(187) Post-Transplant Cyclophosphamide in Unrelated Donor Allogeneic Stem Cell Transplantation with Reduced Intensity and Nonmyeloablative Conditioning Regimens for Graft-Versus-Host Disease Prophylaxis

Poster Abstract: Allogeneic hematopoietic cell transplant (HCT) is a potentially curative therapy for primarily hematologic malignancies accomplished with the infusion of human-leukocyte antigen (HLA)-compatible matched related (MRD) or matched unrelated donor (MUD) hematopoietic cells to restore a competent immune system. This is preceded by chemotherapy and/or radiation, known as a conditioning regimen. This serves to treat the underlying disease and suppress the recipient’s immune system to allow for donor cell engraftment with limited rejection. Conditioning regimens may be myeloablative (MAC), reduced intensity (RIC), or nonmyeloablative (NMA) depending on patient-specific factors and considering balancing graft-versus-tumor (GVT) and graft-versus-host disease (GVHD) effects. GVHD is a significant contributor to non-relapse mortality (NRM) occurring when donor cells attack the recipient’s organ systems. Effective immunosuppression as GVHD prophylaxis is key. The current prophylaxis recommendation for MRD or MUD HCTs is a combination of a calcineurin inhibitor and an antimetabolite. Post-transplant cyclophosphamide (PTCy) as part of GVHD prophylaxis has been previously established in haploidentical HCT recipients by demonstrating meaningful reductions in the incidence and grade of GVHD, with low rates of NRM and relapse. Use has expanded to MRD and MUD HCT recipients and evaluated in several studies that have similarly shown reductions in GVHD parameters with conflicting results on rates of relapse and overall survival (OS).

UofL Brown Cancer Center started utilizing PTCy in RIC and NMA MUD HCTs in 2020. While studies have evaluated PTCy in this setting, they have been small and included limited hematologic malignancies and MAC regimens. This study will review the impact of this practice on our institution’s rates of GVHD.

The purpose of this study is to evaluate real-world safety and efficacy of PTCy in MUD allogeneic HCT. The primary objective is the rate of acute and chronic GVHD. Key secondary endpoints include rates of NRM, relapse, and OS at 6-months and 1-year.

This is a retrospective cohort review of recipients of a RIC or NMA MUD HCT for a hematologic malignancy. Patients transplanted prior to 2020 will serve as the historic control GVHD prophylaxis regimen (tacrolimus/mycophenolate) and be compared to those transplanted later and received the PTCy protocol. Continuous variables will be presented by summary statistics and categorical variables by frequency distributions. Simple linear, logistic, Cox univariable, and multivariable regression analyses will be performed. Results will be declared significant at a level of 5% without adjusting for multiple comparisons.

Final results to be presented at HOPA Annual Conference.

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