Xin Huang

Splenic stroma drives mature dendritic cells to differentiate into regulatory dendritic cells

The fates of dendritic cells (DCs) after antigen presentation have been studied extensively, but the influence of lymphoid microenvironments on DCs is mostly unknown. Here, using splenic stromal cells to mimic the immune microenvironment, we show that contact with stromal cells promoted mature DCs to proliferate in a fibronectin-dependent way and that both stromal cell contact and stromal cell–derived transforming growth factor-β induced their differentiation into a new regulatory DC subset. We have identified an in vivo counterpart in the spleen with similar phenotype and functions. These differentiated DCs secreted nitric oxide, which mediated the suppression of T cell proliferation in response to antigen presentation by mature DCs. Thus, our findings identify an important mechanism by which the microenvironment regulates immune responses.

Enhanced antitumoral effect of adenovirus-mediated cytosine deaminase gene therapy by induction of antigen-presenting cells through stem cell factor/granulocyte-macrophage colony-stimulating factor gene transfer.

Suicide gene therapy has been studied intensively for the treatment of cancer. A limited antitumoral effect was obtained by intratumoral injection of adenovirus harboring Escherichia coli cytosine deaminase gene (AdCD) in tumor-bearing mice followed by continuous administration of 5-fluorocytosine (5FC). To address the drawbacks of the limited potential for the induction of antitumoral immunity by CD suicide gene therapy, we hypothesized that antigen-presenting cells (APCs) might contribute to the efficient induction of an antitumoral immune response in tumor-bearing mice undergoing suicide gene therapy. We preinjected the mice with murine stem cell factor (SCF)-encoding adenovirus (AdSCF) and murine granulocyte-macrophage colony-stimulating factor (GM-CSF)-encoding adenovirus (AdGM-CSF); after 7 days, the mice were inoculated with CT26 colon adenocarcinoma. AdCD was injected intratumorally into tumor-bearing mice followed by 5FC administration. The results showed that AdSCF/AdGM-CSF treatment could increase the number, surface molecule expression, and function of APCs efficiently. A more significant growth inhibition of established tumors and a prolongation of the survival period were observed in tumor-bearing mice after AdSCF/AdGM-CSF pretreatment in combination with AdCD/5FC therapy when compared with mice treated with AdSCF or AdGM-CSF in combination with AdCD/5FC, or AdCD/5FC alone (P < .01). Cytotoxic T-lymphocyte activity was induced efficiently after the combined therapy, and mRNA of tumor necrosis factor-α, interleukin-4, interferon-γ, and interleukin-2 was present in the tumor mass after combined therapy, suggesting that a more potent antitumoral response was induced by enhanced APCs. Our results demonstrated that AdSCF/AdGM-CSF pretreatment could activate APCs, and that these APCs could present the tumor antigens released from AdCD/5FC-killed tumor cells and activate the antitumoral response of the host, thus increasing the therapeutic efficiency of suicide gene therapy.

In vivo distribution and gene expression of genetically modified hepatocytes after intrasplenic transplantation

To investigate the feasibility and efficacy of liver gene therapy mediated by intrasplenic transplantation of genetically modified hepatocytes, the normal mouse liver cell line BNL CL. 2 cells were introduced with Neo-resistant (NeoR) gene or interleukin-2 (IL-2) genein vitro, and transplanted intrasplenically into normal syngeneic mice (2 x 106 cell/mouse); subsequently, the expressions of the introduced genesin vim were detected. The RT-PCR results showed that NeoR mRNA expressions were detectable in livers 24 h after transplantation and lasted over 11 weeks. Moreover, The NeoR mRNA was detected to be expressed temporarily in spleens (24 h–1 week) and lungs (24–96 h) after transplantation. After intrasplenic transplantation of IL-2 gene-modified BNL CL.2 cells, the stable expressions of IL-2 mRNA in the livers of transplanted mice were detectable by RT-PCR (24 h–11 weeks), and certain levels of IL-2 (5–40 pg/mL) remained in the peripheral blood. When IL-2 gene-modified BNL CL. 2 cells were transplanted intrasplenically to treat the metastatic liver colon carcinoma-bearing mice, the survival time of the treated mice was significantly prolonged. The data indicate that intrasplenic transplantation of genetically modified hepatocytes could allow for oriental distribution in host livers and long-term survival of the transplanted liver cells, and effective expression of exogenous genesin vim, suggesting that this can be a candidate approach to liver-directed gene therapy.

Cloning and characterization of a novel deletion mutant of heterogeneous nuclear ribonucleoprotein M4 from human dendritic cells

To identify differentially expressed genes from antigen-stimulated human dendritic cells (DC), subtractive cloning was adopted and more than ten novel genes differentially expressed were cloned. One is a deletion mutant of heterogeneous nuclear ribonucleoprotein (hnRNP) M4 in which the residues from 159 to 197 of hnRNP M4 have been absent. The deletion mutant was shown to be co-expressed with hnRNP M4 in cell lines. The mutant was expressed in antigen-stimulated DC but not in normal DC. Northern blot analysis revealed the presence of a major hnRNP M4 deletion mutant mRNA transcript of 2.4 kilobase with the highest levels in peripheral lymphocytes, lung, liver and spleen. It was also expressed in bone marrow-derived stromal cells (BMSC), BMSC treated with several cytokines but not in BMSC treated with TNF-α. The results revealed a new member of hnRNP family and suggested that hnRNP would participate in antigen process and presentation.

EXPERIMENTAL STUDIES ON RADIATION-INDUCIBLE HUMAN TNF GENE THERAPY FOR CANCER

Tumor necrosis factor (TNF) has certain radioprotective effect on host tissue and is capable of enhancing the antitumor effect of radiotherapy. In addition, the transcriptional regulation of the promoter region of Egr-1 gene is activated by ionizing radiation. So we fused Egr-1 promoter with hTNF-α cDNA, and resultantly constructed a double-copy and radiationinducible retroviral vector named as pETDC. After packaged with Psi-2 and Crip cellsin vitro, the hTNF recombinant retroviruses were in the titers of 4×105 CFU/ml. By infection of murine fibroblast cell line NIH3T3 and murine melanoma cell line B16.F10 with the recombinant retroviruses and followed by G418 resistant selection, two positive clones secreting TNF at the levels of 2.1 ng/ml and 1.1 ng/ml respectively were generated. After exposure to 20 Gy ionizing radiation, TNF secretions from the two positive clones were elevated to 13.8 ng/ml (6.6-fold) and 5.7 ng/ml (5.2-fold) respectively. Furthermore, hTNF-α expression in pETDC-transfected cells was confirmed by RT-PCR. These data provide an experimental bases for the application of TNF gene therapy combined with local radiotherapy in cancer patients.

Identification and characterization of DEDDL, a human-specific isoform of DEDD.

Death effector domain (DED) containing molecules are usually involved in the intracellular apoptosis cascade as executioners or regulators. One of these molecules, DEDD, was identified as a final target of the CD95 signaling pathway by which it would be transferred into the nucleolus to inhibit RNA polymerase I-dependent transcription. Here we describe a longer isoform of DEDD, DEDDL, produced by alternatively splicing, as an immune cell-specific DED-containing molecule. It is only expressed in human T lymphocytes and dendritic cells (DCs), and the mRNA expression in DCs was elevated upon inductive maturation. In cell lines MCF-7 and Jurkat, the overexpression of DEDDL could induce apoptosis more potently than that of DEDD. That DEDDL could bind FADD and cFLIP more potently than DEDD in vivo was revealed by cotransfection and immunoprecipitation. This may explain why DEDDL is a more potent apoptosis inducer, because DED-containing proteins usually induce apoptosis through DED binding. Finally, why DEDD and DEDDL are unstable in the overexpression and other studies may be explained by the finding that they are potential substrates of active caspases.