This in turn can be overcome by conjugation to PEG which results in an increased half-life to proteins to which it is attached, either by avoiding renal clearance since polymer increases the apparent size of the molecule to above the glomerular filtration limit, and/or through evasion of cellular clearance mechanisms (Chapman 2002; National Horizon Scanning Centre 2004)

This in turn can be overcome by conjugation to PEG which results in an increased half-life to proteins to which it is attached, either by avoiding renal clearance since polymer increases the apparent size of the molecule to above the glomerular filtration limit, and/or through evasion of cellular clearance mechanisms (Chapman 2002; National Horizon Scanning Centre 2004). of a humanized anti-TNF-alpha monoclonal antibody. PEGylation increases the half-life, reduces the requirement for frequent dosing, and possibly reduces antigenicity as well. Certolizumab has been shown in Phase III trials to achieve and maintain clinical response and remission in Crohns disease patients. It improves the quality of life. Certolizumab pegol will be indicated for moderately to severely active GNE-7915 Crohns disease, but it is not yet licensed in Europe or the US. It is not possible to construct an algorithm for treatment, but when compared with infliximab the two principal advantages are likely to be lower immunogenicity (as shown by anti-drug antibodies, absence of infusion reactions, and low rate of antinuclear antibodies), and a subcutaneous route of administration. These two factors may be sufficient to promote it up the pecking order of anti-TNF brokers. or em tolerogenic /em . It is the immunogenic response ( em immunogenicity /em ) that is potentially harmful to the recipient. Humanization of an antibody promotes homology with human proteins, which reduces their antigenic profile, but even human proteins can be immunogenic in humans. Consider the antibodies that develop to recombinant Factor VIII or insulin. Consequently the concept that humanization of its own account reduces immunogenicity is usually false (Clark 2000). Immunogenicity depends not only around the molecular conformation of the protein, but also on dose, delivery, frequency, concomitant therapy, and individual. The ability of polyethylene glycol (PEG) to reduce the immunogenicity of foreign proteins has been under investigation, with a view to the production of designed monoclonal antibodies that are effective but less immunogenic (Clark 2000; Chapman 2002). Implications of humanization Humanization is usually a separate antibody engineering strategy that has tried to tackle the immunogenicity of therapeutic antibodies, but as indicated above is not the whole answer. Humanized antibodies can be generated where the antigen-binding CDRs are murine, while the rest of the antibody, including the antibody variable (V) region framework regions (FRs), is usually human. The problem is usually that during the humanization process, the antibody affinity is frequently reduced. This reduction in affinity might be minimized by careful selection of human FRs Rabbit polyclonal to ITPK1 that are homologous to the original antibody, or by reintroducing the important murine FR residues back into the designed antibody (Clark 2000). Examples of humanized monoclonal antibodies include visilizumab (antiCD3, Nuvion?), trastuzumab (anti-HER-2, Herceptin?), and alemtuzumab (antiCD52, Campath?). Mass manufacture The manufacturing of antibodies and antibody fragments is usually costly. A potential answer has been to express fragments of antibodies such as Fab’ in microbial expression systems such as em Escherichia coli /em . This is more economical and yields much higher amounts of protein as a result of large fermenter volumes and shorter fermentation occasions compared with mammalian cell fermentation. The problem here is that these antibody fragments have very short circulation occasions in vivo. This in turn can be overcome by conjugation to PEG which results GNE-7915 in an increased half-life to proteins to which it is attached, either by avoiding renal clearance since polymer increases the apparent size of the molecule to above the glomerular filtration limit, and/or through evasion of cellular clearance mechanisms (Chapman 2002; National Horizon Scanning Centre 2004). Half-life is usually increased progressively as the size of PEG GNE-7915 is usually increased; values increase almost 7-fold for a single 25-kDa PEG chain, and 13.5-fold for a single 40-kDa PEG chain (Chapman 2002). Reducing immunogenicity The potential benefits of PEGylation are (Chapman 2002): Reduced antigenicity and immunogenicity of the molecule to which PEG is usually attached. Improved plasma half-life thereby reducing the requirement for frequent dosing. Improved solubility. Enhanced proteolytic resistance of the conjugated protein. Improved bioavailability via reduced losses at subcutaneous injection sites. Reduced toxicity. Improved thermal and mechanical stability of.