Monoclonal antibodies case studies

The reader, doubting that this method is sufficiently rigorous, may think that it is not possible to discover a radically new determinant by testing monoclonal antibodies with antigens that are already well known. In any case, after having found an active sequence, it is possible to modify it chemically or enzymically so as to create an original structure. If this modification increases the immune response, we arrive closer to the authentic specificity of the monoclonal antibody being studied. This is how an unknown determinant may be discovered. Whatever may be, monoclonal antibodies have served to point out the differences between embryonic and adult cells, between normal and cancerous cells. In this chapter we present a few characteristic examples and a brief survey of certain experimental techniques. 

Tumor Necrosis Factor There are two types of tumor necrosis factor TNF-a and TNF- 8. Of the two, TNF-a has been studied in more detail. TNF-a is a 157 amino acid polypeptide. It is a mediator of immune regulation, including the activation of macrophages and induction of the proliferation of T cells. Another TNF-a function is its cytotoxic effects on a number of tumor cells. Recent research, however, concentrates on its property in the stimulation of inflammation, particularly in the case of rheumatoid arthritis. Clinical trials are being conducted with drugs to block TNF-a with anti-TNF-a monoclonal antibodies. These antibodies target the excessive levels of TNF-a in the synovial fluid of joints and provide relief to sufferers of rheumatoid arthritis (Exhibit 4.10). 

Studies in pre-clinical models with human tumours are often carried out in (immuno)defi-cient mice. However, particularly in the case of monoclonal antibody-directed therapy, it is important to recognize that these models, while useful, frequently over-predict activity and under-predict toxicity because the target antigen is tumour-specific in the animal but only tumour-associated in man. 

The opposite case, of over-selecting a patient population, has also been seen recently, and with another ERBB 1 inhibitor— the monoclonal antibody cetuximab. Initial studies were conducted in patients whose tumors had immunohistochemical evidence of EGER expression (25). This ultimately led to inclusion of this criterion in the drug label. It was subsequently found that benefit from cetuximab may also occur in the absence of ERBBl expression (26). 

In support of Dr. Shi s opinion is the fact that in some cases the absolute specificity of even monoclonal antibodies can be questioned. The absorption control cannot always determine whether the protein bound in the tissue is the same protein used for absorption. The monoclonal antibody may instead recognize a similar epitope of an unrelated protein, especially following tissue fixation. Absorption controls therefore may not provide the specificity of the antibody for a protein under study in the tissue. 

After a comprehensive introduction, the basic PK/PD properties of peptides, monoclonal antibodies, antisense oligonucleotides and gene delivery vectors are reviewed. In the second part, the book covers a number of challenges and opportunities in this field such as bioanalytical methods, bioequivalence and pulmonary delivery. The text finishes with a detailed presentation of some real-life examples and case studies which should be of particular interest to the reader and integrate many of the concepts presented earlier in the text. 

Size-exclusion HPLC is particularity useful in either direct pharmacodynamic studies of the radiolabeled product or indirect studies that employ a labeled monoclonal antibody. In order to observe shifts in apparent MW due to noncovalent binding interactions, the mobile phase for these analyses should be a physiological buffer and the ligand size cannot be less than half that of the labeled protein. In cases where complexation may interfer with in vivo targeting, size-exclusion HPLC can be used prior to clinical administration of the potential or existing biotechnology product to establish the most effective regimen or dose. 

In conclusion, studies on isolated cells allow measurements on homogeneous cell populations under well-defined conditions and can aid in the interpretation of metabolic changes seen by NMR in the same or similar cells in the intact animal. In some cases the cells may be a valid system for study in their own right. For example, there have been several NMR studies of commercially important mammalian cell lines which are used in the biotechnology industry for the production of various monoclonal antibodies and recombinant proteins with therapeutic or analytical applications (Mancuso et al., 1990 Gillies et al., 1991). 

For most of the other monoclonal antibodies, species cross-reactivity has been limited to nonhuman primates. For these molecules the need to conduct reproductive and developmental studies has to be carefully considered on a case-by-case basis. S5A states that nonhuman primates are best used when the objective of the study is to characterize a relatively certain reproductive toxicant, rather than detect a hazard. The nonhuman primate reproductive toxicity studies are not powered to detect infrequent events. 

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