* pregnancy or breast feeding, * anticipated transfer to another hospital, which is not a study site within 72 hours of randomisation, * need for invasive mechanical ventilation at time of inclusion, * evidence of uncontrolled bacterial pneumopathy or active infection other than sars-cov-2 (laboratory confirmation), * primitive pulmonary arterial hypertension, * cardio-vascular co-morbidity: * history of vascular ischemic events (myocardial infarction or stroke) or congestive heart failure or peripheral arterial disease, * history or current significant cardiac rhythm disorders (e.g., ventricular tachycardia), * known medical history of proven symptomatic postural hypotension, * known cancer (solid or blood) in the last 5 previous years or previous haematological disorders (malignancies and other chronic conditions) or having received bone marrow transplant, * inadequate haematological function defined by: * neutrophil count \< 1.0 x 109/l, * haemoglobin \< 9.0 g/dl (90 g/l), * platelets \< 100 x 109/l, * kaliemia \< 3.5 mmol/l and/or total calcemia \< 2.2 mmol/l, * inadequate hepatic function defined by aspartate aminotransferase (ast) and/or alanine aminotransferase (alt) \> 3 x upper limit of normal (uln) and/or total bilirubin \> 2 x uln, * patients with known allergy to plerixafor or its excipients. * previous (within 4 weeks) or current participation in another clinical study other than an observational study. * patients with auto immune disease treated or not,

* pregnancy or breast feeding, * anticipated transfer to another hospital, which is not a study site within 72 hours of randomisation, * need for invasive mechanical ventilation at time of inclusion, * evidence of uncontrolled bacterial pneumopathy or active infection other than sars-cov-2 (laboratory confirmation), * primitive pulmonary arterial hypertension, * cardio-vascular co-morbidity: * history of vascular ischemic events (myocardial infarction or stroke) or congestive heart failure or peripheral arterial disease, * history or current significant cardiac rhythm disorders (e.g., ventricular tachycardia), * known medical history of proven symptomatic postural hypotension, * known cancer (solid or blood) in the last 5 previous years or previous haematological disorders (malignancies and other chronic conditions) or having received bone marrow transplant, * inadequate haematological function defined by: * neutrophil count \< 1.0 x 109/l, * haemoglobin \< 9.0 g/dl (90 g/l), * platelets \< 100 x 109/l, * kaliemia \< 3.5 mmol/l and/or total calcemia \< 2.2 mmol/l, * inadequate hepatic function defined by aspartate aminotransferase (ast) and/or alanine aminotransferase (alt) \> 3 x upper limit of normal (uln) and/or total bilirubin \> 2 x uln, * patients with known allergy to plerixafor or its excipients. * previous (within 4 weeks) or current participation in another clinical study other than an observational study. * patients with auto immune disease treated or not,

pregnancy or breast feeding, anticipated transfer to another hospital, which is not a study site within 72 hours of randomisation, need for invasive mechanical ventilation at time of inclusion, evidence of uncontrolled bacterial pneumopathy or active infection other than sars-cov-2 (laboratory confirmation), primitive pulmonary arterial hypertension, cardio-vascular co-morbidity: history of vascular ischemic events (myocardial infarction or stroke) or congestive heart failure or peripheral arterial disease, history or current significant cardiac rhythm disorders (e.g., ventricular tachycardia), known medical history of proven symptomatic postural hypotension, known cancer (solid or blood) in the last 5 previous years or previous haematological disorders (malignancies and other chronic conditions) or having received bone marrow transplant, inadequate haematological function defined by: neutrophil count < 1.0 x 109/l, haemoglobin < 9.0 g/dl (90 g/l), platelets < 100 x 109/l, kaliemia < 3.5 mmol/l and/or total calcemia < 2.2 mmol/l, inadequate hepatic function defined by aspartate aminotransferase (ast) and/or alanine aminotransferase (alt) > 3 x upper limit of normal (uln) and/or total bilirubin > 2 x uln, patients with known allergy to plerixafor or its excipients. previous (within 4 weeks) or current participation in another clinical study other than an observational study. patients with auto immune disease treated or not,

pregnancy or breast feeding, anticipated transfer to another hospital, which is not a study site within 72 hours of randomisation, need for invasive mechanical ventilation at time of inclusion, evidence of uncontrolled bacterial pneumopathy or active infection other than sars-cov-2 (laboratory confirmation), primitive pulmonary arterial hypertension, cardio-vascular co-morbidity: history of vascular ischemic events (myocardial infarction or stroke) or congestive heart failure or peripheral arterial disease, history or current significant cardiac rhythm disorders (e.g., ventricular tachycardia), known medical history of proven symptomatic postural hypotension, known cancer (solid or blood) in the last 5 previous years or previous haematological disorders (malignancies and other chronic conditions) or having received bone marrow transplant, inadequate haematological function defined by: neutrophil count < 1.0 x 109/l, haemoglobin < 9.0 g/dl (90 g/l), platelets < 100 x 109/l, kaliemia < 3.5 mmol/l and/or total calcemia < 2.2 mmol/l, inadequate hepatic function defined by aspartate aminotransferase (ast) and/or alanine aminotransferase (alt) > 3 x upper limit of normal (uln) and/or total bilirubin > 2 x uln, patients with known allergy to plerixafor or its excipients. previous (within 4 weeks) or current participation in another clinical study other than an observational study. patients with auto immune disease treated or not,