Neutrophil granulocytes are required for effective Bacillus Calmette-Guérin immunotherapy of bladder cancer and orchestrate local immune responses.

The role of polymorphonuclear neutrophil granulocytes (PMN) in antitumoral immune responses displays a striking dichotomy. Under inflammatory conditions, PMN may promote tumor growth and progression. In contrast, especially in the context of therapeutic interventions, PMN can exert important antitumor functions. However, until now, the mechanisms of PMN-mediated activation of tumor immunity are poorly defined. Based on a murine model of Bacillus Calmette-Guérin (BCG) immunotherapy of bladder cancer, we provide evidence for a novel immunoregulatory role of this leukocyte subset. PMN immigrate into the bladder after intravesical BCG instillation and depletion of PMN from tumor-bearing mice completely abrogated antitumor efficacy of BCG. PMN stimulated with BCG in vitro as well as PMN isolated from the urine of BCG-treated patients were a major source of the chemokines interleukin-8, growth-related oncogene-alpha, macrophage inflammatory protein-1 alpha and of the inflammatory cytokine migration inhibitory factor. In vitro, BCG-stimulated PMN indirectly induced T-cell chemotaxis via the accessory function of activated monocytes. In vivo, depletion of PMN from BCG-treated mice significantly impaired CD4(+) T-cell trafficking to the bladder. These data show that PMN direct the migration of effector cells to the bladder and by this means are indispensable for effective tumor immunotherapy. Thus, our findings provide evidence for a novel early immunoregulatory role of these innate immune cells in local antitumor immunity.