Tumor-directed cytotoxicity in multiple myeloma--the basis for an experimental treatment approach with interleukin 2.

There is growing evidence that in multiple myeloma (MM) tumor-directed immune responses exist, might influence tumor progress and could be putative targets for immunotherapeutic approaches. Peripheral blood T lymphocytes are capable of suppressing monoclonal immunoglobulin production of autologous myeloma plasma cells in vitro. This activity can be enhanced by stimulation with mitogens, OKT3 monoclonal antibody or interleukin 2 (IL-2), and is obviously mediated by cytolytic T lymphocytes as demonstrated in a cytotoxicity assay using purified MM plasma cells as targets. The lytic activity is significantly higher when the effectors are prestimulated with irradiated autologous MM plasma cells. Based on these results 18 MM patients of advanced stages with tumor progress received 9 x 10(6) IU/m2 recombinant IL-2 (Proleukin) twice daily on days 1 and 2 and 0.9 x 10(6) IU/m2 twice daily for five subsequent days per week s.c. from days 3-56 (q 12 weeks). During therapy the number of eosinophils increased 15-fold, CD4+ T lymphocytes were activated as demonstrated by CD25 antigen expression and CD56+ natural killer (NK) cells expanded in the peripheral blood. NK cell activity and lymphokine-activated killer cell activity were significantly enhanced. IL-2 therapy induced endogenous IL-2 production and elevated soluble IL-2 receptor serum concentrations. Tumor response was observed in 6/17 evaluable patients. These data indicate that low-dose IL-2 treatment can stimulate immune enhancement in MM patients despite their characteristic tumor-induced immunodeficiency, and has proven to have limited efficacy in advanced MM patients.