Integrin Alpha 4 Inhibition Prolongs the Survival of NSG Mice Engrafted with CD19-Negative Post-CART19 Relapsed B-ALL.

Despite therapeutic advancements and improved patient outcomes, relapsed and refractory B-cell acute lymphoblastic leukemia (r/r B-ALL) after anti-CD19 chimeric antigen receptor T-cell (CART19) therapy due to antigen loss remains a critical unmet clinical need. In this study, we identify that integrin α4 is consistently expressed on B-ALL cells before and after CART19. CRISPR/Cas9-mediated CD19 knockout in primary B-ALL cells did not alter integrin α4 expression, further suggesting stable integrin α4 expression independent of CD19 a stable target. Using the United States Food and Drug Administration (FDA)-approved anti-integrin α4 antibody natalizumab (NZM), we demonstrated effective disruption of leukemia cell adhesion to both VCAM-1, the primary integrin α4 ligand, and to stromal OP9 cells, thereby critically reducing interactions with the leukemia-supportive microenvironment. Most importantly, NZM treatment markedly extended survival in NSG mice engrafted with post-CART19-relapsed B-ALL compared with controls. Our work establishes integrin α4 as an ideal marker for identifying leukemia cells in patients receiving CART19.