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Ensuring a correct entitlement to claim priority from earlier application is key for all patent rights holders, but some recent cases at the European Patent Office (EPO) bring into focus how the EPO assesses this, and things rights holders and their representatives need to be aware of from an early stage of (if not before!) a patent application’s lifetime.

We reported back in January 2020 on the long-awaited EPO Appeal Hearing for The Broad Institute’s CRISPR/Cas9 patent EP 2 771 468. The Board of Appeal decided to uphold the Opposition Division’s finding that the EP 2 771 468 does not have a valid claim to two key priority documents. This resulted in the patent being revoked for lacking novelty, as loss of the earliest two priority dates resulted in fatal prior art becoming citable against the claims. The original opposition hearing for this took place back in January 2018 and we discussed the concept of priority and the issues at the heart of this case in our ‘Getting Priority Right in Europe’ Article shortly after in 2018.

Now some time has passed we thought it would be interesting to look to some more recent EPO Board of Appeal cases to see if the EPO is applying the law consistently, and to see if there’s any lessons to be learnt from these cases. We note a lot of the issues arise with US originating provisional applications.


Priority in Europe – brief summary

As discussed in more detail in our earlier article, ‘right of priority’ is a legally separate and transferrable right to a patent/patent application’s ‘property right’ (the right to the actual application/patent), and as such it must be assigned separately. If a subsequent application claims priority from an earlier application, the applicants of the subsequent application must include all applicants from the earlier application, or a clear chain of entitlement to priority to the new/different applicants must be evident.

Importantly, the EPO does not accept that assignments of applications automatically include assignment of priority too (T 1201/14), and one cannot retroactively assign the right of priority, any attempt to do this contravenes Article 87(1) EPC.

Thus, in order to show valid transfer of priority rights, any assignment must be shown to be executed prior to the filing of the subsequent application (typically a PCT application claiming priority to a national phase application). A good summary is provided in EPO technical Board of Appeal case T 1201/14:

The successor in title with respect to the right to claim priority from a first application according to Article 87(1) EPC 1973 must prove that it indeed owned,

(i) before the filing of the later European application,

(ii) the right of priority relating to the first application for the purpose of filing the later European application claiming that priority.


Whilst there had been EPO Board of Appeal decisions and cases in the past related to entitlement of priority (see e.g. T 1103/15, T 1201/14 and T 0517/14), the high-profile nature of this Nobel Prize winning technology, the prestige of the applicants, and the sheer number of opponents (9) meant that this was a case closely watched by many.

The applicant’s Appeal against the revocation of EP 2 771 468 hinged on the lack of assignment of right of priority of one of the original applicant (also inventor, as it was a US provision application where inventors were named as applicants) on the two key (also earliest filed) priority documents the European application in question claimed priority from. In the original opposition hearing evidence was presented that this applicant (Luciano Marraffini) did not transfer his right of priority derived from the two US provisional filings in question to any of the three applicants of the PCT application before the filing date. None of the inventor, Rockefeller University (his employer) or their successors in title were named as applicants for the PCT application. Thus, priority of the two earliest priority applications was not validly claimed. This resulted in the two key/earliest priority claims falling down, the patent become open to a number of novelty attacks, and the patent was revoked.

At the Appeal hearing The Broad Institute attempted to convince the EPO that US national law is the relevant law for determining if they had a valid claim to priority, and under US law all persons who filed the Priority Application in respect of the actual invention claimed were applicants, and priority was therefore validly claimed. It was found in (subsequently carried out) inventorship analysis, the person whose name was missing from the Subsequent Application was not an inventor of what was claimed therein. Their arguments included declarations from high profile figures such as John Doll, the former commissioner of patents at the US Patent and Trademark Office, and Lord Hoffman, a former UK Judge and former Lord of Appeal in Ordinary in the UK. The Board did not find these arguments persuasive, they ruled national law cannot be used to justify not having a successor in title at the filing of the patent application.

The Board also did not agree with their other lines of argument, i) that the EPO has no power to rule on entitlement to priority (the Board ruled it does), and ii) that ‘any person’ of Article 4A(1) of the Paris Convention and Art. 87(1) of the European Patent Convention (EPC) means not all applicants need to be present on any subsequent applications claiming priority from the earlier application (the Board ruled ‘any person’ does not = ‘any one person’ needing to be present, all must be).

The Board of Appeal were clear in their ruling that they find the case law in this area is well established, and thus no referral was made to the EPO’s Enlarged Board of Appeal for further consideration of the legal issues at hand. The patent remained revoked. This was just one of many applications by the same applicants claiming priority to the two priority applications in question, and to date 6 European divisional applications have been filed in this family alone, so the exact facts of the priority situation could be explore in more detail in the future.

We look at a couple of other Board of Appeal cases that have ruled similarly, and in short this looks set to be how the EPO handles this issue for the foreseeable future. Some of these other cases also highlight some useful practice points:


T 0407/15 (The University Of Western Ontario)

This decision relates to the applicant’s appeal of the Examining Division’s decision to refuse European patent application EP 2 252 901.

Here a PCT application was filed 11 March 2009 by The University of Western Ontario claiming priority from two earlier US provisional applications 61/035 540 and 61/035 777. These US applications were again filed jointly by multiple (here three) inventor/applicants. As noted by The Board “The right of priority belongs to them jointly, as in T 788/05 (point 2)”.

This case particularly notes the clear distinction made by the EPO between the aforementioned two different and independent rights generated when an application is filed: i) the right to the application in question; and ii) the right of priority.

At the hearing the appellant failed to provide any evidence that such a transfer took place and that the applicant, rather than the 3 priority application applicant/inventors, was entitled to claim these priority rights.

Most interesting in this case, both US provisional applications 61/035 540 and 61/035 777 contained an “Assignee information” section which identified “The University of Western Ontario” as the assignee. However, in The Board ruled that “This is, however, not sufficient to establish that the priority rights derived from either application have also been transferred to the applicant.”. Whilst the Board does not give indication of what would be sufficient to establish the priority rights had been correctly assigned, it seems here indication that the eventual applicant was the assignee, even at the time of filing of the priority documents, was not enough. The Board was clear that an assignee does not necessarily have priority rights assigned, it could just have been property rights.

Here, the Board of Appeal found claims to lack inventive step due to new prior art citable because of the lack of priority.




This decision relates to the patent proprietor (the appellant) filing an appeal against the decision of the Opposition Division to revoke the patent at the opposition hearing.

Again, here the application in question claimed priority to a US provisional application filed in the name of the inventors. Summarising a multiple document trail somewhat: The inventors were employees of “The General Hospital Corporation” and each was bound by the “Intellectual Property Policy 2002” (document D31), and in an Invention Disclosure Form (D40), the inventors detailed their invention and “agree[d] to assign all right, title and interest in this invention to The General Hospital Corporation d.b.a Massachusetts General Hospital in accordance with the Intellectual Property Policy [‘the IP Policy’ (D31)] and the Intellectual Property Acknowledgement“.

However, the patentee (appellant) submitted that document D51, in turn, showed that a reallocation with respect to the invention at issue to the named applicant of the PCT document (the appellant), and the priority right had been assigned.

Document D51 confirmed, that “The Massachusetts General Hospital (the “MGH”) owns all Intellectual Property created by Members with Professional Staff appointments at the General Hospital”.

The board noted document D51 as “the key piece of evidence that purports to demonstrate that the right to claim priority from document D1 had been transferred to the appellant”. However, the Board found that D51 “did not demonstrate to the required standard of proof that a reallocation of priority rights, had taken place by the filing date … because document D51 is unsigned and therefore it cannot provide conclusive evidence that the reallocation policy, set out therein, was in fact adopted.” (emphasis added by us).

So whilst no strict rules are laid out in the law, this case demonstrates that the EPO will apply some sort of assessment of documents, and that the documents are signed is a test they will apply.

Some key points to note for the future were also made in this case:

  • The board confirmed that the applicant bears the burden of proof for demonstrating that the reallocation of ownership of the priority right took place; and
  • the appropriate standard of proof to be applied in this factual situation is not the balance of probabilities, but “in cases where all evidence supporting a specific statement of fact (for instance a public prior use) is within the power and knowledge of one party”, the Boards of Appeal will apply a stricter standard of proof, namely the standard “beyond reasonable doubt” (see decision T 472/92, OJ EPO 1998, 161, point 3.1 of the reasons and Case Law of the Boards of Appeal, 9th edition, 2019, III.G.4).

We also note that in this case it was agreed by all parties the following principles were true:

(i) the EPO is entitled to examine whether or not an applicant can claim the priority of a previous filing;

(ii) the applicant can only claim the priority of document D1 if a transfer from the inventors to the applicant occurred before the filing date of the subsequent application (here a PCT application, document D2);

(iii) the question of whether such transfer occurred should be determined according to national law (emphasis added by us, see note below);

(iv) the relevant national law, in the present case is US law: federal law where the effect of the assignment is concerned, state law where the construction of the contract is concerned.

We note that it is the transfer which is to be assessed under national law, not the legal principles of timing of assignment of priority right (i.e. interpretation of Article 4A(1) of the Paris Convention and Art. 87(1) of the EPC) as was discussed in T 0844/18.

This is a useful checklist for cases in this area and cements the principles from the T 0844/18 (CRISPR-Cas/BROAD INSTITUTE) case are being followed consistently by the Boards of Appeal.


Conclusion and Best Practice Notes

It is key for applicants and their representatives to understand and track priority rights when filing any applications claiming priority from an earlier application. The case law in Europe is clear and the right should be checked and correctly assigned where necessary before filing of any applications claiming priority to an earlier application.

Where the applicants of the first application and a subsequent application (e.g. a PCT application) are not identical, it has to be proven that the right of priority derived from the first application has been transferred by the applicant of the first application to its successor in title. The exact nature of the how the assignment of priority right can occur is not set in stone, but some form of distinct assignment of priority right is clearly required, and must be correctly executed prior to filing the subsequent application.

When it is clear there are problems likely to arise and perhaps an assignment cannot be carried out in time, different filing strategies can be considered, e.g. filing an application claiming priority with the same applicants as the original filing, and then assigning the application to the new owner afterwards.

If you would like any advice on such matters, please don’t hesitate to get in touch. We regularly advise clients on such issues, and would be more than happy to take a look.