Furthermore, early CD4+ T cell reconstitution (defined by CD4+ T cell >50 × 106/L within 100 days after UCBT) resulted in better leukemia-free survival (LFS) (HR = 0.24, p = 0.003), improved OS (HR = 0.16, p = 0.0014) with lower NRM (HR = 0.20, p = 0.0072). This evidence concerns the gene CD4 and leukemia.