S. Katzav

Interactions between the local tumor and its metastases.

The generation of metastases by tumor cells is an end result of a sequence of processes, each of which is controlled by distinct properties of the metastatic cell. Thus, the detachment of carcinoma cells from the local tumor graft, their binding to and penetration through capillary endothelia, their dissemination within the blood circulation, their homeotypic aggregation in the blood vessels of target organs, their recognition and hence their binding to normal endothelial or other cells of their metastatic sites, their capacity to induce angiogenesis at these new anatomical sites, each of these steps might be a function of properties of metastatic cells which nonmetastatic tumor cells may not possess. Indeed, many of the experimental approaches to the mechanisms associated with the control of metastasis were based on the demonstration that a) tumor cells constitute a diverse population with regards to their metastatogenic potential (1-3), and b) metastatogenic cells are endowed with specific properties, distinct from those which characterize cells of the local growth. These properties should control each of the sequential stages leading to the growth of metastases. Thus, studying the metastatic Lewis lung carcinoma (3LL), we demonstrated that individual clones of the 3LL tumor differ in their metastatic potency (4). Cells of a clone capable of generating metastases manifested a significantly lower susceptibility to NK cells than cells of a nonmetastatogenic clone (4). This property could determine their survival while disseminating in the circulation (5-7). Since the selection for NK resistance concomitantly selected for increased metastatogenic potency (6), and since the inoculation of a nonmetastatic clone to NK-deficient beige (Bg/Bg) mice resulted in the generation of metastases (4), it appeared that this cell-surface property might be causally related to the metastatic capacity of the cells. We also demonstrated (7, 8) that cells from lung metastases (M-3LL) differ in their cell surface antigens from the cells of the local 3LL (L3LL), thus enaNing immunoselective processes to operate in tumor dissemination. It was also found that the metastatic 3LL cells are capable of enzymatic degradation of the collagen type II which characterizes the basement membrane of blood vessels. Yet, although such and other differences between the metastatic and the nonmetastatic 3LL cells were demonstrated, it appears that once the two populations segregate in vivo, thus forming a growing local tumor and progressively growing lung metastases, regulatory interactions operate between them. The interactions which we shall review stem from the observation that the surgical removal of the local tumor is followed by an accelerated growth and an increased incidence of lung metastases (9). This observation thus suggested that the local tumor exerts an inhibiting

Somatic cell hybridization between bovine leukemia virus-infected lymphocytes and murine plasma cell tumors: Cell fusion studies with bovine cells☆

Hybridization of peripheral blood lymphocytes from bovine leukemia virus-infected cows with murine myeloma cells resulted in the generation of hybrid cells secreting immunoglobulins composed of various combinations of heavy and light chains of both bovine and murine Ig origin. Some hybrid cells derived from the light-chain producer, but non-secretor murine myeloma NSI cell line, secreted IgM molecules composed of bovine mu-chain linked to bovine and/or murine light chains. Other hybridomas secreted mouse and bovine light-chain dimers and/or monomers, or failed to secrete any Ig polypeptide chain whatsoever. Immunoglobulins secreted by hybridomas obtained upon hybridization of bovine cells with the IgG-secreting murine myeloma P2X63 cell line, contained bovine mu-chain in one of the seven hybridomas obtained, and bovine light chain in two of them. All the cell lines secreted murine light- and gamma-chains.

Immunobiological diversity of metastatic cells

The analysis of antigenic and immunogenic properties of tumor cells and of mechanisms of antitumor response should furnish the basis for the investigation of methods aimed at immunotherapy of malignant diseases. One may expect that such methods will be especially effective in the prevention of metastatic progression following surgical removal of the primary tumor mass. Immunotherapeutic approaches are based either on nonspecific stimulation of the host’s immune system or on the specific immunization of the organism against tumor cells originating in the surgically removed tumor. These immunization procedures are expected to stimulate the development of cytotoxic lymphocytes or antibodies which are capable of inhibiting tumor growth and destroying metastatic tumor cells. Another experimental approach to immunotherapy is based on the adoptive transfer to the diseased host of lymphocytes sensitized in vitro against tumor cells [1].

Gene Products of the Major Histocompatibility Complex Control the Metastatic Phenotype of Tumor Cells

To generate metastases, neoplastic cells should be capable of detaching themselves from the local growth, of invading extracellular matrices, of penetrating basement membranes of blood of extravasating while manifesting, in many cases, specific recognition of target organs, and of inducing angiogenesis essential for the growth of metastasis. Since the local tumor cell population was shown to be diverse with respect to the metastatic competence of its individual cells (1), nonmetastatic cells of a metastatic tumor may be impaired with regards to all, a few or any one of the sequential steps culminating in metastatic growth. Recent studies in our laboratories of two metastatic tumors, the 3LL Lewis Lung Carcinoma and the T10 Sarcoma, indicated that metastatic clones and nonmetastatic clones synthesize and secrete similar levels of collagenase IV (2), an enzyme which was previously implicated as part of the enzymatic weaponry for metastatic penetration of basement membranes (3). And although the synthesis of another relevant enzyme, plasminogen activator, was higher in metastatic compared to nonmetastatic clones (4), this did not seem to represent a rate-limiting factor in the initial invasion processes (4).

Immunomodulation of Tumor Metastases

The local tumor cell population seems to be diverse with regard to the metastatic competence of its individual cells (1). Cells capable of generating metastases, have to detach themselves from the local cell population, to penetrate basement membranes of blood capillaries, to migrate via the blood circulation, while undergoing cell aggregation, to extravasate at the target organs, and to induce angiogenesis for the metastatic growth.

Immunogenetic Determinants Controlling the Metastatic Properties of Tumor Cells

The generation of metastases by tumor cells is preceeded by a sequence of processes, each of which is controlled by different properties of the invading cells. Thus, the detachment of tumor cells from its local population might be associated with alterations in cell-to-cell recognition patterns, its metastatic penetration through the basement membrane of blood capillaries might require the synthesis of specific enzymes capable of degrading membrane proteins (Liotta et al., 1977; Strauli and Weiss, 1977), its “homing” to specific organs might be determined by specific adherance to the normal cells of the target organ (Kramer and Nicolson, 1979), whereas its growth at its new site might require the secretion of angiogenic factors (Folkman and Hochberg, 1973; Folkman and Handeschild, 1981).

Membrane IgM of bovine lymphocytes

The membrane immunoglobulins of peripheral blood lymphocytes (PBL) obtained from four bovine-leukemia-virus infected calves and from a normal cow were isolated and characterized. They were found to consist of an IgM exhibiting a mu-chain of an apparent molecular weight (AMW) of 95,000 daltons, which is 10,000 daltons more than found for the mu-chain of serum IgM. It thus seems that this is a property of membrane-bound IgM of bovine origin.

Immunogenetic Determinants of Metastatic Cells

The progression of metastases is controlled by a series of cellular interactions between host and tumor cells. The generation of blood-bourne metastases is initiated by tumor cells capable of adhering to capillary basement membranes, followed by penetration, apparently via enzymatic degradation, of its proteins (1–3).

The Immunogenetics of MHC Controlled Antigenic Determinants on Lewis-Lung-Carcinoma (3LL) Cells

The transplantation antigens controlled by the major histocompatibility complex (MHC) of mammals play a cardinal role in the control of immune processes. These alloantigens determine the ability to evoke effector cells directed against antigens expressed on malignant cells transformed by either chemical or viral carcinogens (1–4). MHC-encoded components may also control the qualitative outcome of an immune process directed against a given antigen on a certain malignant target cell. Thus, the preferential elicitation of antibody-producing cells, suppressor cells, killer cells, or lymphokines producing T cells against a cell-surface antigen may depend on the nature of the neighboring MHC components that form a complex with tumor antigens. Therefore, to elucidate immune tumor—host relations, one has to analyze both quantitatively and qualitatively whether MHC components expressed on tumor cells are different in their immunogenic properties from those expressed on normal somatic cells. Such differences might be relevant to the capacity of tumor cells to attack the immune barriers of the host and disseminate from its original site of growth to distant anatomical locations.

IMMUNOGENETIC PROPERTIES OF TUMOR METASTASES11Supported by PHA grant No. 28139 awarded by the National Cancer Institute, Department of Human Health Services, Bethesda, Maryland, USA and by the Schilling Foundation, Essen, FRG.

ABSTRACT Cells of the local growth of the T10 sarcoma, originated in a (C57BL × C3H)F1 mouse, express predominantly the H-2 b haplotype, whereas cells of its lung metastasis express both the H-2 b and the H-2 k . Cloned cell populations express either the H-2 b or the H-2 b and the H-2 k . Only the latter clones are capable of generating metastases. Nonmetastatic H-2 b positive, H-2 k negative clones, upon serial passaging, acquire the H-2 k , and concomitantly acquire metastatogenic potency. Thus, tumor progression toward increased malignancy, associated with alteration in the expression of H-2 determinant, takes place within cloned tumor cell populations.