The RPCI-WM1 cell line was cultured as previously described [38 (link), 72 (link)]. The myeloma cell line RPMI-8226 (8226) and the HEK293T cell line were purchased from American Type Culture Collection (ATCC). MM.1s was provided by Steven Rosen (City of Hope), and KMS12-PE was purchased from the Japanese Collection of Research Bioresources Cell Bank (JCRB). Myeloma cells were cultured as previously described [73 (link)].