Immunological and chemical studies of cell surfaces from normal and transformed BALB/c fibroblasts have shown alterations associated with transformation. The cells studied include normal lines which do not cause tumors when injected into BALB/c mice, viral transformants, and spontaneous transformants which cause tumors that either regress or grow progressively, killing the host. The spontaneously transformed progressors include cell lines which are immunogenic and nonimmunogenic as determined by the ability of tumor excision to protect an animal from subsequent rechallenge by tumor cells. Tumor-bearing mice produce lymphocytes which are nonspecifically cytotoxic for all the normal and transformed lines. Some of the cell lines induce specific antibody formation in BALB/hosts. Antisera have been prepared in rabbits which are specific for the transformed cell lines. These antisera can be used to determine specific surface changes on the transformed cells. Chemical studies have shown glycolipid alterations between the normal cells and some, but not all, of the transformants. Glycoproteins labeled by lactoperoxidase-125I or [3H] glucosamine were compared by SDS gel electrophoresis. Results from these studies do not show changes associated with malignancy. Individual glycoprotein regions from gels were treated with pronase, and the glycopeptides compared by Sephadex G50 chromatography. Alterations in glycopeptides from several cellular glycoproteins are the only changes which appear to be associated with malignancy.

This work describes the detection, isolation, and partial characterization of a BALB/c mouse fibroblast cell surface antigen. This antigen migrates as a polypeptide of approximately 100,000 daltons in a discontinuous sodium dodecyl sulfate/polyacrylamide gel electrophoresis system, can be labeled by either lactoperoxidase-catalyzed cell surface 125I iodination or metabolic incorporation of [3H~glucosamine, and can be isolated by concanavalin A affinity chromatography. This cell surface glycoprotein is antigenic in BALB/c mice and has been correlated with the rejection of immunogenic tumor cells. Also, antiserum specific for Moloney leukemia virus precipitates the 100,000-dalton cell surface protein from viral and immunogenic spontaneous transformants. This virus-related antigen comigrates on sodium dodecyl sulfate gels with the major iodinated cell surface protein of these transformants. (1)(2)(3)(4). The viral transformants, and some spontaneous transformants, were shown to be immunogenic; i.e., inoculation of attenuated cells would protect against subsequent tumor challenge. Two of the spontaneous transformants were shown to be cross-immunogenic and therefore must share a tumor-specific transplantation-type rejection antigen. The tumorigenic properties of these two cell lines are quite different, because one causes tumors that always regress and the other can be lethal to the host. We have previously reported that these immunogenic lines have augmented levels of a 100,000-dalton cell surface glycoprotein as compared with normal cells or nonimmunogenic transformants (4, 5). We now use biochemical and immunological methods to isolate the 100,000-dalton glycoprotein, and we demonstrate its antigenicity in the BALB/c system and its antigenic crossreactivity with Moloney leukemia virus (MLV).MATERIALS AND METHODS Cell Lines and Cell Cultures. All cell lines were derived from BALB/c mice. A31 is a cloned line of BALB/c 3T3 fibroblasts and was a gift from G. Todaro of the National Institutes of Health. c5 is a transformed cell line cloned from A31 as previously described (1, 3). c5T was isolated from a tumor caused by injecting c5 cells into a BALB/c mouse. MSC was derived from a Moloney strain murine sarcoma virus-induced tumor in a BALB/c mouse and was a gift of S. Russell of the Scripps Clinic and Research Foundation. 3T12T cells were isolated from a tumor caused by injecting 3T12 cells (from G. Todaro) into a BALB/c mouse. Cells were grown in monolayer cultures in antibiotic-free Dulbecco's modified minimal essential medium supplemented with 10% fetal calf serum (Grand Island Biological Company, Berkeley, CA). Routine tests for mycoplasma contamination were performed (6-8). Cultures testing positive were not used for any experiments and were discarded.Antisera. New Zealand White rabbits were inoculated subcutaneously with freeze-thaw-disrupted c5T or 3T12T cells. The inoculations were at multiple sites on a bimonthly schedule over an 18-month period. The rabbits were bled by venous puncture and sera were...