A novel conditioning regimen involving haploid immune cell infusion combined with umbilical cord blood transplantation for the treatment of juvenile myelomonocytic leukemia.

Juvenile myelomonocytic leukemia (JMML) is a rare and highly malignant hematological tumor that occurs in children. Allogeneic hematopoietic stem cell transplantation remains the primary treatment for the vast majority of children with JMML. However, busulfan-based myeloablative conditioning regimens do not effectively solve the problem of low survival and high recurrence rates after transplantation. We previously achieved good results in the treatment of JMML with complementary transplantation and found that only one of the five patients who relapsed had umbilical cord blood (UCB) engraftment (blood 2019 134:4181). To further investigate the feasibility of UCB transplantation in JMML, we developed a novel regimen and performed a long-term follow-up analysis to evaluate its effectiveness and safety. In this multicenter, single-arm, retrospective clinical study, 17 children with JMML were treated with a novel regimen consisting of haploid immune cell infusion combined with UCB transplantation. After a median follow-up of 48 months, relapse was observed in 1 in 17 patients, with a cumulative relapse incidence rate of 6.7%. The 5-year overall and event-free survival rates were 87.4% and 82.4%, respectively. Among the included patients, seven experienced grade II-IV acute graft-versus-host disease (GVHD), including two patients with grade III-IV acute GVHD, resulting in cumulative incidence rates of 41.0% and 11.8%, respectively. Additionally, a total of two patients in the cohort developed chronic GVHD, and the cumulative incidence of chronic GVHD at 5 years was 11.8%. Conclusion: Our results suggest that, combined with a suitable regimen, UCB transplantation may be an effective and safe option for the treatment of JMML.