Natural anti-tumor serum reactivity in BALB/c mice. I. Characterization and interference with tumor growth

Analysis of Rabbit and Guinea PIG Complement Efficiency in Cytotoxicity Tests against Fibrosarcoma and Lymphosarcoma Cells

In a complement-dependent 51Cr cytotoxicity assay, using as target murine fibrosarcoma or lymphosarcoma cells, the rabbit complement (RC) was more efficient than guinea pig complement (GPC) when tested either with strong antisera, such as anti-histocompatibility sera, or with weak sera, such as sera from normal mice shown previously to possess a natural antitumor response. The high efficiency of RC was not due to activation by antibodies of a different class or specificity than those activating GPC. In fact, both 2-mercaptoethanol (2-Me)-sensitive or-resistant immunoglobulins could activate both RC and GPC, and the results of absorption tests indicated that the antibodies detected using either of the 2 complements were directed against the same specificities. In addition, the results of tests searching for cooperative antibodies excluded that a cooperative effect might be responsible for the high efficiency of RC. With weak antisera, sera of different rabbits were found to have different complement activity.

Regulation of natural antibody binding and susceptibility to natural killer cells through Zn(++)-inducible ras oncogene expression

Changes in the natural resistance phenotype were examined for the 2H1, 10T 1/2 cells expressing the activated human H-ras oncogene under the transcriptional regulation of the zinc-inducible mouse metallothionein-I promoter. Culture of the cells in 50 microM ZnSO4 induced an increase in ras protein p21 levels which were maximal within 1 day. Natural-antibody (NAb) binding was significantly increased following 2 days of cell culture in ZnSO4 and continued to increase up to 4 days. The increased NAb binding returned to uninduced levels within 2 days following the removal of added zinc ions from the culture medium. The cells also exhibited a significant increase in natural killer (NK) cell sensitivity following 2 days in ZnSO4. This was maintained as long as the zinc was in the medium, but returned to uninduced levels within 1 day following its removal. The results show that NAb binding and susceptibility to NK cells increased following ras oncogene expression in 10T 1/2 cells and that both parameters were regulated by p21 expression. Repeated i.v. administration of whole-serum NAb prior to tumor inoculation reduced the number of early tumors following s.c. injection of Zn(++)-induced 2Hl cells into Zn(++)-treated C3H/HeN mice, consistent with an in vivo role for NAb in the defense against ras-transformed cells. In contrast, small but statistically significant reductions in NAb binding were observed following v-H-ras transformation of NIH 3T3 cells or v-src transformation of 10T 1/2. The data argue for an NAb- and NK-cell-susceptible phase of ras-induced tumor development which is a prerequisite for these mediators to contribute to a first line of defense against incipient neoplasia, and suggest that characteristics of the recipient cell and the transforming oncogene are important in determining the natural resistance phenotype.

The immune system during the precancer period: naturally-occurring tumor reactive monoclonal antibodies and urethane carcinogenesis

Previous results obtained in our laboratory suggested that natural antibodies reactive with L5178Y lymphoma cells play a role in the induction of lung tumors by the chemical carcinogen urethane. In order to characterize some of the naturally-occurring L5178Y reactive antibodies we prepared hybridomas that secreted natural monoclonal IgM antibodies reactive with L5178Y lymphoma cells. In the present study we characterized some of these antibodies and provided further proof as to their role in urethane carcinogenesis. One hybridoma secreted a cytotoxic antibody that reacted only with mouse lymphoma cell lines. Other non-cytotoxic monoclonal L5178Y-reactive antibodies showed various degrees of cross-reactivity with syngeneic, allogeneic and xenogeneic cells of normal or malignant origin. One of these antibodies reacted much better with activated T cells than with resting ones. Four groups of mice were treated with urethane. Three groups were injected twice a week during 5 months with different IgM preparations of natural monoclonal antibodies. The mice in the fourth group were not treated with IgM and served as controls. Five months after the urethane treatment the mice were sacrificed and the number of tumor foci in the lungs of each mouse was determined. The results show that the group treated with the cytotoxic monoclonal antibody 1.80 had a significant decrease, while the group treated with the IgM myeloma protein 104E had a significant increase in the number of tumor foci compared to urethane-treated mice that did not receive any IgM treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Naturally-occurring tumor-reactive autoantibodies: a monoclonal antibody from normal mice reacts with tumor cells and with DNA

A natural IgM monoclonal antibody, 1.67, was generated from apparently healthy unstimulated BALB/c mice. This antibody reacted with L5178Y murine T cell lymphoma, with human Raji cells, and with several normal cells. Further analysis of its ligand binding capacity disclosed strong binding to single-stranded DNA (ssDNA). However, this naturally-occurring monoclonal antibody binds to different epitopes on cell membranes and on DNA than another anti-DNA monoclonal antibody (18/103/1) from human origin. This conclusion was based on competition assays. Furthermore, NOA 1.67 lacks the 16/6 idiotype expressed on the 18/103/1 antibody. The 16/6 idiotype is shared by human and mouse lupus monoclonal autoantibodies that bind simultaneously to lymphoid cells and DNA. This is a first report on a natural autoantibody that binds to malignant and to normal cell membrane(s) as well as to ssDNA. It may have regulatory functions controlling malignancy and or autoimmunity.

Bone marrow graft rejection as a function of antibody-directed natural killer cells

There is conclusive evidence that acute bone marrow transplant rejection in lethally irradiated mice is caused by natural killer (NK) cells. The rejection of marrow allografts is exquisitely specific and is controlled by antigenic determinants encoded in or near the H-2 gene complex. The specificity of in vivo marrow graft rejection contrasts with the in vitro specificity pattern of NK cells in cytotoxicity assays. We therefore examined how NK cells cause H-2-specific marrow graft rejection in vivo. Several experimental approaches are presented that suggest that natural antibody, present in responder strains of mice, specifically directs NK cells in an antibody-dependent cytolytic and/or cytostatic reaction, resulting in marrow graft rejection. The following evidence for this mechanism is documented. The ability to reject a marrow graft can be passively transferred by serum from responder to allogeneic nonresponder mice and the specificity of rejection can be mapped within the H-2 region. Serum-induced marrow graft rejection is abrogated following depletion of immunoglobulin, and the serum of responder mice is able to induce a specific antibody-dependent cytotoxic reaction in vitro.

Studies on the level of natural antibodies reactive with various tumor cells during urethane carcinogenesis in BALB/c mice

Serum from young normal BALB/c mice was found to contain IgM antibodies able to mediate complement-dependent lysis of certain syngeneic or allogeneic tumor target cells. The titer of such naturally occurring antitumor antibodies ( NATA ) was found to increase with aging. A longitudinal serological study comparing the cytotoxicity potential of NATA from normal and from urethan-treated BALB/c mice was performed. It was found that urethan-treated mice that did not develop primary lung-adenomas within the duration of the experiment had significantly lower NATA titers, against one out of 4 target cells assayed, than urethan-treated animals that developed lung adenomas. This difference was evident in two independent experiments. The results suggested that the lower NATA activity of the urethan-treated mice that did not develop tumors existed even before exposure to the carcinogenic insult. This raises the possibility that certain populations could be segregated according to their natural antibody profile into those individuals which will develop primary tumors within a certain period if exposed to a subthreshold amount of carcinogen, and those which will not.

Complement-dependent cytotoxicity of anti-human osteogenic sarcoma monoclonal antibodies

Two mouse monoclonal antibodies against the human osteogenic sarcoma 791T were examined for their capacity to exert complement-dependent cytotoxicity against a panel of human tumour cell lines. Cytotoxicity was most evident against the immunizing tumour 791T although significant reactivity was directed against other osteogenic sarcomas. In admixture, the 2 antibodies displayed synergism in their cytotoxicity although this was only demonstrable with defined ranges of antibody concentration. The cytotoxicity of these antibodies was dependent upon the use of rabbit serum as complement and no tumour-cell lysis was produced using human, guinea-pig or mouse serum complement. The more potent cytotoxic antibody failed to modify the outgrowth of 791T tumour xenografts in immunodeprived mice even though localization of antibody at the tumour site has been demonstrated (Pimm et al., 1982).

Natural antibodies carrying a cross-reactive idiotype enhance tumor growth in the rat

A population of Fab fragments was identified in the papain-solubilized fraction of membranes of a rat chemically-induced sarcoma, KMT 17. The Fab fragments were partially purified by gel filtration and column electrophoresis. A rabbit antiserum against the partially purified Fab fragments was raised and shown to be specific for Fab fragments by immunoelectrophoresis. Furthermore, four lines of evidence indicated that the KMT 17 Fab fragments carry a cross-reactive idiotype: (1) the antiserum could bind only with a restricted population of normal Fab fragments having a pl of 6.3; (2) an unrelated antibody (WKA anti-SRBC) showed a weak cross-reactivity (less than 6%); (3) syngeneic antisera against the KMT 17 could bind with the 125I-KMT 17 Fab preparation that was purified by an immunoabsorbent column with the rabbit anti-KMT 17 Fab antiserum (anti-idiotype antibody); (4) the rabbit anti-KMT 17 Fab antiserum could bind with neither heavy nor light chains of WKA IgG. The natural antibody carrying the idiotype was found in normal serum and in various organs as well, especially in the lung of the conventional rats. In addition, the fractions containing Fab fragments (Frll) were shown to enhance tumor growth when injected into syngeneic animals, whereas Fab-free fractions that were separated from the Fab fragments by column electrophoresis showed no enhancing activity. These results strongly suggested that a population of Fab fragments carrying a cross-reactive idiotype was responsible for the enhancement of tumor growth. Mechanisms for the biological function of natural anti-tumor antibodies carrying a cross-reactive idiotype are discussed.

Murine natural anti-tumor antibodies. II. The contribution of natural antibodies to tumor surveillance

The objective of this study was to investigate whether natural anti-tumor antibodies (NAb) contributed to the surveillance of small inocula of syngeneic tumors. Experiments were designed to distinguish between NAb and NK-mediated host resistance. Four approaches were used: (1) the isolation of tumor variants differing in their tumorigenicity and susceptibility to these mechanisms, and to activated macrophages; (2) a comparison of the effects of adjuvants on the modification of both host resistance and the activity of these effectors; (3) the relationship between the ontogeny of the natural resistance mechanisms and tumorigenicity in aged mice; and (4) the use of a Winn-type assay. These studies provided support for a role in natural resistance correlated with both the ability of tumors to bind NAb, and the production of NAb in adjuvant-stimulated mice. Furthermore, the frequency of tumors observed after tumor challenge more closely correlated with the ontogeny of natural antibody than NK cells, and tumors coated with NAb were less tumorigenic than controls. The reduced tumorigenicity of an NK-sensitive tumor, when compared to an NK-resistant variant of the same line, provided evidence for NK-cell-mediated natural resistance in young adult mice. It was concluded that natural resistance to tumors is a complex phenomenon dependent on the tumor phenotype, as well as the activity of several effector mechanisms, and that natural anti-tumor antibody must be considered an important component of host resistance.

H-2 associated resistance to leukaemia transplantation: natural killing in vivo

Natural resistance in vivo was studied by injecting non-immunized mice with leukaemia cells prelabelled with the thymidine analogue 131I-iododeoxyuridine. There was a decrease in the survival of the leukaemia cell inoculum as determined by whole-body gamma counting, and a failure of the leukaemia cells to survive in the spleens of mice which were not H-2 identical with the transplant. H-2-associated resistance could be measured within 24 h of leukemia inoculation and was strongest in the spleen and absent from the liver. Although all strains of mice tested were able to resist H-2 non-identical cells, resistance in irradiated (800--900 R) mice was restricted to certain strains and their F1 hybrids, notably those of the C57BL family. Resistance in both non-irradiated and irradiated mice was not due to classical immunological rejection. Mice with either genetic or induced T-cell deficiency showed full resistance, and circulating preformed antibody could not account for the rejection observed. Treatment with silica or with 89Sr abrogated natural resistance in non-irradiated as well as irradiated animals; these treatments had previously been shown to abolish both bone-marrow graft rejection in irradiated mice and in vitro natural killing. Resistance against leukaemia transplantation in irradiated C57BL mice appeared to depend on Hh-1 (H-2D) incompatibility between the host and the graft, again suggesting that bone-marrow graft rejection, and perhaps natural killer activity, is a subset of a more general paraimmune or non-adaptive rejection mechanism.

Macrophage-dependent, NK-cell-independent "natural" surveillance of tumors in syngeneic mice

The present study, which was designed to further characterize the "natural" T-independent rejection of syngenetic tumours (Greenberg and Greene, 1976), has revealed the following points: (1) no detectable DBA/2 NK cell activity was demonstrated against the syngeneic tumour lines studied, and these tumours were indensitive to NK cells from high-activity strains; (2) in addition the tumour frequencies in old and young mice receiving small tumour inocula were identical, in contrast with the reported decline in NK cell activity with age, suggesting that the surveillance of small inocula of these tumours was NK-cell-independent; (3) injection of silica intraperitoneally enhanced the frequency of tumours in normal and immunodeficient AT x BM mice, suggesting that the rejection mechanism was macrophage-dependent; (4) the effects of silica injection were maximal if administered 3 days prior to tumour injection, indicating that the period of time in which the rejection mechanism must act was very limited; (5) silica markedly decreased the survival of AKR mice dying of spontaneous tumours, providing evidence that the effect of this agent was not limited to model systems but would influence the appearance of spontaneous tumours; (6) reticuloendothelial stimulants such as mycobacterium butyricum and proteose peptone decreased the tumour frequency of small tumour inocula, indicating that the effector mechanism can be stimulated; and (7) soluble tumour antigen enhanced the tumour frequency in normal and immunodeficient mice, suggesting that the specific receptor molecule of the surveillance mechanism was not thymus-dependent.

Murine natural anti-tumor antibodies. I. Rapid in vivo binding of natural antibody by tumor cells in syngeneic mice

A competitive radioimmunoassay (RIA) for the detection of cell-bound antibody was used to study the in vivo acquisition of immunoglobulin (Ig) by tumor cells. Several tumor lines acquired Ig rapidly between 3 and 18 h after intraperitoneal implantation into normal syngeneic mice and this Ig was recovered by elution with basic or acid buffers. The Ig eluted from the L5178Y lymphoma showed higher binding to the L5178Y than to thymocytes, bone-marrow cells, 1509a sarcoma and P-815-X2 mastocytoma. In addition, binding of the eluates to the L5178Y was specifically inhibited by L5178Y cells or by solubilized membrane antigens of the L5178Y. The in vivo acquisition of Ig by the L5178Y could also be blocked by the IV and IP injections of tumor antigen although both L5178Y and 1509a solubilized membrane antigens were effective. Some of the Ig acquired by the tumor cells was found to be complement-fixing antibody since normal rabbit complement lysed 80% of L5178Y cells obtained from the peritoneal cavity of syngeneic mice 18 h after implantation, but did not lyse in vitro L5178Y cells. The in vivo binding of the complement-fixing antibodies was also inhibited by tumor antigens in the same way as the acquisition of Ig detected by RIA. It was shown that the acquisition of Ig during the first 18h of IP growth was a T-independent phenomenon because tumor cells acquire as much Ig in AT X BM mice as in sham-thymectomized controls. In a study with 11 different clones derived from the L5178Y lymphoma, a high correlation (r = 0.75, p less than 0.005) was found between the amount of Ig acquired after in vivo implantation and the amount of Ig bound to the cells after in vitro incubation with normal syngeneic serum. It is suggested that the rapid in vivo acquisition of Ig was due to the in vivo binding of natural antibodies to tumor cells.

Natural anti-tumor serum reactivity in BALB/c mice. II. Control by regulator T-cells

By a complement-dependent cytotoxicity test, 37 sera from 1- to 18-month-old BALB/c mice were tested for natural anti-tumor and anti-thymus immune reactivity. The level of anti-tumor and anti-thymus antibodies increased with age, and a high individual variability, particularly evident in the older animals, was found. The appearance of the spontaneous antibodies was correlated to the T-cell status of mice. Animals with the higher spleen T-cell content were those with the higher anti-thymus and the lower anti-tumor natural antibody level, and vice versa. In T-deprived mice the anti-tumor response increased, whereas the anti-thymus response was not influenced. An inoculum of T cells from young to older syngeneic mice yielded a decrease of the anti-tumor response and an increase of the anti-thymus response. Homeostatic immunologic mechanisms, in which the cellular and the humoral system alternate in the tumor cell control, are suggested.