## Facts

- Mycogen Plant Science, Inc. owned U.S. Patent No. 5,380,831 relating to genetically engineered plants expressing *Bacillus thuringiensis* (Bt) insecticidal proteins.
- The patent included method claims for producing Bt-expressing plants and product claims (including claims 13 and 14) directed to specific synthetic DNA sequences for plant expression.
- Related family patents were previously litigated in another action, where a jury found those related claims invalid based on Monsanto’s prior invention, and that judgment was affirmed on appeal.
- In this case, Mycogen sued Monsanto in the Southern District of California for infringing the ’831 patent based on Monsanto’s Bt transgenic plant activities.
- Monsanto sought summary judgment that (i) the method claims were invalid under 35 U.S.C. § 102(g) due to Monsanto’s prior invention, (ii) there was no liability under 35 U.S.C. § 271(g) for processes performed before the ’831 patent issued, and (iii) prosecution history estoppel barred the doctrine of equivalents for product claims 13 and 14.
- The district court granted summary judgment for Monsanto on all three grounds, relying in part on issue preclusion from the earlier litigation for the § 102(g) ruling.
- On appeal, Monsanto also argued that the judgment should be affirmed on the alternative ground that the patent lacked enablement under 35 U.S.C. § 112 ¶ 1.

## Issues

1. Whether summary judgment of invalidity of the ’831 method claims under 35 U.S.C. § 102(g) was proper, including whether issue preclusion from the earlier litigation resolved prior-invention questions for the ’831 claims.
2. Whether 35 U.S.C. § 271(g) permits liability based on processes practiced before the patent’s issuance.
3. Whether prosecution history estoppel barred Mycogen from asserting the doctrine of equivalents as to product claims 13 and 14.
4. Whether the appellate court should affirm invalidity on the alternative basis of lack of enablement under 35 U.S.C. § 112 ¶ 1.

## Decision

- The Federal Circuit reversed summary judgment that the method claims were invalid under § 102(g), holding that the district court resolved disputed issues of material fact on prior invention and therefore could not dispose of the issue on summary judgment.
- The court affirmed the ruling that § 271(g) does not impose liability for acts occurring before the issuance of the patent.
- The court affirmed that prosecution history estoppel barred the doctrine of equivalents for claims 13 and 14, and on rehearing adhered to that result after further review of the prosecution history.
- The court declined to affirm invalidity on enablement and remanded for the district court to address enablement in the first instance.
- Disposition: reversed in part, affirmed in part, and remanded.

## Legal Principles

- Summary judgment is improper where the record contains disputed material facts on § 102(g) prior-invention questions; related prior litigation does not automatically preclude litigation of prior invention for different claims where factual issues remain.
- 35 U.S.C. § 271(g) does not apply to conduct occurring before the patent issues; patent rights do not attach retroactively to pre-grant process activity.
- Prosecution history estoppel applies when an applicant narrows claim scope to obtain allowance (including by accepting narrow examiner-proposed language and canceling broader claims), barring use of the doctrine of equivalents to recapture surrendered subject matter.
- An appellate court may decline to affirm invalidity on an alternative fact-dependent theory (such as enablement) when the district court has not made the needed determinations.

## Conclusion

The Federal Circuit required further fact-finding before invalidating the ’831 method claims for prior invention, while enforcing § 271(g)’s pre-issuance limit and holding that Mycogen’s narrowing prosecution history foreclosed equivalents for the patent’s key DNA sequence product claims.


Mycogen Plant Sci., Inc. v. Monsanto Co., 252 F.3d 1306 (Fed. Cir. 2001)