Clinical outcome of hematopoietic stem cell transplantation for juvenile myelomonocytic leukemia: A Single center in China

Abstract Objective: To evaluate the safety and efficacy of hematopoietic stem cell transplantation (HSCT) in the treatment of juvenile myelomonocytic leukemia (JMML). Methods: A retrospective analysis was conducted on 142 JMML pediatric patients who underwent HSCT at our center from October 2018 to February 2025. The median age at transplantation was 33 months (range: 11–99 months). The transplantation methods comprised: haploidentical + cord blood complementary transplantation (CT) (83 cases), haploidentical donor lymphocyte infusion (DLI) + cord blood transplantation (DLI+CB) (19 cases), unrelated donor transplantation (MUD) (27 cases), haploidentical post-transplant cyclophosphamide (PTCy) transplantation (PBSCT) (9 cases), and haploidentical ex vivo T-cell-depleted (TDH) transplantation (4 cases). In the CT group, haploidentical peripheral blood stem cells (PBSCs) (MNC >15×10^8/kg) were infused on day 0. GVHD prophylaxis included cyclophosphamide on days +3 and +4, along with FK506 and mycophenolate mofetil (MMF). Unrelated cord blood was infused on day +6. For the DLI + CB group, haploidentical donor lymphocytes (4–8×10^8/kg) were administered on day -11, followed by conditioning with CY, BU, TT, and Flu from day -8 to -3. Unrelated cord blood was infused on day 0, the unrelated cord blood matching requires ≥7/10 HLA locus , and Kir assay was carried out at the same time. Cord blood with Haplotype Cen-Bx was preferred. GVHD prophylaxis included FK506 and MMF. Among the 27 unrelated donor transplantations, 25 were 10/10 HLA-matched, and 2 were 9/10 matched. The conditioning regimen consisted of BU+CY+TT+Flu±ATG-F, with a median PBSC mononuclear cell count of 8.6×10^8/kg infused on day 0. GVHD prophylaxis included FK506 and MMF. The haploidentical PTCy group followed the same infusion strategy as the complementary group. Four patients received ex vivo αβT-cell-depleted (TDH) transplantation without routine post-transplant immunosuppression. Results: With a median follow-up of 45 months (range: 7–81 months). The overall survival (OS) and leukemia-free survival (LFS) rates for all 142 patients were 92% and 91.7%, respectively. All 4 TDH transplant patients survived. The OS rates were 97.5% for the CT group (83 cases), 82.3% for the DLI + CB group (19 cases), 86.7% for the MUD group (27 cases), and 77.8% for the haploidentical PTCy group (9 cases). No statistically significant differences were observed between groups (P=0.057). The cumulative incidence of grade II–IV acute GVHD was 16.2% (23 cases), including 7 cases of grade III–IV. Chronic GVHD occurred in 18.3% (26 cases), primarily involving the skin, with 2 cases affecting the lungs, 1 the joints, and 2 the liver. Post-transplant viral reactivation was mostly transient, with HHV6 being the most common. Two cases progressed to viral encephalitis. Other viral reactivations included 5 cases of CMV and 2 of adenovirus. Three cases of veno-occlusive disease (VOD) were reported, 2 of which were mild. Conclusion: HSCT demonstrates significant clinical efficacy and relative safety in treating JMML. Different transplantation methods yielded high survival rates, with complementary transplantation showing particular advantages. TDH transplantation exhibited promising preliminary results, warranting further exploration.