Inclusion Criteria:

- Age: 18 years or older (including 18 years); male or female

- Laboratory-confirmed SARS-CoV-2 or COVID-19 infection as determined by polymerase
chain reaction (PCR) or other commercial or public health assay.

- Bilateral lung infection confirmed by imaging.

- Severe disease that meets one of the following conditions: (i) At rest, finger blood
oxygen saturation ≤ 93% or PaO2/FiO2 ≤ 300 mmHg; (ii) Requiring non-invasive or
invasive mechanical ventilation; OR (iii) Requiring high flow oxygen ≥ 15L/min

- Hospitalized for no more than 5 calendar days at the time of screening

Exclusion Criteria:

- Any previous and/or current clinically significant disease or condition that has not
been stable within 3 months prior to enrollment, or acute illness, planned medical/
surgical procedure, or any trauma that occurred within 2 weeks prior to enrollment.

- Chronic obstructive pulmonary disease (COPD) patients requiring inhaled
corticosteroid, long-acting beta-adrenergic agonists, long-acting anticholinergics, or
long-term oxygen therapy (Part 1 only).

- Pulmonary interstitial disease, pulmonary alveolar proteinosis, and pulmonary
granulomatosis.

- Cardiovascular event in the 3 months prior to study drug administration: acute
myocardial infarction or unstable angina pectoris, severe arrhythmia (multiple sources
of frequent ventricular premature beat, ventricular tachycardia and ventricular
fibrillation); New York Heart Association Classification (NYHA): Class III-Class IV.

- Blood system disorders or routine blood analysis test abnormalities: Hemoglobin < 8
g/dL; Absolute neutrophil count (ANC) <1500 × 109/L; Platelets < 50 × 109/L.

- Dependence on glucocorticoid treatment equivalent to methylprednisolone 2 mg/kg/ day
or more or long-term use of anti-rejection or immunomodulatory drugs.

- Subjects that have been on invasive mechanical ventilation for ≥120 hours at the time
of dosing

- Subjects that require ECMO.

- Pregnant or breastfeeding females.