Introduction Infant leukemia, including AML and ALL occurring within the first year of life, is a rare and aggressive disease with poor prognosis. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a crucial treatment option, but the impact of pre-transplant remission and minimal residual disease (MRD) on outcomes in this population remains unclear. Furthermore, the comparative effectiveness of haploidentical versus unrelated donors needs further evaluation to optimize transplant strategies.Methods We retrospectively analyzed 126 infants with leukemia who underwent allo-HSCT at Hebei Yanda Lu Daopei Hospital and Beijing Lu Daopei Hospital between March 2013 and December 2024. The primary outcome was 3-year overall survival (OS), analyzed based on pre-transplant remission status and minimal residual disease (MRD), as determined by flow cytometry (FCM) or gene-based PCR testing.

Results Among the 126 infant leukemia patients, 81 had acute myeloid leukemia (AML) and 45 had acute lymphoblastic leukemia (ALL), with a male-to-female ratio of 81:45 and a median age of 8.6 months (range, 1–12). Prior to transplantation, 100 patients were in first complete remission (CR1), 18 in ≥CR2, and 8 had no remission (NR). All patients (100%) achieved successful engraftment. The median follow-up was 39 months (range, 1–120) as of May 31, 2025.In infants with AML (iAML), 3-year overall survival (OS) was 74.5% (50/66) in CR1, 71.4% (5/7) in ≥CR2, and 33.3% (2/6) in NR (P=0.0105). Among 73 iAML patients in remission, 3-year OS was comparable between those with FCM-positive MRD (74.3%, 20/73) and FCM-negative MRD (74.3%, 53/73). No significant OS difference was found between haploidentical HSCT (74.4%, 46/61) and matched unrelated HSCT (70%, 7/10; P=0.464).In infants with ALL (iALL), 3-year OS was 91.1% (30/34) in CR1 and 72.7% (8/11) in ≥CR2 (P=0.191). Patients with MRD positivity by FCM or gene PCR had inferior survival (60%, 3/5) compared to MRD-negative patients (85.6%, 35/40; P=0.026). Among iALL patients in remission, 3-year OS was 91.7% (13/15) with unrelated HSCT and 81.7% (24/29) with haploidentical HSCT (P=0.274). In iALL patients with KMT2A rearrangement (KMT2A-r), 3-year OS was 86.7% (29/33) vs. 74.0% (9/12) in those without KMT2A-r (P=0.146).

Conclusion Allo-HSCT offers favorable outcomes in infant leukemia, especially with pre-transplant remission. Non-remission predicts poorer survival. MRD status was prognostic in iALL but not iAML. Survival was similar between haploidentical and unrelated donors. iALL patients with KMT2A-r may benefit, pending further validation.

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2025
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