Stimulation of antitumour immunity by intrapleural instillation of a Viscum album L. extract.

Intrapleural administration of mistletoe extracts is reported to result in pleurodesis in cancer patients with malignant pleural effusions. In a recent study, 20 consecutive cancer patients with malignant pleural effusions were treated intrapleurally with the mistletoe extract Helixor. The overall response rate for pleurodesis was 72%, with only 1.2% displaying side effects of the World Health Organization classification I. The decline of tumour cells in the effusion liquid correlated negatively with the number of instillations. However, the elimination of tumour cells was associated with a transient increase in macrophages and eosinophils, and a constant increase in CD8+T cells. Compared to the responder group, the non-responders exhibited high proportions of macrophages, CD8+T cells and T cells with human leukocyte antigens with DR specificity (HLA-DR) in the effusion liquid, compatible with a disturbance of macrophage/T cell co-operation and thus failure to eliminate the malignant cells. The preliminary results suggest that mistletoe-mediated pleurodesis is due to a stimulation of antitumour immunity rather than mechanical sclerosis.