IP Law Daily, PATENT—Fed. Cir.: Federal Circuit revives lawsuit over muscular dystrophy treatment patent, (Feb 23, 2026)

By Carolin Dennis, B.Sc., LL.B., LL.M.

The district court erred in concluding that the asserted claims of the ’617 patent, covering a treatment for one type of muscular dystrophy, Duchenne muscular dystrophy, were invalid.

The U.S. Court of Appeals for the Federal Circuit has reversed the district court’s summary judgment of ineligibility of the patent related to a biotech company’s competing gene-therapy technology for the treatment of a type of muscular dystrophy, Duchenne muscular dystrophy. The Federal Circuit determined that the claimed host cells contain a recombinant nucleic acid molecule that, by definition, is markedly different from anything occurring in nature, and therefore are not patent-ineligible claims to naturally occurring subject matter (Regenxbio Inc. v. Sarepta Therapeutics, Inc., No. 24-1408 (Fed. Cir. Feb. 20, 2026)).

The University of Pennsylvania owns U.S. Patent No. 10,526,617 (the ’617 patent). The ’617 patent is titled “Method of Detecting and/or Identifying Adeno-Associated Virus (AAV) Sequences and Isolating Novel Sequences Identified Thereby,” and is directed to genetically engineered host cells that contain adeno-associated virus rh.10 sequences. REGENXBIO, Inc. licensed the ’617 patent from the University of Pennsylvania and used it to develop an AAV gene therapy product for Duchenne muscular dystrophy. Sarepta Therapeutics, Inc. and Sarepta Therapeutics Three, LLC (Sarepta) developed and manufactured a competing product, referred to as SRP-9001, which treats Duchenne muscular dystrophy using the AAV variant rh.74 gene therapy vector.

REGENXBIO Inc. and The Trustees of the University of Pennsylvania (collectively, REGENXBIO) filed a patent infringement suit in the district court against Sarepta for infringing claims 1–9, 12, 15, and 18–25 of the ’617 patent. Both parties moved for summary judgment of patent eligibility under 35 U.S.C. § 101. The district court granted Sarepta’s motion and held that all asserted claims of the ’617 patent were ineligible under § 101. REGENXBIO appealed.

The Federal Circuit noted that the claimed host cells include a recombinant nucleic acid molecule that does not and cannot exist in nature. Specifically, the claims require (1) “recombinant” nucleic acid, which means segments of nucleic acid from one source are artificially manipulated or inserted into the nucleic acid of another source through gene splicing; and (2) a nucleic acid molecule capable of encoding a sequence at least 95% identical to an AAV rh.10 sequence and a “heterologous” non-AAV sequence, where “heterologous” means from a different species. Thus, the recombinant nucleic acid molecule must be spliced together via human intervention from at least two different species to meet the claim limitations. Thus, the Federal Circuit found that like the man-made plasmid combining four naturally occurring bacteria in Diamond v. Chakrabarty, 447 U.S. 303 (1980), 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 non-naturally occurring manufacture or composition of matter.

Sarepta cited ChromaDex, 59 F.4th at 1283 to support its view to the contrary. However, the Federal Circuit noted that ChromaDex did not undermine Chakrabarty. The claims in ChromaDex expressly required the composition to “increase NAD+ biosynthesis.” In other words, the claims define the structure of the composition not just by the identity of its components but also by the overall function of the recited composition. The Federal Circuit noted that the claimed host cells contain molecules that are markedly different from anything naturally occurring, so it need not reach the question whether they are markedly different based on unclaimed functions. Thus, even when considering that question, Chakrabarty supported holding the claims eligible.

Sarepta also urged the Federal Circuit to set aside the claims as a whole and focus on isolating the AAV rh.10 sequence because the other claim limitations were conventional and would not themselves be patentable advancements. However, the Federal Circuit was not persuaded and declined to read out or ignore limitations in a claim merely because they may be found in the prior art or within the knowledge of a skilled artisan.

The Federal Circuit also found that the claimed host cells here contain a recombinant nucleic acid molecule that, by definition, is markedly different from anything occurring in nature. The claimed host cells are, therefore, not patent-ineligible claims to naturally occurring subject matter. Further, the Federal Circuit concluded that under the framework established in Mayo Collaborative Services v. Prometheus Laboratories, Inc., 566 U.S. 66 (2012), and Alice Corp. Pty. Ltd. v. CLS Bank International, 573 U.S. 208 (2014), at step one, the asserted claims are not directed to a product of nature. If the claims are not directed to a patent-ineligible concept under Alice step one, the claims satisfy § 101 and the Federal Circuit need not proceed to the second step.

Accordingly, the district court’s summary judgment of ineligibility under 35 U.S.C. § 101 was reversed and remanded for further proceedings.

The Case is No. 24-1408.

Judge: Stoll, K.

Attorneys: Susan E. Morrison (Fish & Richardson P.C.) for Regenxbio Inc. James Baker (Quinn Emanuel Urquhart & Sullivan, LLP) for Sarepta Therapeutics, Inc.

Companies: Regenxbio Inc.; Sarepta Therapeutics, Inc.

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