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Leighton Zhao is an associate in Merchant’s Minneapolis office. As patent litigation attorney, Leighton focuses his practice on a variety of fields, with a special focus on life sciences. 

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Leighton Zhao is an associate in Merchant’s Minneapolis office. As patent litigation attorney, Leighton focuses his practice on a variety of fields, with a special focus on life sciences.

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<h2 class="wp-block-heading">A Clear Path to Patent Law</h2>

Leighton always had the desire to go to law school thanks to his upbringing. Both his parents were engineers, and throughout his childhood he was surrounded by many of their fellow engineer friends and colleagues. Some of these engineers made a career change by going to law school, and watching their career paths made a significant impression on Leighton.

Leighton always had the desire to go to law school thanks to his upbringing. Both his parents were engineers, and throughout his childhood he was surrounded by many of their fellow engineer friends and colleagues. Some of these engineers made a career change by going to law school, and watching their career paths made a significant impression on Leighton.

In high school, Leighton participated in policy debate. This further spurred his interest in becoming an attorney, as he was energized by the art of strategy and formulating articulate arguments.&nbsp;

In high school, Leighton participated in policy debate. This further spurred his interest in becoming an attorney, as he was energized by the art of strategy and formulating articulate arguments.&nbsp;

Knowing he needed to study a technical field for his future patent law career, Leighton attended Northwestern University. He earned his Bachelor’s degree in Integrated Science, Math and Chemistry and graduated magna cum laude.

Knowing he needed to study a technical field for his future patent law career, Leighton attended Northwestern University. He earned his Bachelor’s degree in Integrated Science, Math and Chemistry and graduated magna cum laude.

Leighton continued his education at Northwestern with a Master’s degree in chemistry. From there, he earned his Juris Doctor at Cornell Law School, where he was an Executive Editor of the Cornell Law Review.

Leighton continued his education at Northwestern with a Master’s degree in chemistry. From there, he earned his Juris Doctor at Cornell Law School, where he was an Executive Editor of the Cornell Law Review.

He completed an internship in patent prosecution to gain a well-rounded perspective of patent law. His scientific, technical, and educational background helps him understand the intricacies and details of clients’ innovations.&nbsp;

He completed an internship in patent prosecution to gain a well-rounded perspective of patent law. His scientific, technical, and educational background helps him understand the intricacies and details of clients’ innovations.&nbsp;

<h2 class="wp-block-heading">Highly Skilled at Complex Research</h2>

Inspired by his former high school science teacher, Leighton chose chemistry as his technical degree due to the field’s interesting research opportunities. Over the course of his education, he developed his strong analytical and research skills, knowing this would support his work in patent law.

Inspired by his former high school science teacher, Leighton chose chemistry as his technical degree due to the field’s interesting research opportunities. Over the course of his education, he developed his strong analytical and research skills, knowing this would support his work in patent law.

As a patent litigation attorney, attention to detail is critical. Leighton’s committed to supporting clients and the legal team by performing thorough legal research and thoroughly analyzing documents and instructions. His work is vital to developing in-depth legal strategies that help protect the inventions of clients.

As a patent litigation attorney, attention to detail is critical. Leighton’s committed to supporting clients and the legal team by performing thorough legal research and thoroughly analyzing documents and instructions. His work is vital to developing in-depth legal strategies that help protect the inventions of clients.

<h2 class="wp-block-heading">A Strong Work Ethic</h2>

One of the keys to Leighton’s success is his strong work ethic. He’s continually motivated to work hard and seek out opportunities.&nbsp;

One of the keys to Leighton’s success is his strong work ethic. He’s continually motivated to work hard and seek out opportunities.&nbsp;

Above all else, Leighton is inspired by his passion for litigation. The field brings fascinating knowledge and ideas to his desk every day, and he greatly enjoys the investigative process and learning about each client’s cutting-edge inventions, ideas and technology.&nbsp;

Above all else, Leighton is inspired by his passion for litigation. The field brings fascinating knowledge and ideas to his desk every day, and he greatly enjoys the investigative process and learning about each client’s cutting-edge inventions, ideas and technology.&nbsp;

Leighton is also a motivated team player who delights in interacting with clients and colleagues while working toward a common goal. He tackles each day with a flexible &nbsp;and collaborative mindset in order to fulfill his vast range of responsibilities and tasks. Leighton’s strong organizational and time management skills are essential to supporting the legal team's efforts.

Leighton is also a motivated team player who delights in interacting with clients and colleagues while working toward a common goal. He tackles each day with a flexible &nbsp;and collaborative mindset in order to fulfill his vast range of responsibilities and tasks. Leighton’s strong organizational and time management skills are essential to supporting the legal team's efforts.

Leighton was born and raised in Minnesota and speaks Cantonese. Outside of work, he’s an avid gamer and enjoys playing soccer.

Leighton was born and raised in Minnesota and speaks Cantonese. Outside of work, he’s an avid gamer and enjoys playing soccer.

Cornell University, J.D. Intellectual Property Law, 

Northwestern University, M.S. Chemistry

Northwestern University, B.A., Chemistry; Mathematics; Integrated Science

Leighton Zhao, Intellectual Property Attorney

Minneapolis

This week, the U.S. Court of Appeals for the Federal Circuit issued an opinion in <a href="https://cafc.uscourts.gov/opinions-orders/22-1946.OPINION.1-2-2024_2246968.pdf">PureCircle USA Inc. v. Sweegen, Inc., No. 2022-1946 (Jan. 2, 2024)</a>, affirming the District Court for the Central District of California’s summary judgment holding that PureCircle’s non-caloric sweetener patents were invalid for lack of adequate written description and as directed to patent-ineligible subject matter.



 Rebaudioside X (“Reb X”) is a non-caloric sweetener naturally produced by stevia plants. PureCircle owns U.S. Patent Nos. 9,243,273 and 10,485,257, which claim a method of synthesizing Reb X using a specific class of enzymes, UDP-glucosyltransferases (“UGT”). PureCircle sued Sweegen for infringement, and the district court granted summary judgment that PureCircle’s patents were invalid. PureCircle appealed.



 The Federal Circuit affirmed. The Court explained that in the context of chemical genus claims, such as the claims of PureCircle’s patents, the written description requirement “requires the disclosure of either a representative number of species falling within the scope of the genus or structural features common to the members of the genus.” The Court held that PureCircle’s patents did not meet either requirement; the specification only disclosed a single, non-representative example of the claimed UGT enzyme genus and failed to disclose any common structural features of the claimed genus. PureCircle argued that the single disclosed example was representative because it contained structural features common to all UGT enzymes. The Court disagreed, holding that the specification did not disclose these common features in a manner that would permit a person of ordinary skill in the art to recognize the members of the genus without extensive trial-and-error testing. The Court accordingly affirmed the district court’s holding that PureCircle’s patents failed to meet the written description requirement.



 The Court likewise affirmed the district court’s holding that certain claims of PureCircle’s patents were directed to unpatentable subject matter under 35 U.S.C. § 101. The Court determined that the claimed enzyme was an unpatentable natural phenomenon because it naturally synthesizes Reb X in stevia plants. PureCircle attempted to distinguish the claims from the naturally occurring process, asserting that stevia plants only produce trace amounts of Reb X, while the claims are directed to at least 50% conversion to Reb X. The Court rejected this argument, holding that the 50% conversion result is still an abstract idea, and that PureCircle’s patents did not disclose how to achieve that result other than by using a naturally occurring enzyme.

Federal Circuit Affirms Summary Judgment Decision Finding Lack of Written Description and Unpatentability Under Section 101

Last week, the U.S. Court of Appeals for the Federal Circuit issued an opinion in <a href="https://www.cafc.uscourts.gov/opinions-orders/23-1603.OPINION.4-15-2025_2498701.pdf">Sage Products, LLC v. Stewart, No. 2023-1603 (Apr. 15, 2025)</a>, affirming the final written decisions of the Patent Trial and Appeal Board invalidating the challenged claims of U.S. Patent Nos. 10,398,642 and 10,688,067.



The patents-in-suit relate to “sterilized” chlorhexidine antiseptics. As construed by the Board, an antiseptic is sterilized if it has been subjected to a suitable sterilization process such that sterility can be validated. The Board invalidated the challenged claims in view of the ChloraPrep Public Assessment Report (“PAR”), which is a publication from the UK’s regulatory equivalent to the FDA evaluating ChloraPrep. The PAR describes ChloraPrep as “sterile” but does not identify the processes by which ChloraPrep is “sterilized.” The Board referred to UK industry standards for sterility to determine the meaning of “sterile” within the PAR.



Sage argued that when the PAR was written, the pharmaceutical industry mistakenly believed that antiseptics such as ChloraPrep were properly sterilized and discovered sterilization issues prior to the invention. Specifically, the US version of ChloraPrep was no longer considered sterile. Sage argued that it was improper for the Board to consider the UK sterility regulations to determine what sterilization techniques would have been used in the PAR because (1) a POSA would not have been familiar with the UK industry standards and (2) the UK industry standards were not included as part of the ground asserted in the petition for inter partes review.



The Federal Circuit affirmed. First, the Court credited the Board’s factual findings that the UK version of ChloraPrep was subject to suitable sterilization processes within the meaning of the patents. The Court also credited the Board’s factual findings that a POSA would have been familiar with the regulatory regimes for products in their industry and the differences in regulation across different countries. Finally, the Court held that it was proper for the Board to determine what a POSA would understand “sterile” to mean in the PAR by reference to extrinsic evidence not presented in the grounds of the petition.

CAFC Affirms PTAB’s Use of Extrinsic Evidence to Understand Term in Prior Art Reference

Last week, the U.S. Court of Appeals for the Federal Circuit issued an opinion in <a href="https://www.cafc.uscourts.gov/opinions-orders/24-1408.OPINION.2-20-2026_2650255.pdf">REGENXBIO, Inc. v. Sarepta Therapeutics, Inc., No. 2024-1408 (Feb. 20, 2026)</a>, reversing summary judgment of patent ineligibility entered by the U.S. District Court for the District of Delaware.



REGENXBIO sued Sarepta, alleging infringement of U.S. Patent No. 10,526,617, which is directed towards genetically engineered host cells containing a recombinant plasmid with a heterologous gene sequence. A recombinant gene is created by splicing together the genetic material. A “heterologous” sequence is spliced material that comes from a different species.



In district court, the parties cross-moved for summary judgment regarding patent eligibility. The district court held that the claims are patent ineligible because they are directed to a naturally occurring phenomenon. Specifically, the district court found that the claims of the ’617 Patent were analogous to the claims held ineligible in Funk Brothers Seed Co. v. Kalo Inoculant Co., 333 U.S. 127 (1948), which involved a mixed culture of naturally occurring species of bacteria, because both cases involve mixing two organisms together. REGENXBIO appealed.



The Federal Circuit applied the “markedly different characteristics” test from Diamond v. Chakrabarty, 447 U.S. 303 (1980), in which the Court determines if the subject matter has “markedly different characteristics” and has “potential for significant utility” from that which is naturally occurring.



The Court found that the recombinant DNA had markedly different characteristics. Sarepta did not contest that the claimed recombinant DNA “does not and cannot exist in nature.” The Court distinguished the claims of the ’617 Patent from Funk Brothers, because the markedly different characteristics test evaluates whether the composition as a whole is naturally occurring rather than whether the individual components of the composition are naturally occurring. The Court held that unlike mixing cultures of bacteria, gene splicing creates a fundamentally new molecule that could not form in nature on its own. The Court also found that the recombinant DNA has the potential for significant utility because the recombinant DNA provides a benefit to gene therapy that none of the individual components provide. The Court held that the functional utility of the composition may be considered even if it is not expressly claimed.

Leighton Zhao

A Clear Path to Patent Law

Highly Skilled at Complex Research

A Strong Work Ethic

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