Immunologic considerations of large volume radiotherapy

There is clinical evidence that the immune response can increase or decrease cancer growth. 1) Cancer is increased in congenital immune deficiency states and in those given immuno-suppressants after renal transplantation; 2) there is a correlation between mononuclear cell infiltration and prognosis; 3) spontaneous regression occurs occasionally on an immunologic basis; 4) cancer specific antigens and antibodies can be demonstrated, and 5) immunotherapy can cause tumor regression. The cells that are responsible for the immune response are 1) families of thymic-derived lymphocytes, or T-cells, ("memory," "effector", "helper" or "suppressor" T-cells), and 2) bursal-derived lymphocytes, or B-cells, which on specific sensitization become either plasma cells that produce cytotoxic or blocking antibody or macrophages (A-cells) that process antigen, and may become "armed" with cytophilic antibody. The main effect of local radiotherapy is to destroy certain families of radiosensitive lymphocytes in the afferent, central and efferent components of the immune response. In Hodgkin's disease, extended field radiotherapy causes a prolonged decrease in the number of lymphocytes in the peripheral blood and a decrease in function of the cells, as determined by RNA and DNA synthesis after culture with mitogen, phytohemagglutinin. There is no correlation, however, with the values after treatment and recurrence of the disease. The effect of local radiotherapy to large volumes of tissues, on the incidence of new primary cancers, is uncertain but the majority of reports show that it is no effect.

Some immunological mechanisms of the influenza virus antitumour effect

Vaccine strains of influenza A virus inhibited the growth of ascitic tumour cells and outbred rats or inbred mice. The infected tumour bearers had an enhanced immune response to viral and specific tumour antigens. These phenomena are apparently due to the formation of complexes of both antigens on cell membranes and increased immunogenicity of such complexes.

Appearance of cytolytic antibodies in sheep lymph following immunisation with tumour cells. Identification of antibody subclasses

Sheep were immunised with mouse P815 tumour cell suspensions and at intervals afterwards lymph was collected draining from the stimulated lymph nodes. The lymph samples were fractionated by column chromatography into IgM, IgG1 and IgG2 antibody fractions; these were then assayed for cytolytic functions on 51Cr labelled target P815 cells. Complement dependent antibodies were assayed using sheep complement; activity was first detected in the IgM fraction 3-4 days after immunisation and in the IgG1 fraction at 5-6 days. No CDA activity was found in fractions of the IgG2 antibody subclass at any time. Leucocyte dependent antibodies were detected only in the IgG fraction, and they appeared simultaneously in both IgG1 and IgG2 subclasses 5-6 days after immunisation.

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.

The use of non-human primates for production of antisera to human tumor-associated antigens

High-titered antisera against human melanoma- and leukemia-associated antigens have been produced in non-human primates. The data from this and from other studies suggest that this model may prove a valuable source of highly specific antisera against a variety of human tumor-associated antigens or alloantigens. Our methods for production and characterization of these antisera are reported.

Cell-mediated immunity to mouse tumors: some recent findings

Lymphocyte mediated immune reactions play a major role in the immunological defense against antigenic tumor cells. Serum factors (antigens, antigen-antibody complexes) can thwart these reactions, perhaps by interfering with a lymphocyte "activation" process. Blocking factors can be eluted from lymphoid cells harvested from tumor-bearing animals. One way of increasing cell-mediated reactivity to tumor antigens appears to be to sensitize (or "activate") lymphocytes against tumor antigens in vitro. Another way may be to inoculate animals with sera containing lymphocyte-dependent and unblocking antibodies. Preliminary evidence is presented that inoculation of such sera from rabbits immunized with mouse embryonie cells and extensively absorbed may delay the appearance of primary, methyleholanthrene-induced sarcomas in BALB/c mice; the mechanisms responsible for this delay remain unknown.

[Enhancement of the immune response following immunization with L1210 cells preliminarily incubated with interferon]

A single intraperitioneal injection of L 1210 cells preincubated in interferon or in "false interferon" was given to mice. These mice were sacrificed on the 10th day, and cytotoxicity of the sera against the L 1210 leukemic cells vas determined in the microcytotoxic test (modification of Terasaki's method). Leukemic cells treated with interferon before the immunization caused a more pronounced immune response in comparison with the cells treated under the same conditions with "false interferon". By the results of cytotoxic reaction immune response was enhanced 2-4-fold.

Defining the heterogeneity of anti-tumor antibody responses

Studies were undertaken to analyze the humoral in vivo and in vitro antibody response of BALB/c mice to a syngeneic MSV-induced tumor cell line. With a sensitive radioimmunoassay, sera obtained from individual progressor and regressor mice were shown to vary greatly in total tumor-specific antibody concentration as well as immunoglobulin class distribution of the antibody, but no significant difference existed between the groups of progressor and regressor mice as a whole. In addition, serum antibodies from all animals were shown to have extensive cross-reactivity against a variety of cell lines chosen to share one or more antigens with the cell line used for immunization. Conversely, when in vitro fragment cultures of splenic tissue from progressor and regressor mice were stimulated with tumor-related antigen, differences in responsiveness among normal, progressor, and regressor mice were observed. In addition, antibodies derived from fragment cultures displayed several different cross-reactivity patterns all of which were more restricted in specificity than serum antibodies.

Release into culture medium of membrane-associated, tumor-specific antigen by B-16 melanoma cells

Serum-free supernatant fluids from monolayer cultures of B-16 mouse melanoma cells were found to contain a soluble membrane associated tumor-specific antigen. The 100,000 g supernatant of the culture fluid induced an antibody response to the B-16 cells both in rabbits and in the mouse strain of origin (C57Bl/6J). Similar supernatant fluids derived from an unrelated cell line (L-929) or from normal C57Bl/6 fibroblasts did not contain the B-16 specific material. Preliminary results indicate that the B-16 specific material is a protein of low molecular weight which is released into the culture fluid chiefly by living cells and, to a lesser extent, by autolysing cells.

Immunological enhancement of a murine tumor allograft by passive alloantibody IgG and F(ab')2

The F(ab')2 fraction of an anti-tumor IgG alloantiserum induced passive enhancement of tumor allografts in inbred mice about as well as did intact IgG; i.e. apparently the Fc fragment is not required for suppressing cellular immunity. Passive F(ab')2, however, was somewhat less efficient than intact IgG or whole alloantiserum in depressing the allohemagglutinin response. The latter finding is in accord with previous observations on the relative inefficiency of F(ab')2 in feedback inhibition of the humoral response of mice to a heteroantigen.

Immunofluorescent studies on chimpanzee humoral responses to human melanoma cells

Eight chimpanzees were immunized, each with a single melanoma cell line. It was found that the serum of only one of the eight chimpanzees showed immunofluorescence with four of the five melanoma cell lines at the membrane surface; but it showed no fluorescence with normal skin fibroblasts, WI-38 cells, HeLa cells, human or monkey kidney cells. With appropriate absorption studies it was found that the antiserum was specific to melanoma cell lines. Trypsinated cells showed bright patchy membrane fluorescence, whereas non-trypsinated cells showed bright full ring fluorescence. The chimpanzee's antibody was C'-fixing IgG. It was concluded that the immunized chimpanzee produced antibody to surface antigen(s) common to four of the five melanoma cell lines tested.

Nutrition and tumor immunity: divergent effects of antitumor antibody

Nutritional deficiency reduces antibody synthetic capacity. Antibody directed against tumor antigens, however, may serve either to heighten tumor immunity, as in antibody-dependent cellular cytotoxicity, or to diminish host resistance to cancer growth by "blocking" cell-mediated tumor immunity. Diets made deficient in specific amino acids are inimical to tumor growth, apparently through reduction of synthesis of blocking antibody. Thus, where tumor immune function is involved, complex and possibly paradoxical effects of nutritional status on tumor growth can be predicted.

Correlation of "sneaking through" of tumor cells with specific immunological impairment of the host

The preferential take of tumors after small-size inocula of transplantable tumor cells has been described for many systems. The phenomenon has been named "sneaking through" or "dilution escape". Using a BALB/c mastocytoma, we have analyzed the immunological parameters accompanying sneaking through that can be observed upon injection of 10(1) to 10(3) living cells. Mice can also be conditioned by injection of low, subimmunogenic numbers of irradiated cells to show increased tumor incidences upon injection of living cells in doses two orders of magnitude above the sneaking through dose. The general immune reactivity of the animals is not impaired under these conditions. However, determinant-specific unresponsiveness is found which can be transferred by spleen cells and therefore seems to be actively maintained. It is concluded that sneaking through of tumor cells is the result of specific immunological impairment of the host's immune system by subimmunogenic small-size inocula of tumor cells.

BCG immunopotentiation of an antitumor response: evidence for a cell-mediated mechanism

BCG-immunopotentiated antitumor immunity was studied in a model in which irradiated murine tumor cells, mastocytoma P815, were injected into subcutaneous sites prepared by a prior injection of BCG; challenge in a distant foot-pad was used as an indicator of specific resistance. The onset of antitumor immunity correlated with the proliferation of lymph node cells draining the immunization sites and the development of delayed type hypersensitivity (DTH) to the tumor. Tuberculin hypersensitivity, however, was depressed during the evolution of DTH to the tumor. Antitumor immunity was transferred locally with spleen or lymph node cells that were sensitive to anti-theta sera and complement but not to anti-lg and complement. They had velocity sedimentation rates in a bovine serum albumin gradient of 3.9-5.9 mm/hour and were relatively resistant to vinblastine at the peak of the immune response. Sera from immunized mice failed to confer antitumor immunity either in vitro or on transfer in vivo.

Evidence for a membrane carrier molecule common to embryonal and tumour-specific antigenic determinants expressed by a mouse transplantable tumour

Rabbits were primed with membrane antigens solubilized from BALB/c embryo cells. After boosting with membrane antigens solubilized from a syngeneic transplantable adenocarcinoma, they developed a 'secondary' response against tumour-specific antigenic determinants. The antibodies against these determinants neither reacted with nor were absorbed by the antigens prepared from embryonal cells. However, the antigen displaying the tumour-specific determinants was bound by a reversed immunoadsorbent of insoluble anti-embryo antibodies. Indirect immunofluorescence experiments performed on adenocarcinoma cells in culture showed that, under conditions where redistribution of cell membrane components was induced, the anti-embryo antiserum aggregated the tumour-specific determinants. The purification of embryo and tumour-specific antigens achieved by affinity chromatography on insoluble antibody columns yielded three polypeptides of molecular weight close to 25,000, 20,000, and 10,000 Daltons respectively. It is suggested that the antigenic determinants responsible for tumour and embryo specificities in adenocarcinoma were located on the same molecule, or, more likely, on molecules which are closely associated in the plasma membrane and that do not dissociated in bile salts.