Two Remaining Challenged WARF Embryonic Stem Cell Patents Upheld in Ex Parte Reexamination

In a March 13 post I reported that the Wisconsin Alumni Research Foundation (WARF) had prevailed in an inter partes reexamination of its patent that claims cultured pluripotent human embryonic stem (ES) cells (7,029,913). That decision will likely be appealed by the third-party challenger Public Patent Foundation (PPF).

On March 5, the two other WARF embryonic stem cell patents (5,843,780 and 6,200,806) that were challenged by PPF were also found valid in final PTO actions (Notice of Intent to Issue Ex Parte Reexamination Certificate). These two reexamination were both ex parte (as opposed to the inter partes examination of the ‘913 patent), and thus PPF will not have an opportunity to appeal these decisions. Both decisions were based on essentially the same logic as the Action Closing Prosecution in the inter partes reexamination: the fact that multiple parties had tried for years without success to derive cultured, immortal ES cells for non-rodent mammals animals, that the prior art reported success only for certain rodents (most notably mice), and thus prior art teaching directed to the derivation of mouse ES cells was not enabling for primate ES cells, nor was there a reasonable expectation that the techniques could be successfully applied to primates.

The ‘806 patent claims are directed stable cultures of human ES cells – the claims are very similar to those in the ‘913 patent, the primary difference being that the ‘913 patent includes the limitation that the cells will proliferate in an undifferentiated state in the absence of leukemia inhibitory fact (LIF). The reexamination resulted in the amendment of the claims to specifically recite that the claimed human ES cells are “derived from a pre-implantation embryo,” and that the cell culture will proliferate in culture “in an undifferentiated state.” These limitations, which were also incorporated into the claims of the ‘913 patent, were probably inherently present in the original claims, but the explicit recitation of the limitations is one positive outcome of the reexamination. For example, the Action Closing Prosecution notes that prior art disclosing human embryonic germ (EG) cells derived from post-implantation embryos are different from ES cells, and thus the prior art EG cells did not anticipate or render obvious Thomson’s human ES cells.

The ‘780 patent claims are directed to stable cultures of primate ES cells – the claims are very similar to those in the ‘806 patent, the primary difference being that the ‘806 patent is limited to human ES cells. This reexamination also resulted in the amendment of the claims to specifically recite that the primate ES cells are “derived from a pre-implantation embryo,” and that the cell culture will proliferate in culture “in an undifferentiated state.”