Predicted Indirectly reCognizable HLA epitopes (PIRCHE) are associated with poorer outcome after single mismatch unrelated donor stem cell transplantation: a study of the Cooperative Transplant Study Group (KTS) of the German Group for Bone Marrow and Stem Cell Transplantation (DAG-KBT)

There is no established standard for selection of mismatched unrelated donors. Indirect recognition of HLA mismatches can be predicted using the model of “Predicted Indirectly ReCognizable HLA Epitopes” (PIRCHE). We performed a multicenter retrospective study evaluating the impact PIRCHE on outcome after allogeneic stem cell transplantation (allo-HSCT) from single mismatched (HLA 9/10 matched) unrelated donors. The study cohort included 424 adult recipients of HLA 9/10 matched unrelated donor transplants (9/10 MUD), treated for AML or MDS at 6 transplant centers across Germany. Detection of PIRCHE was associated with lower overall survival (OS) (47 vs. 57%, p = 0.04), higher non-relapse mortality (NRM) (32 vs. 20%, p = 0.05), and higher incidence of chronic graft-versus-host disease (GVHD) (49 vs. 31%, p = 0.04) at 2 years. Cumulative incidence of acute GVHD grade 2–4 at 6 months was not significantly different (30 vs. 23%, p = 0.2). OS for 9/10 MUD with no PIRCHE was similar to 10/10 MUD (57 vs. 55%). In multivariate analysis, PIRCHE retained negative impact on OS (RR 1.5, 95% CI 1.0–2.1, p = 0.03) and NRM (RR 1.7, 95% CI 1.0–2.9, p = 0.03). To the best of our knowledge, for the first time, we show the association of PIRCHE and survival outcome after allo-HSCT. The PIRCHE model, if validated in an independent cohort, may allow selection of permissible HLA mismatches that enable improved transplant outcome.