Low-dose ATG/PTCy for graft-versus-host disease prevention in haploidentical transplantation: a single-center experience

Jian Hong¹Xinglin Liang¹Jing Ni²Min Ruan¹Zhangbiao Long¹Jifei Dai¹Li Liang¹Mingya Yang¹Ziyang Zhang¹Shihao Zhang^3,4Jian Ge¹Mingzhen Yang¹Qingsheng Li^1*

• ¹Department of Hematology, First Affiliated Hospital of Anhui Medical University, Hefei, China
• ²Department of Hematology, Xuanwu Hospital, Capital Medical University, Beijing, Beijing Municipality, China
• ³Institute of Clinical Pharmacology, Anhui Medical University, Hefei, Anhui Province, China
• ⁴Key Laboratory of Anti-Inflammatory and Immune Medicine, Ministry of Education, Anhui Collaborative Innovation Centre of Anti-Inflammatory and Immune Medicine, Hefei, China

The combination of anti-thymocyte globulin (ATG) and post-transplant cyclophosphamide (PTCy) has been administered for graft-versus-host disease (GVHD) prophylaxis of haploidentical hematopoietic stem cell transplantation (haplo-HSCT) in recent years. Varied doses of ATG and PTCy were applied in multiple studies with promising outcomes. 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 42.9%, 34.7% and 12.2%, respectively. The 2-year CIs of overall and moderateto-severe chronic GVHD were 44.7% and 27.7%, respectively. The 2-year overall survival, disease-free survival, non-relapse mortality and CI of relapse were 66.7%, 54.8%, 25.5% and 19.7%, respectively. Between 7.5 and 5 mg/Kg ATG groups, no significant difference on CIs of acute GVHD was observed. Interestingly, pre-ATG ALC impacted the occurrence of acute GVHD.With a cutoff point of 0.585×10 9 /L, low ALC group showed reduced CIs of grade I-IV (16.7% versus 58.0%, p=0.01), II-IV (16.7% versus 45.1%, p=0.06) and III-IV (0 versus 19.4%, p=0.05) acute GVHD as compared to high ALC group.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.