Api m 10, a genuine A. mellifera venom allergen, is clinically relevant but underrepresented in therapeutic extracts.

BACKGROUND: Generalized systemic reactions to stinging hymenoptera venom constitute a potentially fatal condition in venom-allergic individuals. Hence, the identification and characterization of all allergens is imperative for improvement of diagnosis and design of effective immunotherapeutic approaches. Our aim was the immunochemical characterization of the carbohydrate-rich protein Api m 10, an Apis mellifera venom component and putative allergen, with focus on the relevance of glycosylation. Furthermore, the presence of Api m 10 in honeybee venom (HBV) and licensed venom immunotherapy preparations was addressed. METHODS: Api m 10 was produced as soluble, aglycosylated protein in Escherichia coli and as differentially glycosylated protein providing a varying degree of fucosylation in insect cells. IgE reactivity and basophil activation of allergic patients were analyzed. For detection of Api m 10 in different venom preparations, a monoclonal human IgE antibody was generated. RESULTS: Both, the aglycosylated and the glycosylated variant of Api m 10 devoid of cross-reactive carbohydrate determinants (CCD), exhibited IgE reactivity with approximately 50% of HBV-sensitized patients. A corresponding reactivity could be documented for the activation of basophils. Although the detection of the native protein in crude HBV suggested content comparable to other relevant allergens, three therapeutical HBV extracts lacked detectable amounts of this component. CONCLUSION: Api m 10 is a genuine allergen of A. mellifera venom with IgE sensitizing potential in a significant fraction of allergic patients independent of CCD reactivity. Thus, Api m 10 could become a key element for component-resolved diagnostic tests and improved immunotherapeutic approaches in hymenoptera venom allergy.

Growth arrest of solid human neuroblastoma xenografts in nude rats by natural IgM from healthy humans.

Neuroblastoma (NB) is the most common extracranial solid neoplasm of infancy and is associated with very poor prognosis in patients with advanced disease. Current therapeutic regimens of advanced NB which combine surgical resection with radiation therapy and/or chemotherapy brought some improvements, but in a significant number of patients, a cure remains elusive. Normal human serum of healthy adults contains natural IgM antibodies that are cytotoxic for human NB cells. In this study, we evaluated the anti-NB activity of these natural IgM antibodies in nude rats bearing solid human NB tumors. A single intravenous (i.v.) injection of purified cytotoxic IgM led to uptake of IgM into the tumors with massive perivascular complement activation and accumulation of neutrophil granulocytes after 24 hours. Five consecutive i.v. injections of purified cytotoxic IgM into NB-bearing animals resulted in complete growth arrest of even large and established solid tumors which lasted for several weeks after discontinuation of the injections, whereas tumors of control animals continued to grow exponentially during the observation period. These studies suggest that natural anti-NB IgM may have a potential as a novel therapeutic modality in the treatment of human NB.

Resistance of human melanoma cells against the cytotoxic and complement-enhancing activities of doxorubicin.

The anticancer agent doxorubicin has two different effects on human SK-MEL-170 melanoma cells: the well known direct cytotoxicity and a marked enhancement of their susceptibility to killing by the R24 monoclonal anti-GD3) ganglioside antibody and human complement. This complement-enhancing effect of doxorubicin is also present after covalent immobilization onto glycerol-coated glass beads preventing cellular uptake of the drug (M. Panneerselvam, R. Bredehorst, and C-W. Vogel, Proc. Natl. Acad. Sci. USA, 83: 9144-9148, 1986). In order to investigate the effect of doxorubicin resistance on the complement-enhancing activity of the drug, we have established a doxorubicin-resistant SK-MEL-170 subline. The development of drug resistance in these melanoma cells was associated with multiple phenotypical changes including an increased expression of at least four high molecular weight plasma membrane proteins or glycoproteins with molecular weights of approximately 220,000, 180,000, 150,000, and 130,000, respectively. The drug-resistant cells accumulated doxorubicin at approximately 2-fold lower amounts in accordance with a 2-fold higher efflux of doxorubicin from these cells. The basal complement susceptibility of the doxorubicin-resistant cells was reduced by more than 60% presumably as a result of the observed reduced expression of GD3 sites and decreased binding of C3b. Most importantly, the doxorubicin-resistant cells were also resistant against the complement-enhancing effect of the free and immobilized drug. The two doxorubicin resistance phenomena, the resistance to the cytotoxic and to the complement-enhancing activities of the drug, seem to be fundamentally different: (a) to achieve comparable cytotoxic and complement-enhancing effects on drug-sensitive and -resistant SK-MEL-170 cells, the drug-resistant cells required 178-fold higher concentrations of free doxorubicin for the cytotoxic effect but only 5-fold higher amounts of the free drug and 12-fold higher amounts of the immobilized drug for the complement-enhancing effect; (b) resistance against the cytotoxic activity of doxorubicin is associated with reduced intracellular drug accumulation, while the data obtained with immobilized doxorubicin indicate that resistance to the complement-enhancing activity of the drug is independent of cellular drug uptake. These data suggest that different mechanisms are responsible for the two resistance phenomena in doxorubicin-resistant melanoma cells.

A novel metastatic animal model reflecting the clinical appearance of human neuroblastoma: growth arrest of orthotopic tumors by natural, cytotoxic human immunoglobulin M antibodies.

Neuroblastoma (NB), the most common extracranial solid tumor in childhood is associated with poor prognosis in patients with advanced tumor stages. Natural human cytotoxic anti-NB IgM antibodies present in the serum of healthy humans are discussed as a potential novel immunotherapeutic regimen against human NB because these antibodies have been shown to affect growth arrest of solid s.c. xenografts of human NB in nude rats. Subcutaneously induced tumors, however, exhibit a different growth pattern compared with the typical growth pattern of NB tumors in humans. Therefore, we developed in this study a novel metastatic tumor model in nude rats that reflects the clinical appearance of human NB and used this model to study the therapeutic efficacy of human anti-NB IgM. Intra-aortal injection of human NB cells in nude rats resulted in the development of large invasive adrenal gland tumors and micrometastases in the liver and bones. Apparently, adrenal glands provide most favorable growth conditions for human NB cells, as documented by the preferential and rapid growth of NB cells in this location. We studied three different treatment protocols of natural human anti-NB IgM. Anti-NB IgM completely inhibited tumor formation and metastases when injected simultaneously with human LAN-1 NB cells (P < 0.05). When antibody treatment was started 6 days after tumor cell injection (i.e., micrometastatic stage), tumor growth was inhibited by 90% (P < 0.05). An anti-NB IgM therapy directed against established tumors (14 days after tumor cell injection) shrank adrenal gland tumors by 90% (P < 0.05). Analysis of the tumors revealed both complement activation and an induction of apoptosis as two independent mechanisms of antitumor function. This study strongly suggests human anti-NB IgM antibodies as new agents for the therapy of neuroblastoma.

Molecular basis of complement resistance of human melanoma cells expressing the C3-cleaving membrane protease p65.

The molecular mechanism of complement resistance of the human SK-MEL-170 melanoma cell line was investigated. The cells have been shown to express the C3b-cleaving membrane protease p65. To delineate the molecular consequences of the C3b-cleaving activity for the complement cytotoxicity, the molecular events during the initiation (R24 monoclonal antibody, C1), amplification (C4, C3), and membrane attack (C5, C9) phases of complement were studied in comparison to a complement-susceptible human melanoma line (SK-MEL-93-2). No cleavage of C4b and C5b, 2 molecules structurally similar to C3b, was observed on the cells during classical pathway activation indicating the specificity of the p65 protease for the C3b molecule. The rapid degradation of C3b by p65 on the surface of complement-resistant SK-MEL-170 cells generates a M(r) 30,000 C3 alpha'-chain-fragment detectable as early as 1 min after complement activation, whereas no such fragment was present in detectable amounts on complement-susceptible cells. As a result of the rapid C3b proteolysis by p65 on resistant SK-MEL-170 cells, less C5 convertases are formed, which in turn results in the formation of a lower number of terminal complement components and membrane attack complexes. R24 antibody and C1q binding to the resistant cells was slightly lower as to susceptible cells. C4 binding studies, however, revealed that the observed difference in antibody and C1q binding has no influence on the complement resistance of SK-MEL-170 cells: significantly more C4b was bound to complement-resistant (1565 +/- 92 fg/cell) as compared to susceptible cells (715 +/- 31 fg/cell). On extraction of the molecular forms of C4 bound to the cell membranes, an additional high molecular weight C4 species--apparently a C4b-C4b homodimer--appeared only on the resistant SK-MEL-170 cells that may function as a residual back-up C5 convertase. Collectively, these results show that SK-MEL-170 human melanoma cells evade complement-mediated cytolysis despite sufficient activation of early components of the classical complement pathway by p65-mediated rapid degradation of surface-bound C3b, leading to a significant reduction in membrane attack complex formation. Thus, rapid cleavage of surface deposited C3b was established as a powerful mechanism of complement resistance.

Delivery of radionuclides to pretargeted monoclonal antibodies using dihydrofolate reductase and methotrexate in an affinity system.

A novel affinity system for a two-phase delivery of radionuclides to tumor cells has been developed. In the first phase, a nontoxic bivalent monoclonal antibody conjugated to an enzyme is targeted to the tumor cells. In the second phase, a radionuclide-derivatized enzyme inhibitor, specific for the enzyme conjugated to the antibody, is administered. The model system selected for this study is the recombinant human enzyme dihydrofolate reductase (rhDHFR) and its high-affinity competitive inhibitor methotrexate (MTX). MTX was labeled with a radionuclide by covalent attachment of diethylenetriaminepentaacetic acid (DTPA) complexed with 111In. Using the gamma-carboxyl residue of MTX for the attachment of DTPA, binding of the inhibitor to rhDHFR was not affected. The inhibitory activities of nonderivatized MTX and DTPA-MTX were indistinguishable. Human K562 erythroleukemia cells were used to evaluate under in vitro conditions the DHFR-MTX affinity system for the delivery of 111In-labeled DTPA-MTX to pretargeted alpha-transferrin receptor antibody-rhDHFR conjugates (alpha-TFR-DHFR). The data demonstrate that the delivery of 111In is dose dependent and highly specific. Under saturating conditions, binding of 111In-DTPA-MTX to alpha-TFR-DHFR-treated cells was 14-fold higher than to cells treated with nonconjugated alpha-TFR antibody. Further experiments indicated that the low level of nonspecific binding of 111In-DTPA-MTX was comparable to that of 111In-DTPA, known for its complete extracellular distribution and rapid clearance through the kidneys. Based on the data of this study, antibody-conjugated rhDHFR and radionuclide-labeled DTPA-MTX complexes provide components for an alternative radioimmunotherapeutic approach that can be expected to result in improved tumor tissue ratios of both the targeting moiety and the radionuclide-labeled derivative as compared to current approaches.

Human natural immunoglobulin M antibodies induce apoptosis of human neuroblastoma cells by binding to a Mr 260,000 antigen.

Sera of healthy humans contain natural cytotoxic IgM antibodies that specifically recognize a Mr 260,000 antigen (NB-p260) on the surface of human neuroblastoma (NB) cells. Here we demonstrate that anti-NB IgM antibodies prepared from different healthy individuals induce, in all human NB cell lines analyzed thus far, typical morphological and biochemical features of apoptosis including nuclear fragmentation, chromatin condensation, and DNA fragmentation. Both the binding of human anti-NB IgM to NB cells and the induction of apoptosis could be inhibited by preincubation of NB cells with murine IgG raised against purified NB-p260. Furthermore, preincubation of human anti-NB IgM with purified NB-p260 immobilized onto a solid support abolished its ability to induce apoptosis in NB cells. Natural human anti-NB IgM failed to bind to and induce apoptosis in control tumor cell lines that lack expression of NB-p260. The anti-NB IgM-induced apoptotic response was also observed in vivo in xenografted human NB tumors. After a single i.v. injection of anti-NB IgM into nude rats bearing solid NB xenografts, many areas of pyknotic cells with fragmented nuclei were observed that stained positive using the terminal dUTP nick end labeling method. In conclusion, the data demonstrate that natural anti-NB IgM antibodies in the sera of healthy individuals are potent mediators of apoptotic cell death of NB cells both in vitro and in vivo. The NB-p260 antigen was identified as the apoptosis-inducing receptor for anti-NB IgM. Whereas natural anti-NB IgM and NB-p260 may be useful tools for immunotherapy of NB, their biological significance remains to be determined.

Determination of 5-AMP in the presence of excess 3'(2')-AMP with the aid of antibodies raised against n6-carboxymethyl-5'-AMP conjugates. Use for the quantitation of pyridine nucleotides and of protein-bound ADP-ribose.

5'-AMP antigens were synthesized by conjugation of N6-carboxymethyl-5'-AMP (Cm65'-AMP) to native or methylated serum albumin. Injection of the antigens resulted in antibodies with high affinity and specificity for 5'-AMP in all animals, thus allowing discrimination against 3'(2')-AMP even when present at 10(4)-10(5) times higher concentrations. This specificity was comparable to that of anti 5'-AMP antibodies raised against Cm65'-AMP serum albumin antigens formed in situ from Cm6ADP-ribose serum albumin conjugates by intracellular or pericellular phosphodiesterases. The hapten in the Cm65'-AMP-methylated serum albumin conjugate appeared to be bound almost exclusively via the N6-position. Due to the free exposure of the 5'-phosphate group in this antigen, the resulting antibodies discriminated 5'-AMP derivatives substituted at the phosphate group more efficiently than derivatives with modifications in the adenine ring. It also led to the concomitant formation of adenosine-specific antibodies due presumably to dephosphorylation of the antigen by phosphatases present in the recipient animals. The conjugates formed from Cm65'-AMP and native serum albumin, which appeared to be linked to a large extent via carboxyl groups of the protein and hydroxyl groups of the ribose, recognized modifications in the adenine ring much better than substitutions at the phosphate group. However, in spite of these relatively small differences in specificity, all three types of antibodies could be used successfully to quantitate by radioimmunoassay protein-bound ADP-ribose in adult rat liver and NAD+-NADH in Ehrlich ascites tumor cells as shown by the excellent agreement of the values obtained with the three antisera.

Key role of mitochondria in cerulenin-mediated apoptosis.

Cerulenin, a fungal metabolite, is known to be a specific inhibitor of fatty acid synthase. Here we report that cerulenin is an effective inducer of apoptosis in different wild-type p53 and mutant p53 tumor cell lines, whereas normal human keratinocytes and fibroblasts are resistant to the apoptotic effect. To get more insight into the mechanisms of how cerulenin induces apoptosis we investigated several signal transduction molecules, including p53, p73, p21/WAF1, Bax, cytochrome c, and caspases 3 and 9. Our data strongly indicate that mitochondria play a key role in the cerulenin-mediated pathway. Bax overexpression correlated with the extent of apoptosis and appears to be regulated in a p53-independent manner. The significance of the mitochondrial pathway for the cerulenin-mediated apoptosis was confirmed by the rapid mitochondrial release of cytochrome c both in wild-type p53 and mutant cell lines. Interestingly, the rapid release of cytochrome c was not accompanied by a breakdown of the mitochondrial potential. Instead, the complete disruption of the mitochondrial function coincided with the appearance of a p18 kDa cleavage product of Bax.

Structure of the major oligosaccharide of cobra venom factor.

Cobra venom factor (CVF), the complement-activating glycoprotein in cobra venom, contains three or possibly four N-linked oligosaccharide chains per molecule and is devoid of O-linked saccharides. Analysis by lectin-affinity staining revealed the presence of complex-type oligosaccharides containing non-reducing terminal alpha-galactosyl residues and fucose residues linked to the proximal N-acetylglucosamine. Sialic acid residues could not be detected. For their structural analysis, the oligosaccharides were released by hydrazinolysis and fractionated on Bio-Gel P-4. Approximately 80% of the eluted oligosaccharides have a size equivalent of 17 +/- 2 glucose units. The major oligosaccharide representing about 45% of the total carbohydrate present in CVF was purified to homogeneity by MicroPak AX-5 HPLC and its structure was analyzed by sequential exoglycosidase digestion. The positions of the glycosidic linkages of the sugar residues were established by methylation analysis of CVF-derived glycopeptides. The data of these analyses indicated that the major oligosaccharide has a symmetrical fucosylated biantennary complex-type structure terminating with unusual alpha-galactosyl residues.

Complement killing of human neuroblastoma cells: a cytotoxic monoclonal antibody and its F(ab')2-cobra venom factor conjugate are equally cytotoxic.

Only a few monoclonal antibodies mediate complement lysis of tumor cells, but for several antibodies it has been demonstrated that a complement-activating function can be introduced by covalent coupling of cobra venom factor (CVF), a non-toxic glycoprotein which is a structural and functional homologue of human complement component C3. In this study we compared the efficacy of complement killing of human neuroblastoma cells by the complement-activating monoclonal antibody 3F8 directed against the GD2 ganglioside antigen with that of its F(ab')2-CVF conjugate. At equal numbers bound per cell the 3F8 antibody and the 3F8 F(ab')2-CVF conjugate were found to be equally cytotoxic in the presence of complement from several species including human. Maximal killing reached up to 98%. The kinetics of killing and the bivalent metal requirement confirmed that the cytotoxic activity of the 3F8 antibody is mediated via the classical pathway and that of the 3F8 F(ab')2-CVF conjugate via the alternative pathway. To achieve a comparable degree of killing, an approximately eight-fold higher concentration of the 3F8 F(ab')2-CVF conjugate was required which appears to be a consequence of the approximately eight-fold lower binding activity of the 3F8 F(ab')2-CVF conjugate compared to the intact 3F8 antibody. Our data suggest that the coupling of CVF to non-cytotoxic antibodies allows the generation of conjugates with a cytotoxic activity similar to that of inherently cytotoxic antibodies.

Quantitation of coronary venous adenosine in patients: limitations evaluated by radioimmunoassay.

Experimental studies have shown that adenosine is rapidly released in response to myocardial ischaemia. To evaluate whether coronary venous adenosine release is a metabolic characteristic of myocardial ischaemia in patients, adenosine concentrations were measured by a highly sensitive and specific radioimmunoassay. In three patients with normal coronary arteries and in seven with obstructive coronary artery disease coronary venous adenosine content was measured at rest and during atrial pacing. When whole blood or plasma were extracted immediately with perchloric acid the adenosine content was found to be lower than that previously reported. Recovery studies showed that the importance of time and temperature at low adenosine concentrations had been underestimated in preceding studies. In patients with coronary artery disease coronary venous adenosine concentration increased from 106.3(48.8) nmol.litre-1 to 114.9(57.0) nmol.litre-1 (NS) during pacing and was 130.4(63.3) nmol.litre-1 (NS) 2 min after pacing. Even in the presence of lactate production enhanced adenosine release was not consistently evidenced. Furthermore, venous adenosine content did not increase in five patients undergoing coronary artery occlusion during angioplasty of the left anterior descending coronary artery. The extremely short half life of coronary venous adenosine appears to preclude its use as an index of myocardial ischaemia in patients.

Expression of a 260 kDa neuroblastoma surface antigen, the target of cytotoxic natural human IgM: correlation to MYCN amplification and effects of retinoic acid.

Human neuroblastoma cells contain a 260 kDa surface-associated antigen (NB-p260) that is recognised by natural cytotoxic IgM antibodies. In this study we demonstrate that NB-p260 is expressed in vivo in a neuroblastoma tumour specimen but not in normal human tissues of neuronal origin. Since MYCN amplification is a clinical marker of neuroblastoma disease progression, we analysed the expression of NB-p260 in human neuroblastoma cell lines with different MYCN amplification status. However, both amplified and non-amplified neuroblastoma cell lines exhibited comparable NB-p260 expression. Treatment of neuroblastoma cells with the differentiation-inducing agent retinoic acid (RA) also had no effect on the expression of NB-p260. Collectively, the data suggest that expression of NB-p260 on human neuroblastoma cells is independent of malignancy and differentiation status of neuroblastoma.

Mechanisms of in vivo anti-neuroblastoma activity of human natural IgM.

Normal human sera of healthy adults contain natural IgM antibodies which are cytotoxic for human neuroblastoma cells. In this study, we evaluated the anti-neuroblastoma activity of these natural IgM antibodies in nude rats bearing solid human neuroblastoma tumours. A single intravenous (i.v.) injection of purified cytotoxic IgM led to uptake of IgM in the tumours with massive perivascular complement activation and accumulation of neutrophil granulocytes after 24 h. Five consecutive i.v. injections of purified cytotoxic IgM into neuroblastoma-bearing animals resulted in complete growth arrest of even large established solid tumours which lasted for several weeks after discontinuation of the injections, whereas tumours of control animals continued to grow exponentially during the observation period. These studies suggest that natural anti-neuroblastoma IgM may have a potential as a novel therapeutic modality in the treatment of human neuroblastoma.

Effect of antibody density on the displacement kinetics of a flow immunoassay.

This study investigates the effect of antibody density on the kinetics of a solid-phase displacement immunoassay. Conducted in flow under nonequilibrium conditions, the assay utilizes a monoclonal antibody to the cocaine metabolite benzoylecgonine, which has been immobilized onto Sepharose beads and saturated with fluorophore labeled antigen. Displacement of antibody-bound labeled antigen by non-labeled antigen occurs when sample is introduced in the buffer flow. Comparison of matrices coated with two different antibody densities revealed that the displacement efficiency is a function of the density of antibody-bound labeled antigen. A higher density of antibody provides a higher amount of displaced labeled antigen, but the displacement efficiency of the assay is decreased. The effect of antibody density on the immunoassay kinetics was analyzed using a mathematical formulation developed to characterize antibody-antigen interactions at solid-liquid interfaces. Higher antibody density proved to be associated with a lower apparent dissociation rate constant. The implications of these results on the design of immunoassays in flow are discussed.

Kinetics of antibody binding at solid-liquid interfaces in flow.

We have developed the theoretical framework for a displacement immunoassay conducted in flow under nonequilibrium conditions. Using a repetitive displacement technique, we determined the displacement rate and apparent dissociation rate constant at different flow rates. Our data suggest that the kinetics are best described by a first-order function. The displacement efficiency, the displacement rate, and therefore the apparent dissociation rate constant were calculated and demonstrated to be flow rate dependent. The theoretical framework developed in this study was successful in predicting the behavior of antigen displacement in flow.

A continuous flow immunoassay for rapid and sensitive detection of small molecules.

An immunosensor operating in continuous flow and capable of detecting low molecular weight antigens is described. The approach differs from previously described continuous flow assays by not requiring incubation steps or the introduction of additional reagents following the loading of the sample into the system. Detection of the antigen is rapid, occurring within 3 min in the system described. The assay is based on the binding of labeled antigen to an immobilized antibody, with subsequent displacement of the labeled antigen when antigen is present in the buffer flow. Signal detection occurs downstream of the antigen recognition event. In this study, the hapten 2,4-dinitrophenol (DNP) as DNP-lysine was used as model antigen. To generate a labeled antigen, DNP was coupled to the terminal amino group of insulin A chain (tetra S-sulfonate form) which provides two tyrosine residues for the introduction of an 125I-label (DNP-Ins-125I) or three carboxyl groups for the attachment of three fluorescein residues (DNP-Ins-Fl). The radiolabeled antigen was used to establish assay conditions. Subsequently, fluorescein was substituted for the radioisotope label in order to develop an assay independent of the restrictions associated with isotopes. Using this flow immunoassay, we were able to detect DNP-lysine down to a detection limit of 143 nM (29 pmol/200 microliters) using DNP-Ins-125I or DNP-Ins-Fl as labeled antigen. The density of immobilized antibody and the flow rate were identified to be critical parameters for the sensitivity of the assay.

Additive cytotoxicity of different monoclonal antibody-cobra venom factor conjugates for human neuroblastoma cells.

Insufficient numbers of antigen molecules and heterogeneity of antigen expression on tumor cells are major factors limiting the immunotherapeutic potential of the few clinically useful monoclonal antibodies capable of mediating complement cytotoxicity and antibody-dependent cellular cytotoxicity. To overcome this limitation, we converted two non-cytotoxic monoclonal anti-neuroblastoma antibodies, designated 3E7 (IgG2b) and 8H9 (IgG1), and the non-cytotoxic F(ab')2 fragment of the cytotoxic monoclonal anti-GD2 antibody 3F8 (IgG3) into cytotoxic antibody conjugates by covalent attachment of cobra venom factor (CVF), a structural and functional homologue of the activated third component of complement. Competitive binding experiments confirmed the different specificities of the three antibodies. In the presence of human complement, all three antibody-CVF conjugates mediated selective complement-dependent lysis of human neuroblastoma cells. Consistent with the kinetics of the alternative pathway of complement, approximately seven hours incubation were required to reach maximum cytotoxicity of up to 25% for the 3E7-CVF conjugate, up to 60% for the 8H9-CVF conjugate, and up to 95% for the 3F8 F(ab')2-CVF conjugate. The different extent of maximal cytotoxic activity of the three conjugates was reflected by corresponding differences in the extent of binding of both unconjugated antibodies and the respective conjugates. Any combination of the three antibody-CVF conjugates caused an additive effect in complement-mediated lysis. Using a cocktail of all three conjugates, the extent of complement-mediated killing could be increased up to 100%. These data demonstrate that by coupling of CVF the relative large number of non-cytotoxic monoclonal anti-tumor antibodies of interesting specificity can be used to design cocktails of cytotoxic conjugates and, thereby, to overcome the problem of insufficient and heterogeneous antigen expression on tumor cells for immunotherapy.

Mono ADP-ribosylation and poly ADP-ribosylation of proteins in normal and malignant tissues.

Three subclasses of (ADPR)n protein conjugates were quantified from intact tissue; proteins carrying poly(ADPR) and two types of mono(ADPR) protein conjugates, one susceptible, the other resistant to neutral hydroxylamine. Mono(ADPR) conjugates were found in all major compartments of the liver cell although the two subfractions were unevenly distributed. Poly(ADPR) protein conjugates appear to be restricted to the nucleus. Independent changes of the subclasses in normal and malignant tissues associated with cell growth and differentiation also point to independent functions. Hydroxylamine-resistant mono(ADPR) protein conjugates of various tissues changed with the degree of terminal differentiation. Formation of poly(ADPR) proteins, on the other hand, was stimulated by treatment of cells with alkylating agents which lead to DNA-fragmentation. This points to an involvement of polyADP-ribosylation in DNA excision repair.