Heather A. Boux

Conformation dependence of a monoclonal antibody defined epitope on free human kappa chains

Chemically and enzymatically modified kappa chains were tested by inhibition radioimmunoassay for their ability to block the binding of antibody K-1-21 with native kappa chains. Complete reduction and carboxymethylation of intrachain disulphide bonds destroyed the free kappa-chain epitope, a result confirmed by Western blotting of unreduced and reduced kappa monomers and dimers. Purified V kappa fragments failed to block the homologous interaction while inhibition was obtained with a pepsin digest yielding predominantly the C kappa region. Dimeric kappa chains were less effective than monomers in the inhibition assay, although HPLC analysis of immune complexes demonstrated the binding of two antibody molecules per molecule of dimer. Thus, the epitope on free kappa chains recognized by K-1-21 is dependent upon conformational integrity of the C kappa domain, the decreased binding activity of dimeric chains possibly being due to minor conformational changes induced by C-domain interactions.

A Monoclonal Antibody with Selectivity for Human Kappa Myeloma and Lymphoma Cells which has Potential as a Therapeutic Agent

K-1-21 is a monoclonal antibody which binds to human free kappa light chains and recognises a determinant, KMA selectively expressed on kappa myeloma and lymphoma cells. KMA is absent on plasma cells and resting B cells from normal adults but can be detected on some foetal B cells and a small proportion of activated B cells. Expression of KMA is greatest on cycling cells. K-1-21 is an IgG1 antibody that elicits ADCC but will not cap the KMA determinant unless a second ligand is present. K-1-21 has potential for practical application.

Detoxification of Pertussis Toxin by Site-Directed Mutagenesis

Pertussis toxin (PT) is a major virulence factor of Bordetella pertussis and also an important protective antigen in vaccines against whooping cough. Unfortunately, the chemical treatments normally used to inactivate the toxin can seriously reduce its immunogenicity; moreover, there are concerns that residual traces of active toxin might possibly account for the rare occurrence of vaccination side-effects. Following recent achievements in cloning and sequencing the TOX operon encoding PT (Locht & Keith, 1986; Nicosia et al. , 1986) , the genetic engineering of a PT analogue lacking toxicity but retaining full immunogenicity has become a major goal in the development of improved pertussis vaccines.

Development of non-toxigenic vaccine strains of Bordetella pertussis by gene replacement.

During the next decade, it is likely that current whole-cell whooping cough vaccines prepared from inactivated Bordetella pertussis will be replaced by component vaccines of defined purity and composition that offer higher efficacy and reduced reactogenicity. The principal B. pertussis antigens under consideration for such vaccines are pertussis toxin (PT), filamentous hemagglutinin (FHA), pertactin (69 kDa protein) and fimbrial agglutinogens. Although PT is a potent immunogen, it is also a major virulence factor of B. pertussis. However, the chemical treatments now used to inactivate PT can reduce its immunogenicity, and depending on the method used, may be susceptible to reversion. An ideal approach to PT detoxification is the genetic replacement or removal of a few critical functional amino acid residues so that three-dimensional structure and immunogenicity are only minimally impaired.