Umbilical Mesenchymal Stromal Cells as Cellular Immunotherapy for Septic Shock

Inclusion Criteria: A participant must meet all the following inclusion criteria at time of randomization to be eligible: 1. At least 18 years of age AND 2. Requirement for admission to the intensive care unit AND 3. Index admission to the intensive care unit AND 4. Cardiovascular organ failure for at least 1 consecutive hour defined by the requirement of at least 5 mcg/min of norepinephrine or 100 mcg/min of phenylephrine or 0.03 U/min vasopressin AND 5. Clinician impression that cardiovascular organ failure is related to infection AND 6. There is at least 1 other acute organ failure according to modified individual Sequential Organ Failure Assessment Scores within 24 hours of meeting Cardiovascular organ failure defined by: 1. Respiratory failure: invasive or non-invasive mechanical ventilation with a positive end expiratory pressure (PEEP) \>/= 5 cm H2O and a partial pressure of oxygen/fractional inspired oxygen concentration (P/F ratio \</= 200), OR high-flow nasal canula oxygen therapy (minimum total flow rate of 30 lpm and 40% FiO2); OR 2. Hematological failure: platelet count of \</= 100 X 10\^9/L OR 3. Acute kidney injury: acute renal insufficiency with a creatinine of \>/= 200 umol/L, or the requirement for new renal replacement therapy, or for participants with known chronic renal failure but not on dialysis, a 50% increase in their baseline creatinine concentration OR 4. Organ hypoperfusion: a lactate \>/= 4 mmol/L Acute organ failures that meet eligibility criteria must not have been present for greater than 48 hours prior to meeting the eligibility criteria. Exclusion Criteria: Patients will be excluded if they have at least one of the following at time of randomization: 1. Another form of shock (cardiogenic, hypovolemic, obstructive) OR 2. History of known chronic pulmonary hypertension with a WHO functional class of IV OR 3. History of severe chronic pulmonary disease requiring home oxygen OR 4. History of severe chronic cardiac disease including congestive heart failure or valvular dysfunction with a New York Heart Association Functional class IV or severe chronic ischemic heart disease with a Canadian Cardiovascular Society angina class score IV OR 5. History of severe chronic liver disease (Child-Pugh Class C or model for end stage liver disease (MELD) Score \>= 15) OR 6. Malignancy in previous 1 year (excluding resolved non-melanoma skin cancer) OR 7. Treating physician impression that death is imminent within the 12 hours after meeting eligibility criteria OR 8. Pregnant or lactating OR 9. Family or patient not committed to aggressive care