United States: Prosecution History Does Not Preclude Unrecited Steps in Process Claim

The U.S. Court of Appeals for the Federal Circuit, finding error in the district court's construction of a process claim, vacated a summary judgment decision and remanded the case for further proceedings. Invitrogen Corp. v. BioCrest Manufacturing, L.P., Case No. 02-1207 (Fed. Cir. May 7, 2003). Invitrogen accused the defendant of infringement of U.S. Pat. No. 4,981,797 (the `797 patent) directed to a process for producing transformable E. coli cells of improved competence. The claimed process required performance of three steps in a specific order, including the step of rendering said E. coli cells competent after growing the cells in a medium at temperature in the range of 18 to 32ºC.

During prosecution, the U.S. Patent and Trademark Office (USPTO) examiner stated that the claimed range of 18 to 32ºC was essential to the invention. The applicants then amended the claims to add the language "improved competence" to the preamble and to replace the originally recited open range of "less than 37ºC" with "18 to 32ºC" and argued that the amendment distinguished the claimed invention from prior art showing growth at 37ºC.

The defendant makes and sells competent E. coli cell lines using a process that includes "incubating" the cells at 37ºC and then growing the cells in a fermenter at 26ºC.

The district court construed the claim to require that cell "growth must be performed at a temperature within 18 to 32ºC" and rejected Invitrogen's argument that the open-ended transition term "comprising" in the preamble permitted coverage over a process where an additional step of growing or "incubating" cells at 37ºC before the step of growing cells in the recited range.

The Federal Circuit reversed, finding that the claim did not preclude additional steps, such as the defendant's incubation step, before or after the recited steps. Specifically, the Court found that the transitional term "comprising" opened the claim to additional, unrecited steps and did not preclude growth by incubation at 37ºC in advance of the first step.

Also, the Federal Circuit noted that the district court's claim construction would exclude an embodiment set forth in an example, a construction that is "rarely, if ever correct" and which would require "highly persuasive evidentiary support" not found here.

Finally, the Federal Circuit found that the district court claim construction improperly ignored the "improved competence" language in the preamble: "[C]lear reliance on the preamble during prosecution to distinguish the claimed invention from the prior art transforms the preamble into a claim limitation because such reliance indicated use of the preamble to define, in part, the claimed invention." Here the court found that the term "improved competence" should have been construed "to require at least a ten-fold competence increase over the prior art method."