Key Points We evaluated interference with integrin alpha4–mediated stromal adhesion as a new acute lymphoblastic leukemia treatment. Integrin alpha4 blockade using natalizumab in combination with chemotherapy sensitizes pre-B acute lymphoblastic leukemia to chemotherapy.

B-lineage acute lymphoblastic leukemia (ALL) arises by transformation of a progenitor (pre-B) cell. Cure rates in adults remain low and treatment is complicated by support provided by the microenvironment to the leukemic cells, indicating an urgent need to better understand the factors that promote their survival.

Natural killer cells from acute myeloid leukaemia patients (AML-NK) show a dramatic impairment in cytotoxic activity. The exact reasons for this dysfunction are not fully understood. Here we show that the glycogen synthase kinase beta (GSK3β) expression is elevated in AML-NK cells. Interestingly, GSK3 overexpression in normal NK cells impairs their ability to kill AML cells, while genetic or pharmacological GSK3 inactivation enhances their cytotoxic activity. Mechanistic studies reveal that the increased cytotoxic activity correlates with an increase in AML-NK cell conjugates. GSK3 inhibition promotes the conjugate formation by upregulating LFA expression on NK cells and by inducing ICAM-1 expression on AML cells. The latter is mediated by increased NF-κB activation in response to TNF-α production by NK cells. Finally, GSK3-inhibited NK cells show significant efficacy in human AML mouse models. Overall, our work provides mechanistic insights into the AML-NK dysfunction and a potential NK cell therapy strategy.

The bone marrow (BM) stromal niche can protect acute lymphoblastic leukemia (ALL) cells against the cytotoxicity of chemotherapeutic agents and is a possible source of relapse. The SDF-1/CXCR4 axis is a major determinant in the crosstalk between leukemic cells and BM stroma. In the current study, we investigated the use of AMD11070, an orally available, small molecule antagonist of CXCR4, as an ALL-sensitizing agent. This compound effectively blocked stromal-induced migration of human ALL cells in culture and disrupted pre-established adhesion to stroma. To examine how to optimally use this compound in vivo, several combinations with cytotoxic drugs were tested in a stromal co-culture system. The best treatment regimen was then tested in vivo. Mice transplanted with murine Bcr/Abl ALL cells survived significantly longer when treated with a combination of nilotinib and AMD11070. Similarly, immunocompromised mice transplanted with human ALL cells and treated with vincristine and AMD11070 had few circulating leukemic cells, normal spleens and reduced human CD19+ cells in the bone marrow at the termination of the experiment. These results show that combined treatment with AMD11070 may be of significant benefit in eradicating residual leukemia cells at locations where they would otherwise be protected by stroma.