the solution. Engvall Application 06/539,754, specification, p. 2, lines 16-27. Published literature
and patents are referred to as describing specific techniques of separation. Engvall Application
06/539,754, specification, p. 2, line 27 to p. 3, line 18. Labeling of antibody and antigen is stated to
be well known and techniques of labeling are said to be generally known. Engvall Application
06/539,754, specification, p. 3, lines 19-28. According to the specification "assay methods involving
biospecific affinity reactions may be grouped into two types of methods, viz, competitive methods
and 'sandwich' methods." Engvall Application 06/539,754, specification, p. 4, lines 1-3.
Sandwich assays are described as involving a first reactant bound to a carrier. According to
Engvall’s specification, the bound reactant is placed into a sample containing a second reactant to be
determined. The bound reactant complexes with the second reactant. The second reactant is then
reacted with a labeled immunochemical counterpart forming a sandwich. Engvall Application
06/539,754, specification, p. 4, lines 8-12. Engvall notes some benefits and problems of sandwich
assays with reference to the importance of specificity of the antibodies used:
When determining an antigen in a sample a sandwich type method is
often preferred since such a method does not require the use of
labeled antigen which in certain cases is difficult to procure.
However, the sandwich assay places particularly stringent
requirements on the specificity of the antibody used and an assay
procedure with multiple incubation and washing steps is usually
required. [Emphasis added.]
Engvall Application 06/539,754, specification, p. 4, lines 13-19.
Engvall describes her invention as an improvement over these conventional sandwich assay
methods. According to the express statements in the specification, the improvement resides in the
use of monoclonal antibodies which react with sterically spaced determinants on the antigen. Thus,
the specification states:
According to the present invention an improved sandwich assay
method of the type set forth in the introductory part above is
provided, which method is characterized in using as antibody (II) and
antibody (III) in said determination antibodies which are monoclonal
and react with sterically spaced determinants of the antigen (I).
[Emphasis added.]
Engvall Application 06/539,754, specification, p. 4, lines 13-19. In identifying the improvement over
conventional sandwich assays affinity is not mentioned. The use of monoclonals is said to provide
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