Gene transfer by retrovirus-derived shuttle vectors in the generation of murine bispecific monoclonal antibodies

A Murine, Bispecific Monoclonal Antibody Simultaneously Recognizing β-Glucan and MP65 Determinants in Candida Species

There is a real medical need of new diagnostic tools for the early recognition of invasive Candida infections. We exploited a rather simple and rapid redox methodology to construct a bispecific monoclonal antibody (bsmAb) that combines a monoclonal antibody (mAb) directed against 1,3-β-D-glucan, a well-known, pan-fungal diagnostic biomarker, with a mAb recognizing MP65, a major immunogenic mannoprotein secreted by C.albicans and other Candida species. The bsmAb (MP65/bglu mAb) was successfully produced and purified at high yields and proved to bind and reveal simultaneously, with high sensitivity, the β-glucan and MP65 antigens in both purified and native forms. The MP65/bglu mAb is the first bispecific antibody generated against a fungal microorganism and may prove useful for the concurrent detection of different and clinically significant Candida biomarkers in patient sera.

Structural, functional, and tissue distribution analysis of human transferrin receptor-2 by murine monoclonal antibodies and a polyclonal antiserum

Human transferrin receptor-2 (TFR-2) is a protein highly homologous to TFR-1/CD71 and is endowed with the ability to bind transferrin (TF) with low affinity. High levels of TFR-2 mRNA were found in the liver and in erythroid precursors. Mutations affecting the TFR-2 gene led to hemochromatosis type 3, a form of inherited iron overload. Several issues on distribution and function of the receptor were answered by raising a panel of 9 monoclonal antibodies specific for TFR-2 by immunizing mice with murine fibroblasts transfected with the human TFR-2 cDNA. A polyclonal antiserum was also produced in mice immunized with 3 peptides derived from the TFR-2 sequence, exploiting an innovative technique. The specificity of all the reagents produced was confirmed by reactivity with TFR-2(+) target cells and simultaneous negativity with TFR-1(+) cells. Western blot analyses showed a dominant chain of approximately 90 kDa in TFR-2 transfectants and HepG2 cell line. Analysis of distribution in normal tissues and in representative cell lines revealed that TFR-2 displays a restricted expression pattern--it is present at high levels in hepatocytes and in the epithelial cells of the small intestine, including the duodenal crypts. Exposure of human TFR-2(+) cells to TF-bound iron is followed by a significant up-regulation and relocalization of membrane TFR-2. The tissue distribution pattern, the behavior following exposure to iron-loaded TF, and the features of the disease resulting from TFR-2 inactivation support the hypothesis that TFR-2 contributes to body iron sensing.

CD38 ligation plays a direct role in the induction of IL-1beta, IL-6, and IL-10 secretion in resting human monocytes

CD38 signaling, either induced by ligation with specific agonistic monoclonal antibody (mAb) or after interaction with CD31, its cognate counter-receptor, is involved in release of IL-1beta, IL-6, and IL-10 cytokines in resting human monocytes. CD38 ligation by the F(ab')(2) IB4 mAb did not induce signals relevant for cytokine secretion and the block of the Fcgamma receptor I (FcgammaRI) by anti-CD64 or FcgammaRII by anti-CD32 mAb did not inhibit CD38-mediated IL-1beta release. Dimerization or multimerization of the CD38 molecule by: (i) cross-linking of the receptor ligated by F(ab')(2) or by (ii) increasing CD38 expression by treating monocytes with IFNgamma were able to restore the truncated CD38-mediated signals involved in cytokine secretion. These data indicate that CD38 receptor-mediated signals operate directly suggesting a Fcgamma receptorial surface molecule independent activation pathway. The key element for the receptor mediated signaling is represented by surface density of CD38 on resting monocytes.

Monoclonal antibodies and therapy of human cancers

This survey is an overview of the applications of murine, humanized and recombinant monoclonal antibodies for in vivo diagnostic and therapeutic applications. Monoclonal antibodies (mAb) have been applied to the diagnosis and therapy of an array of human diseases. The initial failures of early clinical trials have been overcome through the production of a new generation of mAb which features reduced immunogenicity and improved targeting abilities. The early models of mAb therapy were focused on enhancing the cytolytic mechanisms against the tumor cells. More recently, successful mAb-based therapies were targeted to molecules involved in the regulation of growth of cancer cells. This has highlighted the relevance of understanding receptor-mediated signaling events, and may provide new opportunities for anti-tumor antibody targeting. Despite all the difficulties, clinical data is outlining an increasingly significant role for antibody-mediated cancer therapy as a versatile and powerful instrument in cancer treatment. One reasonable expectation is that treatment at an earlier stage in the disease process or in minimal residual disease may be more advantageous.

CD38 is functionally dependent on the TCR/CD3 complex in human T cells

One of the functions of surface CD38 is the induction of phosphorylation of discrete cytoplasmic substrates and mobilization of cytoplasmic calcium (Ca2+). The present work addresses the issue of whether the signaling mediated via CD38 operates through an independent pathway or, alternatively, is linked to the TCR/CD3 signaling machinery. We studied the signals elicited through CD38 by the specific agonistic IB4 monoclonal antibody (mAb) by monitoring the levels of cytoplasmic Ca2+ and the induced phenotypic and functional variations in T cell growth. IB4 mAb presented the unique ability to increase cytoplasmic Ca2+ levels, which correlated with the phosphorylation of the PLC-gamma1. These effects were blocked by phorbol 12-myristate 13-acetate (PMA) and were dependent on the presence of a functional TCR/CD3 surface complex, no effects being recorded on mutant Jurkat cells lacking part of the CD3 structures. CD38 signaling appeared to share with TCR/CD3 the ability to induce apoptotic cell death in Jurkat T cells, an event paralleled by specific up-regulation of the Fas molecule and inhibited by cyclosporin A. CD28, a costimulatory molecule, is synergized by increasing CD38-induced apoptotic cell death. The results indicate the existence of a strong functional interdependence between CD38 and TCR/CD3.

CD38 Functions Are Regulated Through an Internalization Step

The endocytosis of the human CD38 molecule has been investigated in normal lymphocytes and in a number of leukemia- and lymphoma-derived cell lines. CD38 internalization was followed using radioiodinated Abs in an acidic elution endocytosis assay to monitor the effects of cross-linking on internalization processes and to quantify the ratio of the internalized molecule. Second, conventional, confocal, and electron microscopies were used to evaluate the morphologic effects induced by ligation of the molecule with Abs mimicking the natural ligand(s). The results demonstrated that internalization is a reproducible phenomenon following CD38 ligation with both agonistic and nonagonistic specific Abs and involving only a fraction of the entire amount of the surface molecule. It is independent from signal transduction as can be inferred by the observation that 1) both agonistic and non agonistic Abs are effective and 2) the dynamic of internalization is much slower than that of cellular signaling. Morphologic studies demonstrated that endocytosis induced as a result of CD38 ligation presents a very specific pathway consisting of subcellular organelles fundamental to the processing of the complex. Our data indicate that down-regulation by endocytosis may be, in parallel with shedding, a regulatory element in activation and adhesion processes mediated by CD38. However, internalization seems not to be a key step in triggering intracellular signaling; more likely, it is a negative feedback control mechanism which interrupts signal transduction or cell-cell cross-talks mediated by membrane CD38.

Syk and ZAP-70 mediate recruitment of p56lck/CD4 to the activated T cell receptor/CD3/zeta complex

During antigen recognition by T cells, CD4 and the T-cell receptor (TCR)/CD3/zeta complex are thought to interact with the same major histocompatibility complex II molecule in a stable ternary complex. Evidence has suggested that the association of CD4 with TCR/CD3/zeta requires the interaction of the protein tyrosine kinase p56lck with CD4. We have taken a biochemical approach to understand the mechanism by which p56lck and, in particular, its src homology (SH) 2 domain contributes to the association of CD4 with TCR/CD3/zeta during activation. We have previously shown that the p56lck SH2 domain binds directly to tyrosine-phosphorylated ZAP-70. Here we formally demonstrate the in vivo association of p56lck with the homologous protein tyrosine kinases Syk and ZAP-70 after CD3 stimulation of Jurkat cells. A tyrosine-phosphorylated peptide containing the sequence predicted to be optimal for binding to the SH2 domain of src family kinases specifically competes for this association, indicating that tyrosine-phosphorylated ZAP-70 and Syk bind to p56lck by an SH2-mediated interaction. We also show that the same peptide is able to compete for the activation-dependent TCR/CD4 association in Jurkat cells. Moreover, ZAP-70 and CD4 cocap only after CD3 stimulation in human T lymphoblasts. We propose that the interaction of the p56lck SH2 domain with zeta-associated tyrosine-phosphorylated ZAP-70 and/or Syk enables CD4 to associate with antigen-stimulated TCR/CD3/zeta complexes.

Bispecific monoclonal antibody anti-CD3 x anti-tenascin: an immunotherapeutic agent for human glioma

Besides surgery, the therapeutic possibilities for the treatment of human gliomas include adoptive cellular immunotherapy, radioimmunotherapy, immunotherapy mediated by chemoimmunoconjugates and, more recently, bispecific monoclonal antibodies (biMAbs). Anti-CD3 x anti-tenascin (TN) is the first reagent of a number of biMAbs under investigation for prospective use in vivo to maximize the cell-mediated cytolytic potential of glioma patients. This biMAb originated from the fusion of 2 parental hybridomas, made resistant by retrovirus-mediated infection to the different metabolic drugs, geneticin and methotrexate, respectively. The resulting hybrid hybridomas were selected on the basis of the double specificity for CD3 and TN, cloned several times and grown under continuous metabolic pressure. The different families of recombinant antibodies were then purified by high-pressure liquid chromatography on hydroxylapatite columns. Immunohistochemical studies on tumor specimens of different origin and histotype have shown that the selected biMAb presented a distribution pattern similar to that of the parental anti-TN MAb, maintaining the same staining homogeneity and intensity. Moreover, the mitogenic activity of anti-CD3 x anti-TN biMAb on peripheral blood mononuclear cells was similar to that featured by the parental anti-CD3 MAb. Furthermore, the hybrid molecule induced TNF-alpha gene expression in activated PBMC. Finally, the anti-CD3 x anti-TN featured the desired killer targeting ability, being able to induce a significantly increased cytotoxic activity against TN+ tumor cells.

CD38 ligation induces discrete cytokine mRNA expression in human cultured lymphocytes

Human CD38 is a surface glycoprotein expressed by different immuno-competent cells such as immature and activated lymphocytes, plasma cells and natural killer cells. It has recently been reported that the CD38 molecule exerts adenosine diphosphate ribosyl cyclase activity and is associated with distinct transmembrane signaling molecules. This study reports that ligation of CD38 by specific monoclonal antibodies (mAb) induces multiple cytokine mRNA expression in cultured peripheral blood mononuclear cells (PBMC). The mRNA for tumor necrosis factor-alpha, interleukin (IL)-1 beta, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-12 were always detected, whereas interferon-gamma and IL-10 mRNA expression were seen in most, but not all PBMC cultures. Low levels of IL-2, IL-4 and IL-5 mRNA were also found. The key observation of this work is that CD38 ligation in PBMC induces a large spectrum of cytokines, many of which overlap with those induced via CD3 activation. The main differences between CD38 and CD3 activation are the low to undetectable levels of IL-2 mRNA, and the sustained IL-1 beta and IL-6 mRNA accumulation found in PBMC cultures following treatment with anti-CD38 mAb. Furthermore, PBMC proliferation was not found to be a prerequisite for CD38-mediated cytokine induction. Together, these results suggest that human CD38 activates a signaling pathway which leads to the induction of a discrete array of cytokines, and that this pathway only partially overlaps with that controlled by T cell receptor CD3.

Retrovirus-mediated transfer of the multidrug resistance gene into human haemopoietic progenitor cells

We report the utilization of cord blood (CB) or bone marrow (BM) derived low density or purified CD34+ cells as a target for human multidrug resistance (MDR1) gene transfer. Cells were cocultivated for 48 h with an irradiated MDR1 retroviral producer line. Since some degree of MDR1 gene expression has been reported to occur in haemopoietic progenitor cells and in peripheral blood cells, efficiency of MDR1 gene transfer was assessed by: (1) Drug selection and culture in presence of 50 ng/ml doxorubicin, 10 ng/ml colchicine and 0.85 micrograms/ml taxol. In uninfected control, 1-2% of CFU-GM and CFU-GEMM were found to be drug-resistant, while 14-31% of original clonogenic activity was found after 2 weeks of culture of transduced cells. Efficiency of MDR1 transfer was significantly enhanced by prestimulation with cytokines, and found to be significantly superior in CB-derived compared to BM-derived progenitors. (2) Analysis of MDR1 gene expression by evaluating MDR1 mRNA through polymerase chain reaction. MDR1 expression was very low in cultures of uninfected controls, whereas, after drug selection, MDR1 mRNA levels in transduced cells was as high as in the MDR1 retroviral producer line (positive controls). (3) Flow cytometric analysis of the expression of CD34 and P-glycoprotein, the product of the MDR1 gene. After MDR1 transduction and 2 weeks of culture, membrane expression of P-glycoprotein was found on 17-25% of viable CD34+ cells. (4) Cytochemical localization by APAAP staining of P-glycoprotein. No specific localization was found in untransduced controls, whereas transduced and cultured CB-cells expressed P-glycoprotein on plasma and nuclei membrane. In conclusion, MDR1 gene transfer into CB- and BM-derived progenitor cells seems a feasible and attractive approach to generate a drug-resistant haemopoiesis.

Biosensor analysis of antigen-antibody interactions as a priority step in the generation of monoclonal bispecific antibodies

A biosensor system aimed at real-time measuring molecular interactions among label-free reactants has been used for a comparative analysis of the binding features (i.e., association-dissociation rates and affinity constants) as well as epitope mapping between bivalent monoclonal antibodies and the derived monovalent bispecific monoclonal antibody. The results show that observed different affinities between parental and derived bispecific antibodies concern the association rate constant, whereas the dissociation rate constants are unaltered. The apparent affinity-constant values determined by solid-phase radioimmunoassay yielded figures almost overlapping with those obtained with the biosensor instrument. The results of the present work indicate that the biosensor system has gained a key role not only as a tool for the study of antigen-antibody interactions, but also for setting up the reference parameters for the selection of the best candidates in the generation of bispecific monoclonal antibodies.

From cells to genes: how to make antibodies useful in human diagnosis and therapy

Monoclonal antibodies (mAb) have great potential value for in vivo diagnosis and therapy in humans. Their antigenic nature is however responsible for severe side effects and successful applications in the clinic have prove to be more limited than was originally hoped. This review summarize both cell biology and molecular biology approaches developed in order to overcome these limitations. Improving methodologies to immortalize cell lines producing human mAbs are reported with a particular attention to the techniques aimed at rescuing B cells expressing high-affinity human antibodies. A major part of this review is devoted to the protein engineering work. Genetic manipulation of mouse monoclonals to produce humanized antibodies and preparation of bacteriophage libraries displaying Ig repertoires are examined. The possibility to extend these approaches to the production of in vitro repertoires and to obviate the in vivo immunization step is also discussed.

Real-time kinetic analysis applied to the production of bispecific monoclonal antibodies for radioimmunodetection of cancer

An automated biosensor system designed for measuring molecular interactions in real-time and without labelling of the reactants has been used to evaluate the association/dissociation rate and affinity constants of bivalent monoclonal antibodies and a monovalent bispecific monoclonal antibody. Observed differences in affinity between parental and bispecific antibody produced were related to the association rate constants, since the dissociation rate constants were in the same range. Values were also closely related to radioimmunochemical data. These results indicate that the biosensor system, besides presenting several advantages for characterizing antigen-antibody interaction, is valuable for selecting monoclonal antibodies with properties which might be useful in the development of bispecific monoclonal antibodies.

Cell retargeting by bispecific monoclonal antibodies. Evidence of bypass of intratumor susceptibility to cell lysis in human melanoma

Intratumor heterogeneity for susceptibility to cytotoxic T lymphocytes (CTL)-mediated lysis represents a major obstacle to cancer adoptive immunotherapy. To overcome the heterogeneity observed in terms of susceptibility of target cells to cell-mediated lysis, in this study we used two purified bispecific monoclonal antibodies (bsmAbs) that recognize molecules expressed by cytotoxic effector cells (CD3 and IgG Fc receptorial molecules), as well as one high molecular weight melanoma-associated antigen (HMW-MAA). The ability of these reagents to enhance or induce a relevant in vitro cytotoxic activity by a CTL clone (CTL 49) isolated from PBL of a melanoma patient was tested on a large panel of autologous and allogeneic melanoma cell lines and clones. Functional studies revealed that the CTL 49 clone lysed all the HMW-MAA+ tumor lines in the presence of bsmAbs and that these reagents affected the target lysis in a cooperative fashion. The effectiveness of bsmAbs in overcoming the heterogeneous susceptibility of human melanoma cells to cell-mediated lysis may find practical implications in cancer adoptive immunotherapy.

Selective high-performance liquid chromatographic purification of bispecific monoclonal antibodies

The recent development of improved production techniques for bispecific monoclonal antibodies (biMAbs) has significantly increased interest in specific purification procedures. In this investigation, a general high-performance liquid chromatographic (HPLC) purification method is proposed that allows highly purified biMAbs to be obtained from mouse ascites fluid containing a mixture of different antibodies, i.e., parental MAbs, active biMAb and a mixture of randomly assembled heavy and light chains. Proteins from ascites fluid were precipitated with ammonium sulphate and applied to a high-performance protein A column to separate the total immunoglobulin fraction. BiMAbs were isolated from other immunoglobulins by two subsequent passages through a high-performance hydroxyapatite (HPHT) column. This purification protocol combines specificity of protein A for immunoglobulin G (IgG) and high selectivity of hydroxyapatite for different IgG idiotypes. All purification steps were performed rapidly and reliably by HPLC. This method was applied to the purification of six different biMAbs with consistently high yields, purity and homogeneity. This general purification method may prove extremely valuable when highly pure preparation of biMAbs is required, as for in vivo use.

Generation of human monoclonal antibodies that confer protection against pertussis toxin

A panel of human monoclonal antibodies reactive with pertussis toxin has been generated by means of Epstein-Barr virus infection. One of these, the 3F11 monoclonal antibody, showed the ability to neutralize in vitro and in vivo the toxic effects of the toxin. Western blot (immunoblot) analysis located the 3F11 epitope on the S3 subunit.

CD38: a multi-lineage cell activation molecule with a split personality

This review reports the characteristics of the human surface molecule CD38, a structure not linked to a definite line and predominantly expressed in early and activated phenotypes. The CD38 molecule consists of a single chain of 46 kDa, spanning the membrane and with the carboxyl terminus located in the extracellular compartment. The CD38 molecule is also involved in the transduction of activation and proliferation signals, which are line unrestricted. The gene coding for the CD38 antigen has been cloned and used for the construction of simian and mouse transfectants expressing the human molecule. These cell models are used for the analysis of several unanswered issues, mainly concerning the in vivo function of CD38, the existence of a natural ligand and of polymorphism in the population.