Supplementary Material for: Successful Cord Blood Transplantation for Idiopathic CD4⁺ Lymphocytopenia

Idiopathic CD4⁺ lymphocytopenia (ICL) is the depletion of CD4⁺ lymphocytes to <300 cells/mm³ without human immunodeficiency virus infection or other causes of lymphocytopenia. ICL causes fatal infections; its etiology remains unclear and it lacks consensus regarding therapeutic options. We report the first patient with ICL who had a successful clinical course following a cord blood transplant (CBT). A 45-year-old woman was diagnosed with ICL and underwent partial hepatectomy for an abscess caused by the Mycobacterium avium complex. No specific gene alterations were detected through next generation sequencing-based evaluation. Following a reduced-intensity conditioning (RIC) regimen consisting of fludarabine, busulfan, and 4 Gy total body irradiation, a single-unit CBT was performed. Neutrophils were engrafted on day +14. CD4⁺ lymphocyte counts increased to over 300 cells/mm³ on day +436. After 75 months, she was alive without any sequelae. CBT with an RIC regimen could be a curable treatment option for ICL.