Haematopoietic stem cell transplantation for juvenile myelomonocytic leukaemia: a descriptive single-centre case series from a resource-limited setting

Background Juvenile myelomonocytic leukaemia (JMML) is a rare myeloproliferative neoplasm of early childhood driven by RAS–MAPK pathway activation, for which allogeneic haematopoietic stem cell transplantation (HSCT) is the only established cure. Data from low- and middle-income countries, where donor access, drug availability and monitoring capacity differ from the settings that generate most published evidence, are scarce. Methods We reviewed all consecutive children with JMML who underwent allogeneic HSCT at a single tertiary centre in northern India between January 2019 and August 2025. Engraftment, graft failure, poor graft function and transplant complications were classified by pre-specified consensus criteria. The analysis is descriptive: proportions are reported with exact 95% confidence intervals (CI) and survival as Kaplan–Meier estimates, without hypothesis testing. Results Eight children (seven boys; median age 19.5 months) received myeloablative fludarabine–busulfan–melphalan conditioning and fresh peripheral blood stem cells from four HLA-matched siblings and four haploidentical parents. Initial neutrophil engraftment occurred in six (75%; 95% CI 34.9–96.8) at a median of 17.5 days, and sustained engraftment in five (62.5%; 95% CI 24.5–91.5). Primary graft failure, secondary graft failure and poor graft function occurred in one patient each, all haploidentical recipients; all four matched-sibling recipients engrafted durably. Cytokine release syndrome (grade 1–2) occurred in three haploidentical recipients and skin-limited grade I–II acute graft-versus-host disease in two patients. Three children died without relapse: two after graft failure (days +28 and +41) and one of a COVID-19/MIS-C–like illness 28 months after transplantation. No relapse occurred. At a median follow-up of 35 months among survivors, five of eight children were alive (62.5%; 95% CI 24.5–91.5); Kaplan–Meier overall and event-free survival at 36 months were 60% (95% CI 19.5–85.2) and 46.9% (95% CI 12.0–76.3), respectively. Conclusions Allogeneic HSCT for JMML, including haploidentical transplantation with post-transplant cyclophosphamide, was feasible in a resource-limited setting, and no patient relapsed. However, graft failure or poor graft function affected three of four haploidentical recipients, and this cohort is far too small to support any comparison between donor types. Donor-specific antibodies, HLA disparity, splenic disease burden, conditioning exposure and graft composition warrant systematic attention in alternative-donor transplantation for JMML in similar settings.