Allogeneic hematopoietic stem cell transplantation (HSCT) and coronavirus disease 2019 (COVID-19) infection can both lead to severe cytokine release syndrome (sCRS) resulting in critical illness and death. In this single institution, preliminary comparative case-series study we compared clinical and laboratory covariates as well as response to tocilizumab (TCZ)-based therapy of 15 allogeneic-HSCT- and 17 COVID-19associated sCRS patients. Reaction to a TCZ plus posttransplant cyclophosphamide (PTCY) consolidation therapy in the allogeneic-HSCT-associated sCRS group yielded significantly inferior long-term outcome as compared to TCZ-based therapy in the COVID-19-associated group (P 5 0.003). We report that a TCZ followed by consolidation therapy with a Janus kinase/signal transducer and activator of transcription (JAK/ STAT) inhibitor given to 4 out of 8 critically ill COVID-19 patients resulted in their complete recovery. Non-selective JAK/STAT inhibitors influencing the action of several cytokines exhibit a broader effect than TCZ alone in calming down sCRS. Serum levels of cytokines and chemokines show similar changes in allogeneic-HSCT- and COVID-19-associated sCRS with marked elevation of interleukin-6 (IL-6), regulated upon activation normal T-cell expressed and secreted (RANTES), monocyte chemoattractant protein-1 (MCP-1) and interferon g-induced protein 10 kDa (IP-10) levels. In addition, levels of IL-5, IL-10, IL-15 were also elevated in allogeneic-HSCT-associated sCRS. Our multi-cytokine expression data indicate that the pathophysiology of allogeneic-HSCT and COVID-19-associated sCRS are similar therefore the same clinical grading system and TCZ-based treatment approaches can be applied. TCZ with JAK/STAT inhibitor consolidation therapy might be highly effective in COVID-19 sCRS patients.  Kulcsszavak: COVID-19, allogeneic-HSCT, severe CRS therapy, CAR-T-cell, multi-cytokine levels