Risk Factors for Graft-Versus-Host Disease (GVHD) in Haploidentical Hematopoietic Cell Transplantation (HCT) Using Post-Transplant Cyclophosphamide (PTCy)

Haploidentical hematopoietic cell transplantation (haploHCT) has been increasing since the advent of post-transplant cyclophosphamide (PTCy). Using the CIBMTR database, we determined risk factors for acute (a) and chronic (c) graft-versus-host disease (GVHD) after haploHCT. Patients with AML, ALL, MDS, or CML who underwent PTCy-based haploHCT (2013-2016) were analyzed and categorized into 4 groups based on conditioning intensity (myeloablative [MAC] or reduced intensity [RIC]) and graft source (bone marrow [BM] or peripheral blood [PB]). 646 patients were identified (MA-BM = 79, MA-PB = 183, RIC-BM = 192, RIC-PB = 192) for analysis. The incidence of grade 2-4 aGVHD at 6 months was highest in MAC-PB (44%), followed by RIC-PB (36%), MAC-BM (36%), and RIC-BM (30%) (p=0.002). The same pattern was found for cGVHD at 2 years: 44%, 35%, 27%, and 25%, respectively (p (Figure). In multivariable analysis ( Table ), RIC-BM had less grade 3-4 aGVHD compared to MAC-BM (HR 0.31, p=0.006) and less cGVHD compared to MAC-PB (HR 0.47, p=0.001). No conditioning-graft source group was significant for grade 2-4 aGVHD or overall survival. To better determine the significance of graft source, a subset analysis of MAC and RIC was performed, showing a trend for increased cGVHD with PB compared to BM in MAC (HR 1.81, p=0.05) and RIC (HR 1.72, p=0.02), however this analysis was not powered to detect differences at 0.01 significance (48% and 56% respectively). Older donor age (>50 vs. Conditioning intensity, graft source, and donor age are risk factors for GVHD after PTCy-based haploHCT. Consistent with published data, our results indicate that the risk of cGVHD is higher after PB and PTCy does not negate this risk. These results support the use of BM as graft source in PTCy-based haploHCT.