The role of Bcl-xL and nuclear factor-kappaB in the effect of taxol on the viability of dendritic cells

Paclitaxel inhibits the hyper-activation of spleen cells by lipopolysaccharide and induces cell death

Paclitaxel was isolated from the bark of the Pacific yew, Taxus brevifolia, and used as an anticancer agent. Paclitaxel prevents cancer cell division by inhibiting spindle fiber function, inducing cell death. A recent study demonstrated that paclitaxel binds to myeloid differentiation protein-2 of Toll-like receptor 4 and prevents the signal transduction of lipopolysaccharide (LPS). Paclitaxel converts immune cells hypo-responsive to LPS. In this study, we investigated whether paclitaxel can inhibit the phenotype and function of immune cells. To accomplish this, we used spleen cells, a major type of immune cell, LPS, a representative inflammatory agent and a mitogen for B lymphocytes. LPS profoundly increased the activation and cytokine production of spleen cells. However, paclitaxel significantly inhibited LPS-induced hyper-activation of spleen cells. Furthermore, we found that paclitaxel induced cell death of LPS-treated spleen cells. These results suggest that paclitaxel can inhibit the hyper-immune response of LPS in spleen cells via a variety of mechanisms. These findings suggest that paclitaxel can be used as a modulating agent for diseases induced by hyper-activation of B lymphocytes. Taken together, these results demonstrate that paclitaxel inhibits the function of spleen cells activated by LPS, and further induces cell death.

Dendritic cell maturation and survival are differentially regulated by TNFR1 and TNFR2

The capacity of dendritic cells (DC) to regulate adaptive immunity is controlled by their maturation state and lifespan. Although TNF is a well-known maturation and survival factor for DC, the role of the two TNFR, TNFR1 and TNFR2, in mediating these effects is poorly understood. By using unique TNF variants that selectively signal through TNFR1 and/or TNFR2, we demonstrate differential functions of TNFR in human monocyte-derived and blood CD1c(+) DC. Activation of TNFR1, but not TNFR2, efficiently induced DC maturation, as defined by enhanced expression of cell surface maturation markers (CD83, CD86, and HLA-DR) as well as enhanced T cell stimulatory capacity. In contrast, both TNFR1 and TNFR2 significantly protected DC against cell death, indicating that innate signals can promote DC survival in the absence of DC maturation. We further show differential activation of NF-κB signaling pathways by the TNFR: TNFR1 activated both the p65 and p52 pathways, whereas TNFR2 triggered p52, but not p65, activation. Accordingly, the p65 NF-κB pathway only played a role in the prosurvival effect of TNFR1. However, cell death protection through both TNFR was mediated through the Bcl-2/Bcl-xL pathway. Taken together, our data show that TNFR1, but not TNFR2, signaling induces DC maturation, whereas DC survival can be mediated independently through both TNFR. These data indicate differential but partly overlapping responses through TNFR1 and TNFR2 in both inflammatory and conventional DC, and they demonstrate that DC maturation and DC survival can be regulated through independent signaling pathways.

Differential effects of Paclitaxel on dendritic cell function

BACKGROUND

The potential utility of dendritic cells (DC) as cancer vaccines has been established in early trials in human cancers. The concomitant administration of cytotoxic agents and DC vaccines has been previously avoided due to potential immune suppression by chemotherapeutics. Recent studies show that common chemotherapy agents positively influence adaptive and innate anti-tumour immune responses.

RESULTS

We investigated the effects of paclitaxel on human DC biology in vitro. DCs appear to sustain a significant level of resistance to paclitaxel and maintain normal viability at concentrations of up to 100 micromol. In some cases this resistance against paclitaxel is significantly better than the level seen in tumour cell lines. Paclitaxel exposure led to a dose dependent increase in HLA class II expression equivalent to exposure to lipopolysaccharide (LPS), and a corresponding increase in proliferation of allogeneic T cells at the clinically relevant doses of paclitaxel. Increase in HLA-Class II expression induced by paclitaxel was not blocked by anti TLR-4 antibody. However, paclitaxel exposure reduced the endocytic capacity of DC but reduced the expression of key pro-inflammatory cytokines such as IL-12 and TNFalpha. Key morphological changes occurred when immature DC were cultured with 100 micromol paclitaxel. They became small rounded cells with stable microtubules, whereas there were little effects on LPS-matured DC.

CONCLUSIONS

The effect of paclitaxel on human monocyte derived DC is complex, but in the clinical context of patients receiving preloaded and matured DC vaccines, its immunostimulatory potential and resistance to direct cytotoxicity by paclitaxel would indicate potential advantages to co-administration with vaccines.