Escape of TA3 tumors from allogeneic immune rejection: theory and experiments

Temporal synthesis and presentation of antigens by cultured B16 melanoma cells

Previous studies have demonstrated the presence of two distinct antigens, B700 and B50, which are unique to murine melanoma. One of these, B700 has been studied in detail, and is present on 5 different murine melanomas; it can function as a transplantation antigen in at least 3 of them (B16, JB/RH and K1735). The synthesis and presentation of these antigens has been studied as a function of cell culture conditions. Direct immunofluorescence studies of cells in serial culture indicate that the expression of B700 and B50 antigens at the cell surface and in the cytoplasm increases as a function of time in culture, over 1-5 days. By day 5, when the cells are confluent, all cells show some degree of antibody binding. Parallel 35S-methionine pulse chase labeling experiments show that incorporation into Triton soluble proteins, and Triton insoluble SDS soluble proteins, increases to a peak at 3.5 days after subculturing, then decreases as the cells reach confluence. Incorporation into proteins shed into the culture supernatant continued throughout the time course of cell growth to confluence. However, as the cells become confluent, total protein synthesis shifts towards greater production of the antigens (both cellular and shed). The sum of the results suggest that tumor growth may succeed in vivo by the wholesale production of "decoy" antigens.

Time dependency of endotoxin-induced resistance to transplantable tumors in mice

A single injection of bacterial endotoxin induced cyclic changes of enhanced or reduced host reactivities, as determined in some measurements of the beneficial effects of endotoxin, such as immune potentiation or protection against lethal irradiation. The results described here show that endotoxin-induced resistance to subsequent challenge with transplantable tumors such as Lewis lung carcinoma or L1210 murine leukemia is similarly time dependent. While certain time intervals between endotoxin treatment and tumor challenge will provide significant protection, others will render the recipients highly susceptible to the same tumor. It was also observed that L1210-bearing mice have a lower resistance to endotoxin injections than tumor-free mice of the same strain.

Characterization of cellular and extracellular plasma membrane vesicles from a low metastatic lymphoma (Eb) and its high metastatic variant (ESb): inhibitory capacity in cell-cell interaction systems

Spontaneously shed extracellular plasma membrane vesicles (ECM) of a highly metastatic murine tumor line (ESb) were compared with plasma membrane vesicles (PM) of the same cells prepared by the nitrogen cavitation method and with ECM and PM preparations of the related low metastatic tumor line Eb. From a previous biochemical analysis it was concluded that the exfoliation of ECM vesicles, which is very pronounced in metastatic ESb cells, is not a random process. This conclusion is further corroborated by the present functional analysis. Compared to ESb PM, ESb-derived ECM were selectively enriched for Fc receptors and depleted in glycoproteins with affinity for hepatocytes. Tumor-derived ECM carried the same tumor antigen as the corresponding tumor line and showed in comparison to PM material an increased inhibitor capacity in a T-cell-mediated tumor-specific cytotoxicity test.

Shedding of plasma membrane fragments. Neoplastic and developmental importance

The phenomenon of shedding of cell surface macromolecules and their importance in the cancer process has been reviewed with particular emphasis on tumor membrane fragments. With cell activation (during growth or stimulation of normal cells), there is an increase in synthesis, processing, insertion, and eventual, intact release of certain membrane proteins, some of which are proteases. In cancer, these events occur spontaneously and without the temporal, physiological, or hormonal control apparent in normal cells. In a previous review (Black, 1980), many of the consequences of shedding tumor products were described, but the nature of the shed material was not clear. It now seems likely that some proteolytic, procoagulant, and immunosuppressive activities of shed material are contained within membrane particulate material (vesicles). Under normal conditions, shed membrane material (particularly proteolytic activity) may be necessary for cell movement and tissue remodeling which occur during embryogenesis. In cancer, shedding of plasma membrane fragments may be responsible for the key features of the malignant phenotype by the presence and release of proteolytic activity producing the separation of tumor cells from the primary site, invasion of the surrounding tissues by tumor cells, and formation of distinct metastases. Shed plasma membrane fragments may play a central role in tumor progression by enhancing the steps of the metastatic cascade, in particular by increasing tumor embolus formation (by enhanced fibrin deposition and platelet aggregation) and vascular permeability, as well as increasing basement membrane degradation. Shed membrane fragments (containing tumor antigens) either alone or complexed with antibody, may be responsible for blocking the cell-mediated immune reaction by the formation of "blocking factors" or by suppressing the formation of cytotoxic immune pathways. The suppression of immune response formation may be due to blocking of antigen presentation by macrophages (due to inhibition of Ia) or by the induction of Ts1 cells.

In vivo shedding of apical plasma membrane in the thyroid follicle cells of the mouse

Clusters of luminal dense bodies, limited by a triple-layered membrane, were found in all follicle lumina in thyroid glands of mice. After thyroxine treatment the number of luminal dense bodies increased, especially in the periphery of the lumen, where the intraluminal bodies often displayed a striking resemblance to microvilli. In hyperplastic goiters, obtained by feeding mice with propylthiouracil, luminal dense bodies were replaced by intraluminal vesicles. During goiter involution the vesicles were gradually replaced by luminal dense bodies; the presence of intermediate forms suggests that vesicles and dense bodies are basically the same formations. Luminal dense bodies were observed in colloid droplets indicating their removal by endocytosis. As demonstrated by electron-microscopic cytochemistry, luminal dense bodies contain a membrane-bound peroxidase, and electron-microscopic autoradiography after administration of 125I indicate that they possess an iodinating capacity. Our observations on mouse thyroid glands suggest that the luminal dense bodies, which appear as vesicles in hyperplastic glands, are formed by shedding of the apical plasma membrane of the follicle cell. The shedding process might be of importance for the turnover of plasma-membrane material.

Monoclonal antibody against a cryptic carbohydrate antigen of murine and human lymphocytes. I. Antigen expression in non-cryptic or unsubstituted form on certain murine lymphomas, on a spontaneous murine mammary carcinoma, and on several human adenocarcinomas

This paper describes an IgM monoclonal antibody (49H.8) which was produced following immunization of BALB/c mice with human neuraminidase-treated erythrocytes (NE-RBC). 49H.8 reacts with NE-RBC, neuraminidase-treated T lymphocytes (NE-T) and NE B lymphocytes of both human and murine origin. Little or no reactivity with untreated T or B cells could be detected. Thus the 49H.8 antigen is "cryptic" in most normal lymphocytes of both humans and mice. In contrast, the 49H.8 antigen was detected in non-cryptic or unsubstituted form on many non-treated murine lymphomas of both B- and T-cell origin, on the spontaneous murine mammary carcinoma, TA3-HA and on several human adenocarcinomas. The 49H.8 antigen appears to be related to the previously described 49H.24 antigen as shown by sugar inhibition experiments. 49H.24 reacts most strongly with the synthetic disaccharide (betaGa1 (I leads to 3)alpha Ga1NAc) but not at all with beta Ga1(I leads to 3)beta Ga1Nac. 49H.24 does not react with any of the murine or human tumors tested. 49H.8 reacts with both the alpha and beta forms of the disaccharide but reacts most strongly with phenyl-beta-galactoside-containing compounds. In contrast, phenyl-alpha-galactoside-containing compounds produced no reaction. The natural determinant detected by this antibody was not determined but various possibilities are considered. 49H.8 was used to detect antigen apparently shed from growing TA3-Ha cells into the serum and ascites of tumor-bearing mice. These observations suggest that the 49H.8 monoclonal antibody will be valuable as a specific reagent for a common tumor-associated antigen shared by certain murine and human tumors, and as a means of assaying shed tumor antigen in circulation as in the TA3-Ha mammary adenocarcinoma model.

Possible role of microtubules in tumor cell surface membrane shedding, permeability, and lympholysis

Low temperature (0 degrees C/1 hr) induced changes in the mastocytoma P815 cell surface morphology which mimicked those induced by alloimmune T-lymphocytes during the cytolytic process. These morphological changes consist of the formation and shedding of membrane vesicles (MV) from the P815 cell surface. When the low-temperature-induced MV shedding process takes place at 22 degrees C, it occurs without changes in membrane permeability to 51Cr, whereas at 37 degrees C, the kinetics of 51Cr release resemble those induced by alloimmune T lymphocytes. The effects of two microtubule-stabilizing agents, deuterium oxide and hexylene glycol, were investigated on the low-temperature-induced MV shedding process as well as on the lymphocyte-mediated cytolysis (LMC) of target cells. These agents were found to inhibit (a) the low-temperature-induced MV shedding, (b) the low-temperature-induced membrane permeability changes to 51Cr, and (c) the LMC process. These data indicate that disruption of microtubules may be involved in all these events.

Fluorescence polarization studies and biochemical properties of membranes exfoliated from the cell surface of rabbit thymocytes in situ

In the course of our work on membrane phenomena related to the differentiation of lymphocytes in the rabbit thymus, we isolated membranous material from the extracellular compartment of this organ. With respect to their ultrastructural appearance, enzyme activity, lipid composition (cholesterol/phospholipid molar ratio, fatty acid composition of total phospholipids, phospholipid composition) and lipid fluidity, these membranes were shown to exhibit characteristics similar to those of purified plasma membranes isolated from disrupted thymocytes. Moreover, their antigenic specificity as determined in a cytotoxicity adsorption test was identical. From our experiments, we hypothesize that the extracellular membrane fragments found in the rabbit thymus are derived mainly from material shed by immature thymocytes.

Spontaneous and detergent-induced vesiculation of thymocyte plasma membranes

An analog of lysophosphatidylcholine (1-dodecyl-propanediol-3-phosphocholine) which does not impair membrane-bound enzymes was used for the induction of shedding of membrane vesicles from intact calf thymocytes. Without liberation of intracellular enzymes such as lactate dehydrogenase (EC 1.1.1.27) the shedded membranes contained 15--25% of the total activity of the plasma membrane enzymes alkaline phosphatase (EC 3.1.3.1), nucleotide pyrophosphatase (EC 3.1.4.1) and gamma-glutamyl transferase (EC 2.3.2.2). Membrane-free supernatants only exhibited trace activities of these enzymes. Without further purification, the specific enzyme activities in shedded membranes were of the same order of magnitude as in purified plasma membranes prepared after nitrogen cavitation of thymocytes. Small amounts of membrane vesicles which showed a different composition could be removed without detergent. These membranes exhibited a 3-fold lower specific activity of the gamma-glutamyl transferase while that of the alkaline phosphatase and nucleotide pyrophosphatase was similar as in detergent induced membrane vesicles. Distinct differences also were found in the protein pattern. The content of total cholesterol and phospholipid in vesicles shed spontaneously or after detergent treatment was nearly identical, however, significant differences were found in the fatty acid composition of the main phospholipids. The content of polyunsaturated fatty acids (linoleic and arachidonic acid) increased in the order: spontaneously shedded membranes, detergent induced vesicles, conventional purified plasma membranes. These results are discussed in terms of the heterogeneous composition of areas of the thymocyte plasma membrane.

Rigid plasma-membrane-derived vesicles, enriched in tumour-associated surface antigens (MLr), occurring in the ascites fluid of a murine leukaemia (GRSL)

Extracellular membraneous vesicles of GRSL leukaemia cells were isolated from the ascites fluid bathing the cells in vivo, and from cell washes. Mammary tumour virus-induced antigens (MLr) expressed on the surface of the cells are enriched on these vesicles as compared to plasma membranes isolated from the cell homogenate. The lipid fluidity of the vesicles is much smaller than that of the plasma membranes, and the content of the pertinent lipid parameters, cholesterol and sphingomyelin, are accordingly greatly increased. The extracellular vesicles which are also enriched in sialic acid and 5'-nucleotidase are apparently derived from the plasma membrane, probably at least partly by exfoliation of selected parts or domains of the surface of living cells. An analogy between this shedding of vesicles, the formation of endocytotic vesicles and the budding of viruses is noted; all these processes select or assemble rigid lipid domains of the cell membrane. The possible participation of surface microvilli and sub-lethal autolysis in the process of shedding is discussed.

Surface membrane changes of T cells induced by syngeneic tumour cells. II. T-cell defects induced by small tumour cell inocula or tumour cell antigens

Injection of a large number of tumour cells, like other strong immunogenic challenges, is followed within 6 h by the uptake of cytophilic Ig (probably complexes) by a subpopulation of T cells. This phenomenon, known as the "6-hour T-cell response" is abrogated when small tumour cell inocula (10(2)), or small amounts of a preparation from tumour cells, which contains tumour antigens, are injected prior to the immunogenic challenge Abrogation of the "6-hour T-cell response" resulted in a decrease in specific anti-tumour cell immunity as tested in vitro by measuring growth inhibition (cytostasis). It has also resulted in loss of the amplifying function on antibody formation against sheep erythrocytes, normally detected in a T-B cell co-operative system when T cells are used 6 h after priming with sheep erythrocytes. It is postulated that this T-cell defect may represent a mechanism by which tumour cells, in the early stages of their growth, interfere with inductive stages of the immune response for a sufficient period of time to allow the tumour to grow beyond immune control.

Resistance of guinea-pig hepatoma cells to complement-mediated lysis induced by ascites fluid or serum from tumor-bearing animals

The mechanisms of tumor cell susceptibility and resistance to cytotoxic antibodies were investigated in the guinea-pig ascites hepatoma (line-1 and line-10) system. Treatment of line-specific rabbit antibody-coated tumor cells by ascitic fluid, by serum of tumor bearers or by tumor extract inhibited subsequent complement-mediated lysis. Inhibition by ascitic fluid and serum was not line-specific, but inhibition by tumor extract was line-specific. Treatment of tumor cells with ascitic fluid or tumor extract prior to exposure to specific cytotoxic antibody and complement did not inhibit lysis. Incubation of cytotoxic rabbit antisera with ascitic fluid, tumor-bearer serum or tumor extract neutralized their complement-dependent cytotoxic activity on tumor cells. Tumor-immune guinea-pigs exhibited line-specific delayed cutaneous reactions after injection with ascitic fluid or tumor extract. Studies with indrect immunofluorescence revealed that exposure to ascites fluid or tumor extract caused a rapid shedding of rabbit antibodies from the tumor cell surface. Evidence is presented indicating that the active fraction of ascites fluid was associated with immune complexes consisting of IgG and tumor antigen in excess. The relevance of these findings to tumor escape from immune destruction in vivo is discussed.

Discussion paper: dual effects of tumor antigens: induction of tumor resistance or tumor growth enhancement

TA3-HA nonspecific tumors growing in ascites form shed their membrane components into the ascites fluid. This product can induce tumor growth enhancement if given together with or after i.p. tumor inoculation in relatively large quantities, but if given i.m. in small quantities, several days before tumor challenge, the mice show an elevated resistance to the tumor. The strictly strain-specific TA3-St line does not release such membrane components into the ascites fluid. It has also been found that the TA3-HA cells have a larger membrane fluidity than the TA3-St cells, as measured by membrane microviscosity, using the Shinitzki procedure. Isolation and gross chemical analysis of the TA3-Ha ascites fluid component was carried out. Results, so far, indicate that the active site of this product is probably carbohydrate in nature. The possible mode of action of such component in tumor growth enhancement is most probably by overwhelming and neutralizing immunocytes capable of recognition and eventually cytotoxic action.

Suppression of immune response to sheep red blood cells in mice treated with preparations of a tumor cell component and in tumor-bearing mice

The frequency of rosette-forming cells (RFC) in spleens of mice immunized with sheep red blood cells (SRBC) was significantly reduced by pretreatment with preparations obtained from tumor extracts. This effect was not produced by preparations obtained by similar methods from normal tissue extracts. Significant suppression of RFC frequency was also found in spleens of mice immunized with SRBC at late stages of tumor growth, as compared to that in immunized controls and in mice bearing tumors at early stages. The results suggest that at late stages, a tumor cell component is released by tumor cells which may be similar to the nondialyzable immune suppressive factor(s) separated by us from tumor extracts, factors found in ascites fluid of tumor-bearing mice and those known to be released from tumor cells in vitro.

Leukemia in AKR mice. I. Effects of leukemic cells on antibody-forming potential of syngeneic and allogeneic normal cells

Cells from the spleen, thymus, lymph node, and liver of leukemic AKR mice suppress in vitro antibody responses of normal syngeneic and semiallogeneic cells. This suppression can be mediated by irradiated leukemic cells, requires cell contact between leukemic and normal cells, and may occur at any time during the in vitro culture period. Leukemic AKR cells do not suppress antibody responses of allogeneic cells, even when allogeneic cells have H-2 or background genes homologous with AKR. Leukemic cells do, however, suppress cells that are unable to respond allogeneically to leukemic AKR cells, such as cells of the F1s of AKR. Suppression of normal AKR antibody responses by leukemic AKR cells may be overcome by addition of irradiated allogeneic cells. The fact that leukemic AKR cells are able to suppress normal lymphocyte responses may be of significance in pathogenesis of leukemia in these mice.

Tumour-associated transplantation antigen in sera of rats with large RSV-induced sarcomas

A factor inhibiting tumour growth in syngeneic hosts was found in the sera of inbred Lewis rats carrying Rous sarcoma virus-induced tumour (RSL). The findings presented here suggest that the serum factor is a tumour-associated transplantation antigen (TATA) shed from the neoplasm into the circulation. All the tumour bearers' sera tested with RSL cells were negative in indirect membrane immunofluorescence;however, on passive transfer into syngeneic rats, they protected the animals against the growth of an RSL tumour inoculum. A similar protective effect was also observed after injection of TATA prepared from RSL cell membranes by solubilization with potassium cholate. When incorporated into Freund's adjuvant, tumour-bearers' sera immunized the animals against a subsequent RSL sarcoma graft. Sera collected from immunosuppressed rats bearing large sarcomas which presumably contain neither tumour-specific antibody nor antigen-antibody complexes, transferred inhibition of tumour growth to syngeneic hosts. Intact immunological reactivity of recipients was a necessary prerequisite for the protective effect of sera, since the passive transfer of an inhibitory serum to immunosuppressed rats did not inhibit tumour growth. We assume that the TATA present in tumour-bearers' serum is released from the growing neoplasm as a result of either cell death or membrane metabolic turnover.