In Amgen v. Hospira[1], a
patent infringement lawsuit (U.S. Patent No. 5,856,298) over the biosimilar
version of Amgen’s Epogen (epoetin alfa), the parties disputed the meaning of
the term "an isolated ... isoform" in claim 1:
1. An isolated biologically active erythropoietin isoform having a single isoelectric point and having a specific
number of sialic acids per molecule, said number selected from the group
consisting of 1-14, and said isoform being the product of the expression of an
exogenous DNA sequence in a non-human eucaryotic host cell.
8. A composition
consisting essentially of two or three erythropoietin isoforms according to claim 1.
Amgen proposed that "an isolated ...
isoform" allows for mixtures of at least one isoform. Hospira proposed that the language allows for
mixtures of only one isoform.
The District Court (Richard Andrews) first discussed
the case law regarding the meaning of the term ‘a’ or ‘an’ in a claim: “That
'a' or 'an' can mean 'one or more' is best described as a rule, rather than
merely as a presumption or even a convention. The exceptions to this rule are extremely
limited: a patentee must 'evince[] a clear intent' to limit 'a' or 'an' to
'one'. . . An exception to the general
rule that 'a' or 'an' means more than one only arises where the language of the
claims themselves, the specification, or the prosecution history necessitate a
departure from the rule."
Despite stating that the exceptions to this rule (limiting
‘a’ or ‘an’ to only one) are extremely limited, the District Court found that the
exception applied “because the plain language evinces a clear intent to claim only
one isoform. The claim language reads ‘an isolated ... isoform.’ Plaintiff's
reading would render the word ‘isolated’ superfluous. Plaintiff's reading would
equate the phrase ‘an isolated .. . isoform’ with ‘an isoform.’” The District Court further emphasized that Claim
1 was amended during prosecution to read "[a]n isolated ... isoform."
The purpose of the amendment was
"to further clarify that an erythropoietin isoform represents a
homogeneous preparation."
After finding that Claim 1 requires only one isoform,
the District Court found Claim 8 to be invalid since it contradicts Claim 1 's
limitation that the isoform is "isolated." Claim 8 requires a mixture
"consisting essentially of two or three" isoforms. Claim 8 thus improperly narrows Claim 1.
The District Court did not discuss the doctrine of
claim differentiation, and how the multiple isoforms of Claim 8 would imply
that Claim 1 is not limited to a single isoform.
The Opinion can be found here:
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