Specific cytostatic effect of lymph node cells from normal and T cell-deficient mice on syngeneic tumor target cells in vitro and its specific abrogation by body fluids from syngeneic tumor-bearing mice

Rejection of allogeneic tumor is not determined by host responses to MHC class I molecules and is mediated by CD4-CD8+ T lymphocytes that are not lytic for the tumor

In previous studies, the murine SaI (A/J derived, KkDd) sarcoma was transfected with the allogeneic MHC class I H-2Kb gene, and expressed high levels of H-2Kb antigen. Contrary to expectations, the tumor cells expressing the alloantigen (SKB3.1M tumor cells) were not rejected by autologous A/J mice. Because these results contradict the laws of transplantation immunology, the present studies were undertaken to examine the immunogenicity of SKB3.1M and SaI cells in allogeneic hosts. Similar to SKB3.1M, SaI cells are lethal in some allogeneic strains, despite tumor-host MHC class I incompatibilities. Tumor challenges of SKB3.1M and SaI cells, however induce MHC class I-specific antibodies and CTL in both tumor-resistant and -susceptible hosts. Although the tumors induce specific CTL, tumor cells are not lysed in vitro by these CTL, suggesting that the tumor cells are resistant to CTL-mediated lysis. Since growth of these tumors does not follow the classical rules of allograft transplantation, and because the tumor is not susceptible to CTL-mediated lysis, we have used Winn assays to identify the effector lymphocyte(s) responsible for SaI rejection. Depletion studies demonstrate that the effector cell is a CD4-CD8+ T lymphocyte. Collectively these studies suggest that the host's response to MHC class I alloantigens of SKB3.1M and SaI cells does not determine tumor rejection, and that effector cells other than classically defined CTL, but with the CD4-CD8+ phenotype, can mediate tumor-specific immunity.

Characterization of cytostatic effector lymphocytes during the development of a syngeneic lymphosarcoma in C3H mice: use of monoclonal reagents to identify T-cell subsets

The development of the in vitro cytostatic capacity of splenic lymphocyte subpopulations from C3H mice carrying the syngeneic Gardner tumor was examined at different times after intramuscular tumor injection. Most mice died between 3 to 6 weeks after tumor injection, while some rejected their tumors or survived longer than 3 months. Cell separation procedures and monoclonal antibodies against T-cell subsets were used to identify the cells responsible in anti-tumor immunity. Cytostatic capacity against tumor cells developed in the T-cell enriched subpopulation of splenocytes 3 days after tumor injection and was partly abrogated by anti-Lyt-1. Effector function of Lyt-2+ T cells and B cells developed later and peaked at around 10 days after tumor injection. Another cell population with cytostatic capacity which was not blocked by anti-Lyt-1, anti-Lyt-2, or anti-Ly-5 was noted to develop early after tumor injection and lacked both T-cell and B-cell markers ("null"). This subpopulation was eluted with T cells from nylon wool columns and comprised up to 50% of the T-enriched fraction of splenocytes in later stages of tumor growth. An interesting characteristic of these "null" cells was susceptibility to T-cell suppression both in early and later stages of tumor growth except in regressor mice which lacked suppressor T cells. The cytostatic capacity of the "null" cells could be restored either by removal of Thy-1+ cells from the T-enriched fraction by panning, or the addition of anti-Thy-1 or F(ab')2 fragments of anti-Thy-1 to the lymphocyte-tumor reaction mixtures. Most mice examined after 10 days of tumor growth were immunosuppressed to varying degrees. Unseparated splenocytes from these mice were not cytostatic but removal of T cells allowed the B cells to exert their cytostatic capacity. A strong underlying B-cell cytostasis was shown to be present in long survivor mice even though their unseparated spleen cells were only weakly cytostatic. T cells did not play a role in the regression of tumors or long-term survival of tumor bearer mice. Splenocytes from regressor mice were strongly cytostatic, their anti-tumor activity residing in the "null" and B-cell populations.

Maternal immunostimulation of a teratocarcinoma-derived cell line, TerCs

Since murine teratocarcinomas and early embryos are known to share cell surface antigens, we investigated the possibility of maternal immune responses to normal pregnancy using teratocarcinoma-derived cell lines as targets. We found that an adherent cell population from both the spleen and peritoneum of syngeneically mated 129/SvSl pregnant females stimulated the uptake of [125I]iododeoxyuridine ( [125I]IUdR) by a teratocarcinoma-derived cell line, TerCs in vitro. Adherent cells from multiparous females did not stimulate the growth of other tumor cell lines. However, levels of natural anti-tumor activity detected in peritoneal cell populations of 129/SvSl virgin females were greatly reduced during pregnancy. Peritoneal cells from multiparous females with growth-stimulating activity were retained on nylon-wool columns and not eliminated by treatment with anti-theta antiserum and complement. Peritoneal cells from virgin females, treated with anti-theta antiserum and complement to eliminate cytotoxic lymphocytes, gained the ability to stimulate the uptake of [125I]IUdR by TerCs cells. [125I]IUdR uptake by cultured normal mouse blastocysts was significantly enhanced by peritoneal cells from multiparous females, while cells from age-matched virgin females had no effect. These results suggest that changes in immunocyte populations occur during pregnancy in the mouse; these changes could promote the growth of the embryo in utero.

Red blood cells coated with tumor cell extracts as targets in 51Cr release assays

Sheep red-blood cells were coated with tumor cell antigens prepared by extractions with 3M KCl. The coated cells were labelled with 51Cr and used as targets in immuno-assays. The technique was found suitable for complement-mediated as well as antibody-dependent cell-mediated reactions, and it offers several applications for use in tumor immunology.

Involvement of peritoneal macrophages in cellular responses to mastocytoma in resistant and susceptible mice

The involvement of peritoneal macrophages in rejection of mastocytoma cells in the C57BL/6 mice was examined in comparison to similar cell responses in susceptible DBA/2 mice. By means of scanning and transmission electron microscopy it was found that macrophages constituted the major cell class responding to the mastocytoma cells in the peritoneum of both mouse strains. However, in the resistant mouse strain macrophages formed the predominant cell type during the course of tumor growth. Furthermore, tissue culture of peritoneal exudate cells from this resistant mouse strain injected with mastocytoma cells five days earlier failed to grow out tumor cells. On the other hand, macrophages decreased in number in the susceptible DBA/2 mouse strain and tumor cells did grow readily in vitro when peritoneal cells containing tumor cells and macrophages were cultured in vitro. These results indicate that macrophages constitute an important cell class in resistance of a mouse strain which is now susceptible to mastocytoma cells. The ultrastructural study provided some insight into the nature of the cell types involved and their interaction with the tumor cell.

A sensitive assay for the detection cytotoxic antibodies to mammalian cell surface antigens

A microcytotoxicity assay for the detection of complement-dependent serum toxicity against adherent cells has been modified to include post-labeling of the target cells with [3H]leucine or [3H]thymidine. The adaptation represents a significant improvement over the visual counting of residual cells. The technique is more objective and less tedious than the original procedure, while retaining the features of economy of cells and sera, reproducibility, and sensitivity. Examples are given which demonstrate the suitability of the modified assay for the analysis of human and mouse tumor antigens using autologous, allogeneic, and syngeneic sera.

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.

Autoimmune interaction measured in a postlabelling microcytostasis assay

A postlabelling microcytostasis assay was developed to assess primary immune interaction between normal rat lymphocytes and autologous testis cells. In this vitro model of experimental autoimmune orchitis (EAO) unprimed T cells respond to a Sertoli-like subpopulation of testis cells during a 4 day culture period. The T effector cells exert a cytostatic effect on the monolayer-forming target cells. The number of remaining target cells, which inversely correlates with the intensity of the autoimmune reaction, is quantified by 51Cr incorporation. The assay is performed in multiple well plastic plates which allow rapid harvesting by cutting off the bottoms of each well. The attached labelled target cells are directly measured on the bottoms without any further transfer step. The method is adapted for the EAO model but may be useful to study primary T cell interaction with any other monolayer-forming target cells.

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.

Studies on the microcytotoxicity test. II. The uptake of amino acids ([3H]leucine or [75Se]methionine) but not nucleosides ([3H]thymidine or [125I]IUdR) or 51CrO24-provides a direct and quantitative measure of target cell survival in the presence of lymphoid cells

We have studied the suitability of various commonly used radioactive materials for the direct post-labeling of adherent rat target cells in long-term cytotoxicity tests. The use of nucleosides at high concentration avoids the necessity of adding fluorodeoxyuridine to enhance nucleoside uptake by target cells, and reduces the degree of non-specific inhibition of nucleoside uptake caused by products released from effector lymphoid cells. However, when [125I]iododeoxyuridine was used for labelling, such inhibition was not completely avoided even at very high nucleoside concentration, necessitating the washing of target cells prior to labelling. Similarly, without prewashing, the uptake of 51CrO24-ions frequently failed to correlate well with the numbers of surviving target cells as assessed by cell counting. On the other hand, radiolabelled amino acids, when present at semi-saturating concentrations, were taken up quantitatively by target cells under all conditions tested. Furthermore, in comparison to [125I]iododeoxyuridine, radioactive amino acids showed little if any toxicity to target cells. The use of the gamma-emitting amino acid analogue, [75Se]selenomethionine, is particularly recommended.

The role of H-2 and H-2-like determinants in syngeneic and allogeneic cytostasis

Specific sensitization against H-2 determinants was affected by immunizing allogeneic mice with spleen and lymph node cells in H-2 congenic combinations. Lymph nodes from the sensitized and non-sensitized mice were respectively cultured together with H-2 syngeneic tumour cell lines. The growth and viability of the tumour cells was subsequently measured by the amount of radiothymidine incorporation. If the tumour cells incorporated less isotope when cultured with the immune cells than with the normal cells this was termed 'cytostasis'. To identify the H-2 genes controlling the sensitization phase in the cytostasis assay, we studied the effect on different transplantable tumour target cells of lymphoid cells from mice sensitized against different congenic spleen cells. The results suggest that the cytostasis assay can can measure an in vitro specific response to H-2-incompatible sensitizing antigens, and that I--B incompatibility, together with K and/or D, is essential to produce effectors. Furthermore, H-2 allogeneic sensitization could induce cytostasis even against tumour cells syngeneic for the H-2 halotype of the responder strain. The implications of these findings are discussed.

Immunogenicity of modified tumor cells in syngenic hosts

Modified tumor cells were used to immunize three murine hosts against syngenic ascitic lymphomas: C3H-6C3HED, BALB/c-P1798, and DBA/2-L1210. When the host was capable of a significant immune response against the malignant cells during progressive tumor growth (e.g., C3H vs. 6C3HED), protective immunization against a larger challenge tumor dose was achieved after fewer vaccinations. Lipopolysaccharide (LPS) enhanced host response to iodoacetamide (IAd) modified P1798 and L1210 so as to confer resistance after fewer immunizations with these weakly antigenic tumors. Similarities among the three systems were also seen. Modified cells may be stored at 4 degrees C several weeks and are effective when 107-108 are given i.p.; resistance appears maximal about one week after vaccination. In immunotherapy trials, C3H mice implanted with 5 x 104 6C3HED cells and treated at least four times with IAd-6C3HED demonstrated a 25% cure rate. A model was presented for evaluating parameters of response to immunotherapy in conjunction with chemotherapy. Cell-mediated immunity in resistant mice was demonstrated by inhibition of DNA synthesis in cultures of lymphoma cells and sensitized peritoneal cells (PEC) compared to that with nonimmune PEC. This assay system may also provide an opportunity for examining the hypothesis of immunostimulation of tumor growth in vitro. Humoral response to modified cells was established by membrane immunofluorescence. Although anti-6C3HED and anti-L1210 appear specific, anti-P1798 antiserum reacts with BALB/c thymocytes and murine fetal antigen.

Characteristics of the effector cells mediating cytotoxicity against antibody-coated target cells. II. The mouse nonadherent K cell

A cell of lymphoid morphology capable of killing antibody-coated chicken erythrocytes was isolated from nonimmune mouse spleen using a combination of carbonyl iron treatment and glass bead column passage. This non-phagocytic effector cell, which is referred to as the nonadherent K (killer) cell, is distinguished from the non-phagocytic myeloid K cell described earlier (Greenberg, A.H., Shen, L. and Roitt, I.M., Clin. Exp. Immunol. 1973. 15:251) by its relatively weak surface adherence properties and low concentration within the mouse spleen. The cell is further characterized by its relatively large size, lack of theta or immunoglobulin determinants, the presence of Mg++-independent complement receptors, affinity for aggregated IgG2 myeloma proteins, inhibition by cytochalasin B and good survival in cell culture. The possible lineage of the cell is discussed.

Secondary specific immune response in vitro to MSV tumor cells

The interactions which occur between antigenic tumor cells and normal or immune lymphoid cells in a 3-day in vitro culture, have been studied with a murine sarcoma virus (MSV)-induced tumor. The 3H-thymidine incorporation of lymphoma cells growing in suspension, and the radioactive-chromium release of freshly sampled lymphoma cells regularly added to the culture, have been compared to determine the part played by immune lymphoid cells in cytolysis and cytostasis of the tumor-cell population. The cytolytic activity increases in the culture from day 0 to day 3. It is due, predominantly, to T-cells, and remains specific to antigens shared by MSV tumors and related lymphomas. This activity would be difficult to detect unless freshly sampled ascitic cells were used as targets, since the lymphoma cells spontaneously lose a part of their sensitivity to immune cytolysis during in vitro culture. The method used in the present experiments is a secondary chromium release test (SCRT), which measures the invitro secondary stimulation of cytotoxic T-lymphocytes (CTL) by tumor cells. In the absence of stimulatory cells, the CTL activity would have rapidly fallen in vitro. The cytostatic activity also increases during the 3 days in vitro, in parallel to the cytolytic activity: it is due to non-T-cells and remains mainly non-specific. The significance of these data for the interpretation of invitro demonstrated cell-mediated anti-tumor immune reactions is briefly discussed, as well as their relevance in the in vivo role of immune CTL.

The use of 2-deoxy-D-glucose to assess changes in tumor target cell membranes in vitro

Following short-term suspension culture, cells from the Balb/C sarcoma Meth A were allowed to incorporate both [14C] leucine and 2-deoxy-D-glucose-1-[3H] (2DG). The 2DG is trapped as a small anionic marker of the cytosol. Deviation from the kinetics of spontaneous efflux of the markers is interpreted as reflecting perturbation of the target cell membrane. In the presence of guinea pig complement and a rabbit antiserum to Meth A, enhanced 2DG efflux was effected in a titer comparable to that detected with a 51Cr-release assay. With a number of alloantisera and syngeneic immune sera, 2DG efflux was enhanced while 51Cr-release was unaffected. Only in the presence of syngeneic immune sera from mice bearing a low tumor mass, syngeneic splenic leukocytes effect a retardation in the spontaneous 2DG efflux. Sera from animals with a large tumor mass were ineffective. Effux of proteins labeled with [14C] leucine was not altered. The phenomenon was not dependent on the presence of a heat-inactivatable syngeneic complement source. The method described provides a sensitive probe of target cell membrane permeability in the tumor model studied. The phenomenon detected is the capacity of serum, sampled relatively early in syngeneic oncogenesis, to direct syngeneic splenic leukocytes to interact with the target cell membrane differentially altering its permeability to the small cytosol marker.

Studies on the effector cell of anti-tumour immunity in a chemically induced mouse tumour system

Spleen cells from mice immunized against a methylcholanthrene induced rhabdomyosarcoma inhibited tumour cell colony formation in vitro and prevented tumour development in vivo in an adoptive transfer test. Treatment of the immune spleen cells with anti-mouse immunoglobulin serum or passage through a nylon wool column, both of which reduced the percentage of immunoglobulin bearing cells in the population to less than 3-4%, did not alter their anti-tumour effects. In contrast, treatment of the spleen cells with anti-BAomicron serum abolished their anti-tumour effects both in vitro and in vivo. These results indicate that T cells are the mediators of tumour immunity in this chemically induced tumour system.

[The lymphocyte cytotoxicity test in tumor immunology (author's transl)]

The cytotoxic action of lymphocytes on cancer cells in vitro indicates sensitization of the patient against his own tumor. The technical difficulities of this test and possibilities of standardization and simplifying the procedure are discussed. Critical steps are isolation of lymphocytes and culturing target cells without loosing their specific antigenic structure. The need for specificity controls both for lymphocytes and tumor cells is emphasized. Labelling tumor cells with isotopes represents a major improvement in evaluating the result. The role of thymus- and bone marrow-dependent lymphocytes as well as blocking factors in the serum of tumor patients can be analyzed in the cytotoxic assay. A better understanding of these mechanisms may facilitate a therapeutic approach by manipulating the interaction of tumor cells and host.

Cytotoxic immune cells with specificity for defined soluble antigens. IV. Antibody as mediator of specific cytotoxicity

Spleen cells from mice immunized against ovalbumin (OA) or dinitrophenylated mouse serum albumin (DM) were found to be specifically cytotoxic in vitro towards target cells (chicken red blood cells) coated with these antigens. Inhibition of specific cytotoxicity was observed when free soluble antigen was added to the incubation mixtures. DM-immune cell cytotoxicity could be specifically and completely inhibited by DNP-lysine and was thus shown to be hapten specific. Complete and specific inhibition was also observed for OA-immune cell cytotoxicity using OA as inhibitor, but compared with the inhibition curves obtained with DNP-lysine, the OA cytotoxicity inhibition curves were shifted by a factor of about one hundred towards lower molar inhibitor concentrations. Very similar results were observed when the serum antibodies of DM- and OA-immune animals were analyzed by passive hemagglutination inhibition. With increasing time after immunization, both cytotoxicity inhibition curves and agglutination inhibition curves, shifted to lower antigen or hapten concentrations. Specific cytotoxicity against antigen-coated target cells was induced in nonimmune spleen cells (a) by serum from immune animals, and (b) by supernatants from in vitro immune cell cultures. In both instances, the factor which induced antigen-specific cytotoxic activity could be absorbed on anti-mouse Ig columns, thus demonstrating its immunoglobulin nature. The ability of target cell bound antibodies to induce cytotoxicity in nonimmune spleen cells was restricted to the 7S antibody class.