Prognostic role of the ratio of natural killer cells to regulatory T cells in patients with multiple myeloma treated with lenalidomide and dexamethasone.

Despite advances in treating newly diagnosed multiple myeloma (NDMM), a biomarker-driven personalized approach remains an unmet need. A combination of lenalidomide and dexamethasone (RD) is a widely available chemotherapeutic option for NDMM. We aimed to find a circulating immune cell-based biomarker to predict prognosis following RD in patients with NDMM. Clinical data and peripheral blood samples of 71 consecutive NDMM patients treated with RD were retrospectively analyzed. Peripheral blood samples were taken at the time of diagnosis. Immune cell populations, including natural killer (NK) cells, T cells, and their subpopulations, were identified by flow cytometry. In univariable analysis, four variables, including low expression (third or lower quartile) of NK cells, high expression (first or greater quartile) of regulatory T (Treg) cells, female sex, and lambda light chain type, could be plausible factors in predicting poor progression-free survival (PFS). With use of the ratio of NK cells to Treg cells (NK/Treg) as a biomarker, the median PFS of patients with low NK/Treg (less than first quartile, n = 18) was significantly inferior to that of patients with high NK/Treg (first or greater quartile, n = 53): 19.8 months versus 57.3 months, p = 0.047. In multivariable analysis, low NK/Treg was significantly associated with poor PFS (hazard ratio: 2.877, 95% confidence interval: 0.001-1.009, p = 0.048), even after adjusting for other confounding factors. NK/Treg at the time of diagnosis might be a useful immune cell biomarker for clinical decision-making for the use of RD in NDMM. Further investigations are needed to improve outcomes of NDMM patients based on the understanding of the role of NK/Treg.