How I treat postimmunotherapy relapsed B-ALL.

Despite significant advancements in single-antigen targeted therapies for B-cell acute lymphoblastic leukemia (B-ALL), nonresponse and relapse persist as major challenges. Antigen escape after blinatumomab or CD19-directed chimeric antigen receptor (CAR) T cells (CD19-CAR), as CD19-negative B-ALL or lineage switch (LS) to acute myeloid leukemia, present diagnostic and treatment complexities. Given the poor outcomes for patients experiencing a postinfusion relapse, particularly those with loss of the target antigen, a strategic approach to diagnosis and treatment is imperative. In this discussion, we outline a systematic approach to managing postimmunotherapy events, categorized by CD19-positive relapse, CD19-negative relapse, and LS. We explore treatment modalities including CD19-CAR reinfusions, humanized CAR constructs, combinatorial strategies, and alternative antigen-targeted therapies, such as blinatumomab and inotuzumab. Challenges in diagnosis, particularly with antigen-escape, are addressed, highlighting the role of next-generation sequencing and multiparameter flow cytometry for myeloid marker monitoring.