Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains the only curative option for high-risk myeloid malignancies. Post-transplant cyclophosphamide (PT-Cy) has proven to be effective for graft versus host disease (GVHD) prophylaxis. Given that graft-versus-tumor (GVT) effect plays a major role in reducing the risk of disease relapse, the application of PT-Cy must balance the risk of relapse. Mixed chimerism (MC) refers to a state of concurrent presence of recipient and donor cells post allo-HSCT which may precede relapse disease.
We investigated the impact of PT-Cy on early MC (EMC) and disease relapse in patients with a myeloid malignancy post allo-HSCT.
This retrospective single-center study included patients that underwent allo-HSCT between 2015 and 2021. Patient and disease characteristics were collected from their electronic health records. EMC was defined as <95% donor cells at day 90-120 post allo-HSCT.
A total of 144 patient that received an allo-HSCT were included in the study. Hundred and eight (75%) patients received PT-Cy as part of the GVHD prophylaxis regimen. The majority underwent allo-HSCT for acute myeloid leukemia (62%) or myelodysplastic syndrome (31%). Sixty-five percent received allo-HSCT from a matched unrelated donor transplant and 65% received myeloablative conditioning regimen. A lower rate of chronic GVHD (p = 0.03) and a higher rate of EMC (p = 0.04) were observed in patients that received PT-Cy. PT-Cy was not associated with overall survival and relapse-free survival. Multivariable analysis identified measurable residual disease status (p = 0.003), hematopoietic cell transplantation-specific comorbidity index (p = 0.012) and chronic GVHD (p = 0.006) as independent prognostic variables for OS. AML-adverse risk (p = 0.004) and EMC (p = 0.018) were independently prognostic for RFS. While EMC overall was not significantly associated with higher risk of relapse, EMC was associated with shorter RFS within adverse-risk AML patients.
Our study shows that PT-Cy was associated with an increased risk of EMC. The predictive value of EMC for relapse remains unclear and may depend on the underlying disease, which should be validated in a larger cohort.

Copyright © 2023. Published by Elsevier B.V.