Bone marrow cells were obtained and separated from heparin-treated blood through density gradient centrifugation (2,200 rpm, 20 min, break 0) using Lymphoprep (Axis-Shield, Oslo, Norway).
Bone marrow plasma cells were enriched using the EasySep Human Whole Blood and Bone Marrow CD138 Positive Selection kit (Stemcell Technologies, Inc., Vancouver, BC, Canada) using EasySep magnets (Stemcell Technologies) or CD138 microbeads (Miltenyi Biotec, Gladbach, Germany) using MS columns (Miltenyi Biotec) according to the manufacturer’s instructions. FITC-Mouse Anti-Human CD138 (BD Pharmingen, San Jose, CA, USA) antibody was used to stain the cells, and the cells were applied directly to flow cytometric analysis using a FACSVerse.