Assignor estoppel doesn’t bar an inter partes review: a 2013 Board decision, precedential as to § II.A only, and the Federal Circuit agree. In 2025 the Acting Director denied review anyway, where inventors who had assigned their rights were behind the petition. In 2026 the Federal Circuit declined to step in.
Before you read
Inventors who assigned a patent start a company, and it petitions for IPR. Can the Office refuse to hear it, even though assignor estoppel doesn’t apply?
Yes. In Tessell (Aug. 22, 2025), the Acting Director acknowledged assignor estoppel doesn’t apply in IPR, but vacated institution and denied the petition as an inefficient use of review.
Part 1 of 7
Robert Schad was a named inventor on a Husky Injection Molding patent. He was also the founder, co-owner, president and CEO of Athena Automation, and one of its two directors. When Athena petitioned to cancel the patent’s claims, Husky made one argument: an inventor’s company shouldn’t be allowed to attack the inventor’s own patent. The Board instituted review of all 22 challenged claims.
| Court or ITC | IPR at the PTAB | |
|---|---|---|
| Assignor estoppel | Can limit validity attacks by an assignor and those in privity | Does not bar the petition (Athena; Arista) |
| Why | An equitable doctrine; the ITC statute allows “[a]ll legal and equitable defenses” | § 311(a): “a person who is not the owner of a patent may file” |
| Discretion to refuse | Not the question | Yes: Tessell (2025) |
Part 2 of 7
Assignor estoppel is an equitable doctrine from the courts. Someone who assigns a patent, often an inventor assigning to an employer, generally can’t later argue in court that it is invalid. The Board began with the text instead: “a person who is not the owner of a patent may file with the Office a petition to institute an inter partes review.” An assignor, no longer the owner, is that person.
The Board contrasted the International Trade Commission, where the statute provides that “[a]ll legal and equitable defenses may be presented in all cases.” “Congress issued no similar statutory mandate to the Office in connection with AIA post-grant reviews.” And “none of Husky’s arguments addresses the language of § 311(a).”
“Congress issued no similar statutory mandate to the Office in connection with AIA post-grant reviews.”
The Federal Circuit later agreed. In Arista v. Cisco, it held that the statute’s language leaves no place for assignor estoppel in IPR.
Part 3 of 7
Tessell’s founders and employees included inventors who had assigned their rights to Nutanix. The Board instituted one of Tessell’s challenges; a related one had been denied. On August 22, 2025, the Acting Director vacated the institution and denied the petition.
The order expressly acknowledged that assignor estoppel does not apply. It found review inefficient where the inventors now argued the claims were unpatentable. Tessell’s argument about broader claims in later patents of the family also lacked a sufficient comparison with the originally filed specification.
Part 4 of 7
Tessell asked the Federal Circuit for mandamus, an extraordinary order directing the Office to act. On February 24, 2026, the court refused in a nonprecedential order.
The tempting reading
If the Director refuses, the Federal Circuit will correct it under Arista.
What the court said
Arista reviewed a final written decision. Tessell challenged a discretionary denial of institution, which the statute largely shields from review, under the demanding mandamus standard. The court also rejected the argument that Athena’s designation, precedential as to § II.A only, created a protected interest in IPR review.
Source
Part 5 of 7
For a company founded by or employing a patent’s inventors, the filing decision has three parts. A yes to the first doesn’t answer the other two.
Part 6 of 7
Choose your side.
Part 7 of 7
The forum split cuts both ways. Because the ITC statute allows “[a]ll legal and equitable defenses,” an inventor’s company could face assignor estoppel at the ITC on the same patent it is free to challenge at the PTAB.
They show
They don’t show
Athena has been precedential as to § II.A only since 2013, but it predates the current discretionary-denial practice, under which a petition can be eligible and still be refused. Tessell is one order, so how often inventor involvement leads to denial isn’t measured.
The takeaway
Assess the risk of refusal before budgeting for the merits, and before treating an appeal as the fallback.
Precedential decisions bind the Board within their designated scope. Informative decisions show the Office’s reasoning but do not bind the Board. Court opinions are cited for what they decided; later history was checked on the date shown above.