Studies on the polyoma-virus-induced tumor-specific transplantation antigen (TSTA)--does middle or large T-antigen play a role?

A short peptide eluted from the H-2Kb molecule of a polyomavirus-positive tumor corresponds to polyomavirus large T antigen peptide at amino acids 578 to 585 and induces polyomavirus-specific immunity

A short peptide in complex with the H-2Kb molecule on PyRMA, a polyomavirus transfectant of the mouse lymphoma cell line RMA, was identified as a polyomavirus tumor-specific transplantation antigen. The peptide was obtained by affinity chromatography, acidic extraction, and reverse-phase high-pressure liquid chromatography (HPLC). In one HPLC fraction, a peptide sequence in which 5 of 8 amino acids, GKxGLxxA, corresponded to residues 578 to 585 of polyomavirus large T antigen was identified. In tumor rejection assays, we therefore tested three related synthetic peptides, corresponding to the octapeptide LT 578-585, GKTGLAAA; the nonapeptide LT 578-586, GKTGLAAAL; and the decapeptide LT 578-587, GKTGLAAALI. The octapeptide was found to give the most effective immunization against the outgrowth of the polyomavirus DNA-positive PyRMA tumor. However, none of the three peptides immunized against the original polyoma-virus-negative RMA line.

Modifications of an immunodominant peptide antigen induce different anti-polyoma tumor responses in two separate mouse strains

An immunodominant polyoma peptide antigen MT162-176 was modified with regard to amino acid (aa) composition in an attempt to analyze its immunogenicity in detail. Twelve modifications of peptide MT162-176, 3 overlapping peptides and 9 peptides with point mutations, were synthesized and used for immunizations of (A.CA x C57BL/6)F1 and CBA mice against the syngeneic polyoma tumors SECA and SEBA. All 3 overlapping peptides MT162-176, MT165-174 and MT170-176, were immunogenic in (A.CA x C57BL/6)F1 mice against SECA, indicating that possibly more than one immunogenic epitope may be recognized within the MT162-176 sequence. In CBA mice, the 2 peptides covering the C-terminal half were immunogenic against SEBA, while the N-terminal peptide was possibly somewhat less efficient. The peptides with aa point mutations induced different anti-tumor responses in the 2 mouse strains. In CBA mice, only one mutant, MT162-176.28, was immunogenic. For (A.CA x C57BI)F1 3 different mutants, MT162-176.29, MT162-176.35 and MT162-176.36 were immunogenic against SECA, while the remaining 6 had lost their activity. These results suggest that a different emphasis of recognition of peptide MT162-176 exists with regard to the 2 mouse strains examined. Furthermore, different immunization procedures were tested. We found that repeated immunizations with peptide without Freund's adjuvant was the most efficient.

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.

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

We previously reported that inoculation of rats with live vaccinia virus (VV) recombinants VVpyMT, VVpyLT expressing either the middle-T (MT) or large-T (LT) proteins of polyomavirus (PyV) can elicit immunity to challenge with syngeneic PyV-tumor cells. We now report the results of cross-vaccination studies. VVpyMT was ineffective against cells expressing LT protein but prevented development of MT-expressing cells. Conversely, the VVpyLT was ineffective against MT-expressing cells. In the two experiments performed, tumor growth enhancement rather than retardation was observed in VVpyLT-vaccinated animals receiving PyV-LT (FRLTI) challenge tumor cells. To determine the location of the major TSTA within MT, a further VV recombinant (VVpyMT/Cfr) was constructed that expresses only the unique C-terminal segment of MT. VVpyMT-Cfr and VVpyMT were equally effective in eliciting tumor immunity, indicating the presence of a major TSTA epitope within the unique C-terminal region of MT.

A single peptide derived from the sequence common to polyoma small and middle T-antigen induces immunity against polyoma tumors

Polyoma virus, an oncogenic virus, fails to induce tumors in immunocompetent rodents due to T cell-dependent mechanisms. The target recognized by the immune system has been functionally defined as polyoma tumor-specific transplantation antigen (TSTA) and has been postulated to be related to the virus three early proteins small T (ST), middle T (MT), and large T (LT) antigens. We show here that immunization with a synthetic peptide corresponding to amino acids 162-176 of polyoma MT and ST was able to decrease tumor progression of polyoma tumors, but not of nonpolyoma tumors. This indicated that these amino acids constitute an epitope of the polyoma tumor-specific transplantation antigen.

Polyoma T-antigen-derived synthetic peptides induce polyoma-virus-specific macrophage migration inhibition

Synthetic peptides, 2 derived from the sequence common to small, middle and large T-antigen, and I derived from the sequence unique for middle T, activated lymphocytes from polyoma-virus-immunized, but not from control mice, to release the lymphokine migration inhibitory factor (MIF). In contrast, purified, bacterially grown, full-length small T-antigen and a middle T-antigen mutant Py 1387T MT (lacking 37 C-terminal amino acids) did not induce lymphokine release, although they were capable of inducing an anti-polyoma TSTA response in vivo.

A polyomavirus tumor-specific transplantation antigen (TSTA) epitope is situated within the N-terminal amino acid sequence common to middle and small T-antigens

An MT cDNA-transformed rat cell line (2.8), that contains only the polyoma middle T-antigen and expresses polyoma TSTA, can be rejected in rats immunized with 1837 cells that carry a host range (A185 hr-t), mutant which expresses a full-length large T-antigen, and nonfunctional N-terminal fragments of small and middle T. This shows that at least one polyoma TSTA epitope is situated in the 113 amino acid N-terminal region, which is common to middle and small T-antigens.

Recombinant polyoma--vaccinia viruses: T antigen expression vectors and anti-tumor immunization agents

Live vaccinia virus recombinants expressing viral antigens have recently been developed as effective anti-viral vaccines. We have examined the possibility of extending this approach to specific anti-tumor immunity, using tumors induced by the polyoma virus (PyV) as a model system. Three recombinant vaccinia viruses, separately encoding the three early proteins of the polyoma virus (large, middle and small tumor (T) antigens) were constructed. Each recombinant efficiently expresses the appropriate T antigen, which exhibits biochemical properties and subcellular localization of the authentic PyV protein. The potential of the recombinants to elicit immunity towards PyV-induced tumors was assessed in rats by a challenge injection of syngeneic PyV-transformed cells. After prior immunization with the large-T or the middle-T viruses, small tumors developed, which later regressed and were eliminated in more than 50% of the animals. In contrast, the small-T virus failed to elicit tumor rejection. Established tumors could also be eliminated by curative vaccinations. No circulating antibodies directed against PyV large-T or middle-T antigens were detected in animals vaccinated with the large-T or middle-T viruses, suggesting that rejection may be due to a cell-mediated immune response.

Immunization against the polyoma tumor-specific transplantation antigen (TSTA) with polyoma T-antigens

The relationship between the polyoma virus tumor-specific transplantation antigen (TSTA) and 2 of the virus proteins coded from the early region of polyomavirus was investigated. Mice were immunized with small T antigen and a truncated mutant of middle T antigen, both purified from genetically engineered Escherichia coli. The 2 proteins induced protective immunity against polyomavirus-induced tumors, but not against non-polyoma tumors, indicating that one or more of the polyoma T antigens are directly involved in a TSTA function.

Studies on the polyoma tumor-specific transplantation antigen (TSTA): selection and characterization of TSTA-negative segregants from somatic hybrids

Two polyoma-TSTA-negative variants were selected independently from a polyoma fibrosarcoma/Moloney lymphoma somatic hybrid, by repeated passages in polyoma-virus-preimmunized mice. One of the variants had lost all its polyoma DNA, while the other only retained a deleted piece of its integrated polyoma DNA. In contrast to the parental hybrid clone, none of the variants produced detectable amounts of T-antigens. This finding indicates that a detectable expression of the products of the polyoma virus early genome, the T-antigens, is important either directly or indirectly for the expression of TSTA.

Tumour prevention and rejection with recombinant vaccinia

Tumour-specific antigens (TSA; ref. 1) have been exploited in the diagnosis and imaging of human cancer and anti-TSA antibodies have therapeutic potential. Vaccination with TSA or anti-idiotypic (TSA) antibodies has also been used to control tumour growth in model systems. An effective immune response nevertheless demands copresentation of antigen with host histocompatibility determinants. We therefore examined whether live vaccinia virus recombinants expressing TSA in cells of the vaccinated host might better elicit tumour immunity. Polyoma virus (PY) is tumorigenic in rodents; because killed PY-transformed cells can elicit tumour immunity, a PY-specific TSA has been postulated. Tumorigenesis involves expression of three early PY proteins, large-T (LT), middle-T (MT) and small-T (ST), but their role as TSAs is unclear. We therefore expressed the three T proteins in separate vaccinia recombinants. Rejection of PY tumours was observed in rats immunized with recombinants expressing either LT or MT. Further, tumour-bearing animals could be induced to reject their tumours by inoculation of recombinants.