Identification of asparagine-linked oligosaccharides involved in tumor cell adhesion to laminin and type IV collagen

MDW4, a wheat germ agglutinin-resistant nonmetastatic mutant of the highly metastatic murine tumor cell line called MDAY-D2 has previously been shown to attach to fibronectin and type IV collagen, whereas MDAY-D2 and phenotypic revertants of MDW4 attached poorly to these substrates. The increased adhesiveness of the mutant cells appeared to be closely related to a lesion in cell surface carbohydrate structures. In an effort to identify the carbohydrates involved in cell attachment, glycopeptides isolated from mutant and wild-type cells as well as from purified glycoproteins were tested for their ability to inhibit the attachment of MDW4 cells to plastic surfaces coated with fibronectin, laminin, or type IV collagen. The addition of mannose-terminating glycopeptide to the adhesion assay inhibited MDW4 cell attachment to type IV collagen. In contrast, a sialylated poly N-acetyllactosamine-containing glycopeptide, isolated from wheat germ agglutinin-sensitive MDAY-D2 cells but absent in MDW4 cells, inhibited MDW4 attachment to laminin. None of the glycopeptides used in this study inhibited attachment of MDW4 cells to fibronectin-coated plastic. Peptide N-glycosidase treatment of the cells to remove surface asparagine-linked oligosaccharides inhibited MDW4 adhesion to type IV collagen, but not to laminin, and the same treatment of the wheat germ agglutinin-sensitive cells enhanced attachment to laminin. Tumor cell attachment to, and detachment from, the sublaminal matrix protein laminin and type IV collagen are thought to be important events in the metastatic process. Our results indicate that tumor cell attachment to these proteins may be partially modulated by the expression of specific oligosaccharide structures associated with the cell surface.

New plasma membrane proteins expressed by a high metastatic variant of a chemically induced tumor

The composition of plasma membrane proteins of related low and high metastatic tumor cells were compared in order to elucidate possible genetic changes which may occur during progression of tumor cells towards metastatic capacity. For this purpose a procedure was worked out which allows the purification of mouse plasma membrane (PM) proteins from biosynthetically labeled cells. PM isolated from the two related T lymphoma lines Eb and ESb, which differ greatly in metastatic capacity, as well as from Con A-activated T cell blasts displayed similar degrees of purification as shown by marker enzyme analysis. When [35S]-methionine-labeled proteins of such PM preparations from cloned Eb and ESb cells were compared by 2-D gel electrophoresis it was found that maps of the highly metastatic variant ESb cells permitted detection of about 50 new protein spots which were not found on the 2-D gel maps of the parental Eb cells. Approximately 80% of these new spots were also found on maps derived from syngeneic splenic Con A blasts. This observation indicated that most of the newly expressed membrane proteins of ESb cells were possible differentiation or cell activation-related and not tumor cell-specific.

Monoclonal antibodies which prevent experimental lung metastases. Interference with the adhesion of tumour cells to laminin

Cellular adhesion is important during metastasis, as metastatic cells must escape from the primary site into lymph and blood systems, there to adhere specifically to sites in distant organs. We have recently selected monoclonal antibodies which prevent adherence of B16 mouse melanoma cells to tissue culture dishes, and also markedly reduce experimental lung metastasis in mice when injected before or with the tumor cells. Here, we investigated which step in the metastatic process may be affected by the antibodies. The possible inhibitory effect of antibody on tumour cell adherence to vascular endothelial monolayers and to purified components of the underlying extracellular matrix - fibronectin, laminin and collagen type IV - was studied using in vitro assays. We found that the antibodies significantly blocked attachment to laminin, suggesting that specific basement membrane components play an important role in attracting or otherwise modifying the behaviour of metastatic tumour cells.

Inheritance of immunogenicity and metastatic potential in murine cell hybrids from the T-lymphoma ESb08 and normal spleen lymphocytes

T-lymphoma cells were fused with normal lymphoid cells to examine the segregation of tumorigenicity and metastatic capacity in the hybrids. In independent fusions the immunogenic ESb08 T-lymphoma line fused successfully with normal syngeneic spleen cells (from DBA/2 and CD1 mice) enriched either with T-cells or B-cells. Ten times fewer hybrids were obtained with B-cells compared to the number obtained with T-cells, and marker assays showed that both types of fusions preferentially generated T-T hybridomas. Some of the hybrids resembled their tumor parent in their ability to form primary and secondary tumors only in irradiated DBA/2 mice, whereas other hybrids lost the high ESb08 immunogenicity, were equally tumorigenic, and in some cases metastatic, in nonirradiated mice. DNA distributions of the original hybrid lines ranged from a hexaploid DNA content (expected for complete hybrids derived from a tetraploid line and normal diploid cells) to a tetraploid DNA content, confirming the reported chromosome instability of T-T hybrids. No correlation was noted between the initial DNA content and tumorigenicity, but in the case of complete hybrids, reduction in the ploidy levels always was observed in the cells of primary and metastatic lesions. One chromosomally stable and highly malignant hybrid (C2), which was analyzed for segregation of chromosomes and for drug-resistance markers, showed preferential loss of chromosomes from the normal T-cell fusion partner. The decreased immunogenicity of this hybrid could not be related to any detectable loss of chromosomes from the ESb08 tumor parent.

Glycoconjugates of murine tumor lines with different metastatic capacities. I. Differences in fucose utilization and in glycoprotein patterns

Since various experimental findings point towards an important role of cell surface carbohydrates - in particular sialic acid - in cancer metastasis, the rationale of this study was to look for possible differences in carbohydrate metabolism and glycoprotein expression in well-defined related tumor lines of different metastatic capacity. The tumor lines analyzed were L5178Y E (= Eb), a low-metastasizing, methylcholanthrene-induced lymphoma of a DBA/2 mouse, and L5178Y ES (= ESb), a spontaneous high-metastatic variant thereof. A non-related, highly metastasizing tumor, MDAY-D2, and ConA-stimulated spleen cells were included in the study. These cell lines were compared for incorporation rates of various labelled carbohydrates and for glycoprotein patterns in SDS-polyacrylamide gels. Marked differences were observed in the incorporation of 3H-fucose, while the incorporation of 3H-galactose and 3H-mannose was similar in the different cell lines studied. Only the metastatic variant ESb incorporated 3H-fucose at a rate similar to that of ConA-stimulated T-cell blasts. Eb cells did not incorporate 3H-fucose while MDAY-D2 had a significantly lower 3H-fucose incorporation rate. Separation and purification of the intracellular products of 3H-fucose by gel filtration and high-voltage electrophoresis revealed in Eb cells a block in the synthesis of fucosylated glycoproteins at the step of the fucose-I-P-guanylyltransferase. No apparent defect in the fucose pathway was detectable in MDAY-D2 cells. An Eb----ESb shifted cell line regained the ability to incorporate 3H-fucose. All tumors displayed unique glycoprotein patterns in SDS-PAGE. Labelling with 3H-mannose revealed the most distinct bands, while labelling with 3H-galactose gave fewer and broader bands. Although clonal instability of metastasizing tumor variants has been frequently reported, subclones of Eb and ESb showed characteristics similar to those of the original cell lines with regard to metastatic capacity, fucose metabolism and glycoprotein expression. These results will be discussed in relation to differences in fucose metabolism and in surface expression of fucose as observed in other tumor systems consisting of high- and low-metastatic lines.

Somatic cell fusion as a source of genetic rearrangement leading to metastatic variants

Tumor cell populations displaying metastatic properties often have higher gene dosage than their less malignant progenitor tumors, as shown by increased ploidy levels, chromosome duplication and gene amplification. The acquisition by tumor cells of high chromosome numbers may be due to endoreduplication or somatic hybridization either between tumor cells or between tumor and host cells. All such mechanisms increase genetic variability and instability in tumor cells since they trigger a polyploidization-segregation cycle. Among the wide variety of segregants which may emerge from high-ploidy cells, variants with increased malignancy can be positively selected in vivo. Evidence for in vivo fusion of tumor and normal host cells has been reported in different tumor systems. However the attainment by tumor-host hybrids of a higher degree of malignancy has only been observed following substantial chromosome segregation. The involvement of a cell of bone marrow origin as preferential host partner in the fusion process has been proved both by studies on tumor-host hybrids in bone marrow radiation chimeras and in vitro hybridization experiments between non-metastatic tumors and normal lymphoreticular cells which have led to the establishment of metastatic variants. Several different segregational mechanisms may bring about homozygosity or hemizygosity of recessive alleles in tumor-host hybrids, leading to their expression. The marked chromosome dynamics of tumor-host hybrids are also responsible for extensive chromosome rearrangements. At the molecular level these may represent mechanisms causing altered oncogene activity. The activation of new oncogenes by transposition or amplification as well as the amplification of previously activated oncogenes are the mechanisms most likely to be responsible for transition from low to high malignancy, occurring through ploidy changes, such as those produced by somatic mating.

Different patterns of lectin binding and cell surface sialylation detected on related high- and low-metastatic tumor lines

We have analyzed cell surface-bound carbohydrates in two different model systems for metastasis composed of closely related tumor cell lines with differing metastatic potential. The first system studied was that of the DBA/2-derived T-lymphoma lines (Eb/ESb) and some recently established sublines of ESb with altered metastatic behavior (ESb-M and ESb-MR). The second system consisted of the highly metastatic MDAY-D2 cells, a wheat germ agglutinin-resistant low metastatic subline MDW40, and two metastatic revertants from the latter. The cells were stained with fluorescein isothiocyanate-conjugated lectins and analyzed by flow cytofluorography. All low-metastatic tumor lines expressed receptor sites for the lectins soybean agglutinin (SBA) and Vicia villosa (VV). The metastatic lines had the respective lectin binding sites blocked by sialic acid (SA). A good correlation was found within the cell lineages Eb leads to ESb leads to ESb-M leads to ESb-MR and MDAY-D2 leads to MDW40 leads to MDW40M1 between reactivity of SBA and VV and metastatic potential. The amount of neuraminidase-accessible SA was similar for all cell types (except MDW40) indicating differences in the positioning of SA. For high-metastatic ESb cells, the sialylation of SBA and VV receptor sites was paralleled by a relative decrease of SA associated with receptor sites for peanut agglutinin. Low-metastatic Eb cells, in contrast, had their peanut agglutinin receptor sites sialylated but expressed asialylated SBA and VV receptor sites. Eb cells were also found to have 2-fold higher activities in galactose-specific sialyltransferases. It is proposed that the differences in positioning of SA on the cell surface leading to masking or unmasking of terminal sugars could influence the metastatic potential of tumor cells.

A mouse hepatocyte carbohydrate-specific receptor and its interaction with liver-metastasizing tumor cells

Spontaneous high-metastatic variants (ESb) of the DBA/2 mouse lymphoma L5178Y which show heavy liver involvement were found to form rosettes in vitro with isolated autologous hepatocytes, whilst low-metastatic sublines of the same tumor (Eb) did not. An analysis of the molecules involved in the hepatocyte:tumor cell interaction was performed by affinity adsorption and SDS-polyacrylamide gel electrophoresis of 125I-labelled membrane components from either the hepatocytes or the tumor cells. The hepatocytes were found to bind ESb tumor cells through lectin-like hepatic binding proteins (HBP) with molecular weights of 52, 56 and 110 Kd and specificity for D-galactosyl and N-acetyl-D-galactosaminyl residues. More than 10 different cell surface glycoproteins of ESb tumor cells and none of Eb-type tumor cells served as ligands in the hepatocyte interaction. The low-metastatic subline Eb formed hepatocyte rosettes only after neuraminidase pretreatment, indicating that lectin binding carbohydrate structures existed in a cryptic form masked on these cells by sialic acid. Although lectin-carbohydrate interactions have been found to play a crucial role in many intercellular recognition processes, this apparently is the first molecular description of such an interaction between organ-derived normal parenchymal cells and tumor cells. The possible relevance of such an interaction for cancer metastasis is suggested by the finding that spleen-selected ESb sublines differed from liver-selected ones in their organotropism as well as in their ability to form hepatocyte rosettes.

Regulation of plasminogen-activator in mastocytoma cells by lymphokines

Culture supernatants from mitogen-stimulated splenocytes were found to stimulate protease production in P815Y mastocytoma cells. Such supernatants increased cell-associated plasminogen activator levels in a dose-dependent fashion, and under serum-free conditions. In contrast to peritoneal exudate cells, tumor-cell plasminogen activator was not enhanced by the mitogen ConA alone. The tumor cell line P815Y may, thus, be used as a homogeneous cell source for the quantitation of lymphocyte factors which activate or inhibit plasminogen activator activity.

Lymphoma cell-mediated degradation of sulfated proteoglycans in the subendothelial extracellular matrix: relationship to tumor cell metastasis

Cloned lines of the methylcholanthrene-induced DBA/2 low-metastatic T-lymphoma Eb line and its highly metastatic variant ESb line were compared for the ability to degrade proteoglycans in the subendothelial extracellular matrix (ECM) produced by cultured endothelial cells. The ECM was metabolically labeled with Na2(35)SO4, and the tumor cell-mediated release of labeled degradation products was analyzed by gel filtration. More than 90% of the labeled material released upon incubation of ESb cells with the ECM, either when exposed or covered with vascular endothelial cells, was in the form of low-Mr, heparan sulfate-containing fragments (Mr approximately 10(4)) compared to high-Mr sulfated proteoglycans (mostly excluded from Sepharose 6B) released by incubation with the low-metastatic Eb cells. The same high- and low-Mr degradation products were obtained by incubation of the ECM with a serum-free medium conditioned by the low (Eb)- and high (ESb)-metastatic sublines, respectively. The high-Mr proteoglycans released by incubation of the ECM with Eb-conditioned medium was further degraded into Mr 10(4) glycosaminoglycan fragments upon a subsequent incubation with ESb-conditioned medium. These fragments were smaller than glycosaminoglycan side chains released by treatment of the ECM with papain or alkaline borohydride, suggesting an ESb-specific endoglycosidase activity. The higher ability of the ESb over the Eb cells to solubilize the glycosaminoglycan scaffolding of the sub-endothelial ECM may, among other properties, facilitate their hematogenous dissemination and extravasation.

Metastatic potential severely altered by changes in tumor cell adhesiveness and cell-surface sialylation

A plastic adherent variant line (ESb-M) of a highly invasive and metastatic murine T cell lymphoma (ESb) was found to have lost its metastatic potential while still being tumorigenic in normal syngeneic hosts. The variant retained most of its ESb-derived antigenic and biochemical characteristics but differed at binding sites for certain lectins with specificity for terminal N-acetylgalactosamine residues. Whereas such sites were masked by sialic acid on metastatic ESb cells, they became unmasked on the adherent variant line. Metastatic revertants of ESb-M cells did not express the respective lectin receptor sites because these were again masked by sialic acid. It is suggested that the masking of specific lectin receptors sites on the tumor cell surface is of crucial importance for metastatis. If freely exposed, these sites may change adherence characteristics of the cells possibly not only in vitro (to plastic) but also in vivo.

Cytogenetic changes during tumor progression towards invasion, metastasis and immune escape in the Eb/ESb model system

Related tumor lines which represent different stages in their progression towards metastatic capacity were investigated and compared at the chromosomal level. The parental low-metastatic tumor line (L5178Y/Eb) was derived from a long-term transplanted, chemically induced T-cell lymphoma of the DBA/2 mouse. The cytogenetic analysis included this Eb line, a spontaneous high metastatic variant thereof which expressed a distinct tumor-associated transplantation antigen (ESb TATA+), and an immunoresistant TATA-negative variant of the latter (ESb TATA-). All three cell lines were characterized by a near-diploid chromosome count and by some common chromosomal markers derived from Nos. 6, 13 and 16 Large-scale chromosomal rearrangments resulted in the formation of eight marker chromosomes in Eb cells, 16 in ESb TATA+ cells and 18 in ESb TATA- cells. Tumor progression in this system showed a tendency to monosomies, which could bring the corresponding genes to a hemizygous state and possibly to a release from repression. Chromosome 15 was trisomic in Eb cells, monosomic in ESb TATA+ cells and hardly detectable in ESb TATA- cells. The Ig heavy-chain gene-carrying region of both chromosomes No. 12 was found in translocation with chromosomes Nos. 5, 13 and 14 (Eb cells) and with Nos. 1 and 17 (ESb cells). ESb TATA- cells differed from ESb TATA+ cells at four different chromosomes (Nos. 5, 8, 14 and 15).

Different expression of Lyt differentiation antigens and cell surface glycoproteins by a murine T lymphoma line and its highly metastatic variant

Cloned lines of the methylcholanthrene-induced DBA/2 T lymphoma Eb and its highly metastatic variant line ESb were analyzed for differences in the expression of serologically detectable cell surface differentiation markers. Flow cytofluorographic analysis of cells stained with fluorescein isothiocyanate-conjugated monoclonal rate anti-mouse Thy-1, Lyt-1, Lyt-2 and complement-dependent cytotoxicity with mouse alloantisera against Lyt-3.2 and Ly-6.2 revealed, for the parental low metastasizing line, Eb, a phenotype of Thy-1+, Lyt-1-, Lyt-2+, Lyt-3+, Ly-6+, whereas the highly metastasizing variant line typed as Thy-1-, Lyt-1+, Lyt-2-, Lyt-3-, Ly-6-. Analysis of galactose oxidase/NaB3H4-labeled glycoproteins from Eb and ESb clones by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate showed further phenotypic differences. Selective binding of radiolabeled glycoproteins to Helix pomatia or Vicia villosa-Sepharose, respectively, allowed the identification of T130 to be expressed on Eb cells and T145 to be expressed on some ESb clones. The latter antigen is expressed on murine cytotoxic T lymphocytes. Immune precipitation analysis revealed that Eb and ESb bear different molecular forms of the T200 antigen. Comparisons of iodinated surface proteins derived from tumor cells either treated or untreated with tunicamycin indicated that many of the differences in membrane proteins between Eb and ESb cells could be attributed to differences in glycosylation. Our results, derived from a defined tumor system of lymphoid origin, show that the progression from a low to a high malignant tumor line can be associated with changes in the expression of various defined cell surface differentiation antigens. The question of a possible relationship between tumor progression and cell differentiation or dedifferentiation is discussed.

High-frequency generation of new immunoresistant tumor variants during metastasis of a cloned murine tumor line (ESb)

A metastatic variant of a chemically induced lymphoma (ESb) from a DBA/2 mouse was found to activate in syngeneic hosts specific anti-tumor cytolytic T lymphocytes (CTL) which recognized on the tumor a distinct tumor-associated antigen. Upon metastasis of a cloned ESb tumor line from an s.c. site to the spleen, the tumor cells which were originally sensitive to lysis by anti-ESb CTL became specifically immunoresistant. The development of immunoresistant variants after tumor-cell transplantation followed a refined kinetic and organ pattern: they were first detected in the spleen, then also in the liver and in the late stage of tumor progression they were the predominant tumor type in all involved organs. No immunoresistant tumor variants were generated in immunoincompetent animals such as nude (nu/nu) mice. Immunoresistant variants also developed when immunosensitive ESb clones were inoculated into animals specifically preimmunized against ESb. In fact, these variants were the only type of cells eventually growing out from such animals causing death from metastasis in spite of the specific immune status of the host. The change of tumor antigen expression described here differs from antibody-induced antigenic modulation in that it is genetically transmitted and stable in tissue culture. The immunoresistant tumor variants which did not preexist in the starting, twice-cloned cell population represent a new type of immune escape variant.

Quantitative determination of disseminated tumor cells by [3H]thymidine incorporation in vitro and by agar colony formation

A new microradioassay for the detection and quantification of disseminated tumor cells in blood and organ samples of tumor-bearing animals has been worked out in a murine total system for tumor metastasis. In contrast to previous prelabeling or in situ labeling procedures, the basis of this assay is a postlabeling in vitro of tumor cell-containing material with [3H]thymidine. Percoll gradient fractionation and autoradiography revealed that most of the isotope was incorporated into tumor cells. Titration curves with tumor cells from tissue culture were run in parallel and allowed to calculate from the radioactivity of a sample that actual number of proliferating tumor cells. The postlabeling assay correlated fairly well with an agar colony test which measure the clonogenic or stem cell potential of a tumor cell population. About 70% of syngeneic animals which had been inoculated s.c. with ESb tumor cells showed increased [3H]thymidine uptake in their blood, particularly at certain time intervals (11 and 21 days). None of these animals lived for more than 2 days longer. The advantages of the new microradioassay and its possible prognostic significance will be discussed.

Clonal analysis of expression of tumor-associated transplantation antigens and of metastatic capacity

ESb, a spontaneous high metastatic variant of the chemically induced T lymphoma Eb, was found previously to express a tumor-associated transplantation antigen (TATA) that was different from that of the parental line. Syngeneic tumor-specific cytolytic T lymphocytes (CTL) were able to recognize the different TATAs of Eb and ESb in vitro and could therefore be used for routine typing. The object of this study was to investigate tumor antigen expression on a clonal level and to compare the in vitro data with the in vivo behavior of the same cell lines.

Our CTL typing analysis of cloned tumor lines revealed that the two populations, Eb and ESb, are distinct and relatively homogeneous with regard to their TATA expression. Furthermore, all ESb clones formed rosettes with antibody-coated erythrocytes, while none of the parental type Eb clones showed this characteristic. The sensitivity to tumor-specific CTL lysis varied with time of tumor cell culture in vitro in a clone-dependent manner.

Variability was also noted in vivo in tumor growth and metastatic spread. Of over 50 ESb clones tested, the majority were highly metastatic while a minority were significantly lower in metastatic capacity. High and low metastatic ESb clones could not be distinguished by their expression of TATAs and of Fc receptors. There was also a considerable individual variability in the hosts, although they were genetically identical. This variability was most probably due to differences in the immune status of the animals.

Antigenic variation in cancer metastasis: immune escape versus immune control

Antigenic variation in cancer metastasis was observed in a syngeneic murine tumor system consisting of a low metastatic parental tumor line (derived from a methylcholanthrene-induced DBA/2 T lymphoma, Eb), a high metastatic spontaneous variant thereof (ESb), and a low metastatic 'revertant' from ESb (ESb-M). All three lines expressed tumor-associated transplantation antigens (TATA) which elicited specific T cell-mediated antitumor immune reactions in the host. The strongest host response was elicited upon intradermal inoculation. It could be followed by (a) the infiltration of the locally growing tumor by host cells, such as lymphocytes and macrophages, (b) the establishment of specific systemic antitumor immunity, (c) the generation of immune cells capable of transferring protective antitumor immunity into a normal syngeneic recipient, and (d) the generation of tumor specific cytotoxic T lymphocytes (CTL). Anti-TATA CTL were used as typing reagents to investigate the stability or variability in the TATA expression by cloned tumor cell lines. Antigenic variability in the TATA expression was seen under various conditions: (a) clone-dependent variation in the sensitivity to anti-TATA CTL lysis upon prolonged growth in tissue culture, (b) qualitative change in the TATA (TATA1 leads to TATA2) upon successive i.p. transplantation of the parental Eb tumor line and, (c) generation of TATA negative immune escape variants (TATA2 leads to TATA-) during metastasis formation from a s.c. site. The relative inefficiency of specific immunization procedures against ESb was found to be due to the effective generation of TATA negative variants by this highly metastatic tumor. The balance between immune control and immune escape could be influenced to the advantage of the host by some means, for instance optimizing the route of antitumor-immune sensitization or by infusion of allogeneic but H-2 identical antitumor-immune T cells. Such immune cells recognized the tumor via minor histocompatibility antigens and thus circumvented the need of TATA recognition. Finally, manipulations at the cell surface of the highly malignant ESb tumor such as those introduced in the ESb-M variant were found to dramatically effect its metastatic potential.

Metastatic tumor cell variants with increased resistance to infection by Semliki Forest virus

Semliki Forest virus (SFV) is an interesting virus for cell interaction studies because it binds directly to the cells' major histocompatibility antigens. We used this reagent to study the expression and functional properties of H-2 molecules on murine tumor lines that are closely related but differ greatly in metastatic capacity. Tumor cell variants with high metastatic capacity showed an increased resistance to virus infection, an effect that was selective for SFV. Although the high metastatic tumor lines did not express less H-2 antigens than the low metastatic ones, they bound much less of the SFV viral glycoproteins.

A rapid method for the isolation of metastasizing tumour cells from internal organs with the help of isopycnic density-gradient centrifugation in Percoll

Metastasizing tumour cells from a DBA/2 mouse T-cell lymphoma could be separated from the invaded tissue by isopycnic centrifugation in continuous Percoll density gradients. The metastasizing tumour cells from spleen, liver and lung, derived from a cloned lymphoma-cell line, showed a buoyant density in Percoll of 1.060 +/- 0.010. They could be separated from the host tissue, which had a higher buoyant density in the case of the spleen cells or a lower density in the case of the dead liver or lung tissue. The separated tumour cells as removed from the gradients were viable, and could be analysed by in vitro and in vivo assays. The separation procedure did not affect the expression by the tumour cells of TATAs and H-2 antigens. Furthermore, the method seemed to be applicable to the separation of human tumour cells from mononuclear cells prepared from blood samples of tumour patients by Ficoll centrifugation.

Metastatic tumor cell variants with increased resistance to infection by Semliki Forest virus

Semliki Forest virus (SFV) is an interesting virus for cell interaction studies because it binds directly to the cells' major histocompatibility antigens. We used this reagent to study the expression and functional properties of H-2 molecules on murine tumor lines that are closely related but differ greatly in metastatic capacity. Tumor cell variants with high metastatic capacity showed an increased resistance to virus infection, an effect that was selective for SFV. Although the high metastatic tumor lines did not express less H-2 antigens than the low metastatic ones, they bound much less of the SFV viral glycoproteins.

Escape of metastasizing clonal tumor cell variants from tumor-specific cytolytic T lymphocytes

A metastasizing variant of a chemically induced lymphoma from a DBA/2 mouse is shown to carry a distinct tumor-associated transplantation antigen (TATA), which can be recognized by syngeneic secondary anti-tumor cytolytic T lymphocytes (CTL). During metastasis of twice-cloned cell lines of this tumor, variants develop that are specifically immunoresistant to lysis by anti-tumor CTL. The variants are detected in the spleen of normal syngeneic mice. They remain stable over long-term passage in tissue culture. The high frequency with which these immunoresistant metastatic variants develop was found to explain the relative ineffectiveness of specific immunization against this metastatic tumor. Compared with organ-selective metastatic variants, the immunoresistant tumor variants seem to arise with a much higher frequency. The change in TATA expression described here differs from antibody-induced antigenic modulation in that it is more stable and genetically transmitted.

Evidence for a plasma membrane redox system on intact ascites tumor cells with different metastatic capacity

A NADH-ferricyanide reductase of the external surface of intact mouse ascites tumor cells grown in culture was shown. The oxidation/reduction reaction was due to enzymatic rather than inorganic iron catalysis as demonstrated by the kinetics and specificity of the reaction. Activities of three markers for cytoplasmic contents were lacking with the intact tumor cells. The dehydrogenase activity was inhibited by p-chloromercuribenzoate, bathophenanthroline sulfonate, and the anticancer drug adriamycin. Sodium azide and potassium cyanide inhibited partially. The response to inhibitors resembled that of isolated plasma membranes rather than that of mitochondria. Concurrent with these findings, neither superoxide dismutase nor rotenone affected the redox activity. The findings provide evidence for the operation of a plasma membrane redox system at the surface of intact, living cells.

Characteristics of alloantigens and cellular mechanisms responsible for gamma-interferon production in primary murine MLC

We have investigated in primary murine MLC alloantigen differences and characteristics of responding cells responsible for gamma-IFN production. Differences at K, D, or I-S-G regions stimulate gamma-IFN release, though higher levels of production have been observed with differences at I-S-G regions. On the other hand, when mice differing in their minor histocompatibility antigens, notably at the MIs locus, were tested, gamma-IFN production took place even between strain combinations not displaying lymphocyte proliferation. Lastly, using different cell depletion techniques, we demonstrate that T-lymphocytes are the cells producing gamma-IFN upon stimulation with alloantigens. These findings show that T lymphocytes can recognize alloantigens by releasing gamma-IFN even without displaying proliferation.

Possible cell surface receptor for Friend murine leukemia virus isolated with viral envelope glycoprotein complexes

Water-soluble multimeric complexes of Friend leukemia virus envelope glycoprotein gp85 bind specifically to C57BL/6 mouse spleen leukocytes. Such complexes were used to isolate cell surface receptors for the virus, using an immunoprecipitation technique. The putative rceptor has a molecular weight of 14,000. Mouse H-2 histocompatibility antigens, which are receptors for Semliki Forest virus, are not receptors for Friend leukemia virus.

The relationship between alloantigen responses in nude mice injected with a low number of congenic thymus cells

BALB/c-nu mice were injected with 10(6) normal congenic thymocytes. This number of cells permits only partial reconstitution and in individual mice some functions were restored and others were not. The relationships between the functions of skin graft rejection, circulating alloantibody production and the ability to generate, in vitro, cytotoxic T cells were studied with regard to the strains CBA and C57BL/6.

Syngeneic tumor cells can induce alloreactive T killer cells: a biological role for transplantation antigens

A chemically induced sarcoma of BALB/c (H-2d) mice, MCG4, is shown to induce in BALB/c lymphocytes a primary anti-tumor cytolytic T lymphocyte (CTL) reaction in vitro. The anti-tumor CTL showed tumor specificity but reacted also with normal cells expressing distinct H-2 alloantigens. The CTL response could be shown to be induced by and directed against alloantigenic determinants expressed on two different molecules, one H-2Kk-like the other H-2Dk-like. The biological significance of these findings is discussed with regard to (i) possibility of derepression of normally silent H-2 genes in tumor cells and normal cells, (ii) generation of alloreactivity in ontogeny, and (iii) role of alloreactive T cells in eliminating cells expressing wrong gH-2 antigens.

Tumor metastases and cell-mediated immunity in a model system in DBA/2 mice. VII. Interaction of metastasizing and nonmetastasizing tumors with normal tissue in vitro

Three mouse tumors known to metastasize in vivo and 3 nonmetastasizing mouse tumors that grow only locally in vivo were examined for their ability to adhere to and invade normal syngeneic lung organ cultures in vitro. All 3 metastasizing tumors adhered to and invaded the normal lung cultures. In contrast, tumors that grow only locally in vivo neither adhered to nor invaded the normal lung tissue. The described system is ideally suited to correlate the in vivo invasiveness of a given tumor with its potential to metastasize in vivo and to study in vitro how to influence the interaction of metastasizing tumor cells with normal tissue.

Hepatocyte-tumor cell interaction in vitro. I. Conditions for rosette formation and inhibition by anti-H-2 antibody

Murine hepatocytes, isolated by an in situ collagenase-perfusion technique and cultured in Petri dishes, were shown to form rosettes with liver-metastasizing syngeneic tumor cells. Pretreatment of the tumor cells with neuraminidase generally increased the binding, whereas pretreatment of the liver cells with neuraminidase abolished the binding completely. The tumor-cell binding may be mediated by the previously described lectin-like receptor of hepatocytes that also was sensitive to neuraminidase treatment and that bound desialylated cells better than normal cells. Anti-H-2 sera could efficiently inhibit the rosette formation of metastatic tumor cells with the hepatocytes, which points to a possible role of H-2 molecules in this interaction of neoplastic and normal cells.

Expression of foreign H-2-like antigens by a chemically-induced murine tumour (MCG4)

Alien H-2k-like antigens were found to be expressed by a methylcholanthrene induced tumour of BALB/c (H-2d) origin. H-2 specificities of the k haplotype were detected on this tumour by a variety of serological techniques, including 51Cr-release cytotoxicity, microradioassay and absorption. The antisera employed were conventional polyspecific alloantisera, typing sera with restricted specificty and monoclonal hybridoma-derived anti-H-2k antibodies. The tumour has a low expression of the private specificty 31, which characterizes Kd molecules, and does not seem to express the private specificities of Dd, Kk and Dk molecules. It appears to express predominantly alien H-2-like antigens which are very similar to but not identical with normal H-2k molecules.

Integration of a virus membrane protein into the lipid bilayer of target cells as a prerequisite for immune cytolysis. Specific cytolysis after virosome-target cell fusion

Structural requirements for membrane antigens on target cells to mediate immune cytolysis were studied in a model system with purified membrane proteins from Semliki Forest virus (SFV). These SFV spike proteins were isolated in the form of detergent- and lipid-free protein micelles (29S complexes) or, after reconstitution into lipid vesicles, in the form of virosomes. Both the 29S complexes and the virosomes were found to bind well to murine tumor cells (P815 or Eb). When these cells, however, were used as target cells in complement-dependent lysis or in antibody-dependent cell- mediated cytotoxicity assays in the presence of anti-SFV serum, they were not lysed, although they effectively bound the antibody and consumed complement. The same tumor cells infected with SFV served as positive controls in both assays. Different results were obtained when inactivated Sendai virus was added as a fusion reagent to the cells coated with either virosomes or 29S complexes. Under these conditions the virosome-coated cells became susceptible to SFV- specific lysis, whereas the 29S complex-coated cells remained resistant. Evidence that the susceptibility to lysis ofvirosome-coated cells was dependent on active fusion and, therefore, integration of the viral antigens into the lipid bilayer of the target cells was derived from control experiments with enzyme-treated Sendai virus preparations. The 29S complexes and the virosomes partially and selectively blocked the target cell lysis by anti-H-2 sera but not by anti-non-H-2 sera confirming our previous finding that major histocompatibility antigens serve as receptors for SFV. The general significance of these findings for mechanisms of immune cytolysis is dicussed.

Production of interferon in the murine mixed lymphocyte culture. II. Interferon production is a T cell-dependent function, independent of proliferation

Interferon production occurs after two days of culture in murine mixed lymphocyte cultures (MLC). This was demonstrated in various combinations of mouse spleen cells differing at the major histocompatibility (H-2) locus. Interferon production could be demonstrated in one-way MLC when F1/parent combinations were used and in reactions in which one partner was treated by puromycin. After treatment of both cell populations with mitomycin C, interferon production occurred in the absence of lymphoproliferation. Interferon production in response to alloantigen did not occur in spleen cell cultures of nude mice and in cultures treated by anti-theta antiserum plus complement indicating that interferon production is a T cell-dependent function.

A syngeneic anti tumor serum recognizing a complex H-2 alloantigen

A methylcholanthrene induced tumor of BALBc (H-2d) origin had a high rate of spontaneous regression when transplanted into syngeneic animals. The tumor induced in BALB/c mice iso-antibodies with high anti-tumor cytotoxic activity. A specificity analysis of such BALB/c anti MCG4 sera revealed that the antibodies were directed against a tumor antigen which is very similar to H-2- alloantigens (e.g. H-2.5) expressed on normal cells of certain foreign mouse strains. The sera also reacted with nine out of ten B10.W congenic strains bearing H-2wi haplotypes derived from wild mice. Whether the tumor antigen is identical with foreign H-2 antigens or only cross-reactive cannot be decided at present.

Tumor metastases and cell-mediated immunity in a model system in DBA/2 mice. IV. Antigenic differences between a metastasizing variant and the parental tumor line revealed by cytotoxic T lymphocytes

The syngeneic cytotoxic T-cell response against a metastasizing murine lymphoma variant was investigated and compared with the response against the non-metastasizing parental tumor line Eb. Anti-tumor cytotoxicity was not detectable in a 4-h 51Cr release assay in spleens taken directly from tumor-bearing animals (primary CMC). After restimulation in vitro (secondary CMC) however, high anti-tumor cytotoxic activity was detected. This activity was mediated by immune T lymphocytes as shown by its sensitivity to treatment with anti-Thy 1.2 serum and complement. Ten cells of the metastasizing tumor ESb, inoculated subcutaneously, were sufficient to raise a local tumor and metastases and to induce cytotoxic T memory cells in the spleens. In contrast, about 104 cells were required to raise a local tumor and to induce splenic cytotoxic T memory cells, when the parental tumor Eb was tested. The specificity studies of the anti-tumor cytotoxic activity demonstrated that cytotoxic T cells could distinguish unrelated, chemically induced syngeneic tumors and also recognize antigenic differences between the parental tumor Eb and its variant ESb. Eb and ESb tumor cells were recognized as carrying distinct antigens at the responder cell level, the stimulator cell level and the target cell level. The in vivo significance of these findings is discussed.

Differences in the expression of histocompatibility antigens on mouse lymphocytes and tumor cells: immunochemical studies

Immunochemical studies have shown that labeled, detergent-solubilized extracts of SL2 (H-2d) lymphoma cells contain components reactive with several anti-H-2 alloantisera of restricted specificity. Anti-H-2k and anti-H-2ja as well as anti-H-2d sera precipitated labeled polypeptides of a molecular weight similar to that of H-2 heavy chains. In addition, all antisera tested precipitated a component of 70000 daltons molecular weight, which is antigenically related to gp 69/71 of Friend murine leukemia virus. Reactions with antisera directed against haplotypes other than H-2d could be blocked by addition of unlabeled, detergent-solubilized extracts of H-2d lymphocytes, or by H-2 antigens against which the antiserum was directed. Sequential immunoprecipitations initially using antisera against the K, D, or L region gene products to remove individual known H-2d antigens have made possible the identification of some molecules responsible for these reactions. The results show that antisera against haplotypes other than H-2d which react with SL2 cells, cross-react with normal H-2d antigens. Quantitative absortion of these antisera with intact or solubilized cells has shown that lymphocytes and tumor cells differ in their expression of some H-2 determinants. The antibodies bind only weakly to intact H-2d lymphocytes, but strongly to the corresponding detergent-solubilized antigens. These results do not, therefore, support the derepression hypothesis put forward earlier.

Interferon production in the murine mixed lymphocyte culture. I. Interferon production caused by differences in the H-2 K and H-2 D region but not by differences in the I region or the M locus

Little has been made previously of the observation that interferon is generated in the murine mixed lymphocyte reaction (MLR). We have found high levels of interferon in the supernatants of MLR between spleen cells of mice of different H-2 type after one to two days of culture. Interferon production was also seen in strain combinations that differed only in the K or D region of the H-2 complex. There was no production of interferon in strain combinations differing in the M locus or in the I region of the H-2 complex. The latter combinations are known not to induce cytotoxic effector cells. Thus, there seems to be a dichotomy in allogeneic determinants between those of the I region and of the M locus inducing primarily lymphoproliferation, and those of H-2K and H-2D inducing cytotoxic activity and interferon production.