Outcomes of Blinatumomab Based Therapy in Children with Relapsed, Persistent, or Refractory Acute Lymphoblastic Leukemia: a Multicenter Study Focusing on Predictors of Response and Post-Treatment Immunoglobulin Production

The management of Refractory/Relapsed B-cell Acute Lymphoblastic Leukemia (R/R ALL) remains challenging. Incorporating blinatumomab in R/R ALL treatment has shown encouraging results. We describe the outcome and predictors of response in children receiving blinatumomab as a bridge to definitive therapy. Immunoglobulin (Ig) G and viral serology before and after therapy were evaluated. Thirty-three patients that failed standard first-line treatments due to relapsed ALL (n = 22), persistent minimal residual disease (MRD) (n = 8), or refractory disease (n = 3) received blinatumomab. Grade 2 toxicity occurred in 27.2% of patients. MRD remission (<0.01%) was achieved in 72.7% of patients. Pre-blinatumomab absolute lymphocyte count (ALC) and MRD/ALC ratio significantly associated with MRD-response. Patients with t(1;19) translocation had lower response rate, compared to all other cytogenetic categories (p = 0.013). One-year event-free survival (EFS) and overall survival (OS) were 69.2% and 79.7%, respectively. Analysis of OS and EFS showed pre-blinatumomab MRD level, ALC, MRD/ALC ratio, t(1;19), and post-blinatumomab MRD remission associated with survival. Following blinatumomab, 83% (15/18) of tested patients had low IgG levels. IgG seronegative status was observed in 83% (12/15) for varicella zoster, 35% (6/17) for herpes zoster, 18% (3/17) for cytomegalovirus, and 26% (5/17) for Epstein Barr virus. Blinatumomab produced encouraging results in children with R/R ALL and low disease burden bridging to definitive therapy. Incorporating baseline genetics and biomarkers may help identify subgroups likely to be responsive/resistant to therapy. Viral serological testing pre- and post-blinatumomab is recommended to optimize supportive and preemptive therapy.