Recent studies suggest that immunization with autologous dendritic cells (DCs) results in a protective immunity and a rejection of established tumors for various human malignancies. It has been reported that a dense infiltration of DCs correlates with a favorable prognosis for several types of cancer. The purpose of this study is to determine whether DCs are generated from peripheral blood monocytes by using cytokines such as granulocyte macrophage-colony stimulating factor (GM-CSF), TNF-α, Flt-3 ligand and IL-4 and to determine if cytotoxic CD8⁺T cells are activated against medullary thyroid carcinoma (MTC) tissue by the DCs.

Peripheral bloods were obtained from two patients with MTC. Mononuclear cells were cultured in the presence of GM-CSF, Flt-3 ligand, TNF-α and IL-4 for 14 days to establish DCs. At day 16, the differentiated cells were analyzed morphologically using electron microscopy. The immunophenotypic features of DCs such as expression of CD1a, CD83, and CD86 were anlayzed by immunofluorescent microscopy. At day 15, DCs were incubated with either thyroid cancer tissue or normal thyroid tissue for an additional 7 days.

The generated DCs showed the classic morphology of DCs including multiple processes and a profuse cytoplasm. Activated cytotoxic T lymphocytes (CTLs) were observed with prominent pseudopods. The CTLs activated by DCs bound to the MTC were observed by scanning electron microscopy. However, normal tissues were free from CTL binding.

We could generate DCs from peripheral blood mononuclear cells. Furthermore, these DCs activate CTLs that are able to attach to MTC tissue. These results suggest that DCs can be used as an adjuvant for immunotherapy of MTC. This study represents the basis for the development of new therapeutic strategies not only for MTC but also for other malignancies.