De-Escalation of Ptcy Dosing in Matched Allogenic Transplants: A Single Institution Retrospective Study
Authors: Ackula Haritha , Medawar Georgio , Cerio Caroline , Roberts Todd F. , Meleveedu Kapil 
Published: November 2021

Abstract
Introduction
The role of post-transplant cyclophosphamide (PTCy) in preventing acute GVHD (aGVHD) and chronic GVHD (cGVHD) has been well established in the haploidentical setting (Al-Homsi AS et al., Post-transplant high-dose cyclophosphamide for the prevention of graft-versus-host disease. Biol Blood Marrow Transplant. 2015;21(4):604-611). More recently, several studies are also supporting its use in matched related and unrelated donors (Williams L et al., Post-transplantation Cyclophosphamide: From HLA-Haploidentical to Matched-Related and Matched-Unrelated Donor Blood and Marrow Transplantation. Front Immunol. 2020;11(April):1-7). But as new emerging data are starting to show some toxicities from that regimen, a reevaluation of the optimal PTCy dose is highly valuable (Duléry R et al., Early Cardiac Toxicity Associated with Post-Transplant Cyclophosphamide in Allogeneic Stem Cell Transplantation. JACC CardioOncology. 2021;3(2):250-259; Goldsmith et al., Posttransplant cyclophosphamide is associated with increased cytomegalovirus infection: a CIBMTR analysis. Blood. 2021;137(23):3291-3305).
PTCy dose de-escalation in preventing GvHD was also evaluated in a phase I/II study (NCT03983850) with initial results indicating that de-escalation of PTCy (DL2, 25 mg/kg/day given in Days 3−4) may provide a feasible and effective approach in preventing severe aGvHD(McAdams MJ et al., Phase I Study De-Intensifying Exposure of Post-Transplantation Cyclophosphamide (PTCy) after HLA-Haploidentical Hematopoietic Cell Transplantation (HCT) for Hematologic Malignancies. Transplant Cell Ther Off Publ Am Soc Transplant Cell Ther. 2021;27(3): S9-S11). However, this was in the setting of haplo-identical transplants. Currently there are no studies that investigate the safety and efficacy of a lower dose of PTCy in matched allogenic transplants.
Methods
We retrospectively selected 37 consecutive patients who underwent transplant at our center from January 2017 to April 2021. Patients who received a mismatched or haploidentical transplants were excluded. 26 matched sibling or matched unrelated donor transplants were further analyzed. These were divided into 3 cohorts according to GVHD prophylaxis: cohort 1 (No-PTCy) received standard calcineurin inhibitor-methotrexate based GVHD prophylaxis (n=16), cohort 2 (PTCy-50) received PTCy at 50 mg/kg (D+3 and D+4) in combination other immunosuppressive drugs (ISD) (n=6), and cohort 3 (PTCy-25) received PTCy at 25 mg/kg (D+3 and D+4) in combination with other ISD (n=4). The reduced PTCy dosing was based on physician discretion due to various reasons (2 cardiac risk, 1 heavy pre-treatment, 1 unknown).
Results
Baseline characteristics are summarized in table 1. Median follow up for all survivors was 523 days (range, 97-1463) while it was shorter for PTCy cohorts at 152 days (97-534). There were zero grade 3 aGVHD in PTCy groups compared to 12.5% (2/16) in No-PTCy cohort (p=0.30). cGVHD was significantly lower in PTCy-50 and PTCy-25 as compared to No-PTCy (0/6, 0/4, 5/16 respectively, p=0.04). The 100-day treatment-related mortality (TRM) was significantly lower in PTCy-25 as compared to PTCy-50 and No-PTCy (0/4, 2/6, 2/16 respectively, p&lt;0.001). There was no viral reactivation (EBV/CMV) in PTCy-25 as compared to 1/6 in PTCy-50 and 5/16 in No-PTCy (p=0.54). The length of hospital stay (LOS) for transplant and the median days for neutrophil recovery (NR) were shorter in PTCy-25 as compared to PTCy-50 and No-PTCy (25.5 days, 31 days and 28.5 days respectively for LOS, p=0.60; 15.5 days, 22 days and 17.5 days for NR, p=0.87). Although the overall survival (OS) seems to favor PTCy-25 (Figure 1), it is limited by short follow up.
Conclusion
De-escalating the dose of PTCy to 25mg/kg x 2 in GVHD prophylaxis regimens appears to be efficacious and safe in patients receiving matched allogenic transplant. Further prospective studies including a larger patient sample and longer follow-up is warranted to investigate lower PTCy dosing in matched transplants over the current standard dosing.
Figure 1 Figure 1.

Disclosures
No relevant conflicts of interest to declare.