Researchers demonstrate that a single transplantation of murine macrophages into the lungs of mice suffering from herPAP can treat this life-threatening disease

Hereditary pulmonary alveolar proteinosis (herPAP) is a rare disease characterized by the slow build-up of lipo-protein material in the lungs due to the failure of highly specialized cells called macrophages, which usually eat away this material from the pulmonary air-space.

"From previous studies, we know that pulmonary macrophage transplantation (PMT) works with bone marrow-derived cells, so we wanted to see if a transplantation with iPSC-derived macrophages would show similar efficacy," says co-senior author Thomas Moritz, a hematologist at the Hannover Medical School.

"We found that single transplantation of iPSC-derived macrophages directly into the lungs of herPAP mice profoundly ameliorates herPAP symptoms over the long term. Moreover, such PMT strategies also may be useful in related diseases."

herPAP disease

Macrophages are immune cells found in every organ of the body that consumes pathogens like bacteria or viruses. "In principle, they're kind of like Pac-Man," says Nico Lachmann, the corresponding senior co-author of the study.

However, in herPAP disease, the macrophages normally found in the air sacs of the lungs, the alveoli, are absent or non-functional. Lachmann and Moritz then wanted to know if directly replacing the absent and non-functional lung macrophages with the iPSC-derived macrophages would have a therapeutic effect.

"Four months after transplantation we could see that the disease was markedly improved in herPAP mice that received the treatment," Moritz says. "And the transplanted iPSC-derived macrophages could function so efficiently because they exhibit great plasticity, which means that after transplantation, they differentiate and adapt to the murine lung environment, turning into the types of macrophages needed."

Moreover, Lachmann and Moritz observed that this plasticity allowed one transplant to be efficient enough to effectively treat the mice for at least six months representing roughly a third of a mouse's lifespan.

"This was a proof of concept study, but if the transplant to the lung worked to improve the conditions of mice with herPAP, we can expect that transplants to other organs — like the liver or brain — might work to improve the conditions of individuals with other similar diseases where macrophages are absent or non-functional," says Lachmann.

"From here, our goal is to perfect this therapy in herPAP patients and then to translate the PMT concept into a long-term or short-term therapeutic approach for other diseases."