Taxol-mediated changes in fibrosarcoma-induced immune cell function: Modulation of antitumor activities

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Abstract
The anticancer drug taxol (paclitaxel) inhibits tumors through multiple cytotoxic and cytostatic mechanisms. Independently of these mechanisms, taxol induces distinct immunological efficacy when it acts as a second signal for activation of tumoricidal activity by interferon-γ(IFNγ)-primed murine normal host macrophages. We reported that tumor-distal macrophages, which mediate immunosuppression through dysregulated nitric oxide (NO) and tumor necrosis factor α (TNFα) production, are differentially regulated by taxol. Because taxol influences tumor cell growth dynamics and activates immune cell populations, we assessed the ex vivo immunosuppressive and antitumor activities of taxol-treated normal host and tumor-bearing host (TBH) macrophages. Pretreatment of such cells with taxol partly reconstituted T cell alloantigen reactivity, suggesting that taxol mediates a limited reversal of TBH macrophage immunosuppressive activity. Taxol-treated TBH macrophages significantly suppressed the growth of fibrosarcoma cells (Meth-KDE) through soluble effector molecules and promoted direct cell-mediated cytotoxicity, indicating that taxol enhanced tumor-induced macrophage antitumor activities. Tumor-induced helper T cells, however, showed a higher sensitivity to direct taxol-induced suppression. These data demonstrate that taxol exerts pleiotropic effects on antitumor immune responses with the capacity to abate the immunosuppressive activities of macrophages and promote macrophage-mediated anti-tumor activities simultaneously, but also directly modulating T cell reactivity. Collectively, these studies suggest that the antineoplastic drug taxol may impart antitumor activity through an immunotherapeutic capacity.