Expression of activated integrin β7 in multiple myeloma patients

Multiple myeloma (MM) is still extremely difficult to cure, and new therapeutic drugs are needed. We recently found that integrin β7 is constitutively activated in MM cells, and chimeric antigen receptor (CAR) T cells targeting activated integrin β7 have a significant anti-MM effect. In this study, we performed flow cytometry analysis of the expression of activated integrin β7 in bone marrow cells from 137 symptomatic MM patients. In 60/137 (44%) MM patients, activated integrin β7 was detected in most MM cells (> 80% of MM cells were in the positive gate). Activated integrin β7 was highly expressed in MM cells even in heavily treated patients. It also showed high expression in many CD38^lo/^-CD138^-CD19⁺B cells, which reportedly include clonotypic B cells, in the bone marrow of MM patients. Taken together, these results suggest that CAR T-cell therapy targeting activated integrin β7 has the potential to benefit many patients with relapsed or refractory MM.