522. Murine iPSC-Derived Macrophages Improve the In Vivo Disease Phenotype of Pulmonary Alveolar Proteinosis Due to Csf2rb Deficiency

Induced pluripotent stem cells (iPSCs) have proven applicability to various areas including disease modeling and cell therapy. Hereditary pulmonary alveolar proteinosis (herPAP) is a rare lung disease caused by mutations within the α- (CSF2RA) or β-chain (CSF2RB) of the GM-CSF receptor gene (CSF2R), resulting in the inability of alveolar macrophages (MΦ) to clear the alveolar spaces from surfactant material. Given the limited treatment options in herPAP, we evaluated the suitability of murine iPSC-derived MΦ (iPSC-MΦ) for disease modelling and as a source for an innovative cell replacement therapy. To this point we first established an efficient and robust protocol to obtain mature and functional MΦ from healthy murine iPSCs. These MΦ closely resemble their counterparts generated in vitro from bone marrow cells with regard to morphology, surface phenotype and function. Furthermore, murine Csf2rb-deficient iPSCs (miPAP) were generated and submitted to our differentiation protocol. miPAP-derived MΦ faithfully recapitulated the defects in GM-CSF signaling and MΦ function present in herPAP patients. Of note, we also evaluated the feasibility, safety and clinical benefit of the intratracheal application of healthy iPSC-MΦ using a clinically relevant in vivo mouse model of herPAP. Following single pulmonary MΦ transplantation (PMT) of 4×106 iPSC-MΦ, specific engraftment was observed in the alveolar spaces for up to 8 weeks as shown by tissue sections and PCR. Moreover, cells displayed donor-specific CD45.1 expression and typical MΦ morphology in vivo and upon re-isolation. No teratoma formation or tissue toxicity was detected in the organs of transplanted mice. Most importantly, following PMT a significant improvement of disease parameters such as reduced protein, M-CSF, GM-CSF and surfactant protein-D (SP-D) concentration was shown in the bronchoalveolar lavage fluid. We also observed a decrease in PAS-positive material in lung sections and a reduction in lung opacity in computer tomography scans. Thus, we here present an efficient differentiation protocol to obtain MΦ from iPSCs for disease modeling and introduce PMT of iPSC-MΦ as an innovative cell therapy for herPAP.