HeLa cells infected with the nondefective adenovirus type 2-simian virus 40 hybrid viruses Ad2+ ND1 or Ad2+ND2 were analyzed for cell surface location of the SV40-specific hybrid virus proteins by indirect immunofluorescence microscopy. Two different batches of sera from SV40 tumor-bearing hamsters, serum from SV40 tumor-bearing mice, or two different antisera prepared against purified sodium dodecyl sulfate-denatured SV40 T-antigen, respectively, were used. All sera were shown to exhibit

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... able T-and U-antibody titers and to specifically immunoprecipitate the SV40-specific proteins from cell extracts of Ad2+ND2infected cells. Whereas analysis of living, hybrid virus-infected HeLa cells did not yield conclusive results, analysis of Formalin-fixed cells resulted in positive cell surface fluorescence with both Ad2+ND1and Ad2+ND2-infected HeLa cells when antisera prepared against sodium dodecyl sulfate-denatured SV40 T-antigen were used as first antibody. In contrast, sera from SV40 tumor-bearing animals were not or only very weakly able to stain the surfaces of these cells. The fact that the tumor sera had comparable or even higher T-and U-antibody titers than the antisera against sodium dodecyl sulfate-denatured T-antigen but were not able to recognize SV40-specific proteins on the cell surface suggests that SV40 tumor-specific transplantation antigen may be an antigenic entity different from Tor U-antigen. 522