SAC-COVID: An FDA-approved Phase III clinical trial evaluating the safety and therapeutic efficacy of CD24Fc in severe COVID-19 patients

Summary: Although most COVID-19 patients exhibit mild to moderate clinical symptoms, a substantial portion requirehospitalization with oxygen support. These patients are classified as having severe COVID-19 and have highrisk of progression to an intensive care unit (ICU) with requirement for invasive mechanical ventilation,extracorporeal membrane oxygenation (ECMO), and carry high risk for mortality. The current proposal seeksto repurpose CD24Fc, a first-in-class biological drug in cancer immunotherapy, to accelerate clinicalimprovement while reducing clinical progression of severe COVID-19 patients. The new drug belongs to thecategory of immunomodulators, and thus complements antiviral therapeutics that are being developed to inhibitSARS-CoV-2 virus replication. In addition to viral damage of lung epithelial cells, the pathogenesis of COVID-19 involves inflammation in response to cellular injuries caused by the virus, which is mediated byinflammatory factors referred to as damage-associated molecular patterns (DAMPs). The prototypical DAMPssuch as HMGB1 and HSP70/90 are released when cells undergo either stress or necrosis, and triggerinflammation by interacting with TLR4 or RAGE. Over 10 years ago, we showed that the CD24-Siglec 10/Gpathway selectively regulates inflammation to DAMPs. Numerous studies have confirmed the role of DAMPsin the pathogenesis of different viral infections. Recent reports from our group in collaboration with others havedemonstrated a critical role for CD24 and Siglecs in inflammation caused by human/simian immunodeficiencyvirus (HIV/SIV). Based on this new understanding, effective treatment of COVID-19 likely requires acombination of both antiviral and non-antiviral-based approaches. Antivirals can limit SARS-CoV-2 replication;while immune modulators can ameliorate inflammation in the lung, protect lung tissue from inflammatoryinjuries, preserve immune function by preventing T cell lymphopenia and functional T cell exhaustion, andprevent cytokine release syndrome (CRS). Given the biology of the CD24-Siglec pathway in limitinginflammation to DAMPs, we hypothesize that the CD24-Siglec innate-immune-checkpoint can be fortified totreated COVID-19 patients and improve outcomes for patients. CD24Fc is an investigational drug thatcomprises the non-polymorphic extracellular region of CD24, which we have shown to be an innate checkpointagainst the inflammatory response to tissue injuries or DAMPs, attached to the Fc region of human IgG1.Preclinical and clinical studies have demonstrated that CD24Fc effectively addresses the major challengesassociated with COVID-19 with excellent safety and therapeutic activity in leukemia patients with high risk ofgraft vs host diseases due to hematopoietic stem cell transplantation (HCT). Building on these excitingdevelopments, we received FDA approval of a clinical protocol for a Phase III clinical trial testing thetherapeutic effect of CD24Fc in protecting COVID-19 patients. The Phase III trial will involve 230 patientsrandomized into blinded CD24Fc arms and placebo, with time to clinical improvement from severe to milddisease and time to clinical progression as the co-primary endpoints. By showing safety and efficacy ofCD24Fc for COVID-19 treatment, our work will provide a new medical countermeasure for the global healthcrisis and potential new pandemic by emerging strains of SARS virus and influenza virus in the future. Therequested funding will cover the first part of the clinical trial that provides clinical proof-of-concept for CD24Fcin COVID-19 patients.