Integrin alpha4 blockade sensitizes drug resistant pre-B acute lymphoblastic leukemia to chemotherapy.

Bone marrow (BM) provides chemoprotection for acute lymphoblastic leukemia (ALL) cells, contributing to lack of efficacy of current therapies. Integrin alpha4 (alpha4) mediates stromal adhesion of normal and malignant B-cell precursors, and according to gene expression analyses from 207 children with minimal residual disease, is highly associated with poorest outcome. We tested whether interference with alpha4-mediated stromal adhesion might be a new ALL treatment. Two models of leukemia were used, one genetic (conditional alpha4 ablation of BCR-ABL1 [p210(+)] leukemia) and one pharmacological (anti-functional alpha4 antibody treatment of primary ALL). Conditional deletion of alpha4 sensitized leukemia cell to nilotinib. Adhesion of primary pre-B ALL cells was alpha4-dependent; alpha4 blockade sensitized primary ALL cells toward chemotherapy. Chemotherapy combined with Natalizumab prolonged survival of NOD/SCID recipients of primary ALL, suggesting adjuvant alpha4 inhibition as a novel strategy for pre-B ALL.