Itacitinib for Prevention of Graft-Versus-Host Disease and Cytokine Release Syndrome in Haploidentical Transplantation.

Haploidentical hematopoietic cell transplantation (haplo-HCT) is an increasingly used treatment for hematologic malignancies. Although post-transplant cyclophosphamide (PtCy) has improved graft vs. host disease (GvHD) prophylaxis in haplo-HCT, patients continue to experience life-threatening complications. IFN-γ and IL-6 are central in the pathophysiology of GvHD and cytokine release syndrome (CRS), and both cytokines signal through Janus kinase (JAK)-1. We tested the effect of adding the JAK-1 selective inhibitor, itacitinib, to PtCy-haplo-HCT to mitigate these complications and improve overall survival. This open-label, single-arm study evaluated the safety and efficacy of itacitinib combined with standard GvHD prophylaxis after haplo-HCT. A total of 42 patients were treated with itacitinib 200 mg daily from day -3 through +100 or +180, followed by a taper. Itacitinib resulted in low CRS grades, all patients had grade 0 (22%) or grade 1 (78%) CRS and there were no cases of grade 2-5 CRS. There were no cases of primary graft failure. No patients developed grade 3-4 aGvHD through day +180. The cumulative incidence of grade 2 aGvHD at day +100 was 21.9%. The 1-year cumulative incidence of moderate or severe chronic GvHD was 5%. The cumulative incidence of relapse at 2 years was 14%. Overall survival (OS) at 1 year was 80%. The cumulative incidence of nonrelapse mortality at day 180 was 8%. Itacitinib, when added to standard GvHD prophylaxis, was well tolerated and resulted in low rates of CRS, acute and chronic GvHD, NRM and encouraging rates of GvHD-free relapse-free survival (GRFS) and OS after haplo-HCT. NCT03755414.