LYMPHOID NEOPLASIA The immunostimulatory effect of lenalidomide on NK-cell function is profoundly inhibited by concurrent dexamethasone therapy

Lenalidomide combined with dexamethasoneisaneffectivetreatmentforrefractory/ relapsed multiple myeloma (MM). Lenalidomide stimulates natural killer (NK) cells and enhances antitumor responses. We assessed NK cell number and function in 25 patients with MM participating in a clinical trial of lenalidomide and dexamethasone. NK cell numbers increased from a mean of 2.20 0.05 105/mL (baseline) to a mean of 3.90 0.03 105/mL (cycle 6; P .05); however, in vitro NKcell–mediated cytotoxicity decreased from 48.9% 6.8% to 27.6% 5.1% (P .0028) and could not be rescued by lenalidomide retreatment. Lenalidomide increased normal donor NK-cell cytotoxicity in vitro from 38.5% to 53.3%, but this was completely abrogated by dexamethasone. Dexamethasone suppression of NK cell– mediated cytotoxicity was partially reversed by a 3-day washout, but these cells remained refractory to lenalidomideinduced enhanced function. Lymphocyte subset depletion experiments revealed that lenalidomide’s enhancement of NK cell–mediated cytotoxicity was mediated by CD4 T-cell production of interleukin 2 and that dexamethasone acted by suppressing interleukin-2 production. Similarly, the reduced ability of NK cells from patients with MM to respond to lenalidomide was also due to impaired CD4 T-cell function. Our findings indicate that lenalidomide immunostimulatory effects on patient NK cells are severely blunted by concurrent dexamethasone administration. (Blood. 2011; 117(5):1605-1613)