The expression of the Bcl‐2 oncoprotein was studied in pre‐treatment bone‐marrow samples from 63 patients with multiple myeloma, using an immunohistochemistry technique. A variable expression of the Bcl‐2 protein was found in myeloma cells. 43% of the patients had strong expression of the Bcl‐2 protein in the malignant cells. Forty patients received α‐interferon, whereas 23 patients received melphalan/prednisone therapy. A significant association (p = 0.012) was found between high levels of Bcl‐2 expression in myeloma cells and resistance to interferon therapy. No such correlation was found in the melphalan/prednisone treated patients. The data indicate that over‐expression of Bcl‐2 may be a cause for resistance to interferon therapy in myeloma and that staining for Bcl‐2 expression in myeloma cells may have a predictive value for this treatment.

Monocytes and lymphocytes from peripheral blood were tested for their susceptibility to the natural killer (NK) cell activity of allogeneic and autologous lymphocytes. Peripheral blood monocytes, but not lymphocytes, were sensitive to the cytotoxic activity of interferon (IFN) activated NK cells. Allogeneic as well as autologous monocytes were sensitive to NK activity, although the killing seemed to be more pronounced in allogeneic combinations. The cells expressing cytotoxic activity for blood monocytes were found to conform to the characteristics of NK cells in the sense that they were activated by IFN, as well as in the sense that they were contained in the same cell fraction as large granular lymphocytes.