Post-transplant cyclophosphamide plus anti-thymocyte globulin lowered serum IL-6 levels compared with post-transplant cyclophosphamide alone after haploidentical hematopoietic stem cell transplantation

Background: Post-transplant cyclophosphamide (PTCy) and anti-thymocyte globulin (ATG) are both common prophylactic strategies for graft-versus-host disease (GVHD) in haploidentical hematopoietic stem cell transplantation (haplo-HSCT). Interleukin (IL)-6 is a surrogate marker for cytokine release syndrome (CRS) and acute GVHD. Method: This study compared the clinical outcomes and complications of haplo-HSCT with PTCy plus ATG versus PTCy monotherapy according to serum IL-6 levels at Chungnam National University Hospital (Daejeon, South Korea) from January 2019 to February 2023. Results: Forty patients who underwent haplo-HSCT were analyzed. There was a significant difference in IL-6 levels between the PTCy plus ATG and PTCy alone groups (7.47 ± 10.55 vs . 117.65 ± 127.67; p = 0.003). More patients in the PTCy plus ATG group had CRS grade 0 than in the PTCy alone group ( p < 0.001). Serum IL-6 levels were associated with grade II-IV acute GVHD (r = 0.547, p <0.001). The cumulative incidence (CI) of grade II–IV acute GVHD was significantly higher in the PTCy alone group (67.9% vs . 4.8%; p <0.001). There was no significant difference in the CI of chronic GVHD between the PTCy plus ATG and PTCy alone groups (72.1% vs . 82.0%; p = 0.730). The CI of 1-year non-relapse mortality was significantly higher in the PTCy alone group compared with the PTCy plus ATG group (42.2% vs . 15.9%; p = 0.022). The 1-year overall survival (OS) was significantly better in the PTCy plus ATG group (75.9% vs . 35.3%; p = 0.011). Conclusion: Serum IL-6 levels were higher with PTCy alone than with PTCy plus ATG. The addition of ATG before stem cell infusion affects IL-6 levels and reduces the incidences of CRS and grade II–IV acute GVHD in haplo-HSCT. This study suggests that PTCy plus ATG as GVHD prophylaxis in haplo-HSCT is beneficial in terms of the clinical outcomes and complications of HSCT.