The Use of Anti-Thymocyte Globulin Is Associated with Increased Chance of Survival Free from Relapse and Graft-Versus-Host Disease after Allogeneic Peripheral Blood Stem Cell Transplantation for Adults with Philadelphia-Negative Acute Lymphoblastic Leukemia: An Analysis By the Acute Leukemia Working Party of the EBMT

BACKGROUND: Allogeneic hematopoietic stem cell transplantation (allo-SCT) is considered a standard of care for adults with high risk Philadelphia-negative acute lymphoblastic leukemia (Ph-neg ALL). During the last decade mobilized peripheral blood stem cells (PBSCT) has become predominant source of graft for allo-SCT. However, as compared to bone marrow, PBSCT is associated with increased risk of chronic graft-versus-host disease (cGVHD). Attempts to reduce the cGVHD rate include the addition of anti-thymocyte globulin (ATG) to the conditioning regimen. The goal of this registry-based, retrospective study was to analyze the effect of ATG on results of allo-PBSCT in adults with Ph-neg ALL.

PATIENTS AND METHODS: 682 patients, aged 18-74 years, with Ph-neg ALL, treated with un-manipulated allo-PBSCT in first complete remission between 1997-2014 were included in the analysis. Conditioning regimen was myeloablative in 550 (81%) cases. Among 339 transplantations from matched sibling donors, ATG was used in 57 (22%) cases. In the 8/8 HLA-matched unrelated setting 204/343 (78%) patients were treated with ATG. Survival free from grade III-IV acute GVHD, cGVHD and relapse (GRFS) was the primary study end-point.

RESULTS: In a univariate analysis the use of ATG was associated with increased probability of GRFS at 3 years (46% vs 38%, p=0.02) as well as decreased incidence of the overall cGVHD (34% vs. 51%, p=0.0001) and extensive cGVHD (12% vs. 25%, p<0.0001). No significant difference could be demonstrated with regard to the incidence of grade II-IV acute GVHD (30% vs. 33%, p=0.41), grade III-IV acute GVHD (8% vs. 11%, p=0.12), relapse (28% vs. 26%, p=0.38) and non-relapse mortality (NRM, 15% vs. 17%, p=0.21) as well as probability of leukemia-free survival (LFS, 57% vs. 57%, p=0.89) and overall survival (OS, 65% vs. 65%, p=0.54).

In a multivariate model adjusted for other potential risk factors, the use of ATG was associated with reduced risk of grade II-IV aGVHD (HR=0.64, p=0.007), grade III-IV aGVHD (HR=0.52, p=0.03), overall cGVHD (HR=0.61, p=0.001), extensive cGVHD (HR=0.4, p<0.0001), and NRM (HR=0.62, p=0.04). No significant effect was found with regard to the incidence of relapse (p=0.27), LFS (p=0.7) and OS (p=0.16). GRFS was significantly increased with the use of ATG (HR=0.74; p=0.009). Among other factors a chance of GRFS was significantly decreased with increasing patient age (HR=1.1 for each 10 years, p=0.02), transplantations with reduced-intensity conditioning (HR=1.61, p=0.0009) and positive recipient CMV serological status (HR=1.3, p=0.02).

CONCLUSIONS: Patients with Ph-neg ALL treated with allo-PBSCT benefit from the use ATG in terms of survival free from GVHD and relapse. The use of ATG should therefore be recommended in this setting. Further studies are needed to explore potential role of the ATG brand and dose.