The inventors of the ‘929 patent discovered that some cells could be frozen and thawed multiple times. They used a process called density gradient fractionation to isolate those cells, finding that 70 percent of them could be refrozen and used again.

U.S. Patent 7,604,929 is focused on hepatocytes, liver cells that are useful for testing, diagnostic and treatment purposes. The cells have a short life span, and freezing them repeatedly can cause damage, according to Prost’s opinion. To study a drug’s impact on the general population, researchers previously had to pull together pools of liver tissue from multiple donors, then unfreeze them all at once for a single use.

U.S. District Judge Milton Shadur ruled that the patent is “directed to an ineligible law of nature: the discovery that hepatocytes are capable of surviving multiple freeze-thaw cycles.”

But, Prost said Tuesday, “that is not where [the inventors] stopped, nor is it what they patented.” Rather, the inventors “employed their natural discovery to create a new and improved way of preserving hepatocyte cells for later use.”

Plus, she wrote, while freezing and thawing hepatocytes was conventional at the time, the process of doing it twice “was itself far from routine and conventional.” Prost’s reliance on that “ordered combination” of steps echoed Judge Raymond Chen’s reasoning turning back a software patent eligibility challenge just last week.

Judges Kimberly Moore and Kara Stoll concurred in Prost’s opinion.