Vaccination against polyoma virus (PyV) tumors using vaccinia-PyV recombinants: a major tumor-specific transplantation antigen (TSTA) epitope resides within the C-terminal segment of middle-T protein

Hamster polyomavirus-encoded proteins: gene cloning, heterologous expression and immunoreactivity

The hamster polyomavirus (HaPV) is associated with spontaneously appearing skin epithelioma of the Syrian hamster Z3 strain. Virus particles prepared from the skin epithelioma cause lymphoma and leukemia when injected into newborn hamsters from a distinct Syrian hamster colony (HaP); in contrast to the skin epithelioma the hemopoietic tumors are virus free but accumulate viral DNA. To study the humoral immune response of HaPV-infected Z3 hamsters we produced recombinant HaPV proteins in Escherichia coli as beta-galactosidase-, TrpE- and dihydrofolate reductase-fusion proteins or as non-fused proteins. Recombinant plasmids carried segments of all putative early and late HaPV proteins. The recombinant proteins were detected in stained SDS polyacrylamide gels and in Western blots using monoclonal anti-TrpE and anti-beta-galactosidase antibodies and sera of HaPV-infected hamsters. Sera from HaPV-infected Z3 hamsters and crude lysates of all clones were applied to Western blots to characterize the humoral immune response in the animals. HaPV-specific antibodies were found to be directed against early protein segments translated from the first common exon and from the second unique exon of LT and MT, resp., as well as against the late proteins VP1 and VP2/3. The almost complete VP2 was recognized by all sera whereas VP1 was detected only by a half of the sera. Our data suggest the presence of at least 2 immunodominant regions in VP2, one in the C-terminal VP1 and at least 4 in early proteins.

Immunization against polyoma tumors with synthetic peptides derived from the sequences of middle-and large-T antigens

We have used 9 synthetic peptides corresponding to sequences of polyoma virus small-T, middle-T and large-T antigens as immunogens in order to map antigenic epitopes that can induce polyoma-tumor-specific immunity in different mouse strains. We found that immunization of mice with synthetic peptides derived from amino acid (aa) sequences common to all 3 T-antigens (aa 1-19), or sequences common to only middle-T and small-T (aa 162-176), as well as synthetic peptides unique for middle-T (aa 269-282 and 371-381), or unique for large-T (aa 108-124, 316-333 and 436-449) can induce immunity against polyoma tumors. The synthetic peptides can be divided into 3 types with regard to immunogenicity; (i) peptides that immunize in more than one mouse strain and may represent immunodominant sites, (ii) peptides that may be immunogenic in only one strain, and thus strain-specific, and finally (iii) peptides that do not immunize in the strains tested so far.

Immunization against human papillomavirus type 16 tumor cells with recombinant vaccinia viruses expressing E6 and E7

Papillomaviruses are etiological agents of epithelial proliferative disease. In man, neoplastic transformation of the uterine cervix has been linked to infection with specific subtypes of human papillomavirus, particularly types 16 and 18. We previously reported that live vaccinia virus recombinants expressing early transforming proteins of other tumor viruses can immunize against challenge with cognate tumor cells and we have extended this approach to HPV16. Neoplastic transformation by papillomaviruses involves expression of early open reading frames (ORFs) E5, E6, and E7, and we report the construction of vaccinia recombinants separately expressing ORFs E5-E7 of HPV16. Primary rat cell lines cotransformed with HPV16 and an activated ras oncogene were established in order to evaluate the potential of the recombinants to elicit antitumor immunity. We report that inoculation of rats with vaccinia recombinants expressing E6 or E7 retarded or prevented tumor development in a proportion of animals challenged by subcutaneous seeding of tumor cells whereas the recombinant expressing E5 was inactive.

Vaccination against tumor cells expressing breast cancer epithelial tumor antigen

Ninety-one percent of breast tumors aberrantly express an epithelial tumor antigen (ETA) identified by monoclonal antibody H23. Vaccinia virus recombinants expressing tumor antigens have considerable promise in the active immunotherapy of cancer, and we have evaluated the potential of vaccinia recombinants expressing the secreted (S) and cell-associated (transmembrane, T) forms of H23 ETA to elicit immunity to tumor cells expressing ETA. Tumorigenic ras-transformed Fischer rat fibroblast lines FR-S and FR-T, expressing the S or T form of H23 ETA, respectively, were constructed for use in challenge experiments. Expression of H23 ETA in these lines was confirmed by Western blotting and immunofluorescence. When challenged by subcutaneous seeding of tumor cells, 97% (FR-S) and 91% (FR-T) of syngeneic Fischer rats rapidly developed tumors that failed to regress. Vaccination with recombinant vaccinia virus expressing ETA-T prior to challenge prevented tumor development in 82% of animals seeded with FR-T cells but in only 61% of animals seeded with FR-S. The vaccinia recombinant expressing the S form was a less effective immunogen, and vaccination protected only 29-30% of animals from developing tumors upon challenge with either FR-S or -T cells. The increased immunogenicity of the recombinant expressing ETA-T was reflected in elevated levels of ETA-reactive antibody in vaccinated animals, confirming that secreted antigens expressed from vaccinia virus are less effective immunogens than their membrane-associated counterparts.