BiochemicalCharacterizationof 1-Butanol-extractedMurineTumor-specific TransplantationAntigens1

This investigation sought to characterize biochemically the tumor-specific transplantation antigens (TSTA) expressed on the cell surface of a panel of chemically induced fibrosarcomas of CSH/HeJ mice. Results suggest a uniform antigenic framework upon which individual specificities are superimposed. The anti gens expressed by the 3-methylcholanthrene-induced fibrosar comas MCA-D, MCA-F, and MCA-2A fulfill the requirements of a TSTA; namely, immunization of syngeneic hosts with irradiated cells or soluble extracts engenders a tumor-specific immune response such that animals resist challenge with the same, but not another, tumor. Brief incubation of intact tumor cells in singlephase aqueous solutions of 2.5% (v/v) 1-butanol extracts an immunoprotective TSTA, but not alloantigenic activity, from MCA-F cells. This extraction protocol was extended to the two other MCA-induced neoplasms. The butanol-extracted TSTA from the three tumors displayed isoelectric pHs of 6.4 to 6.6 following preparative ¡soelectricfocusing. The tumor-specific im munoprotective activity from all three tumors displayed an ap parent molecular weight of 150,000 (150 kDa) during highperformance gel permeation chromatography. The Chromato graphie properties of the 150 kDa antigens were unaffected by reduction using dithiothreitol, but incubation in acetate buffer, pH 3.0, dissociated the 150 kDa complex into at least two components with molecular weights of 70 to 100 kDa and 20 to 40 kDa. Only the smaller component displayed TSTA activity. The presence of two major components in the 150-kDa antigen was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. TSTA activity was sensitive to digestion with pronase, papain, chymotrypsin, and a-mannosidase, but resist ant to DNase, RNase, neuraminidase, trypsin, endoglycosidase H, and a mixed-function glycosidase. In addition, the TSTA activity was unaffected by heating. These data demonstrate that MCA carcinogenesis results in the expression of immunologically unique epitopes on biochemically related glycoproteins and sug gest a unified mechanism for the generation of TSTA polymor phism.