E. Frederick Wheelock

The role of macrophages in defense against neoplastic disease.

Publisher Summary This chapter reviews the role of macrophages in defense against neoplastic disease. Macrophages do exert both natural and adjuvant-stimulated, afferent and efferent antineoplastic activities. Macrophages appear to be essential for the uptake and processing of tumor antigens preceding the initiation of an effective immune response. Additionally, the macrophage alteration of antigen may promote successful immunization as opposed to the induction of tolerance or production of enhancing or blocking factors. The macrophage might further enhance the immune response by stimulating the proliferation of immunocompetent cells through the production of lymphocyte-activating factor (LAF) or the delivery of macrophage-contained adjuvant. Aided by cytophilic antibody, specific macrophage arming factor (SMAF), macrophage migration inhibitory factor (MIF), interferon, nonspecific opsonins, or nonspecific activation, macrophages, either alone or in concert with other immune cells, can exert both immune and nonimmune cytotoxicity toward neoplastic cells. This antitumor activity is most likely mediated through a nonphagocytic, contact-dependent mechanism, associated in only a few systems with the release of soluble toxic substances. Such direct macrophage-mediated antitumor activity, as well as macrophage-mediated induction and the amplification of antitumor immune responses, appear to contribute significantly to host survival and deserve careful consideration in both the experimental and clinical study of animal and human neoplastic disease.

The effect of particle size on the immunodepressive properties of silica

Abstract Five silica preparations were tested in the mouse for their effects on the in vivo humoral immune response to SRBC, the in vitro macrophage phagocytosis of SRBC and the in vitro blastogenic response of non-adherent spleen cells to Con A and LPS∗. One silica preparation was composed exclusively of small particles and produced the greatest depression of all functions tested with the least variability in results. Four of the silica preparations were heterogeneous with respect to particle size, and the heterogeneous preparations containing the highest percentage of small particles had the most depressive effect on the in vivo humoral immune response to SRBC and on in vitro macrophage phagocytosis of SRBC but not on the in vitro blastogenic response to mitogens. All 4 heterogeneous preparations produced great variability in each of the functions tested. Small sized particles from the 4 heterogeneous preparations were prepared by differential sedimentation, and were more depressive in the in vitro assays for macrophage phagocytosis and lymphocyte blastogenesis than the corresponding unfractionated heterogeneous preparation. The large sized particles either had no effect or enhanced both functions. All unfractionated silica preparations were toxic for non-adherent spleen cells, but the homogeneous small particle preparation and the small particles from the heterogeneous preparations were more cytotoxic. These data indicate that silica has a direct depressive effect on both macrophage and lymphocyte functions and that the depressive effects are inversely related to particle size.

Group-specific cytolytic antibody directed against the major glycoprotein (gp70) of murine leukemia viruses in serum of mice with dormant FLV infections☆

Abstract Serum of mice with dormant Friend leukemia virus (FLV) infections contains cytolytic activity against FLC-745 cells, a Friend erythroleukemic cell line. FLC-745 cells express only one cell surface FLV-coded antigen, shown by competition radioimmunoassay experiments to be FLV virion gp70. AKR virus blocks completely the cytolytic activity of serum but cannot block the precipitation of gp70 from detergent-disrupted 125 I-labeled cells. These results indicate that the FLC-745 cytolytic antibody in serum from mice with dormant FLV infections is directed against virion gp70 and is group specific. Furthermore, this serum contains a type specific gp70 antibody which is not lytic for FLC-745 cells.

In vitro depression of cellular immunity by friend virus leukemic spleen cells.

Murine spleen lymphocytes show a marked depression in their response to concanavalin A (Con A) 14 days after Friend virus (FV) infection. This depression is related to the appearance of FV antigen-containing cells in the spleen. Statolon treatment 3 days after FV inoculation suppresses FV disease and restores the responsiveness of lymphocytes to Con A. The addition of as few as 1 leukemic to every 5 normal spleen cells inhibits the Con A response of the latter cells. Normal spleen lymphocytes are not inhibited by the addition of FV or leukemic spleen cell culture fluid. Leukemic cells have an increased avidity for Con A and preferentially remove it from the culture medium. However, increasing the concentration of Con A in the medium did not overcome the depressive effects of the leukemic spleen cells on normal cells, indicating that depression of the normal cellular response to Con A had been produced by the leukemic cells. The data suggest that this depressive effect is mediated via membrane-membrane contact between the two cell types.

INFLUENCE OF IMMUNE STIMULATORS ON VIRAL LEUKEMOGENESIS

Injection of RNA, extracted from statolon by the SDS-phenol method, into FLV-infected mice 24 hours before SRBC immunization restored the immune response to SRBC to normal levels. Leukemosuppression was observed in 50% of the RNA-treated FLV-infected mice. These RNA-treated mice were clinically normal 25 days after infection, whereas all untreated infected mice developed erythroleukemia. Furthermore, all RNA-treated mice with suppressed erythroleukemia produced antibody which was cytotoxic for Friend leukemia cells. Our studies, and studies by others, indicate that the immunostimulatory and leukemosuppressive principle in statolon appears to be a dsRNA.

Tumor Dormant States in Man

Tumor dormancy is a state in which lethal tumor cells persist under growth restraint in a clinically normal host for a prolonged period of time. Restraint on the tumor cell population may be either active, as a force which either arrests tumor cells at some stage in the cell cycle or which lyses them at the same rate at which they proliferate, or it may be passive, as in the absence of a factor which tumor cells require for proliferation, such as a hormone for hormone-dependent tumors or as essential nutrient in a vascular deficient tumor. The tumor dormant state is terminated by an event which results in either the destruction of all tumor cells, or the rapid increase in tumor cell numbers and development of a recurrent tumor.

DISCUSSION PAPER: HUMORAL IMMUNE RESPONSES TO TUMOR-ASSOCIATED ANTIGENS

As with cellular immune responses, in which both cytotoxic killer cells and immune suppressor lymphocytes have been identified, the humoral response to tumor-associated antigens has been shown to function to both the benefit and the detriment of the host. In the category of humoral immune responses that have been beneficial to the host, we have heard, in the report by Dr. Hu from Dr. Lima’s laboratory, that antibody directed against cell surface antigens on tumor cells induced by reticuloendotheliosis virus can suppress the tumor after it has developed. I will describe another example from my studies. I presented evidence earlier this week, at the companion Conference on Immunobiology of Cancer,’ that doublestranded RNA from Penicillium stoloniferum mycophage can completely suppress established Friend leukemia virus (FLV) leukemia in mice and does so by acting as an adjuvant, stimulating production of an antibody that is both virus neutralizing and cytotoxic for the leukemia cells. Since many who are here today were not at the preceding conference, I will summarize that material very briefly. The antibody response to sheep erythrocytes, as measured by quantitation of hemolysin-producing spleen cells by use of the Jerne plaque technique, is depressed in FLV-infected mice and can be restored to normal levels by an RNA-rich extract from the P. stoloniferum mycophage. We have evidence that the active immunostimulatory substance is RNA. Multiple phenol extractions gave a 100-fold increase in specific activity of RNA. Spectrophotometric data confirm that the substance is RNA, and the fact that it is not be affected by RNase at high salt concentrations but is destroyed by RNase at low salt levels gives additional evidence that it is a double-stranded RNA. Administration of this RNA-rich extract after FLV results in leukemosuppression. Mice in which the FLV infection is suppressed produce high titers of antibody that are cytotoxic to FLV leukemia cells. We have good evidence that this FLV-cytotoxic antibody effects suppression of the leukemia.2 If we administer the antibody itself to FLV-infected mice, it can suppress the disease completely. Interestingly, the DBA-2 mouse is complement deficient, and we have found that DBA-2 mouse serum has potent anticomplementary activity that blocks the cytolytic action of antibody in vitro at concentrations that exist in vivo. We therefore are not quite sure how the antibody exerts its effect in vivo, but we suspect the mechanism to be antigenic modulation. Humoral immune responses may act to the detriment of the host. There are several tumor systems in which antibody is produced that is cytophilic but not cytotoxic, even in the presence of complement. The ability of such antibody or antigen-antibody complexes to block the cytotoxic action of killer lympho-

Chapter 16. Immunotherapy of Cancer

Publisher Summary This chapter describes the various aspects of immunotherapy of cancer. The existence of an immunological response by a host to his tumor has been documented. Deficiencies in one or more components of this response may either predate and be a prerequisite for development of the tumor or be a consequence of progression of the tumor. Vaccines consisting of whole autogenous or allogeneic cells or membrane fractions from tumors have been used in animals to induce resistance to subsequent tumor challenge, and in man, to improve the immune response to an established tumor. The role of macrophages in tumor rejection is actively investigated. Certain compounds that exhibit antitumor activity have been shown to act via the macrophage, probably through macrophage-mediated cytotoxicity. Statolon, a double stranded RNA mycophage from Penicillium stoloniferum, induces interferon in DBA/2 mice and suppresses established Friend virus leukemia (FV). Suppression of FV erythroleukemia is dependent upon the immunostimulatory effects of statolon, a property not shared by other interferon inducers, such as Newcastle disease virus and poly I:poly C that has no leukemosuppressive effects.