Purification of a Tumoral Marker Recognized by Monoclonal Antibody Po66 and Associated with Human Lung Squamous Cell Carcinoma

Monoclonal antibody (MAb) Po66, a murine IgG1, was raised by immunization against human lung squamous cell carcinoma. When injected intravenously, Po66 showed prolonged retention in the tumor. It recognized an intracellular antigen. The human lung squamous carcinoma cell line SK-MES-1 expresses the antigen recognized by MAb Po66 and was used as a source of biological material for its purification. The SK-MES-1 cell line was labeled in culture with [35S]methionine and its lysate was immunoprecipitated with Po66 immobilized on Protein G-Sepharose. The precipitate contained three proteins (47, 50 and 69 kDa) absent in the controls. The 69 kDa polypeptide was further purified by anion exchange and immunoaffinity chromatographies. To date, no other tumor marker expressed in non-small cell lung cancer with these characteristics has been described and as such this marker is interesting for future use in immunotherapy and in diagnosis.

Biodistribution of 111indium-labeled macrophages infused intravenously in patients with renal carcinoma

PURPOSE

We have previously reported a clinical trial on the intravenous injection of autologous activated macrophages (AAM) in 15 patients with renal carcinoma. The present paper concerns scintigraphic investigations performed in 11 of these patients after injection of 111indium oxinate-radiolabeled AAM.

METHODS

AAM were prepared from mononuclear cells (MNC) collected by apheresis from patients treated simultaneously with granulocyte-macrophage colony-stimulating factor (GM-CSF). MNC were cultured for 6 days in the presence of GM-CSF and exposed for 18 h to gamma-interferon, the AAM were then separated by elutriation and injected.

RESULTS

After intravenous infusion, radiolabeled AAM were transiently retained in the lungs, where they predominated in the first hour. Later on, radioactivity accumulated in liver and spleen and then decreased from the first and second day, respectively. In one patient, two foci of radioactivity were detected in the lungs 1 h after injection, and persisted thereafter. Their association with tumor lesions was uncertain. This observation possibly resulted from the presence of granulocytes in the radiolabeled AAM populations of this patient. It seems that MNC collected from GM-CSF-treated patients and cultured in the presence of GM-CSF enables the differentiation of granulocytes.

CONCLUSIONS

A series of 11 investigations confirms the previously reported distribution pattern of intravenously injected AAM. It is possible that in patients treated with hematopoietic cell-mobilizing agents, granulocytes develop in cultures designed to produce monocyte-derived antigen-presenting cells.

Treatment of metastatic renal cell carcinoma with activated autologous macrophages and granulocyte--macrophage colony-stimulating factor

Fifteen patients with progressive metastatic renal cell carcinoma were treated with granulocyte-macrophage colony-stimulating factor and intravenous infusions of activated autologous macrophages (AAMs). The latter were prepared from leukapheresis-separated mononuclear cells cultured in the presence of granulocyte-macrophage colony-stimulating factor, exposed to gamma interferon, and submitted to elutriation to separate AAMs. Three intravenous injections of AAMs were performed within a 2-week interval. This treatment cycle was repeated once or twice, in cases of tumor response or stabilization. Ninety-seven preparations containing a mean 3 x 10(9) AAMs were administered and usually well tolerated. One partial response, eight stabilizations and six progressions were observed. The median time to progression and median overall survival time after inclusion were 7 and 9 months, respectively. The cells injected did not accumulate substantially in tumor lesions, as shown by scintigraphic imaging of indium-111-labeled AAMs. Thus, combined granulocyte-macrophage colony-stimulating factor and AAM treatment was well tolerated and resulted in transitory stabilization (n = 8) or partial regression (n = 1) in 9 of 15 patients.

Autologous human macrophages and anti-tumour cell therapy

Most technical problems concerning the production of human macrophages have been resolved by cultures in hydrophobic plastic, gas-permeable bags. This process enables collection of non-adherent macrophages and is well adapted to the safety requirements of cell therapy. Under optimized culture conditions, about one billion macrophages are currently obtained from a single leukapheresis product. In most clinical trials, macrophages have been activated by interferon-gamma (IFNgamma). The injections have little or no toxic effect. The anti-tumour activity of the intravenous (i.v.) administrations is more pronounced in certain protocols than in others. The mechanism remains poorly understood. In vitro, the cytolytic effect of macrophages requires cell-to-cell contact but macrophages injected i.v. show no particular tropism for tumour tissue. This could result from modifications in adhesion molecules occurring during monocyte-macrophage differentiation which might modify recruitment in inflammatory foci. Macrophages can, however, infiltrate tumour cell clusters, which could explain their improved efficacy when injected intratumorally (i.t.). Moreover, several arguments would favour the use of macrophages as human tumour antigen-presenting cells (APCs). In vitro, macrophages are as efficient as monocyte-derived dendritic cells (MDDCs) in stimulating cytotoxic T lymphocyte (CTL) clones or circulating CTL precursors.

Human monocyte-derived macrophages and dendritic cells are comparably effective in vitro in presenting HLA class I-restricted exogenous peptides

Recent experimental data have shown that mice could be immunized efficiently, in particular against cancer, by the injection of antigen-loaded dendritic cells (DC) or macrophages (MPH). In the present work, these two antigen-presenting cells (APC) were prepared in humans from circulating mononuclear cells (MNC). MPH were obtained from MNC that were cultured in hydrophobic plastic bags and purified by elutriation. DC were from the culture of adherent elutriation-purified monocytes in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). The two APC were prepared in parallel from the same donors and their phenotype and antigen-presenting capacity were compared. DC differed from MPH by a higher expression of HLA-DR and CD23 and a lower expression of CD14, CD64 and of adhesion molecules. DC and MPH were comparably effective in (a) enhancing the mitotic response of autologous lymphocytes to immobilized anti-CD3 (accessory function); (b) presenting melanoma peptides to specific cytotoxic T lymphocyte (CTL) clones; and (c) stimulating the generation of CTL directed against a myxovirus influenza peptide. However, DC were more effective than MPH in inducing the mitotic response of allogeneic peripheral blood leucocytes (PBL), possibly because of their higher expression of HLA class II molecules. In conclusion, DC and MPH prepared from blood MNC did not differ substantially in their ability to activate HLA class I-restricted T-cell responses by exogenous peptide presentation.

Generation of multinucleated giant cells by culture of monocyte-derived macrophages with IL-4

Culturing human monocytes in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) has been reported to provoke the formation of multinucleated giant cells (GCs). In the present work, GCs were generated in a two-step procedure in which macrophages were first differentiated from monocytes before being fused into GCs. The two cytokines used acted sequentially. GM-CSF was required for monocyte differentiation and IL-4 for macrophage fusion. Macrophages were purified from cultures of blood mononuclear cells maintained for 7 days in plastic bags. When seeded in conventional plastic-ware in the presence of IL-4, these macrophages showed an increased motility, spread in thin cytoplasmic lamellas, regrouped in clusters, and within 1-3 weeks, differentiated into GCs. Multinucleated cells also appeared in IL-4-untreated macrophage cultures but the number of nuclei did not exceed 2 or 3, compared with more than 30 in the presence of IL-4. Scanning electron microscopy of GCs showed highly developed pseudopods. GCs reacted with anti-CD11b, -CD54, -CD68, -HLA-ABC, and -HLA-DR monoclonal antibodies and AMH-152 but were CD14- and CD64-negative. Both untreated and IL-4-treated macrophages conserved pinocytic and phagocytic activity. Thus, IL-4 induced a differentiation process in which macrophages lost markers like CD14 and CD64, acquired an enhanced membrane motility, and fused in multinucleated GCs.

Expression of MAGE genes in esophageal squamous-cell carcinoma

The genes MAGE-1, -2, -3 and -4 are expressed in tumors of different histological types, but not in normal tissues, with the exception of testis and placenta. Short peptides derived from MAGE-1 and MAGE-3 gene products are recognized by cytolytic T lymphocytes when presented by HLA-class-I molecules, and represent potential targets for specific immunotherapy. We have determined whether esophageal carcinoma patients should be eligible for MAGE-peptide-based vaccine therapies. The expression of genes MAGE-1, -2, -3 and -4 in tumor samples was assessed by reverse-transcription and polymerase-chain-reaction amplification. Out of the 49 esophageal squa-mous-cell carcinomas studied, 53% expressed MAGE-1, 49% MAGE-2, 47% MAGE-3 and 71% MAGE-4. Eighty-four percent of the tumors expressed one or more of the four MAGE genes. Owing to the high incidence of MAGE gene expression in esophageal squamous-cell carcinoma, a large proportion of patients could be suitable candidates for immune therapies involving tumor-specific antigens encoded by MAGE genes.

Treatment of human lung carcinoma xenografts with a combination of 131I-labelled monoclonal antibody Po66 and doxorubicin

Po66, a mouse monoclonal antibody, is directed against an intracytoplasmic antigen present in human lung squamous cell carcinoma cells. In previous work it was found that the co-administration of 125I-radiolabelled Po66 and doxorubicin strongly enhanced the uptake of radioactivity by the tumour. The present-work was designed to evaluate, in a tumour-bearing mouse model of lung carcinoma, the ability of 131I-labelled Po66 to retard tumour growth when injected alone, or in combination with doxorubicin (8 mg kg-1 at 1-week intervals). A single dose of 550 microCi 131I-Po66 alone had no effect on tumour growth, whereas three fractionated doses of 250 microCi 131I-Po66 decreased it over two doubling times from 14.5 +/- 1.5 days for untreated control mice to 24.8 +/- 2.7 days. Mice treated with doxorubicin alone had a double tumour doubling time of 22.6 +/- 4.9 days, compared to 35.2 +/- 2.9 days (1.55-fold increase) in mice treated with doxorubicin and a single dose of 550 microCi 131I-Po66. Doxorubicin combined with three fractionated doses of 250 microCi 131I-Po66 provoked a twofold decrease in tumour growth compared to mice treated with doxorubicin alone. The administration of fractionated doses of 131I-Po66 simultaneously with doxorubicin resulted in a highly delayed mortality, which was not observed when 131I-Po66 was administered after doxorubicin. Thus, in a non-small-cell lung tumour model, a 131I-radiolabelled monoclonal antibody, directed against an intracellular antigen, significantly potentiated the effect of chemotherapy. Such a therapeutic approach could be used as an adjuvant therapy and improve the effect of chemotherapy on distant small metastases.

Adhesion molecule expression and response to chemotactic agents of human monocyte-derived macrophages

Human monocyte-derived macrophages have been proposed as agents of anti-tumour immunotherapy. The aim of the present study was to investigate in vitro the properties of these cells likely to control their recruitment to the sites of inflammation and tumours. The expression of adhesion molecules involved in the binding of monocytes to endothelial cells was modified during monocyte-macrophage differentiation, with a significant increase in CD11c, CD14 and intercellular adhesion molecule-1 (ICAM-1). Monocyte-derived macrophages were sensitive to chemoattractants, in particular to the monocyte-specific chemokine monocyte chemotactic protein-1 (MCP-1). They responded by an increased expression of adhesion molecules and were attracted by the cytokine in an under-agarose migration assay. The migration response, however, decreased after days 4-5 of monocyte differentiation into macrophage. In conclusion, human monocyte-derived macrophages show alterations of surface structures involved in the recognition of inflammatory endothelium. This may explain why the cells are poorly recruited to the sites of inflammation and tumours when introduced into the circulation.

Internalization of human macrophage surface antigens induced by monoclonal antibodies

Drugs intended to be endocytosed by macrophages may be transported by MAbs directed against these cells. Twenty MAbs were investigated for this purpose. The binding of these MAbs to macrophages obtained from a 7 day culture of blood monocytes showed that anti-CD11b and anti-CD14 recognized the highest number of cell surface antigen sites. Further assays determined that anti-CD63, Mo5 and anti-CD33 were the MAbs that induced the strongest modulation of the corresponding antigens, the highest rate being with anti-CD63. Endocytosis of antigen-antibody complexes was evidenced by the presence of MAbs in the cytoplasm. Anti-CD63 MAbs induced the highest internalization in this assay. For most MAbs, however, the density of antigen sites and the intensity of antigen modulation were not predictive of the amount of MAb detected in the cytoplasm.

Monoclonal antibody Po66 uptake by human lung tumours implanted in nude mice: effect of co-administration with doxorubicin

The efficacy of radioimmunotherapy of tumours with radiolabelled monoclonal antibodies (MAbs) depends on the amount of antibody taken up by the tumour and on its intratumoral distribution. In the case of MAbs directed against intracellular antigens, increasing the permeability of the cytoplasmic membrane may augment the bioavailability of the antigen for the antibody. This raises the question whether the induction of tumour necrosis by chemotherapy can enhance the tumour uptake of radiolabelled monoclonal antibodies. In this work, the effect of doxorubicin on the biodistribution of Po66, an MAb directed against an intracellular antigen, was studied in nude mice grafted with the human non-small-cell lung carcinoma cell line SK-MES-1. After injection on day 0 of 125I-labelled Po66, tumour radioactivity increased up to days 3-5, and then remained unchanged to day 14. The combined administration of 125I-labelled Po66 with 8 mg kg-1 doxorubicin, in two doses separated by 7 days, doubled the radioactivity retained by the tumour. Histological and historadiographic analysis showed, however, that the drug induced cellular damage. In the absence of doxorubicin, the accumulation of Po66 was restricted to some necrotic areas, whereas with doxorubicin the necrosis was more extensive and the antibody more evenly distributed. These results suggest that chemotherapy and immunoradiotherapy combined would enhance tumour uptake of radioisotope and promote more homogenous distribution of the radiolabelled MAb. This would promote eradication of the remaining drug-resistant cells in tumours.

Fate of mouse macrophages radiolabelled with PKH-95 and injected intravenously

Mouse macrophages purified by elutriation from thioglycollate-induced peritoneal exudate cells were labelled with indium-111-oxine and injected intravenously into mice. A substantial amount of unbound radioactivity remained in the circulation, suggesting that the radionuclide was not stably bound to the cells. Culture experiments with radiolabelled cells showed that indium-111 was released in the medium. Another cell marker, PKH-95, an iodine-125-labelled aliphatic compound insertable into the cell membrane, bound more stably than indium-111. Five minutes after injection of 125I-PKH-95-labelled macrophages, about 98% of the cells were in a non-circulating pool. It was checked that PKH-95 labelling did not compromise the viability and functions of the macrophages and that autologous erythrocytes and blood mononuclear cells labelled with PKH-95 remained in the circulation after i.v. injection. One hour after injection, 125I-PKH-95-labelled macrophages were distributed mainly in lung (36%), liver (19%) and spleen (5%). Subsequently, radioactivity decreased in the lung while increasing in liver, spleen and in an artificially induced footpad inflammation. The radioactivity accumulation in the inflammation persisted at least for 7 days. It represented a small proportion of radioactivity injected (0.2%) but was trapped very specifically in the inflammation. This raised the hypothesis that macrophages of the non-circulating pool could be released in the circulation and recruited into the inflammation with slow kinetics.

Biodistribution of monoclonal antibody Po66 in a human lung tumour-bearing mouse model: effect of blood exchange on tumour antibody uptake

We report a method designed to improve the specificity of tumour uptake after intravenous injection of an anti-tumour monoclonal antibody (MAb). It consists in increasing the blood clearance of the MAb injected in order to diminish its tissue activity, without altering tumour binding. Po66, an MAb directed against lung squamous cell carcinoma, was radiolabelled with 125I and injected i.v. into tumour-bearing nude mice. Radioactivity uptake by the tumour reached a plateau on days 3-5 which persisted up to day 14 after antibody injection. The radiolabelled Po66 remaining in the circulation on day 5 after injection was removed by means of exsanguination and blood transfusion. This blood exchange technique depleted circulating radiolabelled MAb by 60%, whenever mice had been injected with Po66 or an unrelated control IgG1. The proportion of radiolabelled Po66 taken up by the tumour 5 days after blood exchange did not differ substantially from that of non-exsanguinated controls (96.1% of controls). In contrast, there was a significant decrease in blood radioactivity (46% of control values on day 5). Blood exchange provoked a 1.8 fold increase in the tumour/blood and a 1.5-1.8 fold increase of the tumour/organ radioactivity ratios. After injection of unrelated radiolabelled IgG1, blood exchange reduced by 50% both blood and tumour radioactivity, and did not increase the tumour/blood or tumour/organ ratios. Hence, removal of 60% of circulating Po66, 5 days after its injection, did not affect the binding or retention of the antibody by the tumour, but would probably constitute a marked improvement if the antibody is used for two-phase radioimmunotherapy.

Characterization of amine oxidase activities in macrophages from human peripheral blood

A sensitive assay for the determination of hydrogen peroxide formation and a method for the identification and characterization of amine oxidases in cells and other oxidase sources of limited accessibility are described. The enzymes are characterized by substrate and inhibitor patterns. The method was applied to the identification and characterization of polyamine oxidizing enzymes in macrophages from human peripheral blood. The major oxidase activity in these cells was found to be a tissue-type polyamine oxidase, but with distinct characteristics. Diamine oxidase and monoamine oxidase activities were also detected in homogenates of macrophages. Since the formation of toxic products by a releasable polyamine oxidase is supposed to be an integral part of a regulatory function of macrophages, we consider our work as a basis for the elucidation of this function.

Interactions between human macrophages and tumor cells in three-dimensional cultures

Human blood mononuclear cells were cultured for 7 days in hydrophobic plastic bags. Macrophages differentiated from monocytes and purified by elutriation were then cocultured with round-shaped aggregates of epithelial cells (spheroids). Spheroids prepared from the SK-MES-1 carcinoma cell line were cultured individually, under constant stirring, in multiwell plates coated with agarose. Macrophage/spheroid interactions were investigated under various experimental conditions. Macrophages activated with interferon gamma aggregated to each other and to spheroids, in contrast to control unactivated macrophages. Histological examination, after staining with a macrophage-specific monoclonal antibody, showed that both control and interferon-gamma-activated macrophages migrated between epithelial tumor cells and infiltrated the spheroids. The addition of anti-ICAM-1 monoclonal antibody inhibited macrophage homotypic aggregation as well as aggregation to and penetration into spheroids. The macrophages did not exert cytolytic effects, as judged by a chromium-51 release assay, but provoked a diminution of tritiated thymidine incorporation by tumor cells. Cytostatic activity was observed with effector: target ratios as low as 1:16, and was maximal (99% at a 1:1 E:T ratio) with macrophages differentiated in the presence of granulocyte/macrophage-colony-stimulating factor. The cytostatic effect was not related to tumor necrosis factor alpha secretion.

Uptake and release of radiolabelled monoclonal antibody Po66 by multicellular aggregates obtained from a lung squamous carcinoma cell line

Po66, a monoclonal antibody (MAb) directed against lung squamous cell carcinoma, has been shown, when injected intravenously, to be retained for a long time in tumors. This property encouraged trials to use Po66 as an agent of metabolic radiotherapy. The suitability of multicellular spheroids to reproduce the in vivo conditions of irradiation of tumors by Po66 was investigated in the present work. Spheroids were formed from the lung carcinoma cell line SK-MES-1. They resembled morphologically small carcinoma nodules with desmosome-like intercellular junctions at the periphery and a central necrotic core. The cells expressing the antigen recognized by Po66 had a heterogeneous distribution and were predominant in the outer layers of the cell aggregates. Spheroids were exposed to radiolabelled Po66. The MAb diffused slowly and reached a maximal incorporation after 4-12 hours incubation. A control unrelated antibody did not penetrate appreciably. Autohistoradiographic experiments suggested that the antibody accumulated in most cells expressing the antigen. The rate of MAb release from the spheroids was very low (T 1/2 = 163 h). Taken together, the data indicate that spheroids might be a relevant model to investigate the parameters controlling Po66-mediated immunoradiotherapy.

111Indium-F(ab)'2-NCA 102 monoclonal antibody: in vitro study of a specific agent for the detection of inflammatory foci

A new antigranulocyte antibody was evaluated in vitro for the detection of inflammatory foci in man. The specificity for polymorphonuclear cells (PMN) of NCA 102, an anti-NCA 95 monoclonal IgG1, was determined with immunohistochemical and cytofluorometrical tests. Its affinity, assessed by Scatchard analysis, was 1.1 x 10(9) L/mol and the number of epitopes per granulocyte reached about 10(5). The biological properties of PMNs incubated with NCA 102 were not inhibited even when coupled with DTPA. A F(ab)'2 fragment was radiolabelled with 111Indium and incubated in the presence of whole blood. More than 65% radioactivity was selectively taken up by the PMN population. These findings indicated that NCA 102 antibody is suitable for sepsis detection.

Effect of an anti-HLA class I monoclonal antibody on the antigenic and transcriptional expression of HLA class I genes in U937 cells

The phenomenon of antigenic modulation was studied in the histiocytic lymphoma line U937. A redistribution of cell surface HLA antigen after incubation of U937 cells with the monomorphic anti-HLA class I monoclonal antibody W6/32 was demonstrated by immunofluorescence analysis. As assessed by hybridization of RNA obtained from W6/32-treated U937 cells with a probe corresponding to the alpha 3 domain of HLA Cw3, prolonged W6/32 incubation (24 to 72 hours) induced a decrease in HLA class I transcript abundance. This decrease was about 25% as compared with untreated control cells. These data indicate that W6/32 incubation can induce changes in HLA class I gene expression not only at the antigenic but also at the transcriptional level. Possible implications for the molecular basis of antigenic modulation are discussed.

Monoclonal antibody AP-282 recognizes a marker for human polymorphonuclear granules

Hybridoma AP-282 was produced by fusing mouse plasmacytoma cells with splenocytes of mice immunized against purified human polymorphonuclear cells. The secreted monoclonal antibody (MAb), AP-282, a mouse IgG1, was found to react strongly with all neutrophilic granulocytes, their bone marrow precursors, weakly with blood monocytes and not with eosinophils. The antigen was resistant to formalin fixation but was destroyed by exposure to fixatives containing acetic acid. Using the APAAP technique, antibody AP-282 strongly labelled neutrophils on sections of frozen cut or paraffin embedded tissues. No staining was seen of non hematopoietic tissues. AP-282 recognized an internal antigen associated to cytoplasmic granules. Chemical investigations on dot blots of whole or of purified cellular extracts indicated that the antigen idenfied by MAb AP-282 was different from those recognized by usual antigranulocyte antibodies, i.e. myeloperoxidase, elastase, cathepsin G and lactoferrin. Thus, antibody AP-282 constitutes a new cytoplasmic marker of neutrophils.

Activation of mouse macrophages by muramyl dipeptide coupled with an anti-macrophage monoclonal antibody

A rat IgG2a monoclonal antibody (mAb3A33) directed against the mouse Mac-1 antigen was conjugated with muramyl dipeptide (MDP) by using an intermediate polymer; under such conditions 75 MDP molecules were bound to one antibody molecule. A poly(L-lysine) polymer substituted with muramyl dipeptide and 3-(2-pyridyldithio)propionyl residues were prepared, the remaining lysine epsilon-amino groups were acylated with D-gluconolactone, leading to a neutral polymer; then a few polymer conjugates were coupled to mAb3A33 via a disulfide bridge. The binding capacity of the monoclonal antibody was preserved after conjugation with MDP-polymer molecules. Mouse peritoneal macrophages, incubated for 24 h with MDP-mAb3A33 conjugate became cytostatic against P815 mastocytoma cells, whereas unconjugated mAb3A33 and MDP-bound to a nonspecific rat IgG2a were ineffective. An enhancement of the cytostatic activity induced by MDP-mAb3A33 conjugate was obtained in the presence of gamma-IFN. These results show that several tens of MDP molecules can be linked to a macrophage-specific monoclonal antibody by using a neutral intermediate polymer without impairing the binding antibody capacity and that this type of MDP conjugate can efficiently activate macrophages and therefore could be the basis of the development of new antitumor therapy.

Monoclonal antibody AMH152 reacts with human monocytes in culture and with inflammatory macrophages

Monoclonal antibodies (mAb) raised against human peritoneal macrophages were selected for their non-reactivity with freshly sampled blood cells. One of these mAb, AMH152, initially non-reactive, bound to monocytes after 18 h of culture, a property which was not shared by an unrelated antibody of the same isotype (IgG1). The induction of the expression of the antigen detected by AMH152 on monocytes in culture was not influenced by the addition of serum or by the substrate used, plastic that favoured adhesion or teflon bags. Overnight incubation at 4 degrees C in adhesion conditions did not enable antigen expression. A 1-h treatment with phorbol myristate acetate or formyl-methionyl-leucyl-phenylalanine did not increase AMH152 binding. Culturing monocytes with cycloheximide tended to inhibit antigen expression. These observations suggested that antigen expression represents an active phenomenon, requiring protein synthesis. The antigen recognized by mAb AMH152 could be visualized on sections of formalin-fixed and paraffin-embedded tissues. Macrophages of healthy lymphoid organs and tissues that expressed CD68 antigen failed to bind AMH152. In contrast, chronic inflammatory lesions, like those of sarcoidosis, tuberculosis and cat scratch disease, contained epithelioid and multinucleated giant cells that reacted with AMH152. In serous exudates of cancer metastases, 10-40% of macrophages were also stained. The antigenic material was essentially present at the cell periphery. Thus, mAb AMH152 recognized a surface antigen, detectable on paraffin-embedded tissue sections, and which accompanied differentiation of monocytes into inflammatory cells. The expression of this antigen on monocytes in culture suggests that these cells underwent an activation process, even when maintained for some hours in teflon bags and in a serum-free medium.

Immunoscintigraphy of human lung squamous cell carcinoma using an iodine-131 labelled monoclonal antibody (Po66)

Monoclonal antibody (McAb) Po66 has been obtained by immunisation of mice against a human lung squamous cell carcinoma. The in vitro reactivity of the antibody with cancer cells and its ability to localise in human lung cancer xenografts growing in nude mice have been reported earlier. Presented here is the first clinical evaluation of the antibody for scintigraphic detection of tumours. Thirty-three patients with histologically confirmed primary non-small cell lung carcinoma were investigated. Twenty-seven of them were explored at the preoperative stage and six at 6 months after surgery. Biodistribution results were obtained from seven operated patients by combining injections of 131I-radiolabelled Po66 and of 125I-labelled unrelated immunoglobulin. The localisation index was three times higher for this specific antibody. Immunoscintigraphy detected 78% of primary tumours and 100% of recurrences. In this short series of patients, immunoscintigraphy proved helpful in the assessment of tumour spread in four patients by visualising localisations in the mediastinum or the contralateral lung which the CT scan had failed to demonstrate. Immunoscintigraphy was also more efficient than plain chest X-ray for the detection of local tumour recurrences.

Macrophage antigens associated with adhesion: identification by a monoclonal antibody specific for Lewis lung carcinoma cells

A monoclonal antibody specific for Lewis lung carcinoma (3LL) cells (Mab 5B5) was found to recognize antigens expressed on murine macrophages and on a macrophage hybridoma line upon cell adhesion on plastic surfaces. These antigens were also present on the surface of murine macrophage tumor M5076 cells which develop solid tumors and metastases. The M5076 tumor cells freshly isolated from the primary tumor and from hepatic metastases strongly bound Mab 5B5 but lost this capacity after adhesion. Freshly isolated thioglycolate-elicited peritoneal mouse macrophages were not labeled by Mab 5B5; however, after 1 h of adhesion, 50% of the adherent macrophages were directly incubated with Mab 5B5 prior to harvesting by scraping. Permeabilization of peritoneal macrophages by saponin showed that the antigens recognized by Mab 5B5 were present inside the cells before adhesion. Similar results were obtained with the 2C11-12 macrophage hybridoma cells. P388D1 cells (a weakly adherent macrophage tumor cell line), HL60 cells (a human promyelocytic cell line), and human monocytes were poorly labeled without permeabilization but were strongly labeled by Mab 5B5 upon permeabilization. The specificity of the monoclonal antibody in relation to the adherence capacity of these cells is discussed.

Blood clearance and organ distribution of intravenously administered polymethacrylic nanoparticles in mice

Polymethacrylic nanospheres (mean diameter 0.25-0.30 microns), prepared by aqueous emulsion copolymerization, were developed as a new site-specific drug delivery system. The nanoparticles were labeled either with indium-111 or iodine-125, and after a single iv injection of labeled particles into mice, their blood clearance and organ distribution were analyzed. A rapid clearance of 111In-labeled nanoparticles from the blood circulation to the mononuclear phagocyte system (MPS) was visualized using external scintigraphic imaging. From 10 to 60 min, radioactivity measurements in blood and organs (liver, spleen, kidneys, lungs, heart) showed that the 125I-labeled nanospheres were rapidly removed from the bloodstream (distribution half-life approximately 3-5 min) and mainly deposited in the liver (60% of the administered dose, 10 min after administration). Up to 1 h, radioactivity in heart and lungs remained insignificant, while in the kidneys, radioactivity levels increased from 8 to 11%.

Distribution of radiolabelled monoclonal antibody Po66 after intravenous injection into nude mice bearing human lung cancer grafts

Monoclonal antibody Po66, produced by immunization against a patient's lung squamous cell carcinoma was found suitable for the scintigraphic detection of human tumours. Surprisingly, the cellular antigen recognized by Po66 was abundant in the cytoplasm of tumour cells but could not be detected on the surface membrane. In the present work the biodistribution of radiolabelled Po66 and of an unrelated immunoglobulin were studied comparatively after intravenous injection into nude mice bearing lung squamous cell carcinoma grafts. Radioactivity distribution among mouse organs and tumour was analysed by gamma counting and autohistoradiography. After injection, radiolabelled Po66 decreased rapidly from the blood in tumour-bearing animals whereas, in controls, it remained at a level comparable to that of the unrelated immunoglobulin. The antibody seemed slowly trapped by the tumour and, 12 days after its injection, distribution ratios between tumour and mouse organs reached values of 20-30 as against 1 in animals injected with the non-specific immunoglobulin. Autohistoradiographic investigations in the tumour confirmed the slow diffusion rate of the antibody, which remained in the vascular spaces up to the 24th hour after injection and diffused afterwards throughout the clusters of tumor cells. Furthermore, radioactivity was detected in cells which, unexpectedly, seemed morphologically unaltered. These cells, the viability of which remains to be determined, were predominant in the central area of the tumours. The results presented constitute new evidence of the ability of an in vivo injected monoclonal antibody to reach a cytoplasmic target inside non-necrotic cells and suggest that the cells permeable to the antibody might be in defective nutritional conditions.

Characterization of the antigen identified by Po66. A monoclonal antibody raised against a lung squamous cell carcinoma

The mouse monoclonal antibody (mAb) Po66 has been shown in previous work to be localized in nude mice xenografts of human lung tumours when injected intravenously [Dazord L et al. (1987) Cancer Immunol Immunother 24: 263-268] and to be suitable for the scintigraphic detection of lung cancers in patients [Dazord L, et al. (1987) in Klapdor (ed) New tumour markers and their monoclonal antibodies. Georg Thieme, Stuttgart, New York, pp 444-450]. The nature of the antigen recognized by Po66 has been investigated in the present work and comparisons are made with antigens recognized by other mAbs prepared in the laboratory. These mAbs were raised either against lung squamous cell carcinoma (mAbs Po43, Po60), or against a bronchio-alveolar carcinoma (mAbs BAM33, BAM45, BAM54 and BAM69). Radioiodinated purified Po66 did not compete for cell binding with any other mAb. All Po and BAM mAbs reacted with tumour cells both cultured in vitro and grown in vivo. They recognized cytoplasmic antigens as judged by immunofluorescence examination of fixed cells or by immunoperoxidase staining of cancer tissues, but could never be visualized by immunofluorescence on the surface membrane of culture cells. The mAbs of the BAM series reacted with vimentin as demonstrated by immunofluorescence staining, showing alterations in the aspect of the filaments under the effect of colchicine. Radiolabelled mAbs Po43, BAM33 and BAM45 bound to partially purified cytoplasmic cytoskeleton components. In contrast, Po66 was never seen associated with intermediary filaments. The sensitivity to enzyme digestion of the antigen associated with Po66 was studied in comparison with those associated with Po43, BAM33 and BAM45. All antigens were sensitive to protease digestion while only the Po66-identified antigen was sensitive to periodate, neuraminidase and alpha-fucosidase. Thus, mAb Po66 identified an antigen of 47 kDa (as determined before) present in the cytoplasm but not related to the cytoskeleton, not detected on the cell surface and glycoprotein in nature.

Scintigraphic detection in mice of inflammatory lesions and tumours by an indium-labelled monoclonal antibody directed against Mac-1 antigen

The monoclonal antibody, 3A33, directed against Mac-1 antigen which is expressed essentially on macrophages and polymorphonuclear cells, was injected i.v. into mice, as part of an attempt to visualize inflammatory lesions and tumours by external scintigraphy. The monoclonal antibody, a rat IgG2a, was conjugated with a bifunctional chelating agent, diethylenetriaminepentaacetic acid at a 1:1 molecular ratio and complexed with 111-indium, a procedure which apparently did not alter its binding to peritoneal macrophages and provided relatively stable cell labelling. An unrelated rat IgG2a of unknown specificity radiolabelled in the same manner as 3A33 served as a control. The uptake of i.v. injected 3A33 by peritoneal macrophages was up to 50 times that of unrelated IgG2a. After i.v. inoculation, the antibody accumulated in the liver, spleen, lung, in foot-pad inflammatory reactions induced by injection of Freund's adjuvant and in experimentally grafted tumours. The 3A33: non-specific IgG2a uptake ratio in inflammatory lesions and tumours, however, was much lower than for peritoneal macrophages and was generally close to 2. This was sufficient to obtain scintigraphic images of inflammations and tumours. The images obtained after injection of 3A33 were clearly of better quality than those given by the non-specific immunoglobulin. They could be improved by subtraction of the vascular images obtained after injection of 99m-technetium serum albumin. The labelling of Mac-1-positive blood mononuclear cells by in vitro incubation with radioactive 3A33 was not intense enough to allow scintigraphic imaging after in vivo re-infusion but seemed more selective than the injection of whole antibody in detecting inflammatory reactions. These results seem interesting in view of the potential human application to the detection inflammatory lesions and the appreciation of tumour inflammatory components. Possible improvements in the technique are discussed.

Regulation of the expression on mouse T lymphocytes of the epitope identified by monoclonal antibody 3A35

Monoclonal antibody 3A35 (MA 3A35) has previously been shown to be an activation marker of macrophages and T lymphocytes. It immunoprecipitated from macrophages a 200-kDa molecule belonging to the T200 family and from T cells a 85-kDa antigen. In the present work, the factors controlling the expression of the epitope identified by MA 3A35 on polyclonal activated T cells and T-cell clones, as well as the ability of 3A35 alone or together with complement to interfere with T-cell functions, were investigated. Corticoresistant thymocytes unreactive with MA 3A35 became fully reactive after 2 days of in vitro stimulation by PMA and IL-2 and the level of reactivity per cell declined to a low level thereafter. In helper and cytolytic T-cell clones, the expression of the epitope defined by MA 3A35 was also maximal soon after antigenic stimulation then declined. In helper-T-cell clones, the epitope remained detectable during the entire culture period, whereas in cytolytic clones its expression was markedly reduced at the end of the culture. The lineage of cytotoxic T lymphocytes (CTL) as studied in a bulk culture of spleen cells primed in vivo against a syngeneic tumor exhibited similar regulation by antigenic stimulation. The CTL precursors were resistant to lysis by MA 3A35 plus complement; after 3 days of culture with the stimulatory antigen, they became highly sensitive but their sensitivity then diminished and mature CTL were completely resistant. MA 3A35 plus complement also killed the activated T cells which responded to macrophage-presented antigens and were thought to be mainly Lyt-1+. Therefore, the epitope identified by MA 3A35 was expressed predominantly at an early stage of T-cell activation. At a late stage, it persisted almost exclusively on helper and Lyt-1+ cells. In addition, MA 3A35 plus complement lysed NK cells, AK cells, and their precursors present in normal spleen. In the absence of complement, MA 3A35 had no detectable effect on T-cell functions.

A new epitope of the T200 molecule family defined by the 3A35 monoclonal antibody and expressed by macrophages and activated T lymphocytes

A monoclonal antibody (mAb), 3A35, produced against mouse macrophages (M phi) was found to react against certain activated T cells. This mAb, a rat IgM, resulted from a cell fusion between a mouse plasmacytoma and rat lymphocytes immunized against mouse M phi. It bound more avidly to activated than to resident M phi. It did not react against B cells and resting T lymphocytes but recognized certain dividing T cells like EL4 lymphoma, concanavalin A-activated and interleukin 2-expanded spleen cells, and helper T cell hybridomas. By contrast, other T lymphocyte-derived cell lines such as YAC-1 and CTLL2 were unreactive. No clear relationship was found between the binding of 3A35 to cells and the expression of L3T4 and Lyt-2 antigens. The specific stimulation of T cell clones with antigen rapidly induced a strong reactivity with 3A35 mAb which declined thereafter to a low (helper clones) or non-reactivity (cytotoxic clones) after 10 days of culture. Immunoprecipitation experiments, performed with M phi derived from bone marrow cell cultures, surface iodinated with 125I or metabolically labeled with [35S]methionine, showed that 3A35 bound to a 200-kDa molecule, shifting to 175 kDa under reducing conditions. In peritoneal M phi activated in vivo, in addition to the 175-kDa band, new bands migrating at 140, 120 and 85 kDa were identified by 3A35 and could be absorbed on a commercial anti-T200 mAb bound to Sepharose beads. After strengthening the cell binding of 3A35 to EL4 lymphoma cells by a cross-linking agent, only a 85-kDa molecule was immunoprecipitated. Thus, 3A35 identifies a new epitope of the T200 molecule family which is expressed on M phi and activated T cells.

A monoclonal antibody (Po66) directed against human lung squamous cell carcinoma immunolocalization of tumour xenografts in nude mice

Po66, a mouse IgG1 monoclonal antibody, was produced by immunization against a patient lung squamous cell carcinoma. The tissue reactivity of the antibody was measured by a radioimmunological assay with enzymatically dissociated cells, by an immunofluorescence test on frozen tissue sections and by peroxidase-staining of paraffin sections. The antibody bound to lung squamous cell carcinoma, oesophagus carcinoma and, inconsistently to lung adenocarcinoma but not to the other tumours tested. Some normal tissues also reacted positively, in particular bronchial serous glands, oesophagus epithelium and renal distal and collecting tubules. In normal and malignant tissues showing epithelioid differentiation, Po66 bound to the intermediate maturation area. The antigen immunoprecipitated by Po66 from lung squamous cell carcinoma appeared as a single band with a molecular weight 47,000 to 50,000 daltons. Purified monoclonal antibody Po66 and an unrelated IgG1 immunoglobulin were labelled with radioactive iodine and injected i.v. into nude mice bearing subcutaneous xenografts of human lung squamous cell carcinoma. The localization index in the tumour was 3.3. Antibody labelled with 131I allowed gamma-scintigraphic imaging of the xenografts which were clearly outlined by days 9 to 11.

A monoclonal antibody (3A33) that reacts with a mouse-specific epitope of Mac-1 antigen

The 3A33 monoclonal antibody, obtained by fusing rat immune lymphocytes with mouse plasmacytoma cells, was directed against mouse macrophages. Antibody 3A33, a rat IgG2a, reacted with macrophages from all the mouse strains tested, with mouse blood monocytes and with 56% of bone marrow cells, but not with T lymphocytes. It immunoprecipitated an antigen with alpha and beta subunits, found to be identical to Mac-1 antigen after cross-absorption experiments with M1/70 monoclonal antibody. The two antigenic determinants of the Mac-1 molecule identified by the 3A33 and M1/70 antibodies both displayed reduced expression on inflammatory macrophages and comparable resistance to trypsin digestion. The sites of the determinants on this molecule seemed close together judging from the ability of both the 3A33 and M1/70 antibodies to block C3bi receptor sites and compete for cell binding. However, unlike antibody M1/70, 3A33 never reacted with human cells bearing Mac-1 antigen. Therefore, two closely related epitopes of the Mac-1 molecule - one specific for mouse and one common to mouse and man, were recognized by these monoclonal antibodies.

Modulation of expression of mouse macrophage surface antigens by monoclonal antibodies

Mouse macrophages from peritoneal cavity were exposed to monoclonal antibodies (MAbs) directed against cell surface antigens and the effect on antigen expression was investigated. The two Mabs used, 3A33 and 3A35, were produced by cell fusion between a mouse plasmacytoma and rat lymphocytes immunized against mouse macrophages. The binding of the MAbs to cell surface was measured by immunofluorescence and flow cytometry or by a radioimmunological technique. When injected i.p. the MAbs diminished the expression of the corresponding antigens but did not alter it when added to cultures of adherent macrophages. Antigenic modulation, however, could be produced in vitro either by inhibiting macrophage adherence during incubation with MAbs or by using a second antibody layer. MAb 3A33 (IgG2a) was more effective than 3A35 (IgM) in provoking modulation. The appearance of re-synthesized antigens on cell surface was not affected by macrophage adherence. The modulated antigens were found to internalize into cytoplasmic vacuoles.

Diminution of circulating polymorphonuclear leucocytes by administration of a monoclonal antibody reacting with granulocytes and monocytes

The monoclonal antibody 3A35 which binds mouse polymorphonuclear leucocytes (PMN) and monocytes was injected intravenously (i.v.) into normal mice. A great diminution of circulating PMN was observed. The percentage of PMN passed through a minimum (2.5%) 20 min after antibody injection and returned to normal value (18.3%) within 24 h. After repeated daily injections, the ability of the antibody to induce granulopenia attenuated. Moreover, mice bearing the 3A35-producing hybridoma as an ascitic tumor had a normal percentage of blood PMN and a normal granulopoiesis as judged from bone marrow cytological examination. Thus, the monoclonal antibody produced a transitory diminution of PMN but could not induce a lasting granulopenia.

Red blood cell polyamines in mice bearing the Lewis lung carcinoma (3LL) and in patients with bronchopulmonary cancers

Experimentally, during Lewis lung carcinoma (3LL) growth, the red blood cell (RBC) polyamine levels increase with tumor volume and are inversely correlated to tumoral concentrations of spermidine and spermine. The RBC level of spermidine is continually correlated to both the volume and the tumoral concentration of this polyamine. Clinically, high levels of RBC polyamine are observed in cases of squamous-cell carcinoma or anaplastic cancer, and not in cases of adenocarcinoma. RBC polyamine levels only permit the establishment of statistical differences between groups of patients. Therefore, clinical use of these molecules as tumor markers depends on an understanding of polyamine distribution within blood.

An anti-mouse macrophage monoclonal antibody reacting with T-derived leukaemic cells

Hybridomas secreting anti-mouse macrophage antibodies were obtained by fusing a murine plasmacytoma with lymphocytes of a rat immunized against mouse macrophages. An IgM, monoclonal antibody (3 A 35) reacted with mouse monocytes, macrophages and polymorphonuclear leucocytes. It did not bind appreciably to erythrocytes, platelets and unstimulated T or B lymphocytes. However, 3 A 35 bound to various murine T-derived leukaemic cells and to a small proportion of Con A-stimulated thymocytes. Cross absorption experiments confirmed the existence of a common antigenic determinant on macrophages and leukaemic cells. The possibility that 3 A 35 identified a previously described antigen common to macrophages and normal or leukaemic T cells was investigated. The antibody was tested against thymocytes and macrophages of various mouse strains, some congenic for H-2 or T1a. The 3 A 35-detected antigen was found to be different from Ly5, Tla and Qa and did not represent a I-J encoded allotypic specificity.

Phase I study of immunotherapy by live Brucella abortus (strain 19 BA) in cancer patients

Twenty-eight patients showing negative responses against Brucella antigens were included in a preliminary trial of immunotherapy by a live Brucella abortus vaccine. Seventeen patients had squamous cell lung carcinoma, eight had acute myeloid leukemia, and three were classified as "others." Brucella abortus strain 19 BA was administered sc in a single injection at doses ranging from 5 X 10(7) viable organisms to 10(10), ie, 40 times the usual vaccine dose. No important toxicity was noted. Edematous reactions at the injection site and febrile responses were infrequent and moderate, hemocultures were all negative, spleen volume did not vary significantly, and cbc showed an increase of polymorphonuclear cells and lymphocytes.

Antitumor activity of cell walls from Brucella abortus

The ip inoculation of inactivated Brucella abortus, strain B19 R, protected mice against a subsequent graft of an ascites lymphoma. The bacterial components responsible for this effect were investigated. Centrifugation supernatants of sonicated bacteria supposed to contain mainly cytoplasmic products did not offer protection against the lymphoma. Cell walls (CW's) prepared by enzyme digestion of pellets of lysed bacteria and checked for purity by electron microscopy prolonged survival of mice and induced cytotoxic macrophages in their peritoneal cavities. CW peptidoglycan (PG) did not seem to play an important part in this effect. Enzyme digestion of CW, in particular by lysozyme, was found to reduce a PG characteristic component (diaminopimelic acid) without altering CW antitumor activity. Conversely, a purified PG preparation did not influence tumor growth. Extraction of CW by an ether:water mixture did not alter its antitumor activity, while incubation in NaOH abolished its activity almost completely. All CW preparations were found to elicit hypersensitivity reactions in Brucella-infected animals.

Differentiation of cytotoxic adherent cells from peroxidase positive cells after intraperitoneal injection of Brucella abortus organisms

The relations between the cytotoxic adherent cells (CAC) and the peroxidase positive adherent cells (PPAC) which appeared after i.p. injection of Brucella abortus were investigated. A kinetic study showed that PPAC preceeded CAC. Twenty-four hours after bacterial injection, almost all adherent cells stained for peroxidase and no cytotoxic activity could be recorded. Cells sampled at this moment acquired cytotoxic properties by cultivation in LPS containing medium. The treatment of the bacterial organisms by HCl or chloroform: methanol (C:M) suppressed their ability of inducing CAC but not that of inducing LPS-activatable PPAC. The substances extracted by C:M could activate PPAC into CAC in vitro. The data presented suggest that CAC differentiate from PPAC, that the recruitment of PPAC is not always followed by their transformation into CAC and that different components of the bacterial organisms might be necessary to achieve the steps of cell recruitment and maturation.

Increased resistance to tumor graft in mice infected by vaccinal strains of Brucella abortus

Kinetics of proliferation in vivo and the effect on murine tumors of the vaccinal strain Brucella abortus B19 and two derivatives, 19BA and B19R, were studied. Inocula of 5 x 10(6) organisms of each strain produced comparable infections peaking on day 8. Several protocols of Brucella treatment yielded favorable results in EL4 lymphoma and Lewis tumor. The treatment for EL4 lymphoma seemed optimal 8--14 days after infection with 5 x 10(6) -- 5 x 10(7) organisms. In comparison with BCG, Brucella grew faster in vivo and accumulated more in the spleen. The effects of BCG and Brucella were comparable on EL4 lymphoma, but BCG was less effective than Brucella on Lewis tumor. The results encourage trials using live Brucella vaccine as an antitumor agent in man.

Resistance to tumor graft in mice treated with inactivated Brucella abortus cultured in smooth or rough phase

Because killed Brucella abortus organisms cultured in smooth (S) or rough (R) phase were known to differentially influence humoral and cellular immune responses and to differ in their effects on T-dependent responses, the antitumor properties of killed B. abortus organisms, cultured in S- or R-phase and then inactivated, were compared in (C57BL/6 X DBA/2)F1 female mice with the use of 6 different transplantable tumors. In solid tumors, the antitumor effects produced by S-preparations were never improved by R-preparations. However, in ascites tumors, R-preparations gave the best antitumor results. These findings suggested that the defense mechanisms acrivated by immunostimulants may differ according to the site of tumor implantation. Among the other experimental factors studied, the route of B. abortus administration had a prominent role. Local injection at the site of tumor implantation before or after the graft gave better results than did systemic treatment. Systemic treatment could enhance the growth of Lewis tumor when applied 5 or 10 days before tumor graft but generally had an antitumor effect when given 1 day after the graft.

Modulation of immune response by killed Brucella abortus organisms: comparison of the effects of smooth and rough strains on T-dependent responses

Inactivated Brucella abortus organisms of the smooth (S) or rough (R) strain were tested comparatively on two T-dependent immune responses: mixed-lymphocyte reaction and delayed-type hypersensitivity. The intravenous injection of S organisms depressed the two tests, whereas R organisms increased mixed-lymphocyte reaction and did not alter delayed-type hypersensitivity significantly. This observation may be helpful in understanding the differences in adjuvant properties of S and R brucellae.

Influence of the antigenicity of Brucella preparations on modulation of the immune response to sheep erythrocytes

The relationship between the expression of surface antigenicity of inactivated Brucella and the immunostimulant properties on the sheep erythrocyte response was studied in mice. The agglutinogenic Brucella abortus B19S preparation was compared to two non-agglutinogenic preparations (B19R and PB), using the plaque-forming and rosette-forming cell tests. When Brucella and antigen were injected together, only non-agglutinogenic preparations, even used at low doses, were able to increase the plaque-forming and rosette-forming cell responses measured 4 days after immunization. When the interval between the previous injection of non-agglutinogenic preparations and that of the antigen increased or when they were injected 24 h after the antigen, the modification of those two responses was no longer observed. After day 4, for the simultaneous injection of Brucella and antigen, B19S and PB preparations induced the best responses; this effect was dose dependent. Thus, in the present experimental situation, the modification of the day 4 response appeared independent of those of the ensuing days.

[Inhibition of antigenic competition by immunostimulants]

The diminution of immune response against SRBC induced in mice, by a prior injection of HRBC was counteracted by addition of certain immunostimulants to SRBC. The intensity of inhibition of antigenic competition was related to the quantity of immunostimulant added to SRBC. Some immunostimulants (B. abortus, lipopolysaccharide) were more active than others (C. parvum, Poly I : C). To inhibit antigenic competition immunostimulant had to be injected after or in mixture with SRBC never before.