Inclusion Criteria:

1. Male or female adult ≥ 18 years of age at time of screening.

2. Subjects hospitalized with severe or critical illness caused by coronavirus 2019
infection as defined below:

A. Severe Illness:

- Diagnosed with COVID-19 by standard RT-PCR assay or equivalent testing within 5 days
of screening

AND

Symptoms of severe systemic illness/infection with COVID-19:

- At least 1 of the following: fever, cough, sore throat, malaise, headache, muscle
pain, shortness of breath at rest or with exertion, confusion, or symptoms of severe
lower respiratory symptoms including dyspnea at rest or respiratory distress

AND

Clinical signs indicative of severe systemic illness/infection with COVID-19, with at
least 1 of the following:

- RR ≥ 30, HR ≥ 125, SaO2 <93% on room air or requires > 2L oxygen by NC in order
maintain SaO2 ≥93%, PaO2/FiO2 <300

AND

- None of the following: Respiratory failure (defined by endotracheal intubation and
mechanical ventilation, oxygen delivered by high-flow nasal cannula, noninvasive
positive pressure ventilation, or clinical diagnosis of respiratory failure in setting
of resource limitations), Septic shock (defined by SBP < 90 mm Hg, or Diastolic BP <
60 mm Hg), Multiple organ dysfunction/failure

B. Critical Illness:

- Diagnosed with COVID-19 by standard RT-PCR assay or equivalent testing within 5 days
of screening

AND

Evidence of critical illness, defined by at least 1 of the following:

- Respiratory failure defined based on resource utilization requiring at least 1 of
the following: Endotracheal intubation and mechanical ventilation, oxygen delivered by
high-flow nasal cannula, noninvasive positive pressure ventilation, ECMO, or clinical
diagnosis of respiratory failure (in setting of resource limitation)

OR

- Shock (defined by SBP < 90 mm Hg, or Diastolic BP < 60 mm Hg or requiring
vasopressors)

OR

-Multiple organ dysfunction/failure

3. Subject, if intubated, positive endexpiratory pressure (PEEP) <15 cmH2O with PaO2/FiO2
>150 mmHg.

4. Electrocardiogram (ECG) with no clinically significant findings as assessed by the
Investigator

5. Subject (or legally authorized representative) provides written informed consent prior
to initiation of any study procedures.

6. Understands and agrees to comply with planned study procedures.

7. Women of childbearing potential and their partner must agree to use at least one
highly effective method of contraception (e.g., hormonal contraceptives [implants,
injectables, combination oral contraceptives, transdermal patches, or contraceptive
rings], intrauterine devices, bilateral tubal occlusion, or sexual abstinence) for the
duration of the study.

Exclusion Criteria:

1. Subjects with do-not-resuscitate (DNR) and/or do-not-intubate (DNI) orders or expected
to be made DNR/DNI in setting of resource limitations or family wishes.

2. Not a candidate for dialysis or continuation of care (or full medical support) in
setting of resource limitations.

3. Subject on continuous vasopressors (at the dose of norepinephrine >20μg/min and/or
vasopressin >0.04 units/kg/min) for >48 hours at time of screening.

4. Subjects who have a history of allergic reactions attributed to compounds of similar
chemical or biologic composition to leronlimab (PRO 140) are not eligible.

5. Inability to provide informed consent or to comply with test requirements

6. Consideration by the investigator, for safety reasons, that the subject is an
unsuitable candidate to receive study treatment

7. Pregnancy or breast feeding

8. Subject participating in another study with for an investigational treatment for
COVID-19.

Note: Subject who were prescribed (1) hydroxychloroquine or chloroquine with or without
azithromycin, (2) Remdesivir, (3) convalescent plasma therapy, or (4) immunomodulatory
treatments (including but not limited to sarilumab, clazakizumab, tocilizumab, and
anakinra) for the off-label treatment of COVID-19 prior to study enrollment may be included
and may continue to receive these agents as part of standard-of-care.