Inclusion Criteria:  Male or females aged ≥ 18 years Moderately ill patients with COVID-19 (defined as Ordinal Scale of 5 or 6): Hospitalized, requiring supplemental oxygen or hospitalized, on non-invasive ventilation or high flow oxygen devices Evidence of pneumonia (pulmonary infiltrates) at chest radiography or computed tomography compatible with COVID-19. Hospitalization for less than 72 hours, receiving standard of care treatment for COVID-19. Laboratory-confirmed novel coronavirus (SARS-CoV-2) infection as determined by polymerase chain reaction (PCR). Subject (or legally authorized representative) provides written or oral informed consent prior to initiation of any study procedures. 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:  Subjects on invasive mechanical ventilation or extracorporeal membrane oxygenation (ECMO). Subjects who have a history of allergic reactions attributed to compounds of similar chemical or biologic composition to leronlimab (PRO 140) are not eligible. Inability to provide informed consent (from subject or legally authorized representative) or to comply with test requirements. Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk associated with study participation or, in the investigator's judgment, make the participant inappropriate for the study. Pregnancy or breast feeding. Subject participating in another study with for an investigational treatment. Suspected or known active systemic bacterial, fungal, or viral infections (with the exception of COVID-19), that may increase the risk for the study participant based on investigator judgement. Participants who are immunocompromised, with known immunodeficiencies, or taking potent immunosuppressive agents (e.g., azathioprine, cyclosporine). Patients with estimated discharge or transfer for other hospital in the first 72 hours of study inclusion. Patients with low probability of survival in the first 48 hours of study inclusion.