Extra-pulmonary aspects of acquired pulmonary alveolar proteinosis as predicted by granulocyte-macrophage colony-stimulating factor-deficient mice

Nebulised granulocyte-macrophage colony-stimulating factor (GM-CSF) in autoimmune pulmonary alveolar proteinosis: a systematic review and meta-analysis

BACKGROUND

Autoimmune pulmonary alveolar proteinosis (aPAP) results from impaired macrophage-mediated clearance of alveolar surfactant lipoproteins. Whole lung lavage has been the first-line treatment but recent reports suggest the efficacy of granulocyte-macrophage colony-stimulating factor (GM-CSF). We aimed to review the efficacy and safety of nebulised GM-CSF in aPAP.

METHODS

We conducted a systematic review and meta-analysis searching Embase, CINAHL, MEDLINE and Cochrane Collaborative databases (1946-1 April 2022). Studies included patients aged >18 years with aPAP receiving nebulised GM-CSF treatment and a comparator cohort. Exclusion criteria included secondary or congenital pulmonary alveolar proteinosis, GM-CSF allergy, active infection or other serious medical conditions. The protocol was prospectively registered with PROSPERO (CRD42021231328). Outcomes assessed were St George's Respiratory Questionnaire (SGRQ), 6-min walk test (6MWT), gas exchange (diffusing capacity of the lung for carbon monoxide (D LCO) % predicted) and arterial-alveolar oxygen gradient.

RESULTS

Six studies were identified for review and three for meta-analysis, revealing that SGRQ score (mean difference -8.09, 95% CI -11.88- -4.3, p<0.0001), functional capacity (6MWT) (mean difference 21.72 m, 95% CI -2.76-46.19 m, p=0.08), gas diffusion (D LCO % predicted) (mean difference 5.09%, 95% CI 2.05-8.13%, p=0.001) and arterial-alveolar oxygen gradient (mean difference -4.36 mmHg, 95% CI -7.19- -1.52 mmHg, p=0.003) all significantly improved in GM-CSF-treated patients with minor statistical heterogeneity (I2=0%). No serious trial-related adverse events were reported.

CONCLUSIONS

Patients with aPAP treated with inhaled GM-CSF demonstrated significant improvements in symptoms, dyspnoea scores, lung function, gas exchange and radiology indices after treatment with nebulised GM-CSF of varying duration. There is an important need to review comparative effectiveness and patient choice in key clinical outcomes between the current standard of care, whole lung lavage, with the noninvasive treatment of nebulised GM-CSF in aPAP.

Opportunistic Infection Associated with Elevated GM-CSF Autoantibodies: A Case Series and Review of the Literature

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is known to play a key role in enhancing multiple immune functions that affect response to infectious pathogens including antigen presentation, complement- and antibody-mediated phagocytosis, microbicidal activity, and neutrophil chemotaxis. Reduced GM-CSF activity and immune response provides a mechanism for increased infection risk associated with autoimmune pulmonary alveolar proteinosis (aPAP) and other disorders involving the presence of GM-CSF autoantibodies. We present a case series of five patients with persistent or unusual pulmonary and central nervous system opportunistic infections (Cryptococcus gattii, Flavobacterium, Nocardia) and elevated GM-CSF autoantibody levels, as well as 27 cases identified on systematic review of the literature.

The Role of GM-CSF Autoantibodies in Infection and Autoimmune Pulmonary Alveolar Proteinosis: A Concise Review

Autoantibodies to multiple cytokines have been identified and some, including antibodies against granulocyte-macrophage colony-stimulating factor (GM-CSF), have been associated with increased susceptibility to infection. High levels of GM-CSF autoantibodies that neutralize signaling cause autoimmune pulmonary alveolar proteinosis (aPAP), an ultrarare autoimmune disease characterized by accumulation of excess surfactant in the alveoli, leading to pulmonary insufficiency. Defective GM-CSF signaling leads to functional deficits in multiple cell types, including macrophages and neutrophils, with impaired phagocytosis and host immune responses against pulmonary and systemic infections. In this article, we review the role of GM-CSF in aPAP pathogenesis and pulmonary homeostasis along with the increased incidence of infections (particularly opportunistic infections). Therefore, recombinant human GM-CSF products may have potential for treatment of aPAP and possibly other infectious and pulmonary diseases due to its pleotropic immunomodulatory actions.

Long-Term Safety and Efficacy of Gene-Pulmonary Macrophage Transplantation Therapy of PAP in Csf2ra-/- Mice

Hereditary pulmonary alveolar proteinosis (PAP) is a genetic lung disease characterized by surfactant accumulation and respiratory failure arising from disruption of GM-CSF signaling. While mutations in either CSF2RA or CSF2RB (encoding GM-CSF receptor α or β chains, respectively) can cause PAP, α chain mutations are responsible in most patients. Pulmonary macrophage transplantation (PMT) is a promising new cell therapy in development; however, no studies have evaluated this approach for hereditary PAP (hPAP) caused by Csf2ra mutations. Here, we report on the preclinical safety, tolerability, and efficacy of lentiviral-vector (LV)-mediated Csf2ra expression in macrophages and PMT of gene-corrected macrophages (gene-PMT therapy) in Csf2ra gene-ablated (Csf2ra^-/-) mice. Gene-PMT therapy resulted in a stable transgene integration and correction of GM-CSF signaling and functions in Csf2ra^-/- macrophages in vitro and in vivo and resulted in engraftment and long-term persistence of gene-corrected macrophages in alveoli; restoration of pulmonary surfactant homeostasis; correction of PAP-specific cytologic, histologic, and biomarker abnormalities; and reduced inflammation associated with disease progression in untreated mice. No adverse consequences of gene-PMT therapy in Csf2ra^-/- mice were observed. Results demonstrate that gene-PMT therapy of hPAP in Csf2ra^-/- mice was highly efficacious, durable, safe, and well tolerated.

Pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) is a syndrome characterized by the accumulation of alveolar surfactant and dysfunction of alveolar macrophages. PAP results in progressive dyspnoea of insidious onset, hypoxaemic respiratory failure, secondary infections and pulmonary fibrosis. PAP can be classified into different types on the basis of the pathogenetic mechanism: primary PAP is characterized by the disruption of granulocyte-macrophage colony-stimulating factor (GM-CSF) signalling and can be autoimmune (caused by elevated levels of GM-CSF autoantibodies) or hereditary (due to mutations in CSF2RA or CSF2RB, encoding GM-CSF receptor subunits); secondary PAP results from various underlying conditions; and congenital PAP is caused by mutations in genes involved in surfactant production. In most patients, pathogenesis is driven by reduced GM-CSF-dependent cholesterol clearance in alveolar macrophages, which impairs alveolar surfactant clearance. PAP has a prevalence of at least 7 cases per million individuals in large population studies and affects men, women and children of all ages, ethnicities and geographical locations irrespective of socioeconomic status, although it is more-prevalent in smokers. Autoimmune PAP accounts for >90% of all cases. Management aims at improving symptoms and quality of life; whole-lung lavage effectively removes excessive surfactant. Novel pathogenesis-based therapies are in development, targeting GM-CSF signalling, immune modulation and cholesterol homeostasis.

Pulmonary alveolar proteinosis in patients with adenosine deaminase deficiency

BACKGROUND

Inherited defects in the function of adenosine deaminase (ADA) cause severe combined immunodeficiency (SCID) and affect many other cells and tissues.

OBJECTIVES

We sought to characterize the frequency and features of pulmonary alveolar proteinosis (PAP) in patients with ADA deficiency.

METHODS

Clinical and laboratory features of all patients with SCID caused by ADA deficiency in a single center were analyzed. Bronchoalveolar lavage (BAL) fluid and lung biopsy specimens were stained with hematoxylin and eosin and periodic acid-Schiff, visualized by means of electron microscopy, and studied for associated infections. As a control group, BAL fluid and biopsy specimens from 22 patients with SCID caused by other genetic abnormalities were similarly assessed.

RESULTS

Among 16 consecutive patients with ADA deficiency, 7 had BAL fluid containing periodic acid-Schiff-positive surfactant-like material with macrophages engulfing degenerating lamellar bodies and/or lung biopsy specimens with alveolar spaces filled with homogeneous granular eosinophilic material and large macrophages. The lung pathology was typical of PAP. Identification of various pathogens coincided with PAP in 3 of these patients. We have diagnosed PAP among patients with ADA deficiency more commonly in the last 10 years than previously (P= .05), likely reflecting increased awareness of this condition. There were no significant differences in the clinical or immunologic characteristics between patients with ADA deficiency with or without PAP. Similar findings of PAP were not found among patients with SCID caused by other genetic abnormalities (P= .001). ADA coupled to polyethylene glycol or allogeneic hematopoietic stem cell transplantation rapidly corrected this pulmonary complication. PAP seems to have contributed to the death of only 1 patient with ADA deficiency.

CONCLUSIONS

ADA deficiency predisposes to the development of PAP, which could be reversed after enzyme replacement or transplantation.

The molecular basis of pulmonary alveolar proteinosis

Pulmonary alveolar proteinosis (PAP) comprises a heterogenous group of diseases characterized by abnormal surfactant accumulation resulting in respiratory insufficiency, and defects in alveolar macrophage- and neutrophil-mediated host defense. Basic, clinical and translational research over the past two decades have raised PAP from obscurity, identifying the molecular pathogenesis in over 90% of cases as a spectrum of diseases involving the disruption of GM-CSF signaling. Autoimmune PAP represents the vast majority of cases and is caused by neutralizing GM-CSF autoantibodies. Genetic mutations that disrupt GM-CSF receptor signaling comprise a rare form of hereditary PAP. In both autoimmune and hereditary PAP, loss of GM-CSF signaling blocks the terminal differentiation of alveolar macrophages in the lungs impairing the ability of alveolar macrophages to catabolize surfactant and to perform many host defense functions. Secondary PAP occurs in a variety of clinical diseases that presumedly cause the syndrome by reducing the numbers or functions of alveolar macrophages, thereby impairing alveolar macrophage-mediated pulmonary surfactant clearance. A similar phenotype occurs in mice deficient in the production of GM-CSF or GM-CSF receptors. PAP and related research has uncovered a critical and emerging role for GM-CSF in the regulation of pulmonary surfactant homeostasis, lung host defense, and systemic immunity.

FoxP3+ regulatory T cells restrain splenic extramedullary myelopoiesis via suppression of hemopoietic cytokine-producing T cells

Extramedullary myelopoiesis occurs in peripheral organs such as spleen and produces many types of myeloid cells with diverse functions in response to inflammation and infection. It is increased during immune responses and chronic inflammation and is a significant factor in regulating inflammatory diseases and immunity. Increased myeloid cells are found in FoxP3-deficient mice but the mechanism has been unclear. We investigated the mechanism by which FoxP3(+) regulatory T cells regulate the extramedullary myelopoiesis. We found that Ab or genetic depletion of FoxP3(+) regulatory T cells greatly increased the number of the myeloid progenitors in spleen during immune responses. Consistently, the splenic myelopoiesis was effectively suppressed by increased numbers of natural or induced FoxP3(+) regulatory T cells. We demonstrated that myelopoiesis is positively regulated by splenic CD4(+) T cells that produce myelopoietic cytokines (GM-CSF and IL-3), and these effector CD4(+) T cells are induced from naive CD4(+) T cells in response to antigenic stimulation. FoxP3(+) regulatory T cells were able to effectively suppress the differentiation of naive T cells into myelopoietic cytokine-producing T cells. This suppression was found to be dependent on cell contact but independent of TGFbeta. Unlike splenic myelopoiesis, marrow myelopoiesis is not significantly affected by FoxP3(+) regulatory T cells. We conclude that FoxP3(+) T cells can negatively regulate splenic extramedullary myelopoiesis by suppressing the naive T cell differentiation into myelopoietic cytokine-producing CD4(+) T cells. Our results provide new insights into regulation of extramedullary myelopoiesis.

Effects of decreased calmodulin protein on the survival mechanisms of alveolar macrophages during Pneumocystis pneumonia

Pneumocystis infection causes increased intracellular levels of reactive oxygen species (ROS) and the subsequent apoptosis of alveolar macrophages (Amø). Assessments of key prosurvival molecules in Amø and bronchoalveolar lavage fluids from infected rats and mice showed low levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) and reduced activation of phosphoinositide-3 kinase (PI-3K). Ubiquitous calcium-sensing protein calmodulin protein and mRNA levels were also reduced in Amø during Pneumocystis pneumonia (Pcp). Calmodulin has been implicated in control of GM-CSF production and PI-3K activation in other immune cell types. Experiments to determine the control of GM-CSF and PI-3K by calmodulin in Amø showed that GM-CSF expression and PI-3K activation could not be induced when calmodulin was inhibited. Calmodulin inhibition also led to increased levels of ROS and apoptosis in cells exposed to bronchoalveolar lavage fluids from infected animals. Supplementation of Amø with exogenous calmodulin increased survival signaling via GM-CSF and PI-3K and reduced ROS and apoptosis. These data support the hypotheses that calmodulin levels at least partially control survival signaling in Amø and that restoration of GM-CSF or PI-3K signaling will improve host response to the organism.

Out of breath: GM-CSFRalpha mutations disrupt surfactant homeostasis

Pulmonary alveolar proteinosis (PAP) is a rare disorder in which surfactant homeostasis in the lung is impaired, causing respiratory distress and, in severe cases, respiratory failure. Most cases of PAP are associated with the formation of autoantibodies against the cytokine granulocyte/macrophage colony-stimulating factor (GM-CSF), which is required for normal surfactant homeostasis and lung function. New studies now identify three patients in whom PAP was caused by mutations in the gene encoding the ligand-binding α chain of the GM-CSF receptor.

Colony-stimulating factors in inflammation and autoimmunity

Although they were originally defined as haematopoietic-cell growth factors, colony-stimulating factors (CSFs) have been shown to have additional functions by acting directly on mature myeloid cells. Recent data from animal models indicate that the depletion of CSFs has therapeutic benefit in many inflammatory and/or autoimmune conditions and as a result, early-phase clinical trials targeting granulocyte/macrophage colony-stimulating factor and macrophage colony-stimulating factor have now commenced. The distinct biological features of CSFs offer opportunities for specific targeting, but with some associated risks. Here, I describe these biological features, discuss the probable specific outcomes of targeting CSFs in vivo and highlight outstanding questions that need to be addressed.

The granulocyte macrophage colony stimulating factor (GM-CSF) regulates amyloid beta (Abeta) production

One of the hallmarks of Alzheimer's disease (AD) is the accumulation of amyloid beta (Abeta) plaques in the brain parenchyma. An inflammatory component to AD has been suggested in association with increased cytokine release. We have previously shown that CD40L stimulation of microglia induces increases in pro-inflammatory cytokines such as interleukin-1beta (IL-1beta), IL-6, IL-8 and GM-CSF. We have also shown that CD40L stimulation increases Abeta levels in HEK-293 cells over-expressing both the amyloid precursor protein (APP) and CD40 (HEK/APPsw/CD40). In this study, we show that GM-CSF neutralizing antibodies mitigate the CD40L-induced production of Abeta in HEK/APPsw/CD40 cells. In addition, we demonstrate that treatment of these cells with recombinant GM-CSF significantly increases Abeta levels. Furthermore, we show that shRNA silencing of the GM-CSF receptor gene significantly reduces Abeta levels to below base line in non-stimulated HEK/APPsw/CD40 cells. Analysis of cell surface proteins revealed that silencing of the GM-CSF receptor also decreases APP endocytosis (therefore reducing the availability of APP to be cleaved in the endosomes). Taken together, our results suggest that GM-CSF operates downstream of CD40/CD40L interaction and that GM-CSF modulates Abeta production by influencing APP trafficking. GM-CSF signaling may be a suitable therapeutic target against Abeta production in AD.