Recombinant vaccinia mucin vector: in vitro analysis of expression of tumor-associated epitopes for antibody and human cytotoxic T-cell recognition.

We have constructed a recombinant vaccinia virus vector that contains human mucin MUC-1 cDNA. Analysis of the recombinant virus isolates showed the tendency of the vaccinia to delete large portions of the mucin tandem repeat region. Epstein-Barr virus (EBV)-immortalized B cell lines from humans and chimpanzees were infected and analyzed for expression of the mucin on the cell surface and the presence of specific epitopes in the tandem repeat region previously shown to be preferentially expressed on tumor cells and recognized by tumor-specific mouse monoclonal antibodies and human cytotoxic T lymphocytes (CTL). We found that this recombinant vector encodes expression of mucin that contains all the epitopes recognized by the antibodies. The tumor-specific epitopes can be further exposed by inhibition of O-linked glycosylation in infected cells. Lack of multiple tandem repeats, however, prevents major histocompatibility complex (MHC)-unrestricted recognition by the CTL of the majority of infected cell lines. Still, we show two examples of an apparent MHC-restricted recognition of vaccinia-encoded mucin that may depend on one or very few rare human lymphocyte antigen (HLA) types capable of presenting the mucin peptides.