Baseline and posttreatment CNS-HLH patient characteristics. Baseline characteristics for all patients in this study, including age at onset of symptoms, nature of clinical symptoms, age at eventual diagnosis, familial HLH mutation, therapy received before CNS-HLH diagnosis, CSF assessment, and hematoxylin and eosin–stained brain biopsy histopathology (20× magnification). Black arrows indicate perivascular lymphocytic infiltrates. Also displayed are T1 MRI scans and NK-cell immunologic tests at diagnosis and after HCT. White arrows indicate contrast-enhancing MRI lesions. -, NK-cell testing not indicated for the patient’s specific mutation. HCT, hematopoietic cell transplantation; IVIG, intravenous immune globulin; MMF, mycophenolate mofetil; NK, natural killer; WBC, white blood cell.