Appeal No. 1997-3945
Application No. 08/410,390
potent immunotoxin suitable for use against human tumor cells.
Figure 1 of Pastan (Cell), page 643, is entitled "Pathway of
Immunotoxin Entry," illustrating the pathway by which
immunotoxins are internalized into cells. This reference
suggests that immunotoxins composed of antibodies to the human
transferrin receptor and either ricin A chain or Pseudomonas
exotoxin A are very effective. See Pastan (Cell), page 646,
second column, first full paragraph.
We are persuaded that a person having ordinary skill in
the art, armed with the disclosures of Pastan '985 and Pastan
(Cell), would have found it obvious to modify the biotinylated
compound of Goodwin by using Pseudomonas exotoxin as the
pharmaceutically active moiety therein. By thus modifying the
system of Goodwin, per the teachings of Pastan '985 and Pastan
(Cell), the hypothetical person having ordinary skill in this
art would have arrived at the subject matter sought to be
patented in claim 1 where the cytotoxic protein is Pseudomonas
exotoxin. Such hypothetical person would have had a
reasonable expectation of achieving a pharmaceutically active
immunoconjugate coupled through the avidin-biotin interaction,
where the interaction takes place in vivo after the
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