Impact of Optimal Doses of Antithymocyte Globulin Conditioning on Graft-versus- Host Disease and Virus Reactivation in Haploidentical Hematopoietic Stem Cell Transplantation

Acute graft-versus-host disease (aGvHD) is an important complication of haplo-HSCT. The Seattle group initially introduced the use of ATG as a treatment for acute graft-versus-host disease (aGVHD) in allogeneic hematopoietic stem cell transplantation (haplo-PBSCT) recipients. Presently, in both myeloablative and reduced-intensity conditioning (RIC) haplo-PBSCT, ATG is part of postengraftment immunosuppressive regimens.

The regimens for prophylaxis of GVHD based on 10mg/kg rabbit anti-human thymocyte immunoglobin (ATG, Thymoglobulin®, Genzyme Polyclonals S.A.S) effectively reduced the occurrence of grade II-IV aGvHD. However, the incidence of cytomegalovirus (CMV) and EB virus (EBV) reactivation were higher due to a slower immune reconstitution. The 100-day cumulative incidence of CMV and EBV viremia were both over 70% in our unmanipulated haplo-PBSCT program. The optimal dose of ATG balancing the efficacy of GVHD prophylaxis and the risk of virus reactivation in haplo-PBSCT remains unknown.

Reports on the pharmacokinetics of Thymoglobulin in allo-HSCT revealed a high variability. Recent pharmacokinetic studies have shown that the half-life of total ATG after transplant is longer than the active ATG (which is available to bind to human lymphocytes and causes the desired immunological effects). And active ATG appears more associated with pharmacodynamics effects. The investigators found that virus reactivation and acute GVHD were highly affected by ATG exposure (area under the curve, AUC) in previous cohort study. The investigators have found an optimal range of active ATG exposure balancing the efficacy of GVHD prophylaxis and the risk of virus reactivation. The incidence of CMV reactivation and III-IV aGVHD reduced to 60%, 6% respectively.

The results suggested that Individualized dosing of ATG has a potential advantage in balancing the efficacy of GVHD prophylaxis and the risk of virus reactivation in haplo-PBSCT. This may improve the survival and quality of life of patients undergoing haplo-PBSCT. A prospective randomized trial is required to compare the efficacy of Individualized dosage of ATG as a prophylaxis for acute GVHD in haplo-PBSCT.