Multiple myeloma: Ecto-5' nucleotidase deficiency of suppressor/cytotoxic (CD8) lymphocytes is a marker for the expansion of suppressor T cells

In this study, 5'NT activity was investigated by radiochemical and cytochemical assays in T cell subpopulations of patients with multiple myeloma (MM). Cytotoxic/suppressor (CD8) and helper/inducer (CD4) lymphocytes were separated from peripheral blood by the panning technique, or sorted with a fluorescin activated cell sorter. 5'NT activity was significantly decreased in MM CD8 lymphocytes compared with the controls. By contrast, it was comparably low in CD4 subpopulations of normal controls and MM patients. The cytochemical assay indicated that a decreased number of 5'NT⁺ cells rather than a decreased activity per cell was responsible for 5'NT deficiency in MM CD8 lymphocytes. CD8 lymphocytes with the suppressor phenotype (OKM1⁺, granular cells) were significantly increased in MM. These data provide a phenotypic explanation for the enhanced suppressor activity displayed by T lymphocytes in MM. A significant correlation was found between the increase of suppressor cells and the decrease of 5'NT⁺ cells. 5'NT deficiency of CD8 lymphocytes can be a biochemical marker for the expansion of suppressor T cells.