Expression of the Serpin Serine Protease Inhibitor 6 Protects Dendritic Cells from Cytotoxic T Lymphocyte–Induced Apoptosis: Differential Modulation by T Helper Type 1 and Type 2 Cells

Dendritic cells (DCs) play a central role in the immune system as they drive activation of T lymphocytes by cognate interactions. However, as DCs express high levels of major histocompatibility complex class I, this intimate contact may also result in elimination of DCs by activated cytotoxic T lymphocytes (CTLs) and thereby limit induction of immunity. We show here that immature DCs are indeed susceptible to CTL-induced killing, but become resistant upon maturation with anti-CD40 or lipopolysaccharide. Protection is achieved by expression of serine protease inhibitor (SPI)-6, a member of the serpin family that specifically inactivates granzyme B and thereby blocks CTL-induced apoptosis. Anti-CD40 and LPS-induced SPI-6 expression is sustained for long periods of time, suggesting a role for SPI-6 in the longevity of DCs. Importantly, T helper 1 cells, which mature DCs and boost CTL immunity, induce SPI-6 expression and subsequent DC resistance. In contrast, T helper 2 cells neither induce SPI-6 nor convey protection, despite the fact that they trigger DC maturation with comparable efficiency. Our data identify SPI-6 as a novel marker for DC function, which protects DCs against CTL-induced apoptosis

Dendritic cell immunotherapy: mapping the way

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Targeting dendritic cells with antigen via dendritic cell-associated promoters.

Item does not contain fulltextThe induction of tumor-specific immune responses is largely dependent on the ability of dendritic cells (DCs) to present tumor-associated antigens to T lymphocytes. Therefore, we investigated the use of DC-associated promoter-driven genetic vaccines to specifically target DC in vivo. Restricted expression of vaccine-encoding genes in DC should enhance specificity and improves their safety for clinical applications. Hereto, 3-5 kb upstream sequences of the murine genes encoding CD11c, DC-SIGN, DC-STAMP and Langerin were isolated, characterized and subcloned into enhanced green fluorescent protein (EGFP) reporter constructs. Upon electroporation, EGFP was expressed in DC cell lines, but not in other cell lines, confirming DC-restricted promoter activity. When these promoters were cloned into a construct upstream of the gene for ovalbumin (OVA), it appeared that DC-STAMP promoter-driven expression of OVA (pDCSTAMP/OVA) in DC yielded the most efficient OVA-specific CD4+ and CD8+ T-cell responses in vitro. Administration of pDC-STAMP/OVA in vivo, using the tattoo gun vaccination system, evoked specific immune responses as evidenced in a mouse tumor model. Adoptively transferred pDC-STAMP/OVA-transfected DCs induced strong CD8+ T-cell proliferation in vivo. These experiments demonstrate that our DC-directed promoter constructs are potential tools to restrict antigen expression in DC and could be implemented to modulate DC function by the introduction of relevant proteins.1 mei 201