Method of expressing therapeutic antibodies in Chinese Hamster Ovary host cells not patentable

This appeal, involving AbbVie’s blockbuster biologic Humira®, proves that even the best lawyering cannot always overcome a close obviousness rejection, particularly when commercial scale of the manufacturing process is the distinguishing feature from the prior art.  Ex parte Salfeld, 2017 Pat. App. LEXIS 4796.  The application claimed a method of producing human anti-TNFα antibodies by culturing a Chinese Hamster Ovary (CHO) host cell transfected with recombinant expression vectors encoding defined light and heavy chain variable regions for a time sufficient to express the antibody, and isolating the antibody.  The examiner rejected the claims for obviousness-type double patenting based on an earlier patent issued to AbbVie that claimed the same method of producing human anti-TNFα antibodies, using the same recombinant expression vectors, without limiting the host cell to CHO cells.

The question on appeal was whether it would have been obvious to use a CHO cell as the host cell in AbbVie’s earlier claimed method. The Patent Trial and Appeal Board (“Board”) held that it would have been obvious, and that AbbVie’s claims were properly rejected for obviousness-type double patenting.

AbbVie made a number of arguments that the prior art did not render the use of CHO host cells obvious because CHO host cells could not be relied upon to manufacture human anti-TNFα antibodies on a commercial FDA-approved scale.  AbbVie’s argued its most significant evidence on this point as follows:

  • The prior art “calls into question the ability of CHO cells to stably produce antibodies on a scale suitable for the production of human therapeutics” because “stability needs to be demonstrated for at least 60 [cell] generations” and the prior art Brown indicated stability for only 20-25 generations.
  • The prior art “indicates that there is variability in the levels of expression obtained for different humanized antibodies” in CHO cells.

These facts and others, according to AbbVie, would have led the person of ordinary skill in the art to select a different host cell for manufacturing human anti-TNFα antibodies on a commercial scale, especially when considering the fact that FDA had never previously approved CHO host cells for the production of humanized antibodies.  The Board rejected AbbVie’s arguments because “commercial scale” and “FDA approval” were not elements of AbbVie’s claims.  According to the Board:

“Appellants focus their contentions and arguments on the premise that the appealed claims and their defined invention must be considered through the lens of ‘an industrial setting,’ of a desire for a host cell ‘suitable for commercial purposes,’ and of ultimate ‘approv[al] by the FDA for therapeutic use.’ However, the claims do not require such features, but only ‘producing a human anti-TNFα antibody, or antigen-binding portion thereof, suitable for therapeutic use in a human subject,’ which we find does not invoke such concerns. Thus, Appellants’ identifying that, in 1996, the two FDA-approved therapeutic antibodies were derived only from myeloma-based cells is not determinative on obviousness.”

One is left to wonder whether AbbVie could have claimed its production method in a manner that took better advantage of this evidence.  For example, could AbbVie have limited the process by the size of the reaction vat, or by specifically stating “a method of producing an FDA-approved antibody on an industrial scale”?  For now we can only wonder.