This study will assess the safety and efficacy of TSC as a treatment for participants who are infected with SARS-CoV-2 (COVID-19).

This trial has two phases. The first phase is an open-label, pharmacokinetic, pharmacodynamic, ascending dose, safety and tolerability lead-in. The second phase is a single-center, randomized, placebo-controlled, double-blind, adaptive, safety and efficacy, pilot.

The lead-in phase will study 4 doses of TSC and enroll 24 participants. Each TSC dose will be administered as an IV bolus injection to 6 unique participants per dose level administered four times per day (every 6 hours) for 5 days. Participants will be assigned in groups of 3, and a Safety Monitoring Committee (SMC) will review Dose Limiting Toxicities (DLTs) after each group of 3 participants. The first group of 3 participants will receive TSC at a dose of 0.25 mg/kg. If there are no DLTs, 3 additional subjects will be studied at 0.25 mg/kg. If there are 0 or 1 DLT among the 6 participants studied at 0.25mg/kg, 3 additional participants will be studied at the next higher dose, 0.5 mg/kg. If there are no DLTs an additional 3 participants will be studied at 0.5 mg/kg. If there are 0 or 1 DLTs among the 6 subjects studied at 0.5 mg/kg, 3 additional participants will be studied at the next higher dose, 1.0 mg/kg. The study will continue in this fashion seeking an observed toxicity rate that is < 0.33 among 6 participants at any one dose level, or TSC at 1.5 mg/kg proves to be safe and tolerable.

As participants complete the initial 5 days of treatment they will continue at their assigned TSC dose four times per day (every 6 hours) for up to 15 days. Participants will be assigned to dose levels in ascending order. The dose range is as follows.

• 0.25 mg/kg TSC + Standard of Care
• 0.50 mg/kg TSC + Standard of Care
• 1.00 mg/kg TSC + Standard of Care
• 1.50 mg/kg TSC + Standard of Care

At the completion of the lead-in the Safety Monitoring Committee (SMC) will examine the resultant safety and blood oxygenation (S:F) data for all participants and determine the optimum, safe and tolerable dose of TSC for use in the pilot study.

Dose Limiting Toxicity (DLT) is defined as any study drug related grade 3 or 4 adverse event during the treatment period, with the exception of pulmonary events in the CTCAE that are known complications of SARS-CoV-2 infection: Acute Respiratory Distress Syndrome (ARDS), Cough, Dyspnea, Hypoxia, Pneumonitis, Pulmonary Edema, Respiratory Failure, or Respiratory, Thoracic and Mediastinal disorders - Other. The SMC will apply clinical judgement in their review of adverse events (particularly abnormal laboratory results).

The two arm, randomized pilot will enroll up to 200 participants, and will be overseen by a Data Safety Monitoring Board (DSMB). TSC dosing will be at the selected optimum, safe and tolerable biologic dose with an active to placebo ratio of 2:1 toward providing the maximum potential benefit to participants. If two doses of TSC are to be studied in the randomized pilot the active to placebo ratio will be 2:2:1. Randomization will be stratified by disease severity, age and presence of pre-specified comorbidities. The treatment arms are as follows.

• TSC + Standard of Care
• Placebo + Standard of Care

Each TSC dose will be administered as an IV bolus injection 4 times per day (every 6 hours) for up to 15 days. Participants randomized to placebo will receive an IV bolus injection of an equivalent volume by participant weight of Normal Saline four times per day (every 6 hours) for up to 15 days.

All study drug administration will be performed by unblinded medical staff. Participants, investigators and caregivers will not see the injection or injection site or be aware of randomization.

Blood oxygenation will be measured via recorded continuous pulse oximetry and the SpO2:Fraction of Inspired Oxygen (FiO2) ratio calculated.

All participants will undergo safety and efficacy assessments including laboratory assays, blood sampling on days 1 through day 15 (while hospitalized) and day 29 by return clinic visit or if still hospitalized.

All participants, whether a part of the lead-in phase or randomized pilot, will be assessed for survival, serious adverse events and adverse events by requested return to the clinic on Day 60.

Inclusion Criteria:

1. Hospitalized subjects with confirmed SARS-CoV-2 infection and hypoxemia, defined as SpO2 < 94% on room air or requiring supplemental oxygen
2. Laboratory-confirmed SARS-CoV-2 infection as determined by PCR, or other commercial or public health assay in any specimen < 72 hours prior to enrollment.
3. WHO ordinal scale score of 3, 4 or 5 at baseline
4. Male or non-pregnant female adult ≥18 years of age at time of enrolment.
5. Subject (or legally authorized representative (LAR)) provides written informed consent prior to initiation of any study procedures.
6. Understands and agrees to comply with planned study procedures.
7. Illness of any duration
8. Women of childbearing potential must have a negative blood pregnancy test at the screening/baseline visit (Day 1) and agree to use a double method of birth control through 30 days after the last dose of study drug.

Exclusion Criteria:

1. Intubated and mechanically ventilated at baseline
2. Receiving extracorporeal membrane oxygenation (ECMO) at baseline
3. Severe organ dysfunction (SOFA score > 10)
4. Patient or LAR unable to provide written informed consent
5. ALT/AST > 3 times the upper limit of normal or serum bilirubin > 1.5 times the upper limit of normal
6. Estimated glomerular filtration rate (eGFR) by Modification of Diet in Renal Disease (MDRD) formula < 30 mL/min/1.73 m^2 or on dialysis
7. Pregnancy or breast feeding.
8. Anticipated transfer to another hospital which is not a study site within 72 hours.
9. Allergy to any study medication

Phase 1 lead-in was conducted; however, the study was completed prior to initiation of Phase 2. Therefore, only data are reported for the lead-in phase, as no data were collected for Phase 2.

AEs were collected for up to 70 days from the start of study drug administration through the 60-day follow-up visit (+10d).

Phase 1 lead-in was conducted; however, the study was completed prior to initiation of Phase 2. Therefore, only data are reported for the lead-in phase, as no data were collected for Phase 2.

Lead-in: no masking. Randomized pilot: The participants, care providers, investigators, and outcomes assessors are masked. The pharmacist, unblinded clinical research associate, and unblinded study drug administrator are not masked.