Very Low Dose of Anti-T-Lymphocyte Globulin Protects Against Severe Forms of Graft Versus Host Disease in High Risk Patients: The Experience in Our Center
Authors: Mora Joan Manuel , Bermúdez Arancha , Cortés Miguel Angel , González Romero Yolanda , Colorado Mercedes , Fernández Martínez Cristina , Cabero Martínez Almudena , Gómez David , Fernández Luis Sara , García Ávila Sara , Yáñez Lucrecia , Ormazabal Irati , Martín Sánchez Guillermo , Arroyo Jose Luis , Núñez Javier , Romón Iñigo , Conde Eulogio , Richard Carlos 
Published: October 2019

Abstract
Background
Patients undergoing hematopoietic stem cell transplantation (HSCT) are at high risk of multiple complications being graft versus host disease (GvHD) one of the most concerning. Addition of anti-T-lymphocyte globulin (ATG-Fresenius ®) reduces the incidence of acute and chronic GvHD however, optimal dose has not yet been established. Standard dose (60 mg/kg) has shown a significantly lower moderate-severe cGvHD yet its effect in Progression Free Survival (PFS) and Overall Survival (OS) is contradictory. Our primary objective was to analyze the efficacy of low ATG dose (21 mg/kg) in the prophylaxis of acute and chronic GvHD. As secondary objective we analyzed non-relapse mortality (NRM), infectious and non-infectious complications, GvHD and relapse free survival (GRFS), overall survival and progression free survival in high risk patients undergoing HSCT.
Patients and methods
We retrospectively analyzed 57 patients who underwent HSCT in our center from 2012 to 2017, receiving a total dose of 21 mg/kg (7 mg/kg on day -3, -2 and -1) of ATG as part of the GvHD prophylaxis, associated to cyclosporine/tacrolimus and MMF/short course-MTX. The conditioning regimen were myeloablative in 42 patients (73.7%). The donor was unrelated in 46 cases (80.7%). Seventeen (29.9%) had a mismatch (16 unrelated, 1 sibling). Stem cell source was peripheral blood in 51 patients (89.4%). Forty six (80.7%) patients were positive for CMV, from these 17 (36.9%) were paired with seronegative donors. The median age was 57 years old (18-70), 38(66.7%) were males. The most frequent diagnosis were Acute Myeloblastic Leukemia (40.4%), myelofibrosis (17.5%) and myelodisplastic syndrome (14%); 28 (49%) had a HCTI score ≥ 3 and 16 (29%) a high risk DRI score. Thirty patients (52.6%) were in complete remission at the moment of HSCT. (Table 1)
Results
Hematopoietic engraftment was observed in 54 patients (94.7%). The median neutrophil and platelet engraftment were 14 (10-34) and 15 (9-28) days, respectively. Primary graft failure occurred in 3 patients (2 myelofibrosis, 1 AML). Twenty (39.2%) out of 51 evaluable patients developed grade 2-4 acute GvHD. The cumulative incidence of grade 3-4 aGvHD was 8.8% (95% CI, 3.2-17.9%). Skin was the most affected organ (62%). We found a cumulative incidence of moderate to severe cGvHD of 35.2% (95% CI 22.7-47.9%), only 5 cases (10.6%) were severe, with a median onset at day 177 (57-893). The median duration of immunosuppresive systemic therapy was 488 days (207-2046) in the group of patients with moderate to severe cGvHD.
Twelve patients died due to transplant related events, 7 were reported before day 100, all of infectious etiology. The NRM at two years was 21.9% (95% CI, 12-33.7%). Eleven patients (19.2%) had at least two episodes of CMV reactivation and one had cytomegalic gastrointestinal disease. One patient developed postransplantation lymphoproliferative disorder associated to Epstein Barr virus. Twenty patients (35%) developed noninfectious complications, being hemorrhagic diathesis, hepatotoxicity and severe mucositis the most frequents.
With a median follow up of 28 months in alive patients (3-67), the GRFS at one year, OS and PFS at two years were 47.6% (95% CI, 42.8-52.2%), 59% (95% CI, 54.5-63.2%) and 52% (95% CI, 46.9-56.5%), respectively. The relapse incidence at two years was 26.3% (95% CI 14.7-39.4%).
Conclusions
In our center, the use of low ATG doses is protective against severe forms of acute GvHD, offering also a moderate protection against chronic GvHD in a cohort with high prevalence of mismatched unrelated donors, high median age and high risk DRI and HCTI. This approach doesn't seem to have a significant negative impact neither in GRFS, OS and PFS at two years.

Disclosures
No relevant conflicts of interest to declare.