Circulating malignant precursors in monoclonal gammopathies

Peripheral blood mononuclear cells (PBMC) from 14 patients with multiple myeloma (MM), 3 patients with benign monoclonal gammopathy, 3 patients with Waldenstrom's macroglobulinaemia (WM) and 2 patients with B‐cell chronic lymphocytic leukemia (B‐CLL) were cultured in vitro in the presence of IL‐3 and IL‐6. After 3 days, actively proliferating immunoblast‐like B cells were apparent in 12/14 cases of MM, 0/3 BMG, 3/3 WM and 0/2 B‐CLL. After 6 d, B blasts had evolved into morphologically evident plasma cells expressing the specific monoclonal light and heavy chains. The data indicate that the concerted action of IL‐3 and IL‐6 synergistically promotes the proliferation and differentitation of circulating plasmacell precursors in malignant monoclonal gammopathies.