Characterization of human IgG1 monoclonal antibody against gangliosides expressed on tumor cells

Engineering the binding site of an antibody against N-glycolyl GM3: from functional mapping to novel anti-ganglioside specificities

The structurally related gangliosides N-glycolyl GM3 and N-acetyl GM3 are potential targets for tumor immunotherapy. 14F7 is a monoclonal antibody able to discriminate the tumor-specific antigen N-glycolyl GM3 from the closely related N-acetyl GM3 on the basis of the presence of a single additional hydroxyl group in the former. A combinatorial phage display strategy, based on the screening of a large library followed by refined mutagenesis, allowed a thorough exploration of the binding chemistry of this unique antibody. Three essential features of the heavy chain variable region were identified: two aromatic rings (in positions 33 and 100D) contributing to the binding site architecture and an arginine residue (position 98) critical for recognition. Directed evolution of 14F7 resulted in novel variants that cross-react with the tumor-associated antigen N-acetyl GM3 and display recurrent replacements: the substitution W33Q and the appearance of additional arginine residues at several positions of CDR H1. Successful conversion of such engineered variable regions into whole cross-reactive anti-GM3 immunoglobulins validated our phage-based approach to study and modify the lead antibody 14F7. The resulting family of closely related antibodies offers new tools to study the mechanisms of cell death induced by antibodies targeting gangliosides. In vitro directed evolution was useful to overcome the technical limitations to obtain anti-ganglioside antibodies. The case of 14F7 illustrates the power of combining library screening with focused site-directed randomization for a comprehensive scanning of protein interactions.

Anti-ganglioside anti-idiotypic vaccination: more than molecular mimicry

Surgery, chemotherapy, and radiation therapy are standard modalities for cancer treatment, but the effectiveness of these treatments has reached a plateau. Thus, other strategies are being explored to combine with the current treatment paradigms in order to reach better clinical results. One of these approaches is the active immunotherapy based on the induction of anti-tumor responses by anti-idiotypic vaccination. This approach arose from Jerne’s idiotypic network theory, which postulates that B lymphocytes forms a functional network, with a role in the establishment of the immune repertoires, in the regulation of natural antibody production and even in the establishment of natural tolerance. Due to the large potential diversity of the immunoglobulin variable regions, the idiotypes repertoire can mimic the universe of self and foreign epitopes, even those of non-protein nature, like gangliosides. Gangliosides are sialic acid-containing glycolipids that have been considered attractive targets for cancer immunotherapy, based on the qualitative and quantitative changes they suffer during malignant transformation and due to their importance for tumor biology. Although any idiotype could be able to mimic any antigen, only those related to antigens involved in functions relevant for organism homeostasis, and that in consequence has been fixed by evolution, would be able not only to mimic, but also to activate the idiotypic cascades related with the nominal antigen. The present review updates the results, failures and hopes, obtained with ganglioside mimicking anti-idiotypic antibodies and presents evidences of the existence of a natural response against gangliosides, suggesting that these glycolipids could be idiotypically relevant antigens.

Lessons learned about the therapeutic potential of the natural human immune response to lung cancer

Lung cancer is the leading cause of cancer deaths; patients with this disease often develop antibodies to their own tumour antigens. TB94 is one such human antibody, and was obtained from the natural immune response from a patient with lung cancer. The data generated so far on TB94 suggest that this human antibody may have clinical applications in the diagnosis and treatment of lung cancer. Since humans make antibodies to tumour antigens, the intelligence of the human immune response can be exploited for the discovery of potential novel antigens. These novel antigens can then be developed for vaccine applications. Creating effective strategies to analyse systematically the natural human immune response to tumour antigens will open up new areas of immunotherapy for the control and eradication of disease.

In vivo detection of small subsurface melanomas in athymic mice using noninvasive fiber optic confocal imaging

Fiber optic confocal imaging, following intravenous administration of fluorescently labeled antibodies and Texas Red-dextran, enabled in vivo detection of melanoma and surrounding blood vessels in athymic mice. Human melanoma cells (three cell lines) and cultured normal human skin cells were implanted intradermally into the haunch skin of anesthetized athymic BALB/C mice and allowed to grow to a maximum size of 2 mm diameter. Using three different fluorescein-isothiocyanate-labeled antimelanoma antibodies, single channel confocal images of melanoma cells were obtained in vivo. Using noninvasive techniques, the overall in vivo melanoma detection rate for tumors within 0.2 mm of the skin surface was 84% (27 of 32 tumors). Normal cultured human skin cells were found to have little or no fluorescence after administration of the fluorescein-isothiocyanate-labeled antibodies and tumors were not labeled by an isotype control antibody. Dual channel imaging of the implanted melanoma tumor and surrounding dermal vasculature in vivo showed increased blood vessel density at the melanoma site. Conventional immunoperoxidase histology confirmed that fiber optic confocal imaging was able to detect melanoma tumors up to 0.2 mm below the skin surface, in vivo.

Effective induction and acquisition of human monoclonal IgE antibodies reactive with house-dust mite extracts

IgE plays a critical role in acute hypersensitivity such as anaphylaxis, asthma, and atopic dermatitis. IgE antibody is, therefore, an essential reagent for studying the mechanisms of these diseases. However, it is difficult to obtain IgE antibody in amounts sufficient for research use because IgE-producing lymphocytes are very rare. To overcome this problem, we investigated the requirements for generating IgE-secreting human hybridomas using in vitro immunization of peripheral blood lymphocytes. First, culture conditions were optimized for IgE production by a combination of the immunomodulatory mediators interleukin-2, interleukin-4, interleukin-6, and muramyl dipeptide. Second, the addition of mite antigen to the cultures resulted in an increased production of antigen-specific IgE as well as antigen-specific IgG and IgM. When activated lymphocytes in these cultures were fused with Burkitt lymphoma cells, ICLU-B, antigen-specific IgE-secreting hybridomas were obtained with high efficiency. These results demonstrate that our culture and in vitro immunization system for human peripheral blood lymphocytes is useful for obtaining antigen-specific IgE.