Low-dose ATG/PTCy for graft-versus-host disease prevention in haploidentical transplantation: influences of ATG doses and pre-ATG absolute lymphocyte count

The combination of anti-thymocyte globulin (ATG) and post-transplant cyclophosphamide (PTCy) has been administered for graft-versus-host disease (GVHD) prophylaxis of haploidentical transplantation (haplo-HSCT) in recent years. However, the optimal doses of ATG and PTCy are yet to be determined. Here, we report the joint use of low-dose ATG (7.5 or 5 mg/Kg) and PTCy (29 mg/Kg) for GVHD prophylaxis in our center and analyze the impact of different ATG doses and absolute lymphocyte count (ALC) before ATG infusion. Fifty-one consecutive leukemia patients who underwent haplo-HSCT with this regimen were included, with 27 and 24 patients receiving 7.5 and 5.0 mg/Kg ATG, respectively. The 100-day cumulative incidences (CIs) of grade I-IV, II-IV and III-IV acute GVHD were 42.0%, 34.0% and 12.0%, respectively. no significant difference on acute GVHD was observed between two ATG groups. Interestingly, with a cutoff point of 0.585×10 ⁹ /L, low pre-ATG ALC group (18 patients) showed reduced CIs of grade I-IV (16.7% versus 56.3%, p=0.01), II-IV (16.7% versus 43.8%, p=0.07) and III-IV (0 versus 18.8%, p=0.05%) acute GVHD as compared to high ALC group (32 patients). The results suggested that this low-dose ATG/PTCy regimen was feasible and pre-ATG ALC levels could influence the occurrence of acute GVHD in this regimen.