ATG Dose Correlates with Acute and Chronic GvHD In Patients Undergoing Reduced-Intensity Conditioning (RIC) Allogeneic Stem Cell Transplantation: A Large Retrospective Monocenter Analysis on 301 Patients.
Authors: Crocchiolo Roberto , Furst Sabine , Castagna Luca , Cheikh Jean El , Faucher Catherine , Deviller Raynier , Oudin Claire , Oudin Claire , Vazquez Alberto , Belmecheri Nawel , Granata Angela , Blaise Didier 
Published: October 2019

Abstract
Abstract 3485

Introduction:
RIC associating Fludarabine-Busulfan-ATG (FBA) is quite popular as preparative for allogeneic hematopoietic stem cell transplantation (RIC-AlloSCT). However the best association us still a matter of debate. Busulfan is crucial for disease control but limited by a dose-dependent toxicity and ATG plays a pivotal role in the prevention of both acute and chronic GvHD but with a potential higher relapse rate. Here we retrospectively compared different FBA regimens among adult patients transplanted at our Institution for a hematological malignancy, with the aim of identifying whether some pre- or peri-transplant variables are predictive of outcome.

Patients and methods:
on 635 patients allografted between May 1998 and Feb 2010, a total of 301 patients affected by malignancy received FBA-based RIC-AlloSCT and were the object of the present analysis. Comparisons between baseline patient, donor and AlloSCT characteristics with transplant outcome were performed: univariate and multivariate Cox regression analysis were used to find any correlation between the above mentioned variables and OS, DFS, NRM, relapse incidence, acute (aGvHD) and chronic (cGvHD) GvHD. Variables with p<0.20 were included in multivariate analysis, and only variables with a p<0.05 were retained in the final model.

Results:
median (range) follow-up was 917 (71-4051) days. Two-year OS, DFS and NRM were 66%, 58% and 20% for the entire cohort. Relapse at two years was 26%. Cumulative incidence of grade 2–4, grade 3–4, overall and extensive cGvHD were: 29%, 12%, 58% and 40%. In multivariate analysis, patient's age was significantly associated with OS, NRM, grade 2–4 and 3–4 aGvHD; disease status at transplant significantly correlated with DFS and relapse incidence. ATG at a dose of 5 mg/kg compared to 2.5 mg/kg, was significantly associated with a reduced risk of developing grade 3–4 aGvHD (HR= 0.46, 95% CI: 0.22–0.99, p=0.05) and cGvHD (HR= 0.33, 95% CI: 0.20–0.54, p<0.0001), without affecting relapse (p=n.s.). Overtime we modified our standard RIC from F5B2A1 (Fludarabine over 5 d, oral Bu over 2 d and ATG for1d) (N=114) to F5BX2A2 (Fludarabine over 5 d, IV Bu over 2 d and ATG over 2 d) (N=84). Population was not similar and notably older (51 vs. 57 years, p<0.0001) in the latter group. Despite this we observed similar NRM (22% vs. 23%: p=n.s.) in patients older than 55 years; in patients younger than 55 F5BX2A2 was associated with better but not statistically significant OS (77% vs. 65% at two years, p=0.21) and reduced NRM (9% vs. 18% at two years, p=0.10).

Conclusions:
in this large monocenter series of adult patients undergoing FBA-based RIC-AlloSCT, the use of ATG at a dose of 5 mg/kg appeared to significantly reduce incidence and severity of cGvHD and grade 3–4 aGvHD compared to ATG 2.5 mg/kg without increasing disease relapse. Moreover, despite patients' disparity between the two cohorts, reduced NRM was observed in patients < 55 years old treated with F5BX2A2 regimen with respect to those receiving F5B2A1.

Disclosures:
Off Label Use: Zevalin is off-label use in conditioning regimen in France.