Rapid Cyclosporine Tapering and Isotretinoin Usage after Unrelated Donor Hematopoietic Stem Cell Transplantation in Juvenile Myelomonocytic Leukemia.

Juvenile myelomonocytic leukemia (JMML) is a rare type of childhood leukemias, and allogeneic hematopoietic stem cell transplantation (HSCT) is known to be the only way to cure the disease. Unfortunately, relapse is still the most frequent cause of treatment failure after transplant in JMML. We investigated the feasibility of inducing graft versus leukemia (GVL) effect and the use of a differentiating agent even after unrelated HSCT in children with JMML. Seven consecutive patients with JMML underwent unrelated HSCT at a median age of 17 months. The sources of grafts were bone marrows (n=3) or HLA 1- or 2-antigen mismatched cord bloods (n=4). Only 3 of the 7 patients were in complete remission before transplantation. Intravenous busulfan, cyclophosphamide, and etoposide were used as preparative agents except in one who was conditioned with TBI-based regimen. Cyclosporine was used universally for GVHD prophylaxis with additional use of short-term methotrexate in bone marrow transplants and of methyl-prednisolone in cord blood transplants. Cyclosporine was tapered rapidly from around 1 month post-HSCT and isotretinoin (75–100 mg/m²/day) was used in selected patients who have any risk factors of relapse. Cyclosporine blood levels were 247.8±91.1, 146.6±104.2, and 88.8±52.6 ng/mL at 1, 2, and 3 months post-transplant, respectively. There was no grade 3 or 4 acute GVHD and only 2 patients developed grade 2 acute GVHD which was improved without additional treatment. Chronic GVHD was developed in 3 (1 limited, 2 extensive) of the evaluable 5 patents, which was all resolved after combined use of immune suppressive agents. Initial chimeric status analysis at 1 month revealed complete donor chimerism (CC) in 4 patients, mixed chimerism (MC) in 2 and autologous recovery (AR) in one. One of the patients with MC and the one with AR were in disease-free status. One patient whose chimeric status changed from CC to MC eventually relapsed. One patient with initial MC with residual disease turned to CC with complete remission. Another patient with initial MC but with no evidence of disease is on treatment with isotretinoin without relapse for 3 months even with persistent MC. The patient with AR relapsed early after transplant. Five patients are alive relapse-free and disease-free with a median follow-up of 16 months after transplant. The Kaplan-Meier probability of event-free survival was 66.7%. We suggest that GVL induction strategy with concomittant use of a differentiating agent might have a role to suppress leukemic relapse in JMML.