Prognostic factors for neutrophil engraftment after haploidentical cell transplantation with PT-Cy in patients with acute myeloid leukemia in complete remission, on behalf of the ALWP-EBMT.

The use of haplo-HCT with posttransplant cyclophosphamide (PT-Cy) is a new standard in the treatment of hematological diseases. A paucity of data exists on risk factors for engraftment failure in haplo-HCT with PT-Cy. We analyzed 1939 adults with acute myeloid leukemia (AML) who received a first haplo-HCT from 2010 to 2019. Status at haplo-HCT was first complete remission (CR1) in 72.5% of patients, secondary AML was reported in 9.9%. Median follow-up was 24.4 months and median age at haplo-HCT was 51 years. Stem cell source was bone marrow (BM) in 42% and peripheral blood stem cell (PBSC) in 58%, and 64% of patients received a myeloablative conditioning (MAC) regimen. Cumulative incidence of primary graft failure (GF) was 6%; GF was reported in 110 patients and 54 died before day +30 with no sign of cell recovery. Overall, 33 patients underwent a second HCT in a median time of 45 days and 13 were alive at last follow-up, the 2-year overall survival (OS) after second HCT being 32.4%. In multivariate analysis, factors independently associated with the risk of nonengraftment were: secondary AML (HR 1.30, p = 0.003), use of RIC (HR 1.22, p < 0.001), and use of BM (HR 1.21, p < 0.001). At 2 years, leukemia-free survival (LFS) and OS for the entire population was 55.2% (95% CI: 52.6-57.6) and 60.9% (95% CI: 58.4-63.3), respectively. Incidence of GF after haplo-HCT with PT-Cy is lower than reported T-cell-depleted haplo-HCT. Optimization of conditioning regimen and graft source should be considered for reducing the risk of GF in haplo-HCT recipients using PT-Cy.