Simultaneous activation of T helper function can augment the potency of dendritic cell-based cancer immunotherapy.

PURPOSE: Simultaneous activation of T helper 1 (Th1) cell function has crucial roles in induction of potent cytotoxic T lymphocyte (CTL) responses in cancer immunotherapy. Here, we investigated whether dendritic cell (DC)-based vaccines loaded with both tumor-associated antigen (TAA)-derived MHC class I and pan-MHC class II peptides could elicit more potent CTL responses through simultaneous activation of Th1 function and reduction in CD4(+) regulatory T (Treg) cell proliferation.
METHODS: C57BL/6 mice bearing LLC1, a mouse Lewis lung cancer cell line, were subcutaneously administered DCs loaded with both LLC-derived MHC class I (MUT1&2) and LLC-unrelated pan-MHC class II (PADRE) peptides (DC-MUT1&2-PADRE). In assays using samples from advanced lung cancer patients, peripheral blood mononuclear cells were stimulated with autologous DCs loaded with both MUC1 MHC class I and PADRE peptides (DC-MUC1-PADRE) in vitro. Subsequently, TAA-specific CTL responses and the population of CD4(+) Treg cells were analyzed.
RESULTS: The population of spleen CD4(+) PADRE-specific cells producing interferon-gamma (IFNγ) was significantly increased by DC-MUT1&2-PADRE administration. Vaccinations with DC-MUT1&2-PADRE decreased the population of CD4(+) Treg cells in spleen and augmented CTL responses, effectively leading to suppression of tumor growth. In assays with human samples, CD4(+) Treg cells were induced less frequently, and MUC1-specific cytotoxicity was enhanced by stimulation with DC-MUC1-PADRE compared with that by stimulation with DC-MUC1 alone.
CONCLUSIONS: Simultaneous activation of Th1 function by DCs loaded with both TAA-derived MHC class I and PADRE peptides augments TAA-specific CTL responses while reducing Treg cell proliferation.