Impact of Underlying Disease and Total Body Irradiation on the Incidence of Graft-Versus-Host Disease After Allogeneic Hematopoietic Cell Transplantation.

Multiple factors have been described to influence the risk of acute or chronic graft-versus-host disease (aGVHD or cGVHD) after allogeneic hematopoietic cell transplantation (HCT), including underlying chronic myeloid leukemia (CML) and high-dose total body irradiation (TBI). However, the impact of the underlying disease or low-dose TBI on the risk of GVHD in the modern era has not been determined. The objective of this study was to determine risk factors for GVHD in the modern era in the setting of antithymocyte globulin (ATG)-based GVHD prophylaxis. This retrospective study included 1219 patients with hematologic malignancy who underwent first peripheral blood allogeneic HCT using myeloablative fludarabine and busulfan conditioning ± low-dose total body irradiation, along with ATG, cyclosporine, and methotrexate as GVHD prophylaxis. The adjusted cumulative incidence of GVHD was compared between patient subgroups using multivariable competing risks regression. When disregarding the underlying disease, risk factors for grade 2-4 aGVHD were donor type other than matched sibling donor (non-MSD) and lack of low-dose TBI (non-TBI). Risk factors for grade 3-4 aGVHD were non-MSD, non-TBI, and CMV donor negative/recipient positive serostatus (D-R+). Risk factors for moderate-severe cGVHD were ≤9/10 HLA match, non-male/male donor/recipient sex, and non-TBI. In models including the underlying disease, additional significant risk factors were chronic lymphocytic leukemia (CLL) for grade 2 to 4 aGVHD (sub-hazard ratio over acute myeloid leukemia [SHR] 3.16, 95% CI 1.97-5.08, P < .001); CLL and acute lymphoblastic leukemia (ALL) for grade 3-4 aGVHD (SHR for CLL 3.54, 95% CI 1.54-8.17, P = .003 and SHR for ALL 2.26, 95% CI 1.26-4.04, P = .006); and myelofibrosis (MF) for moderate-severe cGVHD (SHR 2.14, 95 CI 1.34-3.41, P = .001). In the modern era when using ATG for GVHD prophylaxis, newly identified risk factors include CLL and non-TBI for grade 2-4 aGVHD; CLL, ALL, and non-TBI for grade 3-4 aGVHD; and MF and non-TBI for moderate-severe cGVHD. These findings, if confirmed in a separate cohort, should be taken into consideration when tailoring the prophylaxis and monitoring of GVHD.