Hematopoietic Stem Cell Transplantation in an International Cohort of Colony Stimulating Factor‐1 Receptor (CSF1R)‐Related Disorder

BACKGROUND: Colony stimulating factor-1 receptor (CSF1R)-related disorder (CSF1R-RD) is an autosomal dominant, rapidly progressive, demyelinating disease leading to death usually within a few years. Because of the central role of CSF1R in microglia functions, allogeneic hematopoietic stem cell transplantation (HSCT) has been suggested as a therapy for CSF1R-RD. OBJECTIVES: To report multicenter clinical (Expanded Disability Scoring Scale [EDSS]), neurocognitive), neuroimaging (Sundal score), and biological (neurofilament light chain [NfL]) outcomes after HSCT in CSF1R-RD. METHODS: We report an international cohort of 17 adult patients (8 females/9 males, 43.3 ± 9.4 years) who were treated in seven transplant centers. Patients were evaluated for a median of 2.5 years post-HSCT, including one patient with follow-up of 8 years. We also report neurological outcomes of the first child transplanted to date with biallelic CSF1R variants. RESULTS: In the first 6 months post-HSCT, 2 patients died from early complications of myeloablative transplantation, and clinical and radiological severity scores worsened in most surviving adult patients. At 12 months post-HSCT, most patients completely stabilized or improved in certain clinical domains. Radiological scores fully stabilized or slightly improved in all but one of the patients. Plasma/serum NfL sharply decreased in most patients after transplantation. Notably, 7/8 adult patients who received a reduced-intensity conditioning regimen displayed similar neurological outcomes as patients who underwent myeloablative transplantation. CONCLUSIONS: After an initial clinical and radiological deterioration in the first 6 months post-transplantation, HSCT can halt disease progression in patients with CSF1R-RD, regardless of their presenting clinical symptoms. The possibility of reduced conditioning regimens in CSF1R-RD opens the way to treat older patients.