A toxicology study of Csf2ra complementation and pulmonary macrophage transplantation therapy of hereditary PAP in mice

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 (and murine homologs). We conducted a toxicology study of PMT of gene-corrected macrophages (mGM-RαMϕs) or saline-control intervention in or wild-type (WT) mice including single ascending dose and repeat ascending dose studies evaluating safety, tolerability, pharmacokinetics, and pharmacodynamics. Lentiviral-mediated cDNA transfer restored GM-CSF signaling in mGM-RαMϕs. Following PMT, mGM-RαMϕs 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-RαMϕs, respectively) and only in mice but not in WT mice. PMT reduced lung disease severity in mice. Results indicate PMT of mGM-RαMϕs was safe, well tolerated, and therapeutically efficacious in mice, and established a no adverse effect level and 10-fold safety margin.