Tumors exhibit immune escape properties that promote their survival. These properties include modulation of Ag presentation, secretion of immunosuppressive factors, resistance to apoptosis, and induction of immune deviation, e.g., shifting from Th1- to Th2-type responses. These escape mechanisms have proven to hamper several immunotherapeutic strategies, and efforts need to be taken to revert this situation. We have studied the immunological effects of introducing CD40 ligand (CD40L), a potent dendritic cell activation molecule, into the tumor micromilieu by adenoviral gene transfer. For this purpose, a murine bladder cancer model (MB49) was used in C57BL/6 mice. The MB49 cells are known to induce IL-10 in the tumor environment. IL-10 potently inhibits the maturation of dendritic cells and thereby also the activation of CTLs. In this paper we show that CD40L immunogene therapy suppresses IL-10 and TGF-β production (2-fold decrease) and induces a typical Th1-type response in the tumor area (200-fold increase in IL-12 production). The antitumor responses obtained were MB49 cell specific, and the cytotoxicity of the stimulated CD8+ cells could be blocked by IL-10. Adenovirus CD40L therapy was capable of regressing small tumors (five of six animals were tumor free) and inhibiting the progression of larger tumors even in the presence of other escape mechanisms, such as apoptosis resistance. Furthermore, CD40L-transduced MB49 cells promoted the maturation of dendritic cells (2-fold increase in IL-12) independently of IL-10. Our results argue for using adenovirus CD40L gene transfer, alone or in combination with other modalities, for the treatment of Th2-dominated tumors.

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Classical midgut carcinoids are serotonin-secreting tumors derived from enterochromaffin cells in the gut. Metastatic disease represents a therapeutic challenge and immunotherapy implies a novel approach for treatment. In order to define antigens suitable for T-cell therapy with a preferential expression in midgut carcinoid tissue a broad screening of genes with preferential neuroendocrine restriction, genes described as over-expressed in various malignancies, and genes encoding cancer-testis associated antigens was performed. The expression of 32 genes was analyzed by reverse transcription polymerase chain reaction (RT-PCR) in 28 midgut carcinoid specimens, in the cell line BON and in normal tissues. Immunohistochemistry (IHC) was used to evaluate protein expression. Expression is shown of genes that have previously not been observed in midgut carcinoid tumors, such as Survivin and GAGEs. Also the expression is confirmed of genes that encode pivotal proteins in enterochromaffin cells, such as TPH1 and VMAT1, and their tissue-restricted expression is indicated. In addition, gene expression of IA-2 and CDX-2 in normal gastrointestinal (GI) tract and in tumor is shown. Protein expression of TPH, VMAT1, and Survivin was detected in tumor tissue. This study elucidates that TPH1, VMAT1, and Survivin should be further investigated as potential target antigens for T cell-mediated immunotherapy of midgut carcinoids.

We have identified a number of immunogenic midgut carcinoid-associated peptide epitopes recognized by CD8(+) T cells. We show that midgut carcinoid patients display immune recognition of their tumors. Memory CD8(+) T cells in patient blood are of great interest when pursuing an immunotherapeutic treatment strategy.

Vesicular monoamine transporter 1 (VMAT1) is an integral protein in the membrane of secretory vesicles of neuroendocrine and endocrine cells that allows the transport of biogenic monoamines, such as serotonin, from the cytoplasm into the secretory vesicles. The full-length VMAT1 transcript is produced from 16 exons. We have identified and characterized an alternatively spliced form of VMAT1 that lacks exon 15, the next to last exon of VMAT1. The new form was therefore denoted VMAT1 15. Exon 15 does not contain an even multiple of three nucleotides. As a consequence, there is a shift of reading frame, and exon 16 is translated in an alternative reading frame, yielding a novel protein with a shorter and unrelated C-terminus compared with the native VMAT1 protein. VMAT1 and VMAT1 15 mRNAs are simultaneously expressed in normal and neoplastic neuroendocrine cells of the GI tract. However, VMAT1 expression is always higher than VMAT1 15 expression. We prove that VMAT1 15 is not localized in large, dense core vesicles as the native form but in the endoplasmic reticulum. Furthermore, while VMAT1 can take up serotonin, VMAT1 15 cannot, indicating different functions for the two forms of VMAT1.