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Purification and Partial Characterization of a Tumor-Specific Blocking Factor from Sera of Mice with Growing Chemically Induced Sarcomas¹

Departments of Biochemistry, Microbiology, Immunology and Pathology, University of Washington School of Medicine, Seattle, Washington 98195 and the Division of Immunology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98104

Abstract

The purification of a blocking factor from the sera of tumor-bearing mice is described. Whole serum with blocking activity—the ability to inhibit specific cell-mediated anti-tumor immunity in microcytotoxicity tests—was fractionated on immunoadsorbent columns containing Sepharose-bound syngeneic normal mouse immunoglobulins and immunoglobulins from tumor-immune donors. The blocking serum was derived from mice which had carried a transplanted methylocholanthrene-induced sarcoma for 21 to 28 days. Elution of the immunoadsorbents recovered the blocking activity in a single fraction. This fraction was radiolabeled and analyzed by SDS gel electrophoresis and Sephadex G-200 column chromatography. The active component of the blocking serum was shown to be a polypeptide of m.w. 56,000.

Specificity testing implied that the factor was likely to be either tumor antigen or an antigen-specific suppressor molecule.

Footnotes

¹ This study was supported by Grants CA 19148 and CA 19149 from the National Institutes of Health, by Grant IM-43 F and Institutional Cancer Grant IN-26 from the American Cancer Society, by Contract NO1 64018 from the National Cancer Institute and by Contract NO1 CP 53570 within the Virus Cancer Program of the National Cancer Institute.

² The first author was supported as a Medical Scientist Trainee (GM 02103), National Institute of Health.