Tregs for the Treatment of Acute Respiratory Distress Syndrome (ARDS) Associated With COVID-19 (regARDS)

Inclusion Criteria: * Diagnosis of ARDS and respiratory failure requiring mechanical ventilation for less than 72 hours at the time of enrollment * PaO2/FiO2 \< 300 and PEEP \> 5 * Male or female, age 18 to 70 years at Screening * Weight \> 40 kg * Documented diagnosis of infection with SARS-CoV-2 virus by PCR * Chest imaging (radiograph or CT scan) with abnormalities consistent with COVID-19 pneumonia that could not be explained by effusions, pulmonary collapse, or nodules; and respiratory failure that could not be explained by cardiac failure or fluid overload * Females of childbearing potential and males must use effective contraception practices from Screening until 28 days after the EOS visit * Females of childbearing potential must have a negative pregnancy test at Screening and within 24 hours prior to dosing of study drug * Able to provide Informed Consent, either by self or by medical proxy * Willing and able to comply with this protocol for the entire duration of the study Exclusion Criteria: * Any history or sign of significant chronic active or recurrent infection or screening laboratory evidence consistent with a significant chronic active or recurrent infection requiring treatment with antibiotics, antivirals or antifungals (other than SARS-CoV-2); ongoing antimicrobial treatments will not be exclusionary if, in the opinion of the investigator, no active infection is present (other than SARS-CoV-2) * Receiving extracorporeal membrane oxygenation therapy * Moribund patients not expected to survive 24 hours after enrollment based on clinical assessment * History of significant underlying pulmonary disease (requiring home oxygen), renal disease (requiring dialysis for chronic kidney disease), hepatic disease (Child-Pugh score ≥ 7), or known history of cirrhosis. * Known or suspected immunodeficiency disease * Positive serology for HBV, HCV, or HIV at Screening * Abnormal CBC defined by: * Platelet count \< 75,000/mm3 * White blood cell count \< 2500/mm3 * Absolute neutrophil count \< 500/mm3 * History of bone marrow or stem cell transplantation * Received any type of live attenuated vaccine \< 1 month prior to Screening or is planning to receive any such live attenuated vaccine over the course of the study * History of lung cancer or any other malignancy requiring active treatment, except adequately treated basal cell carcinoma or in situ carcinoma of the uterine cervix * Any female who is pregnant or breastfeeding, or any female who is planning to become pregnant during the study and follow-up period * Any condition that, in the investigator's opinion, may compromise study participation, present a safety risk to the subject, or may confound the interpretation of the study results * A QT duration corrected for heart rate by Fridericia's formula (QTcF) \> 450 millisecond (msec) for males or \> 470 msec for females, based on either single or averaged QTcF values of triplicate ECGs obtained over a 3-minute interval * Currently enrolled in another investigational device or drug study