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PHYLOS trial: PTCy as GvHD prophylaxis after mismatched unrelated HCT
By Ella Dixon
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HLA mismatches remain one of the greatest challenges to successful allogeneic HSCT and are associated with increased incidence of aGvHD and non-relapse mortality (NRM).1 In vivo T-cell depletion is utilized for GvHD prophylaxis in mismatched unrelated donor (MMUD) HSCT transplant; however, GvHD outcomes remain inconsistent.1 PTCy has shown efficacy as a GvHD prophylactic for HLA-mismatch in familial haploidentical transplant.1 The prospective, multicenter phase II PHYLOS trial (NCT03270748) assessed clinical outcomes using PTCy in combination with a calcineurin inhibitor and MMF as GvHD prophylaxis in 77 patients with AML (n = 64) or MDS (n = 13). The primary endpoint was the cumulative incidence (CI) of Grade II–IV aGvHD at 100 days post-MMUD transplant. Results were published in Blood Advances by Raiola et al.1 |
| Key learnings |
| The 100-day CIs of Grade II–IV and Grade III–IV aGvHD were 18.2% and 6.5%, respectively. The 1-year CI of moderate cGvHD was 13.4% and 9.4% for severe cGvHD. 92% of patients achieved full-donor chimerism with complete neutrophile engraftment by Day 30. |
| At 1 year, the OS was 78.6%, with a graft-relapse-free survival of 55.3%, suggesting that PTCy leads to acceptable long-term outcomes. Relapse at 1 year was reported in 23.8% of patients, leading to death in 12% of patients. |
| The 1-year NRM rate was 9.1%, with sepsis being the most common non-relapse cause of death. The most common SAEs included infections and infestations (27%), GI complications (24%), and hematologic/lymphatic toxicities (14%). The most common toxicity was oral mucositis (34%). |
| These findings indicate that PTCy leads to a low rate of aGvHD and improves clinical outcomes of MMUD transplantation, offering a viable GvHD prophylaxis strategy, with outcomes comparable to haploidentical transplants. Further comparative studies with other GvHD prophylaxis strategies are warranted. |
Abbreviations: aGvHD, acute graft-versus-host disease; AML, acute myeloid leukemia; cGvHD, chronic graft-versus-host disease; CI, cumulative incidence; GI, gastrointestinal; HLA, human leukocyte antigen; HSCT, hematopoietic stem cell transplant; MDS, myelodysplastic syndromes; MMF, mycophenolate mofetil; MMUD, mismatched unrelated donor; NRM, non-relapse mortality; OS, overall survival; PTCy, post-transplant cyclophosphamide; SAE, severe adverse event.
- 1. Raiola AM, Bruno B, Risitano A, et al. Post transplant cyclophosphamide as GvHD prophylaxis in patients receiving mismatched unrelated HCT: the PHYLOS trial. Blood Adv. 2025. Online ahead of print. DOI: 10.1182/bloodadvances.2024015173
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