Cellular Immunotherapy for Septic Shock

Inclusion Criteria: A participant must meet all three inclusion criteria to be eligible: 1. Admission to an Intensive Care Unit AND 2. Cardiovascular failure that is present within the first 24 hours of admission to the ICU and is defined by the requirement for at least 15 mcg/min of norepinephrine or at least 200 mcg/min of phenylephrine or at least 0.03 U/min of vasopressin, or a combination of norepinephrine and phenylephrine that is equivalent to the total required doses (e.g. norepinephrine 8 meq/min and phenylephrine 100 mcg/min) for at least 4 consecutive hours. Participants must still require vasopressor(s) at the time of MSC infusion to be eligible. AND 3. At least 1 additional organ failure, or organ hypoperfusion, as defined by the modified Multiple Organ Dysfunction Score (MODS). Criteria for organ dysfunction or organ hypoperfusion must be met within the first 24 hours of ICU admission. These include: 1. Respiratory failure: mechanically ventilated with a positive end expiratory pressure (PEEP) of at least 5 cm H20, and a partial pressure of oxygen/fractional inspired oxygen concentration (P/F ratio) less than or equal to 200 on 2 separate occasions. 2. Hematological failure: platelet count of less than or equal to 100 X 109 /L that has decreased by at least 50 x 109/L. 3. Acute renal failure: acute renal insufficiency with a creatinine of greater than 200 umol/L that has increased by at least 50 umol/L, or the requirement for continuous renal replacement therapy, or for participants with known chronic renal failure but not on dialysis, a 50% increase in their baseline creatinine concentration. 4. Organ hypoperfusion: a lactate of at least 4 mmol/L Acute organ failures that meet eligibility criteria cannot have been present for more than 48 hours prior to admission to the ICU. Exclusion Criteria: 1. Another form of shock (cardiogenic, hypovolemic, obstructive) that is considered by the treating critical care staff physician as the dominant cause of shock. 2. History of known chronic pulmonary hypertension with a WHO functional class of III or IV 3. History of severe chronic pulmonary disease requiring home oxygen 4. History of chronic severe cardiac disease including congestive heart failure or valvular dysfunction with a New York Heart Association Functional Class of III or IV, or severe ischemic heart disease with a Canadian Cardiovascular Society angina class score of III or IV. 5. History of severe chronic liver disease (Child class C) 6. Malignancy in the previous year (excluding resolved non-melanoma skin cancer). Participants will be excluded from the CISS2 trial if they have received any surgery, chemotherapy, or radiation for a malignancy in the previous 12 months. 7. Chronic immune suppression (chronic steroid use or chemotherapy) 8. Pregnant or lactating 9. Enrolment in another interventional study 10. Treating physicians' impression is that the participant is moribund and that death is imminent within the subsequent 12 hours of meeting eligibility criteria 11. Family, participant, or physician not committed to aggressive care. Any limitation of care will exclude the patient from enrolment in the CISS2 trial (ex: no intubation, no use of vasopressor agent(s), no renal support therapy). 12. Less than 18 years of age