Antibody antigen selection

By similar logic, protein affinity Hbraries have been constmcted to identify protein—protein combining sites, as in antibody—antigen interaction (19) and recombinant Hbraries have been made which produce a repertoire of antibodies in E. coli (20). In another case, a potential DNA-based therapeutic strategy has been studied (21). DNAs from a partially randomized Hbrary were selected to bind thrombin in vitro. Oligonucleotides, termed aptamers that bound thrombin shared a conserved sequence 14—17 nucleotides long. 

In fields such as biosensing, analyte binding often relies on very specific molecular recognition interactions that nature has supplied, such as antibody-antigen interactions or strands of complimentary DNA forming double hefices. Unfortunately, because versatile and highly selective receptors for TNT or other explosive molecules are not available, chemists are left to rely on less specific interactions. 

The issue of which antibody to select for an assay is not a new problem. Certainly anyone involved in the development of an immunoassay has been faced with this choice. Consider attempting to create a multianalyte, microarray-based micro-ELISA of modest density (10 to 100 analytes) and determining which capture antibodies to use based upon their affinities, stabilities, and cross-reactivities. For a sandwich assay, add in the 10 to 100 analyte-specific secondary (reporter) antibodies and determine their levels of cross-reactivity with each other and with the specified antigens and capture antibodies. In other words, achieving high performance for all analytes with a microarray immunoassay is indeed a formidable challenge. 

Positive selection is not recommended as these procedures may induce signaling pathways in CLL cells due to antibody/antigen interactions. Purity of CLL cells is assessed by flow cytometry using anti-CD19, anti-CD5, and matching isotype control... 

Figure 10.3. Schematic representation of monoclonal antibody production using immortalized hybrid cells that secrete antibodies selective for the target antigen. The mortal, immune B cells Isolated from mice immunized with a target antigen are fused with myeloma, immortal B cells that express defective antibodies. The selecting of antigen-specific, immortal hybrid cells (hybridomas) results in identification of unique clones of cells that express antibodies with high specificity and affinity (monoclonal antibodies). These cells are cloned and expanded for large-scale monoclonal antibody preparations.

Monoclonal antibodies directed against specific antigens such as CD3, CD4, CD25, CD40, IL-2 receptor, and TNF-a (discussed below) much more selectively influence T-cell subset function. The high specificity of these antibodies improves selectivity and reduces toxicity of the therapy and alters the disease course in several different autoimmune disorders. 

Once antibodies and antigens have been developed, they must be incorporated into an assay system for visualization of the primary antibody-antigen reaction. To accomplish this task effectively, an assay format and procedures to visualize the antibody-antigen reaction must be first selected, the necessary reagents must then be prepared, and the final immunochemical method including sample preparation must be optimized for the intended application. 

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