Evidence for the existence of circulating monoclonal B-lymphocytes in multiple myeloma patients.

Multiple myeloma is characterized by the proliferation of a single clone of plasma cells producing a homogeneous immunoglobulin fraction. In this disease, plasma cells home essentially in the bone marrow. However, controversy exists whether peripheral blood B-lymphocytes in patients with multiple myeloma (MM) are part of the malignant clone. We investigated clonal immunoglobulin gene rearrangement (IgGR) in T-cell-depleted peripheral blood mononuclear cells as well as in bone marrow of these patients. Seven out of 17 MM patients demonstrated an identical IgGR in bone marrow and peripheral mononuclear cells, these patients were in an active stage of the disease. In nine patients in plateau phase, clonal IgGR could not be detected in peripheral blood. Peripheral mononuclear cells from ten patients with monoclonal gammopathies of undetermined significance (MGUS) were also examined and no IgGR was detected. The existence of monoclonal B-lymphocytes in the circulation of patients with MM suggests a mechanism whereby the malignant clone homes in the bone marrow through peripheral blood. These findings may also be used for the evaluation of patients with active myeloma and the determination of plateau phase.