Natural killer cell frequency and function in patients with monoclonal gammopathies

We evaluated the frequency and the functional activity of peripheral blood mononuclear cells (PBMCs) with natural killer (NK) cell phenotype in patients with monoclonal gammopathies. CD16+ and CD56+ PBMCs were strongly increased in monoclonal gammopathies of undetermined significance (MGUS) and multiple myeloma (MM). Furthermore, increased frequency of CD16+/CD3+ PBMCs was found in 7/15 patients with MGUS, indicating that T lymphocytes with NK-like phenotype are expanded in at least a subset of these patients. However, despite the increased frequency of PBMCs with natural killer phenotype, the functional NK activity was as comparable in both MGUS and MM patients as in normal individuals. The discrepancy between the expansion of circulating NK cells and the normal NK activity in patients with monoclonal gammopathies requires further investigation. However, at least in some MGUS patients, this discrepancy could be accounted for by the expansion of PBMCs with the rare phenotype CD16/CD3 which have been reported not to mediate significant NK activity.