Measurement of macrophage-mediated cytotoxicity against adherent and non-adherent target cells by release of 11 indium-oxine

Assay for macrophage-mediated anti-tumor cytotoxicity

This unit describes a procedure for determining ability of mouse macrophages to lyse tumor cells in vitro. The Basic Protocol outlines a three-stage assay that includes: (1) culture of macrophages (freshly explanted from mice or grown from a cell line) with suspected activating reagents; (2) extensive washing of the cultured macrophages to remove residual reagents, followed by incubation with [(111)In]-labeled tumor cells to allow lysis to occur; and (3) collection of cell-free culture supernatants and measurement of cytolytic activity as a function of (111)In released from tumor cells destroyed by activated macrophages. The Support Protocol outlines a method for radiolabeling tumor cells with [(111)In]oxine.

Constitutive expression of functional CD40 on mouse renal cancer cells: induction of Fas and Fas-mediated killing by CD40L

CD40, a member of the TNF receptor superfamily, is expressed on B cells, dendritic cells, and some tumor cells, including melanoma and bladder carcinoma. In this study, we report that both mouse and human renal carcinoma cells (RCC) also constitutively express functional CD40. Treatment of mouse RCC with CD40L induced strong expression of genes and proteins for ICAM-1 and Fas, and this expression was further enhanced by combining CD40L with IFN-gamma. Similar effects were demonstrated using an agonist anti-CD40 antibody. The increased levels of Fas expression on RCC after treatment with CD40L plus IFN-gamma resulted in potent killing by either FasL-positive effector cells or agonistic anti-Fas antibody. The combination of CD40L plus IFN-gamma also significantly enhanced killing of RCC by tumor-specific CTL lines. Our results demonstrate that constitutively expressed CD40 is functionally active and may provide a molecular target for the development of new approaches to the treatment of RCC.

A novel method to analyze viral antigen-specific cytolytic activity in the chicken utilizing flow cytometry

In order to overcome some of the main drawbacks that have emerged in the conventional assays for cytotoxic T-lymphocytes (CTLs) in the chicken, a novel approach to analyze viral antigen-specific cytolytic activity utilizing flow cytometry was developed. In this method, the target cells were distinguished from the effector cells by pre-labelling them with a fluorescent dye PKH67. Cell death was detected with propidium iodide which labels the DNA of damaged cells. Flow cytometric assay also enables phenotyping of the effector cells by direct or indirect immunofluorescence staining of lymphocyte surface molecules. The results showed that specific cytotoxic T cells were observed in the blood of chickens primed with fixed avian reticuloendotheliosis virus strain T transformed MHC-compatible B cells. Phenotypic analysis of the effector cells from blood demonstrated CTL activity both in CD8+ and CD4+ T cell populations and the majority CTLs were TCR2+ cells.

Antagonistic effect of NK cells on alternatively activated monocytes: a contribution of NK cells to CTL generation

Natural killer (NK) cells fulfill essential accessory functions for the priming of antigen-specific cytotoxic T lymphocytes (CTLs). On the basis of a NKG2D-ligand-positive tumor model, we obtained results implicating NK-mediated regulatory as well as NK-mediated cytolytic activities in the initiation and persistence of CTL activity. Indeed, CD8(+) T-cell-dependent tumor rejection requires NK cell function in vivo, because tumors will progress both on depletion of NK cells or in the absence of optimal NK activity. Here we provide evidence that the absence of NK cells during subcutaneous tumor growth will abrogate generation of antitumor CTL responses and that this process can be linked to the expansion of alternatively activated monocytes. Indeed, our in vitro studies demonstrate that in splenic cultures from NK-deficient tumor-bearing mice, lack of type 1-associated cytokines correlates with the presence of type 2 (alternatively activated) monocytes and the production of type 2 cytokines. Furthermore, these type 2 monocyte-containing splenic adherent populations potently suppress subsequent memory CTL restimulation. We evaluated the role of NK lytic effector functions in the efficient switch of the immune system toward classical (type 1) activation by including differentially activated monocytic populations as targets in cytotoxicity assays. The results indicate that the accessory function of NK cells depends partially on the ability of activated NK cells to preferentially engage type 2 antigen-presenting cells. Thus, when the immune system tends to be type 2 oriented, NK cells can drive an efficient type 2 --> type 1 switch in the population of antigen-presenting cells to provide signaling for the generation of CTLs.

Synergistic engagement of an ineffective endogenous anti-tumor immune response and induction of IFN-gamma and Fas-ligand-dependent tumor eradication by combined administration of IL-18 and IL-2

IFN-gamma is a critical component of the endogenous and many cytokine-induced antitumor immune responses. In this study we have shown that the combination of IL-18 and IL-2 (IL-18/IL-2) synergistically enhances IFN-gamma production both in vitro and in vivo, and synergizes in vivo to induce complete durable regression of well-established 3LL tumors in >80% of treated mice. We have observed a nascent, but ineffective, host immune response against 3LL that depends on endogenous IFN-gamma and IL-12 production and the Fas/Fas ligand (Fas-L) pathway. The combined administration of IL-18/IL-2 engages this endogenous response to induce tumor regression via a mechanism that is independent of NK and NKT cells or IL-12, but is critically dependent on CD8(+) T cells, IFN-gamma, and the Fas/Fas-L pathway. These studies demonstrate the importance of IFN-gamma as well as the Fas/Fas-L pathway in both endogenous and cytokine-driven antitumor immune responses engaged by IL-18/IL-2 and provide preclinical impetus for clinical investigation of this potent anti-tumor combination.

IFN-gamma-dependent delay of in vivo tumor progression by Fas overexpression on murine renal cancer cells

The role of Fas in the regulation of solid tumor growth was investigated. Murine renal carcinoma (Renca) cells were constitutively resistant to Fas-mediated killing in vitro, but exhibited increased expression of Fas and sensitivity to Fas-mediated killing after exposure to IFN-gamma and TNF. Transfected Renca cells overexpressing Fas were efficiently killed in vitro upon exposure to anti-Fas Ab (Jo2). When Fas-overexpressing Renca cells were injected into syngenic BALB/c mice, there was a consistent and significant delay in tumor progression, reduced metastasis, and prolonged survival that was not observed for Renca cells that overexpressed a truncated nonfunctional Fas receptor. The delay of in vivo tumor growth induced by Fas overexpression was not observed in IFN-gamma-/- mice, indicating that IFN-gamma is required for the delay of in vivo tumor growth. However, there was a significant increase of infiltrated T cells and in vivo apoptosis in Fas-overexpressing Renca tumors, and Fas-overexpressing Renca cells were also efficiently killed in vitro by T cells. In addition, a strong therapeutic effect was observed on Fas-overexpressing tumor cells by in vivo administration of anti-Fas Ab, confirming that overexpressed Fas provides a functional target in vivo for Fas-specific ligands. Therefore, our findings demonstrate that Fas overexpression on solid tumor cells can delay tumor growth and provides a rationale for therapeutic manipulation of Fas expression as a means of inducing tumor regression in vivo.

Complete molecular remissions induced by patient-specific vaccination plus granulocyte-monocyte colony-stimulating factor against lymphoma

Lymphomas express a tumor-specific antigen which can be targeted by cancer vaccination. We evaluated the ability of a new idiotype protein vaccine formulation to eradicate residual t(14;18)+ lymphoma cells in 20 patients in a homogeneous, chemotherapy-induced first clinical complete remission. All 11 patients with detectable translocations in their primary tumors had cells from the malignant clone detectable in their blood by PCR both at diagnosis and after chemotherapy, despite being in complete remission. However, 8 of 11 patients converted to lacking cells in their blood from the malignant clone detectable by PCR after vaccination and sustained their molecular remissions. Tumor-specific cytotoxic CD8+ and CD4+ T cells were uniformly found (19 of 20 patients), whereas antibodies were detected, but apparently were not required for molecular remission. Vaccination was thus associated with clearance of residual tumor cells from blood and long-term disease-free survival. The demonstration of molecular remissions, analysis of cytotoxic T lymphocytes against autologous tumor targets, and addition of granulocyte-monocyte colony-stimulating factor to the vaccine formulation provide principles relevant to the design of future clinical trials of other cancer vaccines administered in a minimal residual disease setting.

Molecular Mechanisms of Immune-Mediated Lysis of Murine Renal Cancer: Differential Contributions of Perforin-Dependent Versus Fas-Mediated Pathways in Lysis by NK and T Cells

Mice bearing the experimental murine renal cancer Renca can be successfully treated with some forms of immunotherapy. In the present study, we have investigated the molecular pathways used by NK and T cells to lyse Renca cells. Renca cells normally express low levels of Fas that can be substantially enhanced by either IFN-γ or TNF-α, and the combination of IFN-γ + TNF-α synergistically enhances cell-surface Fas expression. In addition, cells pretreated with IFN-γ and TNF-α are sensitive to lysis mediated by Fas ligand (FasL)-expressing hybridomas (dllS), cross-linking of anti-Fas Abs or soluble Fas (FasL). Lysis via Fas occurs by apoptosis, since Renca shows all the typical characteristics of apoptosis. No changes in levels of bcl-2 were observed after cytokine treatments. We also examined cell-mediated cytotoxic effects using activated NK cells and T cells from gld FasL-deficient mice, and perforin-deficient mice, as well as wild-type C57BL/6 and BALB/c mice. Interestingly, the granule-mediated pathway predominated in killing of Renca by activated NK cells, while the Fas/FasL pathway contributed significantly to cell-mediated killing of Renca by activated T cells. These results suggest that killing of Renca tumor cells by immune effector cells can occur by both granule and Fas-mediated cytotoxicity. However, for the Fas-mediated pathway to function, cell surface levels of Fas need to be increased beyond a critical threshold level by proinflammatory cytokines such as IFN-γ and TNF-α.

A tetrazolium-based colorimetric MTT assay to quantitate human monocyte mediated cytotoxicity against leukemic cells from cell lines and patients with acute myeloid leukemia

The MTT-colorimetric monocyte mediated cytotoxicity assay, based upon the ability of living cells to reduce 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide (MTT) into formazan, was evaluated using leukemic cells from five representative human leukemic cell lines and from 28 patients with acute myeloid leukemia (AML). An excellent linearity between absorbance and leukemic cell number was observed up to 5 x 10(4) cells/well and 50 x 10(4) cells/well for all cell lines and patients samples tested, respectively, in a 96-wells microtiter culture system. A huge variability in the susceptibility of leukemic cells to purified and IFN-gamma-activated human monocytes could be observed at effector-to-target cell (E:T) ratios of 1. The mean signal-to-noise ratio of the MTT assay for monocyte-leukemic cell mixtures from patients was 2.69 +/- 0.39 at E:T 1. In conclusion, the MTT based monocyte mediated cytotoxicity assay should be useful for studying the susceptibility of a variety of leukemic cells from cell lines and from patients with AML to monocytes in a rapid, sensitive and semi-automated manner.

Leukemic cell lysis by activated human macrophages: significance of membrane-associated tumor necrosis factor

In this study, we analyzed the mechanism(s) of leukemic cell lysis by human macrophages. Peripheral blood monocyte-derived macrophages were activated with recombinant interferon-gamma and lipopolysaccharide and their lytic activity against two leukemic cell lines (K562 and HL-60 cells) was assessed by an 111In releasing assay. Activated macrophages lysed these leukemic cells, and the lytic activity against leukemic cells was almost completely inhibited by anti-tumor necrosis factor (TNF) antibody. The macrophage-lysate prepared from activated macrophages also exhibited significant lytic activity against leukemic cells; this lytic activity was inhibited by anti-TNF antibody. The leukemic cells that we used for the cytotoxicity assays were resistant to recombinant TNF. The culture supernatant of activated macrophages did not show any lytic activity. These findings suggest that cell-associated TNF plays a role in macrophage-mediated cytotoxicity against leukemic cells.

Activation of cytolytic activity in peripheral blood monocytes of renal cancer patients against non-cultured autologous tumor cells

Our purpose was to evaluate the ability of blood monocytes of renal cancer patients to become cytotoxic against fresh, autologous tumor cells. Fresh target cells were obtained by mechanical enzymatic dissociation of tumor and normal renal tissue. The A375 cell line, derived from a human melanoma, and the SW626 cell line, derived from a human ovarian carcinoma, were used as positive target cell controls. Monocytes from renal cancer patients and normal volunteers were activated in vitro with lipopolysaccharide (LPS), or muramyl tripeptide (MTP-PE), or multilamellar vesicle liposomes containing MTP-PE (MLV-MTP-PE), with or without a pre-incubation with r-IFN-gamma, and tested for cytotoxicity in a 72-hr 111Indium-release assay. All patients were tumor-free at the time of the monocyte study. No difference in cytotoxic activity was observed between monocytes from healthy volunteers and those from cancer patients. Freshly dissociated tumor cells were as susceptible to tumoricidal monocytes as the 2 cell lines. Moreover, no cell population appeared to be resistant to activated monocytes, which were cytotoxic to both allogeneic and autologous fresh tumor cells. Activated monocytes maintained their ability to discriminate between normal and neoplastic cells and were not cytotoxic against autologous or allogeneic normal non-neoplastic cells. Our data indicate that MLV MTP-PE liposomes activate peripheral blood monocytes from cancer patients to a tumoricidal status against fresh, dissociated non-cultured autologous tumor cells.

Preservation of immune effector cell function following administration of a dose-intense 5-fluorouracil-chemotherapy regimen

In a phase II clinical trial of 5-fluorouracil (5FU) plus N-(phosphonacetyl)-L-aspartate (PALA) therapy administration, a number of slowly developing clinical responses were observed. Because of this, a variety of immune parameters were sequentially studied in 21 patients on this trial. Of the 21 patients studied, 20 provided sufficient samples to compare baseline with subsequent values, 10 of the 20 patients responded to treatment. Responders and non-responders did not differ in any studied parameter at baseline. After 2 months of therapy, non-specific monocyte cytotoxicity (NSMC), antibody-dependent monocyte cytotoxicity (ADMC) and natural killer (NK) activity were higher in the entire study population, but these increases were not statistically significant. When responders and non-responders were evaluated separately, it was apparent that the trend was due solely to the changes observed in the responding patient population. When mean lysis values for each patient group were determined for each studied time point, it was possible to generate a mean area under the cytotoxicity/time curve (AUC) for each studied parameter. NSMC and ADMC did not differ in responders and non-responders. However, NK activity was significantly greater by mean AUC analysis (P = 0.006) in the responding group; NK activity was maintained in the responders, but decreased in non-responders. When lymphocyte and monocyte expression of the surface markers beta 2-microglobulin, HLA-DR, CD56, HNK-1, CD16 and interleukin-2 receptor were evaluated, there were no differences among responders and non-responders at baseline by mean AUC analysis or when comparing baseline with non-baseline values. It is concluded that although baseline immunological characteristics do not identify patients who are likely to respond to weekly 5FU and PALA, treatment is not associated with deleterious effects on the immune effector function parameters evaluated in this study, there being no effects on expression of a variety of associated cell-surface molecules.

Separation of soluble amoebicidal and tumoricidal activity of activated macrophages

Macrophage-conditioned medium (M phi CM) prepared from mouse peritoneal macrophages activated in vivo with bacillus Calmette-Guérin (BCG) or Propionibacterium acnes and triggered with lipopolysaccharide in vitro contained tumoricidal and amoebicidal activity. The murine fibroblast cell line L929 was used as the indicator of tumoricidal activity and Naegleria fowleri amoeba was used to detect amoebicidal activity in M phi CM. The protease inhibitor, soybean trypsin inhibitor, decreased tumoricidal activity but had little effect on amoebicidal activity in M phi CM. Anti-TNF alpha antiserum inhibited tumoricidal activity in M phi CM. The antiserum reduced amoebicidal activity in BCG-activated M phi CM but had no effect on amoebicidal activity in P. acnes-activated M phi CM. Recombinant TNF alpha, rIL-1 alpha, or rIL-1 beta independently did not affect cytolysis of amoebae. Also, rTNF alpha had no effect on the growth of amoebae. Preparative flat-bed electrofocusing of BCG-activated M phi CM yielded fractions that exhibited different amoebicidal and tumoricidal activity profiles. Three domains of activity were analyzed (acidic, neutral, and basic). Anti-TNF alpha antiserum eliminated tumoricidal activity, but not amoebicidal activity, in fractions from the acidic domain. A combination of anti-TNF alpha and anti-IL-1 alpha antisera failed to eliminate amoebicidal activity in fractions from the basic domain. These results indicate that different factors are responsible for macrophage amoebicidal and tumoricidal activity. The amoebicidal factors in M phi CM affected cytolysis of several species of amoebae.

The interaction of Naegleria fowleri amoebae with murine macrophage cell lines

The present study was undertaken to determine whether murine macrophage cell lines exhibited in vitro amoebicidal activity comparable to that elicited by activated murine peritoneal macrophages. Peritoneal macrophages activated in vivo by bacillus Calmette-Guérin or Propionibacterium acnes demonstrated significant cytolysis of Naegleria fowleri amoebae. The macrophage cell line RAW264.7 also effected cytolysis of amoebae, but to a lesser extent than that elicited by activated peritoneal macrophages. However, the macrophage cell lines, J774A.1 and P388D1, did not exhibit amoebicidal activity. Macrophage conditioned medium prepared from RAW264.7 macrophages mediated cytolysis of L929 tumor cells but had no effect on N. fowleri amoebae. In addition, neither recombinant tumor necrosis factor nor recombinant interleukin-1 exhibited amoebicidal activity. Scanning electron microscopy of co-cultures revealed that N. fowleri bound to activated peritoneal macrophages and RAW264.7 macrophages. These results suggest that RAW264.7 macrophages treated in vitro with lipopolysaccharide are similar to macrophages activated in vivo in that they effect contact-dependent cytolysis of Naegleria fowleri amoebae. The RAW264.7 macrophages are unlike primary macrophage cultures in that they either do not release soluble amoebicidal factors into the conditioned medium or they release insufficient quantities.

Lysis of human leukemic cells by monocyte-derived macrophages activated with interferon-gamma and interleukin-2

Cytolysis of leukemic cells by peripheral blood-derived macrophages was examined by means of an in vitro 111In release assay. Monocytes prepared on culture dishes lyse YK-M2. However, when monocytes were cultured in vitro and transformed into macrophages, they lost most of their lytic activity. The addition of human recombinant interleukin-2 (rIL-2) on day 5 in culture enhanced the lytic activity significantly. Similarly, treatment of macrophages with human recombinant interferon gamma (rIFN-gamma) promoted the lysis of YK-M2 and K-562, although the extent of lysis was smaller than that by rIL-2. Macrophages activated with rIL-2 and rIFN-gamma also lysed human leukemic cells. Activated macrophages lysed leukemic cells of acute myelocytic leukemia more than acute lymphocytic leukemia cells. Macrophages derived from the peripheral blood of patients with leukemia were examined for their lytic activity against YK-M2. The patient's macrophages lysed more YK-M2 than did control macrophages when they were activated with rIL-2 and rIFN-gamma. The macrophages of two patients also demonstrated autologous leukemic cell lysis.

Differential in vitro modulation of suppressor and antitumor functions of mouse macrophages by lymphokines and/or endotoxin

Peritoneal macrophages of normal mice exhibited natural suppressor activity, as indicated by their ability to inhibit the proliferation of spleen cells in response to stimulation with phytohemagglutinin (PHA) or concanavalin A (Con A). Their suppressor function could be modulated in vitro with a variety of treatment regimens. High-dose lipopolysaccharide (LPS) (LPSH; 10 micrograms/ml) or lymphokines (supernatant from Con A-stimulated spleen cells) plus low-dose LPS (LPSL; 10 ng/ml) caused a reduction in the suppressor activity of adherent peritoneal macrophages. In contrast, these same treatments induced the macrophages to become tumoricidal and cytostatic for tumor cells, indicating a major dissociation between the regulation of suppressor and cytotoxic activities of macrophages. The lack of correlation between these activities was further demonstrated by macrophages that had been activated in vitro by Corynebacterium parvum: these cells expressed high tumoricidal and cytostatic activities, and also strong suppressor activity. The suppressor function could be selectively downregulated by in vitro pretreatment with LPSH.

Inhibition of pluripotent hematopoietic stem cells of bone marrow by large granular lymphocytes

Previous studies suggested that natural killer (NK) cells are involved in the regulation of the growth and differentiation of pluripotent hematopoietic stem cells. To establish whether the effector cells responsible for the in vivo resistance to bone marrow (BM) transplants and the in vitro inhibition of colony-forming units (CFU) may represent identical or overlapping populations, we used a rat system for syngeneic BM transplantation, with and without the transfer of large numbers of peripheral blood large granular lymphocytes (LGLs). BM reconstitution was measured by the in vivo formation of syngeneic CFU in the spleen (CFU-s). Because of the very low frequency of CFU-s in normal rat BM, we fractionated BM cells in Percoll density gradients, which provided a 2- to 5-fold enrichment in CFU-s in the lower-density fractions. Although these fractions contained less than 10% of the total cells, they contained greater than 75% of the CFU-s and allowed for the transfer of significantly fewer donor cells. At the time of BM transplantation, radiation-resistant asialoganglioside GM1-positive LGLs, with high NK activity, accounted for a significant percentage of the lymphoid cells in the irradiated recipient. The in vivo regulatory role of these cells on engraftment was demonstrated by their depletion (by i.v. injection of small amounts of anti-asialo-GM1 antiserum before BM transplantation), which resulted in a significant increase in the number of CFU-s. Conversely, a 50% inhibition in CFU-s was found when CFU-s-enriched BM fractions were preincubated in vitro with LGLs. Additional experiments, involving selective in vivo depletion of NK cells followed by LGL repopulation, directly demonstrated the involvement of LGLs in the regulation and growth of syngeneic pluripotent hematopoietic stem cells. Our results further support the hypothesis that LGLs are involved directly or via humoral factors in the homeostasis and regulation of hematopoietic stem cell growth and differentiation.

A murine macrophage cell line, immortalized by v-raf and v-myc oncogenes, exhibits normal macrophage functions

In vitro immortalized cell lines with the morphology and phenotype of mature macrophages (M phi) have been generated by infecting freshly isolated bone marrow cells from C3H/HeJ mice with a recombinant retrovirus carrying v-raf and v-myc oncogenes. All of the clones obtained had M phi-like phenotypes, and one such clone, GG2EE, has been compared to normal M phi to ascertain the effects of immortalization on the expression of the biological functions of the lines. GG2EE cells expressed cytotoxic activity against L5178Y, P815 or RL male 1 target cells in response to stimulation with interferon-gamma (IFN-gamma) and heat-killed Listeria monocytogenes; in contrast, they failed to kill YAC-1 target cells. GG2EE cells did not constitutively express I-A or I-E antigens; nevertheless, I region-coded antigens could be induced by IFN-gamma treatment. GG2EE cells produced interleukin 1 upon stimulation with a T cell-derived lymphokine; they were weakly phagocytic, yet became highly phagocytic following IFN-gamma treatment. Since c-fos mRNA is augmented in peritoneal exudate M phi by protein kinase C activators but not by IFN-gamma, we evaluated the effects of calcium ionophore, phorbol myristate acetate, L-alpha-1-oleoyl-2-acetoyl-sn-3 glycerol (OAG) and IFN-gamma on the levels of c-fos mRNA in GG2EE cells. We found that calcium ionophore, PMA and OAG stimulation enhanced the expression of c-fos mRNA, but IFN-gamma treatment did not. The kinetics of c-fos induction in GG2EE cells were also comparable to those observed in peritoneal exudate M phi. Overall, the GG2EE cell line has the same biological properties as normal tissue M phi. Because it is capable of both constitutive and inducible M phi-like functions, this cell line provides a valuable tool for studying the molecular mechanisms controlling induction and/or expression of biological activities in M phi. It is striking that a cell line immortalized in vitro by two oncogenes, v-raf and v-myc, behaves, according to the criteria mentioned above, like a normal M phi population.

Regulation of bone marrow cell survival in short-term cultures: a new macrophage function

The involvement of macrophages (M phi) in the regulation of bone marrow (BM) cell survival in short-term cultures was studied. We developed a system to measure the survival of fresh BM cells in vitro, by evaluating 111indium (111In) release from prelabeled BM cells. 111In release was proportional to cell death and inversely related to the number of trypan blue excluding cells. Upon 24 hr of culture in conventional medium, more than 50% of BM cells died. In order to investigate whether BM cell death could be reduced by coculture with other cell types, 111In-labeled BM cells were incubated for 24 hr with peritoneal M phi, thymocytes (THY), or polymorphonuclear cells (PMN) and then assayed for their survival. We found that coculture of BM cells with M phi dramatically increased BM survival, whereas THY or PMN consistently failed to enhance BM survival. The ability to promote BM cell survival, here designated nurse activity, represented a novel function of M phi and was further characterized. The stage of activation of M phi did not influence their nurse activity, since M phi elicited in vivo by proteose-peptone, thioglycollate, or Bacillus Calmette-Guérin, as well as resident M phi unstimulated or activated in vitro with lipopolysaccharide, equally sustained survival of BM cells. BM-derived M phi (adherent cells from BM cultures maintained in 20% L-cell-conditioned medium for 14 days) were equally effective in exerting nurse activity. Moreover, nurse activity was also exerted across the histocompatibility barriers. Supernatants from M phi cultures or killed M phi were ineffective. We propose that the nurse effect of M phi on BM is a primitive function that may play an important role in the development of the hemopoietic system.

In vivo cytotoxicity assays with 111In-labeled tumor cells: comparison with [125I]iododeoxyuridine-labeled cells and effects of chelators and inoculation site

The fate of cells inoculated in nude mice can be determined using human tumor cells prelabeled with 111In oxine (111InOx). To facilitate elimination of extracellular 111In released from killed cells, an appropriate metal chelating agent is administered to the host mice. With calcium disodium edetate administered by various routes, highly significant differences in the rates of 111In loss were observed for viable compared to killed cells after i.p. or i.m. inoculation. Radioactivity was eliminated at similar rates for mice bearing viable cells labeled with 111In or with [125I]iododeoxyuridine (125IUdR). For killed cells, 111In was eliminated somewhat less efficiently than 125I. The 111In-prelabeling method allows facile and sensitive determination of host-mediated cytotoxicity for inoculated tumor cells.

Interferon-mediated protection of B16 melanoma cells from cytotoxicity by activated macrophages

Corynebacterium parvum-activated macrophages (M phi), purified by adherence, were cytotoxic for B16 melanoma cells maintained in vitro. Pretreatment of the melanoma cells for 18 hr with interferon-alpha/beta or -gamma (IFN-alpha/beta or -gamma) caused a reduced susceptibility of the B16 cells to M phi-mediated cytotoxicity. The IFN-induced protective effect of B16 cells from cytotoxic M phi was found to be dose dependent. In addition, IFN-gamma was more protective than IFN-alpha/beta. The protective effect observed with partially purified IFN was reproduced by using highly purified IFN-alpha/beta or recombinant IFN-gamma. Monoclonal antibodies to IFN-gamma neutralized the protective effect provided by IFN-gamma. These results show that the susceptibility of a tumor cell line to killing by activated M phi can be altered by IFN pretreatment.

Augmentation of NK activity and/or macrophage-mediated cytotoxicity in the liver by biological response modifiers including human recombinant interleukin 2

Administration of several biological response modifiers (BRMs) to mice strongly augmented natural killer (NK) activity of leukocytes isolated from the liver. This augmentation of NK activity was induced by two synthetic molecules (MVE-2 and poly ICLC), by two BRMs of bacterial origin (formalin-fixed Propionibacterium acnes: P. acnes and a streptococcal cell wall preparation designated OK-432), as well as a single injection of human recombinant interleukin-2 (hrIL 2). All of these BRMs augmented NK activity in the liver to a greater degree than in the spleen. In addition, adherent leukocytes (greater than 90% macrophages) isolated from the liver following P. acnes administration also exhibited augmented macrophage-mediated cytotoxicity. This cytotoxicity was characterized as macrophage mediated and distinguished from NK activity, on the basis of adherence purification, kinetics of cytotoxicity, and target cell selectivity. The results demonstrate that a variety of BRMs induce augmented natural immunity in the liver and suggest that such organ-associated immune responses may play an important role in the antimetastatic effects of BRMs.

NIH/3T3 cells transfected with human tumor DNA containing activated ras oncogenes express the metastatic phenotype in nude mice

NIH/3T3 cells transfected with DNA from malignant human tumors produced experimental and spontaneous metastases in nude mice. In contrast, parent or spontaneously transformed NIH/3T3 cells failed to metastasize. The transfected clones contained either activated c-Harvey-ras or N-ras oncogenes. A representative clone (T71-17SA2) which was used to assess selected cellular and host factors relevant to the metastatic process produced lung metastases in 100% of the NIH nude mice recipients, secreted augmented levels of type IV collagenase, and invaded human amnion basement membrane in vitro. Expression of the metastatic phenotype was not related to decreased sensitivity to natural killer cells or macrophage-mediated cytotoxicity. Analysis of the cellular DNA from the T71-17SA2 transfectant and its corresponding metastases, both of which contained activated N-ras oncogenes, revealed a twofold increase in the N-ras-specific DNA sequences in the metastatic cells. Thus, transfection with human tumor DNA containing activated ras oncogenes can induce the complete metastatic phenotype in NIH/3T3 cells by a mechanism apparently unrelated to immune cell killing.

Modulation of formation of tumor metastases by peritoneal macrophages elicited by various agents

We have studied the formation of experimental B16 melanoma metastases in the lungs of mice inoculated IV with tumoricidal or nontumoricidal peritoneal macrophages elicited by various agents. IV inoculation of peritoneal M phi elicited by Brewer's thioglycollate medium (TG-M phi) 1 day before the injection of B16 melanoma cells dramatically increased the number of metastatic foci in the lungs. NIH thioglycollate broth and proteose peptone each elicited a relatively low number of M phi, which were morphologically distinguishable from TG-M phi and did not influence the yield of B16 melanoma colonies in the lungs. Resident or C. pravum-elicited M phi also did not augment metastasis formation. TG-M phi became highly tumoricidal after IP stimulation with poly I:C. However, tumoricidal TG-M phi inoculated IV 1 day before IV inoculation of B16 melanoma cells did not have an antimetastatic effect. On the contrary, both tumoricidal and nontumoricidal TG-M phi augmented metastasis formation. Poly I:C treatment had a substantial antimetastatic effect in the normal mice, but not in mice with adoptively transferred TG-M phi. Histological analysis revealed that IV-inoculated TG-M phi (tumoricidal or nontumoricidal, either viable or disrupted) induced severe intravascular reaction in the lungs, but not in the liver or kidney. This reaction manifested in the aggregation of the various blood cells, preferentially neutrophils. These reactions were not observed after IV inoculation of PM phi or NIH TG-M phi. Intravascular inflammatory reactions induced by TG-M phi may be responsible for the augmentation of metastasis formation, partly by suppression of NK reactivity and mostly by the acceleration of the processes of tumor cell extravasation. These data may provide some insight into the failure to achieve systemic adoptive immunotherapy using activated peritoneal TG-M phi.

NIH/3T3 cells transfected with human tumor DNA containing activated ras oncogenes express the metastatic phenotype in nude mice

NIH/3T3 cells transfected with DNA from malignant human tumors produced experimental and spontaneous metastases in nude mice. In contrast, parent or spontaneously transformed NIH/3T3 cells failed to metastasize. The transfected clones contained either activated c-Harvey-ras or N-ras oncogenes. A representative clone (T71-17SA2) which was used to assess selected cellular and host factors relevant to the metastatic process produced lung metastases in 100% of the NIH nude mice recipients, secreted augmented levels of type IV collagenase, and invaded human amnion basement membrane in vitro. Expression of the metastatic phenotype was not related to decreased sensitivity to natural killer cells or macrophage-mediated cytotoxicity. Analysis of the cellular DNA from the T71-17SA2 transfectant and its corresponding metastases, both of which contained activated N-ras oncogenes, revealed a twofold increase in the N-ras-specific DNA sequences in the metastatic cells. Thus, transfection with human tumor DNA containing activated ras oncogenes can induce the complete metastatic phenotype in NIH/3T3 cells by a mechanism apparently unrelated to immune cell killing.

Determination of cytotoxicity in vivo using 111indium-labeled human tumor cells

Loss of radioactivity from nude mice was determined after inoculation of human tumor cells prelabeled with [111In]indium oxine (111InOx). Elimination of 111In was increased somewhat by treating the mice with diphtheria toxin (DT), which is toxic selectively for human cells compared to mice. Calcium disodium edetate (CaNa2EDTA), a metal chelating agent, facilitated elimination of 111In and increased the difference in the rates of loss of radioactivity from mice bearing viable compared to DT-killed cells.

The inhibitory effect of phenothiazines on NK-mediated cytolysis of tumor cells

Non-toxic concentrations of fluphenazine caused a marked (90%) inhibition of NK-mediated cytolysis of YAC-1 tumor cells. The biologically inactive sulphoxide derivative was not inhibitory and the efficacy of inhibition of other compounds was directly correlated (r = -0.96, p less than 0.02) with their reported affinities for calmodulin. Fluphenazine may act on the earliest stages of the target-effector interaction since conjugate formation between CBA effectors and YAC target cells decreased from 20% to 6% (p less than 0.02) upon pre-treatment with fluphenazine. However, fluphenazine was not selective for NK cells since cytotoxic T lymphocytes, derived from both mixed lymphocyte culture and by concanavalin A stimulation, revealed depressed cytolytic activity against P815 tumor targets after fluphenazine treatment. Tumoricidal activity by activated macrophages and effectors of antibody-dependent cell-mediated cytotoxicity was also blocked. Fluphenazine inhibition was reversible, since addition of 1.25-5 micrograms/ml of the calcium ionophore A23187 to fluphenazine-treated effectors restored NK binding and cytolytic functions to normal levels. Calmodulin was isolated from NK-enriched populations by affinity chromatography on sepharose-fluphenazine columns. Pre-treatment of effector cells with [3H]fluphenazine and isolation of calmodulin by immunoprecipitation and SDS-polyacrylamide gel electrophoresis showed that fluphenazine entered the cells and bound a calmodulin-like molecule. These data are compatible with the suggestion that fluphenazine inhibits NK function by inactivating the calcium-calmodulin complex and thereby altering binding events in the target-effector interaction. Other actions of the phenothiazines are also possible.

Evidence for a gamma-interferon receptor that regulates macrophage tumoricidal activity

Gamma-interferon (IFN-gamma) is the macrophage-activating factor (MAF) produced by normal murine splenic cells and the murine T cell hybridoma 24/G1 that induces nonspecific tumoricidal activity in macrophages. Incubation of 24/G1 supernatants diluted to 8.3 IRU IFN-gamma/ml with 6 X 10(6) elicited peritoneal macrophages or bone marrow-derived macrophages for 4 h at 37 degrees C, resulted in removal of 80% of the MAF activity from the lymphokine preparation. Loss of activity appeared to result from absorption and not consumption because (a) 40% of the activity was removed after exposure to macrophage for 30 min at 4 degrees C, (b) no reduction of MAF activity was detected when the 24/G1 supernatant was incubated with macrophage culture supernatants, and (c) macrophage-treated supernatants showed a selective loss of MAF activity but not interleukin 2 (IL-2) activity. Absorption was dependent on the input of either IFN-gamma or macrophages and was time dependent at 37 degrees C but not at 4 degrees C. With four rodent species tested, absorption of murine IFN-gamma displayed species specificity. However, cultured human peripheral blood monocytes and the human histiocytic lymphoma cell line U937 were able to absorb the murine lymphokine. Although the majority of murine cell lines tested absorbed 24/G1 MAF activity, two murine macrophage cell lines, P388D1 and J774, were identified which absorbed significantly reduced amounts of natural IFN-gamma. Purified murine recombinant IFN-gamma was absorbed by elicited macrophages but not by P388D1. Normal macrophages but not P388D1 bound fluoresceinated microspheres coated with recombinant IFN-gamma and binding was inhibited by pretreatment of the normal cells with 24/G1 supernatants. Scatchard plot analysis showed that 12,000 molecules of soluble 125I-recombinant IFN-gamma bound per bone marrow macrophage with a Ka of 0.9 X 10(8) M-1. Binding was quantitatively inhibitable by natural IFN-gamma but not by murine IFN alpha. IFN-beta competed only weakly. Monoclonal antibodies against IFN-gamma either inhibited or enhanced MAF activity by blocking or increasing IFN-gamma binding to macrophages, respectively. These results indicate that IFN-gamma reacts with a receptor on macrophage in a specific and saturable manner and this interaction initiates macrophage activation.

Role of protein synthesis in the activation of cytotoxic mouse macrophages by lymphokines

The role of protein synthesis during the activation of macrophages (M phi) by lymphokines (LK) was studied. Peritoneal murine macrophages elicited by proteose-peptone (pM phi) were activated with LK (supernatants from normal mouse spleen cells pulsed with concanavalin A) and tested for cytotoxicity in an 18 hr assay against 111In-labeled L5178Y lymphoma target cells. Reversible (cycloheximide and puromycin) or poorly reversible (emetine and pactamycin) inhibitors of protein synthesis were added during activation, and their effects on pM phi-mediated cytotoxicity and pM phi protein synthesis were measured. Minimal concentrations of inhibitors, reducing the rate of protein synthesis by more than 90% without toxic effects on macrophages, were chosen. Exposure of pM phi to LK for 2 to 18 hr in the presence of reversible inhibitors of protein synthesis did not affect the induction of cytolytic activity, indicating that protein synthesis was not required during the activation period. In contrast, activation of macrophages for 2 hr in the presence of poorly reversible inhibitors of protein synthesis resulted in a considerable reduction of cytolytic activity. The impairment of cytotoxic activity was also evident when pM phi were treated with such drugs during the first 2 hr of an 18 hr exposure to LK or when LK-activated macrophages were treated for 2 hr with the drugs before the addition of the targets. These results demonstrate that active protein synthesis is not required during the exposure of pM phi to LK, but that new proteins have to be synthesized to allow the expression of the cytotoxic activity in LK-activated pM phi.

Cell mediated lympholysis; a modified technique using 111indium-oxine-labelled targets

The isotope 51Cr generally used in the cell mediated lympholysis (CML) assay suffers from the disadvantage of low specific activity, poor incorporation and high spontaneous release, limiting the CML assay to 4-6 h. We have labelled PHA derived human lymphoblasts with the isotope 111indium (using 111indium-oxine) and evaluated these cells as targets in CML. The level of 111In-oxine incorporation decreased rapidly in the presence of serum; in the absence of serum approximately 85% of the available isotope in the supernatant was incorporated into the blasts. Under the labelling conditions used, spontaneous release was 1.6-2%/h on average allowing an effector phase of 18 h. About 5-8% of the released isotope was reutilized by the effector cells during an 18 h incubation period. Extending the CML assay from 6 to 18 h greatly increased the cytotoxicity. At an effector to target ratio of 25:1, the average per cent specific release increased from 15 to 50%. The use of 111In-oxine labelled targets in the CML therefore increases the sensitivity of the test and allows fewer effector and target cells to be used as compared with 51Cr techniques.

Selective inhibition by monosaccharides of tumor cell cytotoxicity mediated by mouse macrophages, macrophage-like cell lines, and natural killer cells

A series of monosaccharides were tested for their ability to inhibit the effector phase of macrophage-mediated cytolysis against two susceptible murine tumor target cells, L5178Y and RL male I. Two monosaccharides, D-mannose and N-acetyl-D-galactosamine, were found to decrease cytotoxicity consistently in a dose-dependent manner. However, D-mannose preferentially inhibited lysis of RL male I target cells with little effect on lysis of L5178Y target cells, while the reverse was found with N-acetyl-D-galactosamine. Neither monosaccharide interfered with the activation of macrophages by polyinosinic:polycytidylic acid. Natural killer cell activity was decreased by a 25 mM concentration of D-mannose but not by N-acetyl-D-galactosamine, although increasing concentrations of N-acetyl-D-galactosamine were inhibitory. Neither monosaccharide affected cytotoxicity by alloimmune T cells. Cytotoxicity of macrophage-like cell lines against tumor target cells was also decreased by monosaccharides but the pattern of inhibition was different from that seen with activated macrophage effector cells. Both D-mannose and N-acetyl-D-galactosamine inhibited glucose oxidation by activated macrophages but only D-mannose significantly decreased protein synthesis of activated macrophages. These results indicate that monosaccharides can inhibit macrophage-mediated cytotoxicity in a selective manner with the pattern dependent on the tumor target cell used in the assay.

Assessment of in vivo natural antitumor resistance and lymphocyte. Migration in mice: comparison of 125I-iododeoxyuridine with 111indium-oxine and 51chromium as cell labels

Clearance of IV-injected tumor cells has been correlated with levels of natural killer (NK) cell activity in recipient animals. Studies of in vivo tumor cell clearance strongly suggest a relationship between levels of NK cell activity and antitumor or antimetastatic effector function. This study outlines the applicability of three radiolabels, [125I]iododeoxyuridine, ( [125I]dUrd), indium-111-oxine chelate ( [111In]Ox), and chromium-51 (51Cr), to studies of tumor cell clearance in vivo. The suitability of these labels for analysis of the in vivo migration patterns of normal lymphocytes or thymus-derived T cells cultivated in vitro (CTC) is also discussed. The results indicate that [111In]Ox and 51Cr compare favorably with the more widely used [125]dUrd as radiolabels for the assessment of IV-injected tumor cell clearance from the lungs of mice. The rates of clearance of both [111In]Ox and 51Cr, like that for [125I]dUrd, correlate closely with levels of NK-cell activity of the host. Further studies with [111In]Ox reveal that treatment of recipients with anti-asialo GM1 serum, a regimen known to suppress NK-cell activity, demonstrates the appropriate reduction in isotope clearance from the lungs after NK suppression. However, clearance data obtained by monitoring levels of radioactivity in the liver after IV injection must be viewed cautiously, since the same cells labeled with [111In]Ox and [125I]dUrd had a different pattern of clearance from the liver. The same inconsistencies in clearance were observed when [111In]Ox and [125I]dUrd were injected intrafootpad (i.f.p.). Similar effects were observed when [111In]Ox or 51Cr was applied to studies of CTC migration. Levels of [111In]Ox and 51Cr remained high in the liver after IV injection, while [125I]dUrd was rapidly cleared. Normal spleen or thymic lymphocytes exhibited the expected homing to the spleen after labeling with [111In]Ox, indicating a suitability of this label for migration studies, except possibly in the liver. These results with CTC and normal lymphocytes should be considered during the formulation of immunotherapy protocols based on cell migration data, since the choice of radiolabel can result in widely divergent levels of radioactivity accumulated in some organs, and may not provide an accurate representation of the presence of viable, intact, or functional cells.

Variation in selectivity of tumor cell cytolysis by murine macrophages, macrophage-like cell lines and NK cells

Several murine tumor-cell lines were tested by isotope release assays for their susceptibility to lysis by either activated peritoneal macrophages (apMPh), macrophage-like (MPh-like) cell lines, or natural killer (NK) cells. The qualitative selectivity of tumor-cell lysis by these different effector cells was quite disparate. The rank order of target cell susceptibility to lysis by apMPh in 24 h assay was L5178Y greater than P815 approximately equal to RL male greater than YAC-1 approximately equal to MBL-2. This was seen regardless of whether peritoneal MPh (pMPh) were activated by LPS or poly I:C. Two MPh-like cell lines, PU-5R and FC-1, had a pattern of cytotoxic activity against these target cells that closely paralleled that associated with apMPh, although levels of reactivity differed quantitatively among the effector cells. In contrast, the MPh-like cell line RAW-264 expressed a qualitatively different pattern of target-cell selectivity, preferentially lysing MBL-2, which was relatively refractory to lysis by other MPh-like cell lines or apMPh in the 24 h cytolytic assay. When spontaneous or interferon (IFN)-augmented NK activity was measured against the same panel of target cells, the pattern of selectivity was qualitatively different from that observed for apMPh. The consistent rank order of susceptibility to lysis by NK cells was YAC-1 greater than RL male 1 greater than P815 approximately equal to L5178Y approximately equal to MBL-2. The characteristic patterns of target-cell selectivity for apMPh or NK cells were the same for all of the strains of mice tested. From the different selectivity patterns of apMPh and NK cells, it is concluded that lysis of target cells is not based solely on inherent sensitivity to cytolysis. Instead, selectivity of lysis is probably due to variations in expression of target-cell structures recognized by each type of effector cell, and/or in susceptibility to the lytic mechanism(s) of the various effector populations.

Role of NK cells in the control of metastatic spread and growth of tumor cells in mice

The ability of BALB/c nude and C57BL/6 mice to eliminate tumor cells from the blood stream was severely impaired after a single inoculation of 0.2 ml of anti-asialo BMI (asGMI) serum, diluted 1:40 to 1:320. The number of i.v.-inoculated YAC-I cells surviving in the lungs of BALB/c nude mice pretreated with anti-asGMI serum was 28 times higher than in the control nude mice. In this respect, nude mice treated with anti-asGMI behaved similarly to beige mice. The increase in the initial survival of tumor cells in the mice that was induced by pre-treatment with anti-asGMI resulted in a substantial increase in the number of artificial lung metastases that developed. In C57BL/6 +/+ mice treated with anti-asGMI and in C57BL/6 beige mice, i.v. inoculation of B16 melanoma cells induced 10 times more metastatic foci in the lungs than in the control C57BL/6 +/+ mice. In contrast, in nude mice which possess higher levels of NK reactivity, metastatic growth was suppressed 7-fold in comparison with intact C57BL/6 +/+ mice. In beige mice and in C57BL/6 +/+ mice treated with anti-asGMI, multiple metastatic foci developed in the liver, whereas in control C57BL/6 +/+ and nude mice, no extrapulmonary metastases were found. These data indicate that B16 melanoma cells are able to grow in the liver, but their growth is ordinarily prevented by NK cells. The antimetastatic defense of C57BL/6 mice treated by anti-asGMI could be restored by transplantation of 40 X 10(6) normal spleen cells. This antimetastatic effect of transplanted spleen cells was mediated by asGMI-bearing cells, since after in vitro pre-treatment of normal spleen cells with anti-asGMI and complement, they lost their ability to inhibit the development of artificial metastases in the lungs of C57BL/6 mice. Suppression of NK reactivity by multiple injections of anti-asGMI (every 4 to 5 days), in C57BL/6 mice inoculated intrafootpad (i.f.p.) with B16 melanoma or 3LL tumor cells, did not influence the growth of local tumors, but dramatically accelerated the development of spontaneous pulmonary metastases. These data demonstrate that NK cells may play an important role in resistance to the dissemination of tumor cells, and therefore contribute to the control of metastasis formation in mice.

Augmentation of metastasis formation by thioglycollate-elicited macrophages

Inoculation of thioglycollate-elicited peritoneal exudate cells (PEC) into C57BL/6 mice reduced the rate of lung clearance of several intravenously (i.v.) injected murine tumor cells, and increased by up to 100-fold the number of artificially-induced metastatic lung nodules produced by the i.v. injection of B16 melanoma or Lewis lung carcinoma (3LL) tumor cells. Maximum effects were observed when PEC were injected either before, or shortly after, tumor cells. Modulation of lung clearance or metastasis formation was observed only with PEC and not with a variety of other cells, such as splenocytes, thymocytes P815 mastocytoma cells, or several macrophage-like cell lines (PU5-1.8 and IC-21). Lysates of PEC were as efficient in reducing lung clearance and augmenting metastasis formation as were intact viable PEC. Lysates of other cell types, including P815 and the macrophage-like cell lines, were unable to produce these effects. PEC populations, enriched for macrophages by adherence to plastic or by percoll density gradient sedimentation, also increased the number of B16-induced artificial metastasis, implicating the macrophage as the cell responsible for these observations.