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Background: Dendritic cells (DCs) play a central role in immune responses and may be useful adjuvants for tumor vaccine therapy. We previously reported that F4/80[sup -]B220[sup -] CD11c[sup +] DC precursors expressing the CC chemokine receptors CCR1 and CCR5 are mobilized rapidly into the circulation in mice injected with Propionibacterium acnes and are recruited into inflammatory tissue by macrophage inflammatory protein 1α (MIP-1α), which binds to CCR1 and CCR5. Here we investigate the mechanisms of DC precursor mobilization and the antitumor effect of these cells in mice. Methods: Numbers of DC precursors in peripheral blood were determined in P. acnes-treated mice (groups of 10 C57BL/B6 [B6] wild-type mice, CCR1[sup -/-] mice, CCR5[sup -/-] mice, and B6 mice treated with antibody to MIP-1α or control antibody) and in B6 mice injected with recombinant MIP-1α. MIP-1α-mobilized DC precursors matured by treatment with granulocyte-macrophage colony-stimulating factor, interleukin 4, and tumor necrosis factor-α and pulsed with B16 melanoma lysates were assayed for their ability to confer protective immunity against tumor challenge in vivo and to induce cytotoxic T lymphocytes against B16 tumor cells in vitro. Results: The recruitment of DC precursors into the circulation by P. aches administration was higher in B6 mice (12.6%, 95% confidence interval [CI] = 9.1% to 16.1%) than in CCR1[sup -/-] (9.0%, 95% CI = 7.5% to 10.5%), CCR5[sup -/-] (6.3%, 95% CI = 5.2% to 7.3%), or anti-MIP-1α antibody-treated (6.6%, 95% CI = 5.7% to 7.5%) mice. Injection of MIP-1α also mobilized DC precursors into the circulation (13.1%, 95% CI = 10.8% to 15.6%). Matured MIP-α-mobilized-DC precursors pulsed with B16 tumor lysates elicited B16-specific antitumor immunity in vitro and in vivo. Conclusions: MIP-1α and its receptors are important in recruiting DC precursors into the circulation. DC precursors mobilized rapidly by MIP-1α may provide sufficient useful DC precursors for DC-based vaccination in cancer treatment. [ABSTRACT FROM AUTHOR]