Hereditary pulmonary alveolar proteinosis (PAP) is a rare interstitial lung disease caused by variations in genes such as CSF2RA and CSF2RB, which disrupt granulocyte-macrophage colony-stimulating factor signaling and impair surfactant clearance. These defects lead to progressive surfactant accumulation in alveoli, resulting in respiratory dysfunction. We describe a 3-year-old girl with Turner syndrome who presented with recurrent cough and dyspnea and was diagnosed with hereditary PAP. Diagnostic evaluation included high-resolution computed tomography (HRCT), lung biopsy, and whole-exome sequencing of peripheral blood cells. The patient received anti-inflammatory antibiotics and underwent therapeutic whole lung lavage via endobronchial endoscopy. A systematic literature review of CSF2RA-associated hereditary PAP was performed. HRCT demonstrated characteristic "crazy paving" patterns, and bronchoalveolar lavage fluid showed positive Periodic acid-Schiff staining. Genetic analysis identified a novel hemizygous variation in CSF2RA (NM_000402.4:c.200_204del, p.Asn67SerfsTer8), confirmed as a de novo pathogenic variant. Whole lung lavage resulted in marked clinical improvement. We report the first documented case of hereditary PAP caused by the CSF2RA variant NM_000402.4:c.200_204del (p.Asn67SerfsTer8), expanding the genetic spectrum of this disease. Our findings reinforce that CSF2RA-related PAP exhibits phenotypic heterogeneity and confirm whole lung lavage as the cornerstone therapy. This case highlights the importance of genetic testing in diagnosing rare PAP subtypes.

Hereditary pulmonary alveolar proteinosis (hPAP) is a rare disorder caused by mutations in the CSF2RA or CSF2RB genes, leading to impaired surfactant clearance by alveolar macrophages and subsequent respiratory dysfunction. A 5-year-old female with a 2-year history of poor weight gain, fatigue, and intermittent fever was evaluated. Clinical evaluation revealed hypoxemia, while high-resolution computed tomography (HRCT) of the chest showed the characteristic "crazy-paving" pattern suggestive of PAP. Bronchoalveolar lavage (BAL) yielded milky fluid with periodic acid-Schiff (PAS)-positive material, and genetic testing confirmed a homozygous mutation in the CSF2RA gene, consistent with hPAP. The patient underwent therapeutic whole lung lavage (WLL), resulting in significant clinical improvement. This case underscores the challenges of diagnosing pediatric hPAP and the value of integrating imaging, pathology, and genetic testing. While WLL remains the mainstay of treatment, further research is needed to develop targeted therapies.

Genetic testing has significantly improved the diagnosis of childhood interstitial lung diseases (chILD), which have long challenged clinicians due to their heterogeneity and poor characterization. It is now imperative to study variants of unknown significance (VUS) to identify pathogenic mutations to optimize diagnosis and screening in patients. Furthermore, the limited treatment options for patients with chILD worsen patient outcomes. Induced pluripotent stem cell (iPSC)-derived models could be a tool to understand the effect of novel VUS and discover new therapeutic interventions. This review seeks to evaluate the fidelity of iPSC-derived models to recapitulate the pathogenic processes of chILD and test therapeutic interventions. This paper performs a systematic search over three databases to identify iPSC-derived models studying disease-causing mutations in pediatric patients with chILD and Hermansky-Pudlak Syndrome. Of the 1452 papers initially reviewed, eight papers met the inclusion criteria using iPSC-derived models to study genetic variants. The diseases covered included common manifestations of chILDs such as surfactant protein deficiencies and hereditary pulmonary alveolar proteinosis, as well as fibrotic disorders like Hermansky-Pudlak Syndrome. These models recapitulated patient histology and key pathogenic features reported in the literature, delivering mechanistic insights into these conditions. Some papers also explored the efficacy of novel treatments, such as gene therapy. iPSC-derived models can mimic aspects of human lung responses to provide a platform for disease modeling and therapeutic testing in chILD. There are opportunities to develop more complex multi-cellular models and for the study of a wider range of variants using these tools.

Pulmonary macrophage transplantation (PMT) is a gene and cell transplantation approach in development as therapy for hereditary pulmonary alveolar proteinosis (hPAP), a surfactant accumulation disorder caused by mutations in CSF2RA/B (and murine homologs). We conducted a toxicology study of PMT of Csf2ra gene-corrected macrophages (mGM-Rα+Mϕs) or saline-control intervention in Csf2raKO or wild-type (WT) mice including single ascending dose and repeat ascending dose studies evaluating safety, tolerability, pharmacokinetics, and pharmacodynamics. Lentiviral-mediated Csf2ra cDNA transfer restored GM-CSF signaling in mGM-Rα+Mϕs. Following PMT, mGM-Rα+Mϕs engrafted, remained within the lungs, and did not undergo uncontrolled proliferation or result in bronchospasm, pulmonary function abnormalities, pulmonary or systemic inflammation, anti-transgene product antibodies, or pulmonary fibrosis. Aggressive male fighting caused a similarly low rate of serious adverse events in saline- and PMT-treated mice. Transient, minor pulmonary neutrophilia and exacerbation of pre-existing hPAP-related lymphocytosis were observed 14 days after PMT of the safety margin dose but not the target dose (5,000,000 or 500,000 mGM-Rα+Mϕs, respectively) and only in Csf2raKO mice but not in WT mice. PMT reduced lung disease severity in Csf2raKO mice. Results indicate PMT of mGM-Rα+Mϕs was safe, well tolerated, and therapeutically efficacious in Csf2raKO mice, and established a no adverse effect level and 10-fold safety margin.

Hereditary pulmonary alveolar proteinosis (hPAP) is a rare lung-related primary immunodeficiency. In hPAP, variants of genes encoding the heterodimeric GM-CSF receptor alpha or beta-chains (CSF2Rα, CSF2Rβ) lead to perturbations in GM-CSF signalling. These perturbations impair the scavenging function of pulmonary alveolar macrophages leading to accumulation of surfactant proteins and lipids within the alveoli. The replacement of defective pulmonary alveolar macrophages can be achieved with allogeneic hematopoietic stem cell transplantation. However, previous reports highlight undesirable pulmonary outcomes associated with this therapeutic approach. We report a 4-year-old developmentally normal girl born of second-degree consanguineous marriage diagnosed with severe form of CSFRα-deficient PAP. She required recurrent whole lung lavage and hence was treated with allogeneic hematopoietic stem cell transplantation. A reduced toxicity treosulfan-based myeloablative regimen with alemtuzumab serotherapy was used for conditioning. Ciclosporin, mycophenolate mofetil and FAM (fluticasone inhaler, azithromycin, montelukast) were used to prevent graft-versus-host disease and immune-related complications of lung. Her post-transplant course was uneventful with full donor chimerism and complete resolution of symptoms. We demonstrate for the first time in a case of severe CSF2Rα-deficient PAP, the successful use of hematopoietic stem cell transplantation as a primary curative treatment, restoring normal lungs both anatomically and functionally. The case report provides evidence for considering allogeneic hematopoietic stem cell transplant in severe forms of CSF2R-deficient PAP.