Monoclonal antibodies immunogenicity

Ricin [9009-86-3], a phytotoxin found in the seeds of the castor oil plant Acinus communis, conjugated to murine monoclonal antibody (Immunogen Corp.), has been approved by the U.S. Food and Dmg Administration (FDA) for the treatment of patients with B-ceU leukemia and lymphoma (59). 

Cheifetz A, Mayer L. Monoclonal antibodies, immunogenicity, and associated infusion reactions. Mount Sinai J Med 2005 72 250-6. 

The first mouse monoclonal antibody specific for human CD3 was produced in 1979 and named orthoclone OKT3. Aside from its use in the laboratory, OKT3 became the first anti-CD3 antibody to be utilized in transplantation medicine, but its wider application was hampered by its immunogenic and mitogenic properties (reviewed in [6]). Consequently, humanized and engineered anti-CD3 antibodies were developed to circumvent these limitations (Table 1). Since T cells and the TCR are involved in many immunological diseases, it is not surprising that the application of CD3 antibodies is not restricted to the field of transplantation. For example, CD3 antibodies are tested in clinical studies of diseases such as autoimmune diabetes (type 1 diabetes), immune-mediated inflammatory arthritis and inflammatory bowel disease [7]. 

Davio et al. (43) report efforts to obtain monoclonal antibodies (mAbs) to STX. Because STX is a small molecule of approximately 300 daltons, well below the size necessary for immunogenicity, a carrier molecule must be conjugated to the hapten (STX). This technique must minimize alterations of the antigenic form. For the anti-STX antibodies tested to date, the ratios of immunoassay response factor to pharmacological potency for various STX derivatives differ substantially, the immunoassay being virtually unresponsive to some of the common natural derivatives (44). 

Figure 13 Structures of haptens used for immunizing and coating antigens in a monoclonal antibody-based immunoassay for diuron. A sensitive assay was developed using coating hapten I that had the handle in a position different from the immunogen hapten. When the oxygen in the urea moiety of hapten I was replaced with a sulfur (hapten 11), increasing the heterology, even greater sensitivity was achieved...

The discovery of monoclonal antibodies and combining them with polymeric prodrugs is the newest approach to overcome the lack of selectivity for disposition in target tissue (23). Recently the selectivity of antibody-targeted polymeric anthracycline antibiotics to T lymphocytes was accomplished (25). In addition decreased immunogenicity of proteinaceous conjugates with IgG and human transferrin has been reported (26). 

Another difficulty is that a peptide may be able to bind to an existing neutralizing monoclonal antibody by an induced-fit mechanism that is somehow driven by the pre-existing structure of the antibody paratope. However, the same induced-fit process may not take place when the peptide is used as the immunogen and is confronted in the host by a large population of B cell receptors allowing a variety of other interactions. 

El-Kasmi, K. C., Deroo, S., Theisen, D. M., Brons, N. H. C. and Muller, C. P. (1999), Crossreactivity of mimotopes and peptide homologues of a sequential epitope with a monoclonal antibody does not predict crossreactive immunogenicity , Vaccine, 18, 284-290. 

Human immunodeficiency virus (HIV) type 1 gpl20 (V3 loop) protein Tomato bushy stunt virus in tobacco leaf HIV epitope detected by V3-specific monoclonal antibodies and human sera from HIV positive patients. Immunogenic in mice when delivered parenterally 17... 

Hepatitis C virus (HCV) HVR1 epitope fused to V. cholerae CTB Tobacco leaf Reacted with HRVl-specific monoclonal antibodies and sera from individuals infected with HCV. HVR1 epitope formed fused to CTB was immunogenic in mice when administered nasally. 62... 

Similar results were recently obtained with a human monoclonal antibody, with KDEL sequences fused to the C-termini of both heavy chains, expressed in tobacco [33]. As observed for the invertase-HDEL fusion, about 90% of the N-linked glycans on this antibody were of the high-mannose type, with 6-9 mannose residues, while a fraction contained the immunogenic P(l,2)-xylose glyco-epitope (Fig. 15.6). However, this antibody was not a(l,3)-fucosylated, a glycan modification occurring in the trans Golgi [34]. 

Immunogenicity. Many, if not most, therapeutic proteins are potentially immunogenic when administered to humans. The likelihood that non-human proteins (e.g. murine monoclonal antibodies Chapter 13) are immunogenic in humans is an obvious one. However, human proteins can also be potentially immunogenic, as discussed in Box 4.1. Antibodies raised in this way can bind the therapeutic protein, neutralizing its activity and/or affecting its serum half-life. 

Based on the above principles, it might be assumed that a therapeutic protein obtained by direct extraction from human sources (e.g. some antibody preparations) or produced via recombinant expression of a human gene/cDNA sequence (e.g. recombinant human hormones or cytokines) would be non-immunogenic in humans whereas foreign therapeutic proteins (e.g. non-engineered monoclonal antibodies) would stimulate a human immune response. This general principle holds in many cases, but not all. So why do therapeutic proteins of human amino acid sequences have the potential to trigger an immune response Potential reasons can include ... 

A number of approaches may be adopted in an attempt to reduce or eliminate protein im-munogenicity. Protein engineering (Chapter 3), for example, has been employed to humanize monoclonal antibodies (Chapter 13). An alternative approach entails the covalent attachment of polyethylene glycol (PEG) to the protein backbone. This can potentially shield immunogenic epitopes upon the protein from the immune system. 

Geng, D., Shankar, G., Schantz, A., Rajadhyaksha, M., Davis, H., and Wagner, C. 2005. Validation of immunoassays used to assess immunogenicity to therapeutic monoclonal antibodies. Journal of Pharmaceutical and Biomedical Analysis 39, 364-375. 

Antibody immunogenicity remains one of the inherent therapeutic limitations associated with administration of murine monoclonals to human subjects. In most instances, a single injection of the murine monoclonal will elicit an immune response in 50-80 per cent of patients. Human anti-mouse antibodies (HAMA) will generally be detected within 14 days of antibody administration. Repeated administration of the monoclonal (usually required if the monoclonal is used for therapeutic purposes) will increase the HAMA response significantly. It will also induce an HAMA response in the majority of individuals who display no such response after the initial injection. The HAMA response will effectively and immediately destroy subsequent doses of monoclonal administered. In practice, therefore, therapeutic efficacy of murine monoclonals is limited to the first and, at most, the second dose administered. 

An obvious strategy for overcoming the immunogenicity problem would be the generation and use of monoclonal antibodies of human origin. This is possible but difficult. Human antibody-producing lymphocytes can potentially be rendered immortal by ... 

Proteins are frequently powerful immunogens and the availability of specific antibodies, particularly monoclonal antibodies, makes the technique of affinity chromatography very useful in the separation and purification of individual proteins. The technique has been used to purify a wide range of proteins such as hormones, membrane receptors and complement proteins. However, it is not restricted to proteins and is potentially applicable to any immunogenic substance. The availability of suitable antibodies is essential and these may be raised by whole animal polyclonal techniques or by monoclonal cell culture. The former antibodies may need some prior purification before being immobilized. 

Numerous problems in the construction of chnically applicable drug targeting moieties still need to be solved. Of these issues, immunogenicity after repeated administration, counterproductive hver clearance, and production 5delds are the most important. Although the problem of immunogenicity is beheved to have been solved for monoclonal antibody therapy by the development of humanized and fully human antibodies [110], for other carrier systems such as modified plasma proteins and peptide modified polymers, this remains an important issue. 

Moron, B., Cebolla, A., Manyani, H., Alvarez-Maqueda, M., Megias, M., Thomas Mdel, C., Lopez, M. C., and Sousa, C. (2008). Sensitive detection of cereal fractions that are toxic to celiac disease patients by using monoclonal antibodies to a main immunogenic wheat peptide. Am. ]. Clin. Nutr. 87, 405M14. 

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