The ground of “patent ineligibility” has been applied fairly widely in US patent practice. However, a recent decision of the Federal Circuit Court in REGENXBIO, Inc. v. Sarepta Therapeutics, Inc., No. 24-01408 (Fed. Cir. 2026) (“REGENXBIO v. Sarepta”) provides welcome relief for applicants seeking to protect biotech inventions in the USA.

The Federal Circuit has held that the genetically engineered host cells for producing gene therapy products claimed in REGENXBIO’s U.S. Patent No. 10,526,617 (“the ‘617 patent”) are products of “human intervention” and therefore constitute patent eligible subject matter.

Background

The claims of REGENXBIO’s ‘617 patent are directed to host cells genetically engineered to contain a recombinant nucleic acid molecule comprising an adeno-associated virus (AAV) capsid sequence and a heterologous non-AAV sequence. These engineered host cells can be used to produce AAV gene therapy products.

REGENXBIO brought an action against Sarepta based on infringement of the ‘617 patent. Sarepta counterclaimed for invalidity.

At first instance, the Delaware District Court invalidated REGENXBIO’s patent claims directed to cultured host cells containing the recombinant nucleic acid sequences. In reaching its decision, the District Court found that combining two naturally occurring DNA sequences did not amount to a patent eligible invention.

The Decision

On appeal, The Federal Circuit held that the lower court had erroneously relied on the 1948 Funk Brothers “bacterial cocktail” precedent in finding that combining two naturally occurring DNA sequences did not create anything new.

In the decision, The Federal Circuit clarified that:

• Structural transformation matters: Unlike a mixture of independent bacteria, splicing heterologous DNA sequences into a single recombinant molecule creates a human-made construct that cannot exist in nature.
• The Chakrabarty standard applies: Patent eligibility should be assessed through the framework of Diamond v. Chakrabarty, 447 U.S. 303 (1980) (“Chakrabarty”). In this regard, The Federal Circuit held that “Chakrabarty defines our inquiry” and therefore the question to be answered was “whether the claimed host cells have “markedly different characteristics” and have “the potential for significant utility” from that which is naturally occurring”¹. Citing Chakrabarty, the court decided that: “the claimed nucleic acid molecules here, although containing naturally occurring segments of DNA, are “not nature’s handiwork” and “not … a hitherto unknown natural phenomenon, but … a nonnaturally  [sic] occurring manufacture or composition of matter.”²

Applying these principles, REGENXBIO’s engineered cells, which contain AAV capsid sequences transformed into them, were held to be patent-eligible.

The European perspective

At the European Patent Office (EPO), Rules 26-29 EPC and the Biotech Directive provide a more applicant-friendly framework under which biological material isolated from its natural environment or produced by means of a technical process is generally considered patentable even if it previously occurred in nature. It is hoped that the ruling in REGENXBIO v. Sarepta will now close the “eligibility gap” between the EPO and the USPTO.

This decision also confirms terms such as “recombinant,” “heterologous,” and “genetically engineered” will be helpful when navigating US subject matter eligibility hurdles and should be included when drafting patent applications directed to biotech inventions.

Footnotes

1.See REGENXBIO v. Sarepta  at p.12

2. See REGENXBIO v. Sarepta at p. 13