John Wesolowski

High-level expression of chimeric antibodies using adapted cDNA variable region cassettes

A rapid and generally applicable method for the modification of immunoglobulin cDNAs was developed so that the variable (V) regions could be expressed as cassettes, together with a variety of constant regions. Murine cDNAs were isolated, sequenced and the V regions joined to short oligonucleotides providing both splice donor sites and unique restriction sites for insertion into an expression vector. Using this strategy we have expressed the V regions of several murine antibodies, together with the human gamma 1 constant region. Although most of these chimeric antibodies were readily expressed, one murine light-chain cDNA sequence could not be expressed in transfected hybridoma cells. Reconstruction experiments indicate that the sequence created by the fusion of the murine leader and variable region blocked expression at the level of RNA accumulation. The methods described, as well as the potential problems of expression, are applicable to both traditional cDNA fragments and those obtained by in vitro amplification techniques.

Antigen binding and biological activities of engineered mutant chimeric antibodies with human tumor specificities.

The constant region of the human gamma 1 chain was mutated either by deleting the second domain (CH2) or by mutating the two hinge region cysteine residues, normally involved in the inter-heavy chain disulfide bond formation, to serines. The effects of these mutations on chain assembly, antigen binding, complement-dependent cytotoxicity (CDC), and antibody-dependent cellular cytotoxicity (ADCC) were measured after expressing the human constant regions together with mouse variable regions encoding anti-tumor cell specificities. The CH2-deleted chimeric antibody was found to have increased antigen binding activity and little (ADCC) or no (CDC) biological activity. The cysteine to serine hinge region mutant antibody had normal or slightly reduced antigen binding activity, greatly reduced ADCC activity, and a reduced, but still significant, ability to mediate CDC. These results reflect the complexity of the interactions between the immunoglobulin domains and their role in balancing the antigen binding and effector functions of antibodies. They suggest further that such antibodies may be useful in applications, such as the in vivo imaging of tumors, where the loss of effector function (e.g., Fc receptor binding) is desired.

Role of inter-heavy and light chain disulfide bonds in the effector functions of human immunoglobulin IgG1

The role of inter-heavy and light chain disulfide bonds in the effector functions of human IgG1 was investigated. This was accomplished by mutating appropriate sites in IgG1 such that the disulfide bond pattern now resembled that of IgG4. The effector functions of the mutant antibody were then compared to native IgG1 and IgG4. The antibody-dependent cell cytotoxicity activity was completely abolished in the mutant and the complement-dependent cytotoxicity assay was reduced fifteen-fold. The results suggest that the inter-heavy and light chain disulfide bond pattern of an antibody molecule play a role in its effector functions.