Comparative Study on Fresenius-ATG Versus Thymoglobuline-ATG for the Graft Versus Host Disease (GVHD) Prophylaxis in Allogeneic Stem Cell Transplantation from Matched Unrelated Donor: A Single Center Experience on 76 Patients
Authors: Polverelli Nicola , Malagola Michele , Turra Alessandro , Skert Cristina , Cattina Federica , Rambaldi Benedetta , Ribolla Rossella , Cancelli Valeria , Schieppati Francesca , Bonetti Marta , Bernardi Simona , Perucca Simone , Zanaglio Camilla , Russo Domenico 
Published: October 2019

Abstract
Introduction . Anti-thymocyte globulin (ATG), has been shown to significantly reduce the incidence and severity of acute and chronic graft versus host disease (GVHD) in pts submitted toallogeneic stem cell transplantation (allo-SCT).
Two different ATG formulations, derived from rabbit immunization against T antigens,thymoglobuline-ATG (tATG) andfresenius-ATG (fATG) are usually employed. However, only few retrospective studies are available in order to compare the efficacy and safety of these two drugs. Moreover, the differential impact of the two formulations on immune recovery has been poorly studied.
Methods. Clinical and laboratory data of 76 pts receivingfATG (30 mg/kg for 3 days beforeallo-SCT) ortATG (10 mg/Kg for 3 days beforeallo-SCT) as GVHD prophylaxis forallo-SCT from matched unrelated donor (MUD) for hematological malignancies at the Unit of Stem Cells Transplantation ofSpedaliCivili of Brescia between 2009 and 2014, were retrospectively collected. Basic phenotype of circulating lymphocytes was assessed by flow-cytometry at 3-months interval fromallo-SCT. The aims of the study were to compare the two ATG formulations in term of incidence of acute and chronic GVHD, infections, non-relapse mortality, relapse-free survival, overall survival and immune recovery. The study was approved by the local Ethic Committee.
Results. Overall, 46 (60%) pts receivedfATG and 30 (40%)tATG as GVHD prophylaxis, in association to cyclosporine andmethotrexate. Baseline characteristics were (median): age, 46 years (range, 17-66); male, 68%; acute leukemia, 53%; complete hematological remission, 51%; HLA full-matched (8/8), 40%; source of stem cells, peripheral blood, 87%;myeloablative conditioning regimen, 49%; median follow-up, 22 months (range, 1-88).
No significant differences were observed between the two populations according age, sex, hematological disease, disease status atallo-SCT, HLA match, stem cell source, amount of CD3+ and CD34+ cells infused and conditioning regimen.
Overall, 26 (57%)fATGand 19 (61%)tATG-exposed pts developed an acute GVHD (p=0.8); among 18 (24%) pts who developedcGVHD, 2 out of 10 (20%)fATGand 6 out of 8 (75%)tATG-receiving pts evolved towards severecGVHD(p=0.05). In particular, the cumulative incidence of severecGVHD, was 5,2% versus 27,6% at 2 years (p=0.03) infATGandtATGgroup, respectively (Figure 1).
Bacterial infections were encountered in 42 (91%) and 25 (81%) (p=0.19), fungal infections in 12 (26%) and 6 (19%) (p=0.58)fATGandtATG-treated pts. CMV reactivation was observed in 28 (61%) and 19 (73%) (p=0.43)fATGandtATG-exposed pts, respectively. However, a trend for a higher incidence of early-CMV reactivation was seen in thetATGgroup, with a cumulative incidence of CMV reactivation at 30 days of 30% versus 52% infATGandtATGcohort, respectively (p=0.09).
No differences were observed betweenfATGandtATGpopulations in term of relapse-related mortality (24% versus 40%, p=0.25), non-relapse mortality (28% versus 20%, p=0.48) and overall survival (52% versus 60%, p=0.71).
Immunologic reconstitution was evaluated in 48 pts (fATG, 64%). As compared totATG,fATGpts showed a significant lower amount of CD3-/CD16+ NK cells (median, 137/mclvs255/mcl, p=0.05) and a trend for lower CD3+CD4+CD25+CD127- T-regcells (5/mclvs11/mcl, p=0.07) and CD4/CD8 ratio (0.26vs0.57, p=0.08) at 3 months fromallo-SCT. At 6 months CD4/CD8 ratio was significantly lower infATGcompared totATGgroup (0.26vs0.42, p=0.01). At 9 months, lymphoid populations did not differ between the two cohorts.
Overall, ATG administration was well-tolerated without grade III-IV adverse events, however an increase in infusion-related events (mainly, fever and chills) was recorded infATGgroup (67%vs32%, p=0.004).
Conclusion. This retrospective study, reporting a quite large population ofallo-SCT pts from MUD homogeneously followed in a single Hematology Center, shows thatfATG-treated pts have a lower incidence of severecGVHD compared totATG. On the contrary a slight increase of early CMV reactivation has been observed intATG group. These differences do not result in a higher relapse-related or overall mortality.
The distinct immune reconstitution as identified by flow-cytometricanalysis, could justify these observations, that need to be validated by prospective studies.
Figure 1 Cumulative incidence of severecGVHD according to type of ATG employed Figure 1. Cumulative incidence of severecGVHD according to type of ATG employed

Disclosures
No relevant conflicts of interest to declare.