The COVID-19 mortality is associated with an increase in interleukin-6 (IL-6) levels. Levilimab is an anti–IL-6 receptor antibody with proven clinical efficacy in patients with severe COVID-19.The aim of the study was to assess the association of COVID-19 severity and levilimab effectiveness with IL-6 levels and to explore the potential for using levilimab in other conditions accompanied by cytokine release syndrome.Materials and methods: the subgroup analysis was based on the data of COVID

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... ents with known baseline IL-6 levels from the CORONA clinical study. Subgroups were formed according to baseline IL-6 levels: ≤5 pg/mL (normal) and >5 pg/mL (elevated). The subgroup analysis included descriptive statistics of the patients and time courses of their clinical and laboratory findings (at screening, on the day of investigational product administration, and further until day 14). In order to compare the percentages of patients who had required rescue therapy, the authors used Fisher's exact test.Results: the subgroup analysis included 91 patients (47 from the levilimab group and 44 from the placebo group). At baseline, the authors observed elevated levels of IL-6 in 31/47 (66%) subjects in the levilimab group and 29/44 (48.4%) subjects in the placebo group. The subjects with elevated IL-6 demonstrated more pronounced clinical signs of pneumonia and abnormalities in inflammatory markers. Elevated baseline IL-6 levels were associated with the need for rescue therapy (OR=3.714; 95% CI: 1.317–9.747; p=0.0183); this association was stronger in the placebo group (OR=8.889; 95% CI: 2.098–33.31; p=0.0036). Also, the placebo group showed long-term abnormalities in the clinical and laboratory findings.Conclusions: IL-6 is one of the key elements in the pathogenesis of cytokine release syndrome related to COVID-19 and other conditions. Elevated IL-6 levels are associated with the severity of COVID-19. Inhibition of IL-6 receptors by levilimab leads to clinical improvement in patients with severe COVID-19, suggesting the effectiveness of levilimab in pathogenesis-oriented therapy for cytokine release syndrome of other aetiologies.