Escape of tumor cells from the host immune system is probably the most difficult obstacle to overcome in attempts to enhance the efficacy of immunotherapy of tumors. To solve the problem, animal models with escape mechanisms found in human tumors are needed. We have already established cell lines with substantially reduced expression of MHC class I molecules that were derived from oncogenic TC-1 cells producing E6 and E7 oncoproteins of HPV16. In this study, we prepared other cell lines from TC-1-induced tumors formed infrequently in mice immunized against the E7 antigen. These clones differed in morphology and both in vitro and in vivo growth properties. After vaccination with the highly efficient anti-E7 DNA vaccine several clones appeared to be quite resistant to induced anti-tumor immunity. Detection of the production of the MHC class I molecules and B7.1 costimulatory molecule did not provide clues to understand the mechanism of immunoresistance of the clones. Therefore, we performed transcriptional profiling using Atlas Mouse Cancer 1.2 Array (BD Clontech). Among the genes differently expressed in the examined cell lines were those of three cytokines influencing immune cells: MCP-1, osteopontin, and midkine. Altered secretion of MCP-1 chemokine was verified by ELISA. In addition, expression of the E7 oncogene was reduced in all TC-1 clones. Most importantly, one of anchor amino acids in the immunodominant epitope of E7 was mutated in all immunoresistant clones. Such mutations of HPV oncogenes must be considered in therapeutic-vaccine development and evaluation.

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