Inclusion Criteria:  Male or female, aged 18 years-old or older Laboratory-confirmed SARS-CoV-2 infection determined by reverse-transcription polymerase chain reaction (RT-PCR) prior to randomization Hospitalized patients Severe COVID-19 pneumonia defined as patients who cannot saturate > 96% on 4 L/min but are NOT on "non-invasive" ventilation nor invasive mechanical ventilation nor Extracorporeal membrane oxygenation (ECMO). Patients on high flow would be eligible if they receive treatment in a non-critical care unit only. Use of contraception or acceptable birth control for the duration of the study in women of childbearing potential Provision of written or verbal informed consent by the patient or designated substitute decision maker  Exclusion Criteria:  Inability to provide informed consent Patients expected to survive less than 24 hours Advanced directives of patient's wishes to refuse intubation. Patients on mechanical ventilation Pregnant women [pregnancy defined as the state of a female after conception and until the termination of gestation, confirmed by a positive human chorionic gonadotrophin (hCG) laboratory test] Breastfeeding Weight > 100 kg or < 50 kg Cancer not in remission or active serious illness unrelated to COVID-19. Any of the following laboratory results at screening: Absolute neutrophil count (ANC) ≤ 1.0 x 109/L, Platelets (PLT) < 50 G /L, Alanine transaminase (ALT) or Aspartate transaminase (AST) > 5N, eGFR < 30 mL/min Current documented bacterial infection Known infection with Human immunodeficiency virus, Treponema pallidum, Hepatitis B antigen (serology consistent with previous vaccination and a history of vaccination is acceptable) or Hepatitis C On-going therapy against tuberculosis, or exposed to tuberculosis or have travelled in areas with high risk of tuberculosis or mycosis within the last 3 months Known allergies to a component of the ProTrans® product Pre-existing chronic respiratory diseases requiring long-term oxygen therapy or severe pulmonary hypertension (PAPS >30 mm HG) or pulmonary fibrosis Pre-existing cirrhosis with basal Child and Pugh of C