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Means-Plus-Function Patent Claims: Anticipating the Outcome of Xencor

Recording of a 90-minute premium CLE video webinar with Q&A

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Conducted on Monday, December 18, 2023

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This CLE webinar will guide patent counsel on means-plus-function (MPF) antibody claims, particularly in light of the USPTO's adverse decision in Xencor. The panel will discuss the potential outcomes and the best practice options flowing therefrom, including best practices to avoid such an adverse decision in future antibody MPF claims.


Nearly all technological fields use MPF claiming. MPF claims, often perceived as narrow, can provide more protection for patent applicants than other claims. Following the Supreme Court's decision in Amgen (2023), many recommended using MPF claims for biopharma inventions. However, in the USPTO's decision in Xencor the Office is possibly closing the door on MPF claims for antibody patents.

There are two central issues: (1) Did Xencor sufficiently describe their antibody in the specification? (2) Assuming Xencor did, is Xencor's claim 9 unpatentable because Xencor did not, in the specification, set forth all possible equivalents to the disclosed antibody?

If (1), Xencor would lose, but the panel will explain how the decision would not be a body blow to MPF claims for antibodies. If (2), Xencor loses, the panel would then rue the future of MPF antibody claims, possibly with weeping, wailing, and gnashing of teeth and otherwise rail against such severe limitations being placed on antibody MPF claims, possibly rendering them worthless.

If the Federal Circuit, however, upholds (1) but not (2), then counsel should worry that failure to describe sufficiently the structure, materials, or acts corresponding to the claimed function under a 112(f) scenario may result in an unpatentable or invalid claim under 112(b). Also, even if (2) is not upheld, counsel will have to use best practices to clearly link the "means for" limitation to structures and/or acts in the specification.

As the panelists will explain, one might conclude that there is little possibility of the Federal Circuit sustaining point (2). Point (1), however, is not so clear. The finding of insufficient description of the antibody in the specification is most likely a question of fact, and it may be that the Federal Circuit will not overturn that factual finding of PTAB. The panelists will explain that if (2) is rejected, then counsel can save the MPF antibody claim by making sure at least one antibody designated as corresponding to the "means for" limitation is, incontrovertibly, sufficiently described.

Listen as our authoritative panel of patent attorneys examines MPF antibody claims, particularly in light of the USPTO's adverse decision on claim 9, and also in light of the Xencor brief and the amicus briefs that have been filed so far. The panel will predict how point (2) will be decided and what are the best practice options flowing therefrom. For educational purposes, the panel will assume arguendo that point (1) will be decided adversely to Xencor and then explain what best practices will be to avoid such an adverse decision in future antibody MPF claims.



  1. MPF antibody claims and the benefits of using them
  2. USPTO decision in Xencor
  3. Written description in Section 112(a) and Section 112(f)
  4. Definiteness of MPF antibody claims under Section 112(b)
  5. Amicus briefs
  6. What's the alternative if MPF is not available
  7. Best practices throughout


The panel will review these and other noteworthy issues:

  • What are the benefits and limitations of using MPF patent claims for antibody patents?
  • What are the potential implications of the USPTO's decision in Xencor?
  • What are the alternatives if MPF is not available?


Brougher, Joanna
Joanna T. Brougher, Esq., MPH

Owner & Principal
BioPharma Law Group

Ms. Brougher is a patent attorney who focuses on all aspects of services related to patents in the areas of...  |  Read More

Irving, Thomas
Thomas L. Irving

The Marbury Law Group

Mr. Irving has 47 years of experience in the field of IP law. His practice includes due diligence, patent prosecution,...  |  Read More

O’Brien, Michelle
Michelle E. O'Brien

The Marbury Law Group

Ms. O’Brien has more than 20 years of experience representing domestic and foreign clients of all sizes in...  |  Read More

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