High Exposure of Rabbit Anti-Thymocyte Globulin (ATG) Is Strongly Associated with Inferior DFS in Pediatric Patients with Malignancy Undergoing Alpha-Beta T-Cell Depleted Haploidentical HCT

The PTCTC ONC1401 trial reported a 75% 2-year disease-free survival (DFS) for pediatric patients with acute leukemia or MDS undergoing AB-TCR/CD19 depleted (AB-TCD) haploidentical HCT. Patients ≥10 years had significantly worse DFS. Conditioning for AB-TCD HCT typically includes rATG (Thymoglobulin®) 3 mg/kg/day on days -12 to -10. Models of rATG pharmacokinetics (PK) show slower clearance in older children. We hypothesized worse DFS seen in older patients may be due to excessive in vivoT-cell depletion by residual rATG post HCT.