Major advances in the analysis of biomolecular structure have emerged from the development of highly specific monoclonal antibodies (MAb) by Köhler and Milstein in 1975 (1). MAb are produced from hybridoma cell lines that secrete a single species of antibody to a unique antigen. The advantages of MAb as reagents for antibody engineering are:

1.	They are extremely pure immunological reagents that can be produced by immunization with a heterogenous antigenic preparation;
2.	They are homogenous with respect to affinity and specificity;
3.	The specificity of the antibody is directed to a single epitope;
4.	The desired MAb can be selected for activity, affinity, and subclass by applying appropriate screening methods; and
5.	Virtually unlimited quantities of MAb can be produced.