01A blocks proliferation and viability of MM cells induced by paracrine APRIL. (A) Supernatant was collected from CD14⁺ cells purified from MM patients (1-5) BM aspirates cultured with media (−, open column), M-CSF (M) (gray column), or M with receptor activator of nuclear factor kappa-B ligand (M+R, black column). APRIL secretion is measured by specific ELISA. APRIL mRNA was also confirmed by real-time qRT-PCR in 1 representative sample (left). (B) Daudi-BCMA/Daudi-empty cells, (C) IL-6–dependent INA6, IL-6–independent MM1S, and (D) RPMI8226, as well as (E) CD138⁺ cells from a relapsed MM patient, were cultured for 3 days with APRIL in the presence or absence of anti-APRIL 01A mAb (10 μg/mL), followed by (B,E) [³H]thymidine uptake and (C-D) luminescence-based viability assays. Two additional patient MM cells were subject to viability and caspase 3/7 activity (F; newly diagnosed) and annexin V/PI (G; relapsed) flow cytometry.