The Federal Circuit recently reversed a jury verdict and billion-dollar judgment in favor of Juno Therapeutics on the grounds that the asserted claims did not satisfy the written description requirement of 35 U.S.C. § 112. See Juno Therapeutics, Inv. v. Kite Pharma, Inc.. This case further builds on the application of the written description requirement to claims that recite functional limitations, and is instructive to patent prosecutors.