Oligoclonal in vitro response of CD4 T cells to vesicles of mistletoe extracts in mistletoe-treated cancer patients.

Mistletoe (Viscum album) extracts are widely used in adjuvant cancer therapy. We have investigated the in vitro responsiveness of T cells from mistletoe-treated cancer patients and untreated healthy donors to various preparations of mistletoe extracts. Proliferation of peripheral blood mononuclear cells from treated but not from untreated patients was observed in response to therapeutically used mistletoe extracts prepared from apple (mali) or pine (pini) host trees. The strongest proliferation was induced by a vesicle preparation of mali extract. Activation was strongly inhibited by interleukin-10. Using a newly developed flow-cytometry assay, we determined that cell growth was restricted to CD4 T cells. Analysis with a panel of monoclonal antibodies against the variable region of the T cell receptor beta chain (V beta) revealed an oligoclonal pattern of CD4 T cell activation. These results indicate that therapeutic administration of mistletoe extracts sensitizes a restricted set of CD4 T lymphocytes in mistletoe-treated patients.