Immunological escape mechanism in spontaneously metastasizing mammary tumors.

Abstract

Immunological and biochemical studies of spontaneously metastasizing and nonmetastasizing rat mammary carcinomas and, their plasma membranes indicated that: (i) all spontaneously metastasizing tumors have little or no demonstrable glycocalyx, while all nonmetastasizing tumors have a thick glycocalyx; (ii) there is a direct relationship between the glycocalyx and immunogenicity, and an inverse relationship with the metastasizing capacity of tumor cells, properties which can be quantitated by levels of the plasma membrane marker enzyme 5'-nucleotidase (EC 3.1.3.5; 5'-ribonucleotide phosphohydrolase) activity; (iii) the absence of glycocalyx from the metastasizing tumor cell surface seems to result from its dissociation from plasma membranes, for solubilized cell surface antigen is readily found in the'blood of metastasizing tumor bearing rats, while there was no detectable tumor cell surface antigen in the blood of the nonmetastasizing tumor hosts tested; (iv) both metastasizing and nonmetastasizing mammary tumors appear to have a common soluble cell surface' antigen; (v) in addition to this common antigen, there is another membrane-bound antigen in the nonmetastasizing, immunogenic tumor cell surface which presumably is the tuinor specific transplantation antigen; and (vi) this antigen is immunobiologically unique, but seems to be immunochemically related to the common soluble antigen. It is postulated that the lack of an immunogenic coat and/or the presence of solubilized tumor cell surface antigen in the blood may provide an immune escape mechanism for tumor cells by interfering with cell-mediated immune response of tumor hosts, leading to their dissemination.In an earlier report one of us (U.K.) (1) described the induction of spontaneously metastasizing mammary carcinomas (MT) in a highly inbred strain of W/Fu female rats by feeding 3-methylcholanthrene in splenectomized, thymectomized, or both splenectomized and thymectomized hosts, and subsequently subjecting the developing tumors to "immunoselection" in vivo. Such tunmors maintained their metastasizing capacity in normal syngeneic rats generation after transplantation generation, indicating that the metastasizing capacity is an intrinsic property of tumor cells. It was further demonstrated that the metastasizing tumor cells were nonimmunogenic while the ordinary methylcholanthrene-induced nonmetastasizing mammary carcinomas in normal female rats were highly immunogenic, as tested by immunization of the hosts with an equal number of radiation-killed tumor cells, followed by a challenge with a counted number of live tumor cells.In order to study the relationship between tumor cell immunogenicity and metastasizing capacity, two spontaneously metastasizing, non-or weakly-immunogenic mammary carcinomas (SAIT-2A and TMT-50), induced in the manner described above, and a spontaneously metastasizing mammary carcinoma induced with 7,12-dimethylbenz(a)-anthracene in a BCG (bacille Calmette-Guerin) inoculated rat (BCG-MT) were selected. They were matched accord...

Plasma membrane associated enzymes of mammary tumours as the biochemical indicators of metastasizing capacity. Analyses of enriched plasma membrane preparations

“…These studies confirm earlier observations (Kim et al, 1975) and lend support to our hypothesis that loss of glycocalyx and shedding of cell surface antigens by spontaneously metastasizing mammary tumour cells result in loss of activity of plasma membrane marker enzymes. Further analyses of glycoproteins, glycolipids, carbohydrate metabolism with respect to glycosyl transferase and glycosidase activities in the plasma membranes are being carried out to elucidate the biochemical mechanism of antigen shedding and acquisition of metastasizing property by malignant tumour cells.…”

“…The most striking observation in the analyses of 5 different plasma membrane marker enzymes in the F3 fraction from 6 spontaneously metastasizing and 4 nonmetastasizing mammary tumours was that the specific activity of all 5 enzymes was much higher in the non-metastasizing ones, and the enzyme activities decreased proportionally as the metastasizing capacity increased (Table V), confirming our earlier observations (Kim and Pickren, 1974;Kim et al, 1975). Therefore, plasma membrane marker enzymes seem to be an accurate indicator for metastasizing capacity of tumour cells in this experimental tumour system and have prognosticating value.…”

“…Since all 5 enzymes are deficient in spontaneously metastasizing tumours which are also lacking in glycocalyx, the biochemical changes representing or responsible for the biological differences between these 2 tumour groups are not likely to be localized in any specific loci of the cell surface, for they may be spread throughout the plasma membranes. Plasma membrane marker enzymes in non-metastasizing tumours are entirely sedimentable with the membrane particulate, while at least 20% of them are solubilized in the cytosol of the metastasizing tumours as observed earlier (Kim et al, 1975). Furthermore, the proportion of F2 fraction is greater in the metastasizing tumours, indicating that the plasma membranes of spontaneously metastasizing tumours are more fragile.…”

“…The standardized tumour transplantation procedure is described elsewhere (Kim et al, 1975). Their metastasizing capacity was rated arbitrarily as: negative (0) Fractionation of subcellular organelles.…”

“…Thus, the level of plasma membrane marker enzymes is considered an accurate indicator for metastasizing capacity in the rat mammary tumour system. IN EARLIER studies (Kim and Pickren, 1974;Kim et al, 1975), it was demonstrated that the level of various plasma membrane marker enzymes correlated roughly with the amount of membrane bound glycoproteins or glycocalyx and the immunogenicity of rat mammary tumour cells, and, inversely, with their antigen shedding property and metastasizing capacity. Since subcellular contaminants tend to interfere with an accurate quantitation of tumour cell plasma membranes, we have directed our efforts towards developing a method whereby the plasma membranes of rat mammary tumour cells, free of contaminations, can be prepared reproducibly.…”