For adults diagnosed with aggressive blood cancers, the promise of targeted immunotherapy can be undermined by the tumor's ability to shed the very protein that makes it a target. This case illuminates a clinically urgent escape mechanism that may become more prevalent as blinatumomab use expands into earlier treatment lines and older patient populations.
A 69-year-old woman with Philadelphia chromosome-negative B-cell acute lymphoblastic leukemia achieved measurable residual disease negativity after a single cycle of blinatumomab, the CD3/CD19 bispecific T-cell engager, following initial hyper-CVAD induction. After the patient voluntarily discontinued therapy, frank hematological relapse occurred within three months of that MRD conversion. The relapsed clone had entirely lost surface CD19 expression while retaining cytoplasmic CD22, providing a viable alternative target. Strikingly, karyotypic analysis revealed an apparent shift from the diagnostic hyperdiploid clone to a seemingly normal karyotype, raising the possibility that a cytogenetically distinct subclone survived blinatumomab-driven immunological pressure. Inotuzumab ozogamicin, a CD22-directed antibody-drug conjugate, achieved a second MRD-negative remission, though disease control proved transient.
CD19 antigen loss following CD19-directed therapy — whether blinatumomab or CAR-T constructs such as tisagenlecleucel — is now a recognized mechanism of immune escape, with reported rates approaching 10–30% in relapsed/refractory B-ALL. This case adds an unusual cytogenetic dimension: the apparent clonal shift suggests that immunotherapy may exert selective pressure on pre-existing minor clones rather than solely inducing antigen downregulation in the dominant clone. The retained CD22 expression underscores the clinical rationale for upfront or sequential CD22-directed salvage. Key limitations are inherent to single case reports — causality and generalizability cannot be established — but the findings reinforce emerging consensus that comprehensive immunophenotypic and cytogenetic restaging at every relapse is non-negotiable. For clinicians and informed patients, this case is a timely reminder that partial or abbreviated immunotherapy courses may optimize conditions for escape clone selection.