What was the core question in Kirin-Amgen?

Whether TKT’s GA-EPO, made by a different process, fell outside Amgen’s EPO patent claims when read with purposive construction.

What test did the court use to read claims?

Purposive construction. Claims are read as a skilled person would, focusing on what the inventor meant, not a narrow literal reading.

Did the doctrine of equivalents decide the case?

The court emphasised purposive construction and concluded that TKT’s method was not within the claims; no infringement was found.

Why did TKT’s GA-EPO not infringe?

Because its gene-activation route materially differed from Amgen’s claimed recombinant DNA process. A skilled person would see the processes as different.

What should students remember from this case?

Claim meaning comes first. Ask how a skilled reader in 2004 would understand the words. Different processes may avoid infringement if outside the claims.

kirin-amgen-inc-v-hoechst-marion-roussel

Kirin-Amgen Inc. v. Hoechst Marion Roussel [2004] UKHL 46

EPO patents and claim scope: how purposive construction treats different manufacturing routes—and why TKT’s GA-EPO avoided infringement.

House of Lords (UK) 2004 Law Lords [2004] UKHL 46 Patent (Biopharma) ~7 min read

CASE_TITLE: Kirin-Amgen Inc. v. Hoechst Marion Roussel PRIMARY_KEYWORDS: EPO patent, purposive construction, doctrine of equivalents SECONDARY_KEYWORDS: GA-EPO, gene activation, infringement analysis PUBLISH_DATE: 2025-11-01 AUTHOR_NAME: Gulzar Hashmi LOCATION: India slug: kirin-amgen-inc-v-hoechst-marion-roussel

Quick Summary

The case asks: if a rival makes the same end-product (EPO) by a different route, does it infringe? The House of Lords read the patent with purposive construction. A skilled reader would see Amgen’s claims were tied to the recombinant DNA route described. TKT’s gene-activation method took a different path. Result: no infringement.

Focus: claim meaning to a skilled person, not strict literalism.
Different process, same product ≠ infringement if outside the claims.
Doctrine of equivalents sits within purposive reading in UK law at the time.

Issues

Does a rival’s EPO made by gene activation fall within claims directed at a recombinant DNA process?
How should claims be read—literal words or purposive construction guided by a skilled reader?

Rules

Purposive Construction: Read the claim through the eyes of a skilled person, focusing on what the patentee meant to cover.
Doctrine of Equivalents (contextual): Non-literal variants may infringe if, in substance, they take the same inventive idea—but scope still turns on claim meaning.
Process vs Product: Where claims centre on a particular process, a materially different route can fall outside.

Facts (Timeline)

Amgen’s EPO by rDNA

Amgen developed EPO using recombinant DNA technology; obtained European patent; marketed as “Epogen”.

TKT’s GA-EPO

Transkaryotic Therapies (TKT) made EPO via gene activation; product called “Dynepo”; labelled GA-EPO.

Import Plan

Respondents proposed to import GA-EPO into the UK market.

Litigation Path

Amgen sued for infringement. Court of Appeal: claims valid, but no infringement. Both sides appealed to the House of Lords.

Timeline graphic for Kirin-Amgen v. Hoechst: rDNA vs gene activation routes

Arguments

Appellant: Amgen

The claims, read purposively, cover making EPO regardless of minor technique shifts.
TKT’s method achieves the same result in substantially the same way.
Skilled readers would treat GA-EPO as falling within the inventive concept.

Respondent: TKT

Claims are tied to the recombinant DNA route; gene activation is materially different.
No textual hook in the claims for our process; a skilled person would not read it in.
Therefore, GA-EPO lies outside the claimed method; no infringement.

Judgment (Held)

The House of Lords held no infringement. Reading the claims purposively, a skilled person would see that TKT’s gene-activation route was not what Amgen’s claims covered. The processes were materially different in mechanism and teaching.

Judgment visual for Kirin-Amgen v. Hoechst: claim scope and different processes

Ratio Decidendi

Claim meaning controls. Under purposive construction, you ask what the skilled reader would understand the patentee to mean at the time. Because the claims taught the recombinant DNA approach, a distinct gene-activation route lay outside their scope.

Why It Matters

Drafting lesson: If you claim a process, say clearly if variants are covered.
R&D strategy: Alternative routes can avoid infringement if claims are narrow.
Exam tip: Always read claims as a skilled person would, not as a grammar exercise.

Key Takeaways

Purposive construction decides scope.
Different process ≠ infringement if outside claims.
Equivalents are bounded by claim meaning.

Biopharma claims must anticipate alternatives.
Skilled person’s understanding is the anchor.

Mnemonic + 3-Step Hook

Mnemonic: “Claim First, Route Next.”

Read the Claim: What would a skilled person understand?
Map the Route: Is the accused process the same route?
Decide Scope: If the route is materially different, no infringement.

IRAC Outline

Issue	Whether GA-EPO made by gene activation infringed claims directed at rDNA production of EPO.
Rule	Purposive construction; possible equivalents, but claim meaning as understood by a skilled person governs.
Application	TKT’s process materially differed in mechanism and teaching; a skilled person would not read it into the claims.
Conclusion	No infringement; TKT’s GA-EPO is outside Amgen’s claimed route.

Glossary

Purposive Construction: Reading claims for what the inventor meant, as a skilled person would understand.
Doctrine of Equivalents: Non-literal variations that capture the same inventive idea may still infringe—within claim meaning.
Gene Activation: Technique that turns on a cell’s own gene to make the protein, rather than inserting recombinant DNA.