Successful treatment with mesenchymal stem cells for steroid-refractory late-onset idiopathic pneumonia syndrome following allogeneic hematopoietic cell transplantation.

The reportedly poor outcome of late-onset idiopathic pneumonia syndrome (IPS) necessitates new approaches to its treatment. A 55-year-old man who had undergone allogeneic hematopoietic cell transplantation (allo-HCT) for myelodysplastic syndrome 1 year ago developed dyspnea with acute skin graft-versus-host disease (GVHD) flare-up while tapering immunosuppressive agents. He presented with acute respiratory distress syndrome with ground-glass opacities in the right upper and left lower lobes. All infectious tests, including multiplex polymerase chain reaction of nasal wash, were negative, and broad-spectrum antibiotic therapy was refractory. The patient was diagnosed with late-onset IPS and was refractory to methylprednisolone pulse therapy. He then showed a favorable response to mesenchymal stem cell (MSC) infusion. After eight infusions of MSCs, he had no IPS recurrence for over one year. Recently, preclinical studies have reported the potential therapeutic utility of MSC infusion for treating IPS, and our case supports its potential for treating late-onset IPS.