Immunomodulatory effects of Viscum album extracts on natural killer cells: review of clinical trials

Abstract

Extracts produced from Viscum album L. (mistletoe) are widely used in complementary medicine for the treatment of cancer. In many preclinical and clinical studies, Viscum album extracts were shown to exert immunomodulatory functions. Natural killer (NK) cells play an important role in cell-mediated immune responses against tumor cells. This article reviews clinical trials that address the influence of the mistletoe extract Iscador on NK cells and discusses the results with regard to the NK cell functions assayed, to putative underlying mechanisms, and to the role of different mistletoe components.

Conclusion: Although many trials demonstrated a positive effect of Iscador treatment on NK cell function, further dedicated studies with optimized treatment schedules and comparable mistletoe doses are necessary to confirm these results regarding involvement of NK cells on the immunomodulatory functions of Iscador therapy and to investigate the clinical relevance of these findings.