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 posttransplant cyclophosphamide (PtCy) has improved graft-versus-host disease (GVHD) prophylaxis in haplo-HCT, patients continue to experience life-threatening complications. Interferon gamma and interleukin-6 are central in the pathophysiology of GVHD and cytokine release syndrome (CRS), and both cytokines signal through Janus kinase 1 (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 (OS). 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 to 5 CRS. There were no cases of primary graft failure. No patients developed grade 3 to 4 acute GVHD (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%. OS at 1 year was 80%. The cumulative incidence of nonrelapse mortality (NRM) 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, and NRM, and encouraging rates of GVHD-free relapse-free survival and OS after haplo-HCT. This trial was registered at www.ClinicalTrials.gov as #NCT03755414.