Mesenchymal Stromal Cell Therapy for Severe Covid-19 Infection

COVID-19 patients Inclusion criteria * Male or female patients aged at least 18 years and up to 70 years * Diagnosed with microbiologically or radiologically confirmed COVID-19 pneumonia as defined by: * Extensive interstitial pneumonia on CT scan, consistent with viral pneumonia, within 10 days prior to randomization * And either positive result of COVID-19 PCR test within 14 days prior to inclusion or positive result of SARS-CoV2 PCR or serology within 14 days after inclusion. * Requiring oxygen administration (SpO2 ≤ 93% on room air): * Group A: in standard or intensive care unit requiring supplemental oxygen * Group B: in intensive care unit under mechanical ventilation administered through a tracheal tube, either: * for less than or equal to 7 days * for 7 to 14 days, with persisting high inflammation (ferritin \> 2,000 µg/L; ferritin \> 1,000 µg/L and rising; lymphocytes \< 800 with CRP \> 70 mg/L and rising or ferritin \> 700 µg/L and rising or LDH \> 300 UI/L or D-Dimers \> 1000 ng/ml), not explained by superinfection. Rising = compared to previous 24H. * Written consent of the patient, or - if impossible (clinical condition precluding capacity to consent) - of his/her legal representative, or - if impossible - of an impartial witness such as a physician from a non-participating department or member of the Ethics Committee. Any consent obtained this way shall be documented and confirmed by way of normal consent procedures at the earliest opportunity when the patient has recovered Exclusion criteria * Ongoing pregnancy. Women of childbearing potential (WOCBP, defined as a premenopausal female capable of becoming pregnant) should use an appropriate method of contraception (oral, injectable, or mechanical contraception; women whose partners have been vasectomized or have received or are utilizing mechanical contraceptive devices). * Extracorporeal membrane oxygenation * Limitations to intensity of care * Life expectancy \< 24 hours * Known allergy to IMP component * Active secondary infection * Any malignancy (except non-melanoma skin carcinoma) within 2 years before inclusion * Pre-existing thrombo-embolic pathology * Signs of an active drug or alcohol dependence, serious current illness, mental illness or any factors which, in the opinion of the Investigator, may interfere with subject's ability to understand and comply with study requirements * Patients with any serious medical condition or abnormality of clinical laboratory tests that, in the Investigator's judgment, precludes the patient's safe participation in and completion of the study. * Participation in another clinical trial(use of anti-viral/supportive drugs for COVID-19 infection on a compassionate use basis is not an exclusion criterion). MSC donors Inclusion criteria * Unrelated to the patient * Male or female * Age \> 18 yrs * No HLA matching required * Fulfills generally accepted criteria for allogeneic HSC donation * Informed consent given by donor Exclusion criteria * Any condition not fulfilling inclusion criteria * Known allergy to lidocaine * Any risk factor for transmissible infectious diseases, in particular HIV