Gene Transfer of CD40-Ligand to Human Dendritic Cells Induces Growth Arrest and Apoptosis of Tumor Cells Mediated by Up-Regulated TRAIL and its Receptors.

Interaction of CD40 and its ligand CD40L is essential for the activation of dendritic cells (DC) followed by the induction of antigen-specific T-cell responses. Recent studies have also indicated that ligation of CD40 on tumor cells directly modulate tumor cell growth. In this study we examined whether gene transfer of CD40L to DC could exhibit direct anti-tumor effect on CD40-expressing tumors. First, we constructed a modified adenoviral vector driving human CD40L gene with CA promoter/enhancer and incorporating the integrin-binding motif, RGD, in the H1 loop of the fiber knob (AxCAhCD40L-F/RGD). At the same multiplicity of infection, cell surface expression of human CD40L on DC after infection with AxCAhCD40L-F/RGD (CD40L-DC) was induced to express superior higher levels of T-cell costimulatory molecules (CD80, CD86, and CD54), DC maturation markers (CD25 and CD83), MHC molecules and the production of IL-12 than soluble CD40L or TNF-a treated DC. In addition to the phenotypic alternation of CD40L-DC, we found that cultivation of tumor cells (including lymphoma, leukemia, glioma, head and neck carcinoma) with CD40L-DC significantly inhibited the expression of phospho-AKT and tumor cell growth in vitro. Importantly, these tumor cells in transwell cocultured with CD40L-DC, but not with TNF-a-treated DC or immature DC, were significantly induced to express apoptosis-inducing death receptors such as TRAIL-R1, TRAIL-R2 and Fas. The ability of CD40L-DC to inhibit tumor-cell growth and TRAIL receptor induction could not be abrogated by neutralizing antibodies specific for CD40L, IFN-b, IFN-g, and IL-12, indicating that these factors were not involved. Additionally, natural killer cells cocultured with CD40L-DC displayed marked up-regulation of TRAIL on their cell surface. To confirm the biological function of TRAIL and its receptors, we assessed the cytotoxic activity of NK cells to various tumors that were stimulated with CD40L-DC. Tumor cells stimulated with CD40L-DC were susceptible to apoptosis by recombinant TRAIL protein and natural killer cells expressing TRAIL. Overall, these results reveal that CD40L-transfected DC could induce direct tumor cell growth arrest mediated by AKT pathway and susceptibility of apoptosis by TRAIL, indicating that CD40L-DC have potential therapeutic implications which we were currently exploring.