a human organism responding to pathogenic challenges and drug interventions. The outcomes of patients with COVID-19 and acute respiratory distress syndrome triggered by the SARS-CoV2 virus remain uncertain. Tocilizumab is an anti-interleukin-6 treatment that exerts encouraging clinical activity by controlling the cytokine storm and improving respiratory distress in patients with COVID-19. We investigate the biological determinants of therapeutic outcomes after tocilizumab treatment. Overall, 28 patients hospitalized due to severe COVID-19 who were treated with tocilizumab intravenously were included in this study. Sera were collected before and after tocilizumab, and the patient's outcome was evaluated until day 30 post-tocilizumab infusion for favorable therapeutic response to tocilizumab and mortality. Hyperreaction monitoring measurements by liquid chromatography-mass spectrometry-based proteomic analysis with data-independent acquisition quantified 510 proteins and 7019 peptides in the serum of patients. Alterations in the serum proteome reflect COVID-19 outcomes in patients treated with tocilizumab. Our results suggested that circulating proteins associated with the most significant prognostic impact belonged to the complement system, platelet degranulation, acute-phase proteins, and the Fc-epsilon receptor signaling pathway. Among these, upregulation of the complement system by activation of the classical pathway was associated with poor response to tocilizumab, and upregulation of Fc-epsilon receptor signaling was associated with lower mortality.
Keywords: COVID-19; anti-interleukin 6 receptor therapy; calprotectin; candidate proteins; proteomics; thrombospondin-1.