In March 2017, Sanofi and Regeneron sought inter partes review of Immunex’s patent US8679487 on the grounds of lack of novelty, relying on a single alleged prior art publication. The PTAB denied the institution of a review, deciding that the petitioners had not established a reasonable likelihood that they would prevail in showing the unpatentability of the patent. This conclusion followed a finding that the patent was entitled to a priority date from before the publication of the prior art relied on.