Abstract

The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway is crucial for immune function and hematopoiesis, which partly explains why cytopenia is a major adverse effect of ruxolitinib, a selective JAK1/2 inhibitor. Hematologic toxicity restricts the use of ruxolitinib during the pre-engraftment phase of allogeneic hematopoietic stem cell transplantation for myelofibrosis and graft-versus-host disease (GVHD) prophylaxis. While some reports have described its use in peripheral blood and bone marrow transplantation, its application in cord blood transplantation (CBT) remains unknown. Herein, we report two cases of CBT in which ruxolitinib was administered to treat GVHD after prior allogeneic transplantation. In Case 1, a patient underwent a third transplant for acute myeloid leukemia, and in Case 2, a patient received CBT for post-transplant lymphoproliferative disorder following transplantation for classic Hodgkin lymphoma. Neutrophil engraftment was achieved in both cases, and Case 2 developed a pre-engraftment immune reaction. Platelet and red blood cell engraftment did not occur in either case, likely due to underlying comorbidities or limited survival, rather than the effects of ruxolitinib. This is the first report documenting successful neutrophil engraftment in CBT with concurrent ruxolitinib administration, suggesting its potential feasibility during the pre-engraftment phase. Further studies are warranted to evaluate its effects on multilineage hematopoietic recovery, infections, GVHD, and relapse risk.