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Immunotherapy of cancer utilizes dendritic cells (DCs) for antigen presentation and the induction of tumor-specific immune responses. However, the therapeutic induction of anti-tumor immunity is limited by tumor escape mechanisms. In this study, immortalized dendritic D2SC/1 cells were transduced with a mutated version of the p53 tumor suppressor gene, p53M234I, or p53C132F/E168G, which are overexpressed in MethA fibrosarcoma tumor cells. In addition, D2SC/1 cells were fused with MethA tumor cells to generate a vaccine that potentially expresses a large repertoire of tumor-antigens. Cellular vaccines were transplanted onto Balb/c mice and MethA tumor growth and anti-tumor immune responses were examined in vaccinated animals. D2SC/1-p53M234I and D2SC/1-p53C132F/E168G cells induced strong therapeutic and protective MethA tumor immunity upon transplantation in Balb/c mice. However, in a fraction of immunized mice MethA tumor growth resumed after an extended latency period. Analysis of these tumors indicated loss of p53 expression. Mice, pre-treated with fusion hybrids generated from D2SC/1 and MethA tumor cells, suppressed MethA tumor growth and averted adaptive immune escape. Polyclonal B-cell responses directed against various MethA tumor proteins could be detected in the sera of D2SC/1-MethA inoculated mice. Athymic nude mice and Balb/c mice depleted of CD4(+) or CD8(+) T-cells were not protected against MethA tumor cell growth after immunization with D2SC/1-MethA hybrids. Our results highlight a potential drawback of cancer immunotherapy by demonstrating that the induction of a specific anti-tumor response favors the acquisition of tumor phenotypes promoting immune evasion. In contrast, the application of DC/tumor cell fusion hybrids prevents adaptive immune escape by a T-cell dependent mechanism and provides a simple strategy for personalized anti-cancer treatment without the need of selectively priming the host immune system.
Survivin is a well-established target in experimental cancer therapy. The molecule is over-expressed in most human tumors, but hardly detectable in normal tissues. Multiple functions in different subcellular compartments have been assigned. It participates in the control of cell division, apoptosis, the cellular stress response, and also in the regulation of cell migration and metastasis. Survivin expression has been recognized as a biomarker: high expression indicates an unfavorable prognosis and resistance to chemotherapeutic agents and radiation treatment. Survivin is an unconventional drug target and several indirect approaches have been exploited to affect its function and the phenotype of survivin-expressing cells. Interference with the expression of the survivin gene, the utilization of its messenger RNA, the intracellular localization, the interaction with binding partners, the stability of the survivin protein, and the induction of survivin-specific immune responses have been taken into consideration. A direct strategy to inhibit survivin has been based on the identification of a specifically interacting peptide. This peptide can recognize survivin intracellularly and cause the degradation of the ligand–survivin complex. Technology is being developed that might allow the derivation of small molecular-weight, drug-like compounds that are functionally equivalent to the peptide ligand.