T-Cell Depletion Improves the Composite End Point Graft-Versus-Host Disease-Free, Relapse-Free Survival after Allogeneic Hematopoietic Stem Cell Transplantation

Introduction: Allogeneic hematopoietic stem cell transplantation (HSCT) is a well-established therapeutic modality for a variety of hematological malignancies. Unfortunately it is associated with significant morbidity and mortality related to cancer relapse and transplant complications, including graft versus host disease (GvHD). GvHD-free, relapse-free survival (GRFS) is a recently reported composite end point which allows estimating risk of death, relapse and GvHD simultaneously [ Holtan et al., Blood 2015 ]. T-cell depletion (TCD) is a well established strategy for GvHD prevention, but is probably associated with increased risk of relapse. In the present work we investigated the effect of partial TCD (pTCD) on GRFS in order to evaluate its impact on patientsO morbidity-free survival. Patients and methods: We performed a retrospective study on 333 patients who underwent allogeneic HSCT for hematologic malignancies at our center from 2004 to 2014 with grafts from HLA identical siblings or HLA 10/10 matched unrelated donors. 171 patients received pTCD grafts, obtained through incubation with alemtuzumab in vitro washed before infusion followed on day +1 by an add-back of donor T cells. 162 patients received T cell repleted (non-TCD) grafts. Donor lymphocyte infusions were given at three months to all patients without GvHD who had received pTCD grafts with reduced intensity conditioning and when needed to patients, transplanted with either pTCD or non-TCD grafts with mixed chimerism. Kaplan-Meier estimates were employed to determine the probability of 1-year and 5-year overall survival (OS), progression free survival (PFS) and GRFS. Events determining GRFS included grade 3-4 acute GvHD, systemic therapy-requiring chronic GvHD, relapse, or death. Differences between survival curves were determined using Log-rank Mantel-Cox test. Cox regression was used to examine the independent effect on OS, PFS and GRFS of clinical factors including age, underling disease, disease status at transplant, disease risk index, conditioning, donor type, stem cell source, year of transplantation and T-cell depletion. Cumulative incidence estimates of relapse and non-relapse mortality (NRM) were calculated with relapse or death from other causes defined as competitive events with the Fine and Gray method. Results: According to institutional practices, the group receiving pTCD grafts comprised more patients transplanted in complete remission (67%) than the group receiving non-TCD grafts (41%, p Conclusion: pTCD appears to improve GRFS in allogeneic HCST recipients without significantly affecting OS and PFS. These results extend our knowledge about the effects of TCD on transplant-related morbidity and mortality, suggesting that pTCD could improve patientsO quality of life by reducing acute GvHD and NRM without impairing the curative potential of allogeneic HSCT. Disclosures Chalandon: Roche: Honoraria, Membership on an entity9s Board of Directors or advisory committees.