Background: The use of dendritic cells (DCs) as a cellular adjuvant provides a promis-ing approach in immunotherapy of cancer. It has been demonstrated that Listeria mono-cytogenes activated DCs pulsed ex vivo with tumor antigens trigger a systemic Th1-biased specific immune response and a single dose of this vaccine will cause a consider-able anti tumor immunity.
Objective: The present study was designed to evaluate the ability of multiple doses of tumor antigen-pulsed DCs, matured in the presence of Lis-teria monocytogenes components in induction of a potent anti-tumor response and the prevention of tumor formation in an experimental model.
Methods: Bone-marrow de-rived DCs (BMDCs) were cultured in the presence of GM-CSF and IL-4. After 5 days, tumor lysates with/without Listeria monocytogenes lysate were added to the culture media for another 2 days. Mice received mature and tumor antigen pulsed dendritic cells subcutaneously in 3 groups. Tumor growth was monitored and two weeks after immu-notherapy, cytotoxic activity of CD8+ T cells was evaluated in different groups. Re-sults: According to the findings, repeated doses of vaccine did not lead to a significant increase in the activity of cytotoxic T cells and decreased tumor growth of immunized animals.
Conclusion: The current study suggests that increased doses of vaccine do not have sufficient efficiency for prevention of tumor induction. Generation of T regulatory responses upon repeated doses of such vaccines should be considered in future investi-gations.