Background Tocilizumab blocks pro-inflammatory activity of interleukin-6 (IL-6), involved in pathogenesis of pneumonia the most frequent cause of death in COVID-19 patients. Methods A multicenter, single-arm, hypothesis-driven trial was planned, according to a phase 2 design, to study the effect of tocilizumab on lethality rates at 14 and 30 days (co-primary endpoints, a priori expected rates being 20 and 35%, respectively). A further prospective cohort of patients, consecutively enrolled after the first cohort was accomplished, was used as a secondary validation dataset. The two cohorts were evaluated jointly in an exploratory multivariable logistic regression model to assess prognostic variables on survival. Results In the primary intention-to-treat (ITT) phase 2 population, 180/301 (59.8%) subjects received tocilizumab, and 67 deaths were observed overall. Lethality rates were equal to 18.4% (97.5% CI: 13.6–24.0, P = 0.52) and 22.4% (97.5% CI: 17.2–28.3, P < 0.001) at 14 and 30 days, respectively. Lethality rates were lower in the validation dataset, that included 920 patients. No signal of specific drug toxicity was reported. In the exploratory multivariable logistic regression analysis, older age and lower PaO2/FiO2 ratio negatively affected survival, while the concurrent use of steroids was associated with greater survival. A statistically significant interaction was found between tocilizumab and respiratory support, suggesting that tocilizumab might be more effective in patients not requiring mechanical respiratory support at baseline. Conclusions Tocilizumab reduced lethality rate at 30 days compared with null hypothesis, without significant toxicity. Possibly, this effect could be limited to patients not requiring mechanical respiratory support at baseline. Registration EudraCT (2020-001110-38); clinicaltrials.gov (NCT04317092).

Granulocyte‐macrophage colony stimulating factor (GM‐CSF) and interleukin 3 (IL‐3) target cells have been studied in vivo in subjects with normal hemopoiesis. GM‐CSF administration elicits a rapid and sustained neutrophilia, monocytosis and eosinophilia due to a direct proliferative stimulus on all progenitors and precursors of the granulomonopoietic lineage. GM‐CSF is also a powerful stimulator of erythroid burst forming unit (BFU‐E) and megakaryocyte colony forming unit (CFU‐MK) proliferation. Its action, however, does not extend to more mature erythroid and megakaryocyte cells suggesting the need for combined treatment with lineage‐specific growth factors such as erythropoietin (Epo) or IL‐6 to obtain a complete myeloid stimulation. When GM‐CSF is discontinued, its action rapidly vanishes, and a rapid decline in the proliferative rate of target cells to values below the initial ones occurs. The potential clinical usefulness of this phenomenon in regard to cancer chemotherapy is discussed. IL‐3 treatment induces only a rapid and marked eosinophilia. Chronic IL‐3 administration, however, increases the proliferation of all myelopoietic progenitors and primes CFU‐GM to become more sensitive in vitro to the action of granulocyte CSF (G‐CSF), GM‐CSF and IL‐5. Whereas an increased IL‐5 sensitivity seems devoid of therapeutic potential, the priming of G‐CSF and GM‐CSF action suggests rational scheduling for a combined treatment of IL‐3 with other hemopoietic growth factors.

Background. Administration of granulocyte‐macrophage colony stimulating factor (GM‐CSF) is followed by a rapid increase in the proliferative activity of the hematopoietic precursors. Within 72 hours after its suspension, however, establishment of a negative feedback results in a reduction of the proliferative activity of the hyperplastic marrow to values below the baseline, suggesting refractoriness of hematopoietic progenitors to the action of cell‐cycle‐specific cytostatic agents. Methods. The hypothesis that short treatment with GM‐CSF before chemotherapy could reduce the hematopoietic toxicity of cytostatics was investigated by administering GM‐CSF glycosylate (Sandoz, Basel, Switzerland/Schering‐Plough, Kenilworth, NJ) subcutaneously with a 5.5 μg/kg protein dosage per day from day–6–day–4 before each course of adjuvant chemotherapy (cyclophosphamide, epirubicin, 5‐fluorouracil/cyclophosphamide, methotrexate, 5‐fluorouracil alternate) in patients with node‐positive breast cancer. Twelve patients were randomized to receive GM‐CSF before chemotherapy or only at chemotherapy. The hematologic picture and dose intensity of chemotherapy were compared in the two groups of patients. Results. In the group of patients receiving chemotherapy only, 22% of the cycles had to be postponed because of leukopenia, with a consequent reduction of the dose intensity, whereas in the GM‐CSF group, the neutrophil counts remained at significantly (P < 0.001) higher levels, and there were no delays in chemotherapy administration. No substantial systemic toxicity was associated with this brief GM‐CSF schedule. Moreover, GM‐CSF treatment did not result in delayed depletion of the hematopoietic pool. Conclusions. Short treatment with GM‐CSF can enable the dose intensity of conventional protocols of proven efficacy to be increased.

Human recombinant interleukin-3 (IL-3; Sandoz AG, Basel, Switzerland) was administered for 7 days to patients with neoplastic disease and normal hematopoiesis. The purpose of the study was to assess IL-3 toxicity, to identify target cells, to define their kinetics of response at different dose levels, and to determine if IL-3 in vivo increased the sensitivity of bone marrow (BM) progenitors to the action of other hematopoietic growth factors. A total of 21 patients entered the study; the dosage ranged from 0.25 to 10 micrograms/kg/d. The effect on peripheral blood cells during treatment showed no significant changes in the number of platelets, erythrocytes, neutrophils, or lymphocytes (and their subsets). A mild monocytosis and basophilia occurred. Eosinopenia, present in the first hours of treatment, was followed by a dose-and time-dependent eosinophilia. IL-3 treatment affected BM cell proliferation by increasing the percentage of BM progenitors engaged in the S-phase of the cell cycle. The effect was dose dependent, with the various progenitors showing different degrees of sensitivity. The most sensitive progenitors were the megakaryocyte progenitors (colony-forming unit-megakaryocyte), then the erythroid progenitors (burst-forming unit-erythroid), and finally the granulo- monocyte progenitors (colony-forming unit-granulocyte-macrophage) whose proliferative activity was stimulated at the higher doses of IL-3. Only a slight increase in the proliferative activity of myeloblasts, promyelocytes, and myelocytes was observed, whereas the activity of erythroblasts was unchanged. The priming effect was such that BM progenitors, purified from patients treated with IL-3, produced more colonies in vitro in the presence of granulocyte colony-stimulating factor (G-CSF; granulocyte colonies), IL-5 (eosinophil colonies), and granulocyte-macrophage CSF (GM-CSF; predominantly eosinophil colonies). These data indicate that even in vivo IL-3 acts essentially as a primer for the action of other cytokines. Therefore, optimum stimulus of myelopoiesis will require either endogenous or exogenous late-acting cytokines such as G-CSF, erythropoietin, GM-CSF, and IL-6 for achieving fully mature cells in peripheral blood. If exogenous cytokines are used with IL-3, it is likely that G-CSF will yield more neutrophils, whereas GM-CSF may enhance eosinophils, monocytes, and neutrophils. Attention to the clinical relevance of each cell type will be necessary and should determine the selection of the combination of cytokines.

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