Study Of The Effect Of Genetic Immunization With Xenogeneic TGF-β On The Efficacy Of DNA Vaccine For Tumor

One of the most significant advances in the field of tumor immunology has been the identification and characterization of the tumor-associated antigens that are recognized by T cells. Some of them, such as the antigens encoded by MAGE family, are nonself-antigens and induce vigorous antitumor immune responses due to the lack of tolerance. By contrast, most of the naturally expressed tumor-associated antigens belong to self-antigens, and therefore may elicit an inefficient immunity owing to preexisting tolerance. Previous studies demonstrate that depletion of a particular cellular subset (for example, CD25+ T cells) or blockade of a particular signaling pathway (for example, CTLA-4) by antibody administration can augment generation of an antitumor response. These observations suggest that, at least in some cases, the tolerance to self-antigens could be a result of the suppression mediated by the tumor and not by the lack of costimulation from innate immunity. A number of factors either secreted directly by tumor cells or secreted by host cells as a result of tumor growth have been shown to exert suppressive effects on the immune system. Among such factors the most prominent is transforming growth factor-beta (TGF-β).It has been found that there is a marked increase in the expression of TGF-β mRNA and protein in human cancers (in vivo). Moreover, in many cancers high expression of TGF-β correlates with more advanced stages of malignancy and decreased survival. In untreated breast cancer patients, plasma TGF-β1 levels were elevated and normalized after surgery. TGF-β is a pleiotropic cytokine with multiple immunosuppressive properties. These properties include inhibition of maturation and activation of dendritic cell (DC), reducing of antigen-presenting capacity of DC, inhibition of T cell differentiation into cytotixic T lymphocytes (CTLs) and Th cells, inhibition of CD4+ T cell differentiation into Th1 cells and Th2 cells, and induction of apoptosis of activated T cells. Because CTLs and T helper type 1 cytokine production are important for effective immune-mediated tumor eradication, suppression of these functions by TGF-β could be an important mechanism whereby it inhibits immune response. It has been reported that blockade of TGF-β signaling in T cells results in the immune-mediated eradication of tumors. Modification with TGF-β antisense oligonucleotide significantly decreases the amounts of TGF-β produced by modified tumor cells and immunization with TGF-beta antisense oligonucleotide-modified autologous tumor vaccine enhances the antitumor immunity of tumor-bearing mice. Neutralization of TGF-β1 using TGF-β1-neutralizing monoclonal antibody or produced by the fusion cells enhances the effectiveness of DC-based immunotherapy. It is presently unclear whether neutralization of TGF-β can enhance the efficacy of DNA vaccines.To address the question in an experimental murine model of melanoma, we have chosen active immunization to induce the generation of TGF-β-neutralizing antibodies and investigated whether genetic immunization of mice with plasmid DNA encoding Xenopus laevis transforming growth factor-beta 5 (aTGF-β5), of which mature chain is approximately 76% identical with that of murine TGF-β1 (mTGF-β1) at the amino acid level, would be effective in inducing the production of mTGF-β1-neutralizing antibodies. The melanoma-associated antigens, including melanoma antigen recognized by T cell 1 (MART-1), gp100, tyrosinase, tyrosinase-related protein 1 (TRP-1) and TRP-2, are derived from normal nonmutated melanocyte lineage differentiation antigens and belong to self-antigens. TRP-2 belongs to the tyrosinase family of melanosomal enzymes involved in melanin synthesis and is expressed in melanocytes and most melanomas. The peptide SVYDFFVWL (mTRP-2aa180-188) corresponding to amino acids 180-188 of murine TRP-2 (mTRP-2) was identified by H-2Kb-restricted CTL specific for B16 melanoma cells. Adoptive transfer of mTRP-2-specific CTLs inhibits the growth of experimental melanoma lung metastas...