Establishment and characterization of a new human oligosecretory myeloma cell line

Multiple myeloma is a neoplasm derived from abnormal plasma cells exhibiting excessive proliferation either within or outside of the bone marrow. While the majority of myelomas are classified into distinct types based on the production of different classes of immunoglobulins, a small percentage of these tumor cells fail to exhibit immunoglobulin secretion and are classified as nonsecretory myelomas. The nonsecretory type is further subdivided into the intracytoplasmic immunoglobulin producer and nonproducer types. Notably, recent studies detected a novel form of myeloma, oligosecretory myeloma, which comprises a portion of the nonsecretory type. While the prevalence of the oligosecretory type increases with disease progression, the mechanism underlying the development of these cells remains unclear. Likewise, oligosecretory myeloma cell lines remain rare. Here, we describe the development of a new myeloma cell line, designated THK-72, from the pleural effusion of a myeloma patient initially diagnosed with IgG kappa type myeloma, which subsequently transformed to oligosecretory myeloma. THK-72 cells proliferated in single suspension culture without any feeder layer or IL-6 supplementation, and no immunoglobulin secretion was detected in the supernatant of these cells by immunoelectrophoresis analysis. Morphological analyses indicated that THK-72 cells had plasmacytoid appearance, while PCR and flow cytometry analyses demonstrated that the cells were negative for B-cell marker and EBV-infection, thereby indicating that THK-72 comprises a “true” myeloma cell line. Interestingly, contrary to the bortezomib resistance observed during the clinical course, the THK-72 cells were sensitive to bortezomib in vitro. As THK-72 arose from a classical myeloma, this oligosecretory myeloma cell line will be useful for studies regarding the biological nature of plasma cell neoplasms.