Using Antibody Fragments

The primary goal of any of these conjugation schemes using antibody fragments is to maintain the activity of the antigen binding site while limiting the size of the final complex with a... 

One limitation to this method should be noted. If the antibody-enzyme conjugate is prepared using antibody fragments such as Fab or F(ab )2, then nickel-chelate affinity chromatography will not work, since the requisite Fc portion of the antibody necessary for complexing with the metal is not present. 

An alternative approach is to use antibody fragments (the Fab domian) raised against a particular protein. This technique has been used with some success for crystallizing a number of membrane proteins, including the CIC chloride channel (Dutzler et al., 2002), a K+ voltage-dependent channel (Jiang et al., 2003), and a cytochrome c oxidase (Iwata et al., 1995). 

While whole antibodies are currently produced in expensive mammahan cell culture systems, for some appHcations the expression of antibody fragments in prokaryotes, yeast or filamentous fungi is an alternative. Tissue penetration is facilitated, and clearance from the blood or kidney is faster using antibody fragments. In addition, PEGylation allows the modification of the half-Hfe, which is another advantage of antibody fragments (see also Part VI, Chapter 2). 

The "stealth" concept may offer two other opportunities for liposome application (1) Conventional immunoliposomes (see Sec. VI.C) have been shown to be removed rapidly firom the circulation by the MPS (Peeters et al., 1987). The combination of the stealth approach for longer circulation with the attachment of antibodies or antibody fragments may provide a means of delivery of drugs to their sites of action with a high degree of specificity. This could be useful for treating leukemia, graft-vs.-host diseases, and HIV disease. 

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