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.