Recombinant GM-CSF for diseases of GM-CSF insufficiency: Correcting dysfunctional mononuclear phagocyte disorders.

Introduction: Endogenous granulocyte-macrophage colony-stimulating factor (GM-CSF), identified by its ability to support differentiation of hematopoietic cells into several types of myeloid cells, is now known to support maturation and maintain the metabolic capacity of mononuclear phagocytes including monocytes, macrophages, and dendritic cells. These cells sense and attack potential pathogens, present antigens to adaptive immune cells, and recruit other immune cells. Recombinant human (rhu) GM-CSF (e.g., sargramostim [glycosylated, yeast-derived rhu GM-CSF]) has immune modulating properties and can restore the normal function of mononuclear phagocytes rendered dysfunctional by deficient or insufficient endogenous GM-CSF. Methods: We reviewed the emerging biologic and cellular effects of GM-CSF. Experts in clinical disease areas caused by deficient or insufficient endogenous GM-CSF examined the role of GM-CSF in mononuclear phagocyte disorders including autoimmune pulmonary alveolar proteinosis (aPAP), diverse infections (including COVID-19), wound healing, and anti-cancer immune checkpoint inhibitor therapy. Results: We discuss emerging data for GM-CSF biology including the positive effects on mitochondrial function and cell metabolism, augmentation of phagocytosis and efferocytosis, and immune cell modulation. We further address how giving exogenous rhu GM-CSF may control or treat mononuclear phagocyte dysfunction disorders caused or exacerbated by GM-CSF deficiency or insufficiency. We discuss how rhu GM-CSF may augment the anti-cancer effects of immune checkpoint inhibitor immunotherapy as well as ameliorate immune-related adverse events. Discussion: We identify research gaps, opportunities, and the concept that rhu GM-CSF, by supporting and restoring the metabolic capacity and function of mononuclear phagocytes, can have significant therapeutic effects. rhu GM-CSF (e.g., sargramostim) might ameliorate multiple diseases of GM-CSF deficiency or insufficiency and address a high unmet medical need.

The Potential Alzheimer's Disease Drug, GM‐CSF, Enhances the Anti‐Viral Immune Response and Reduces Mortality in a Mouse Model of COVID‐19

Background COVID‐19 results in increased expression of inflammatory cytokines and Alzheimer's disease (AD) biomarkers of neuronal damage, but inflammation‐targeting clinical trials have yielded poor to mixed results. Our studies of other disorders with an inflammatory component, including AD, chemobrain, Down syndrome, normal aging, and West Nile Virus infection, showed that treatment with the ‘pro‐inflammatory' cytokine granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) in humans or mouse models alleviated clinical, behavioral, and pathological features. Most recently, we completed a Phase 2 clinical trial (NCT01409915) using sargramostim/Leukine (rhuGM‐CSF) in mild‐to‐moderate AD participants, which showed that three weeks of sargramostim treatment improved MMSE scores and improved ATN blood biomarkers of AD pathology (Potter et al., 2021). Therefore, we proposed that human GM‐CSF may be repurposed to promote both the innate and adaptive immune responses in COVID‐19 patients to reduce viral load and mortality. Method We investigated GM‐CSF's effects in eight‐week old male and female human ACE2 (hACE2) transgenic mice infected intranasally with 104 PFU of SARS‐CoV‐2 virus and followed them for 14 days. Mice received daily IP injections of either recombinant murine GM‐CSF or saline. Viral titers, anti‐spike protein antibody levels, and mortality were assessed. Results Intranasal inoculation of hACE2 transgenic mice with 104 PFU SARS‐CoV2 virus resulted in high viral titers in lungs and brains and over 85% mortality. GM‐CSF treatment beginning one day post‐infection increased anti‐spike protein antibody titers, lowered mean lung viral titers proportionately (p = 0.0020), and increased the odds of long‐term survival by up to 5.8‐fold (p = 0.0358), compared to saline. Conclusion GM‐CSF represents a new approach to the treatment of COVID‐19 by recruiting inflammation and the immune system to attack SARS‐CoV‐2 infection and promote survival. GM‐CSF is likely to have a significant advantage over current approaches to the treatment of COVID‐19, including anti‐virus monoclonal antibodies, drugs designed to inhibit viral replication, and immunosuppressants, because, unlike short‐term antivirals, it activates the endogenous immune system, with likely long‐term increases in immune memory required for protection against re‐infection, Based on its mode of action as a natural stimulator of the immune response, GM‐CSF should be effective against all current and future SARS‐CoV‐2 variants.

Recruiting the innate immune system with GM-CSF to fight viral diseases, including West Nile Virus encephalitis and COVID-19.

As the coronavirus disease 2019 (COVID-19) pandemic grows throughout the world, it is imperative that all approaches to ameliorating its effects be investigated, including repurposing drugs that show promise in other diseases. We have been investigating an approach to multiple disorders that involves recruiting the innate immune system to aid the body's healing and regenerative mechanism(s). In the case of West Nile Virus encephalitis and potentially COVID-19, the proposed intervention to stimulate the innate immune system may give the adaptive immune response the necessary time to develop, finish clearing the virus, and provide future immunity. Furthermore, we have found that GM-CSF-induced recruitment of the innate immune system is also able to reverse brain pathology, neuroinflammation and cognitive deficits in mouse models of Alzheimer's disease and Down syndrome, as well as improving cognition in normal aging and in human patients with cognitive deficits due to chemotherapy, both of which exhibit neuroinflammation. Others have shown that GM-CSF is an effective treatment for both bacterial and viral pneumonias, and their associated inflammation, in animals and that it has successfully treated pneumonia-associated Acute Respiratory Distress Syndrome in humans. These and other data strongly suggest that GM-CSF may be an effective treatment for many viral infections, including COVID-19.