The significance of CD49f expression in pediatric B-cell acute lymphoblastic leukemia.

Objectives: CD49f is an adhesion molecule present on malignant lymphoblasts in B-cell acute lymphoblastic leukemia; it is associated with a poor prognosis. CD49f expression has been proposed as a marker for measurable residual disease (MRD) marker, but this marker has yet to be implemented in clinical practice.

Methods: In this study, we used flow cytometry to detect CD49f expression by leukemic blasts in paired bone marrow and cerebrospinal fluid samples at diagnosis and bone marrow at day 15 of treatment.

Results: At diagnosis, 93% of bone marrow and 100% of cerebrospinal fluid lymphoblasts expressed CD49f. The intensity of CD49f expression statistically significantly increased during treatment (P < .001). In MRD-negative end-of-treatment samples, only a small population of hematogones expressed CD49f. Interestingly, the intensity of CD49f expression varied among the different groups of recurrent genetic abnormalities. The ETV6::RUNX1 fusion and ETV6::RUNX1 combined with the high hyperdiploid group were associated with increased expression, whereas the Philadelphia-like group showed low CD49f expression. The lower CD49f expression at diagnosis predicted a lower MRD rate at day 15 of treatment.

Conclusions: We concluded that CD49f can be used as an MRD marker and possible prognostic factor in B-cell acute lymphoblastic leukemia.