Applicants prevailed in the recent Commissioner’s Decision Re Chugai Seiyaku and Kabushiki Kaisha (CD 1398, hereinafter “Kaisha”) [1] from the Patent Appeal Board (“PAB”) and can now claim humanized antibodies in cases where the antigen has been well characterized, even in the absence of complementarity determining region (“CDR”) sequences or evidence that the humanized antibodies had been made as of the filing date. This decision marks another incremental step towards modernizing Canadian examination practice regarding antibodies, and it could also have broader implications.

Institut Pasteur and Sloan-Kettering: The Rigid Rule

Traditionally, patent examiners have blocked applicants from pursuing claims to non-exemplified antibodies since the 1995 decision Re Institut Pasteur Application (CA 1206) [2]. In Institut Pasteur, the PAB rejected claims to non-exemplified monoclonal antibodies, holding that making the claimed antibodies would have required “considerable and protracted experimentation” [3]. This decision established the Canadian Patent Office’s practice that claims directed to monoclonal antibodies would only be allowed if the specification included at least one working example demonstrating the preparation of such an antibody.

Similarly, in the 2009 decision Re Sloan-Kettering (CD 1296) [4], the PAB held that claims to a humanized antibody were not adequately described or enabled, emphasizing the lack of CDR sequence information in the application at issue, among other factual considerations. Since Sloan-Kettering, examiners have taken the rigid position that CDR sequences must be disclosed when non-exemplified humanized antibodies are claimed.

Immunex: Monoclonal Antibody Claims Get Some Support

In 2010, the Commissioner allowed monoclonal antibody claims without a working example in Re Immunex Corporation (CD 1302) [5], essentially reversing the previous position of the Patent Office set out in Institut Pasteur. In Immunex, the Commissioner accepted the PAB’s rationale that a working example of a monoclonal antibody is not necessary when there is a direct structural relationship and specific immunoreactivity between the antigen and the monoclonal antibody and that the antigen has been fully characterized through the provision of an amino acid sequence [6]. Nonetheless, for humanized antibodies, the rigid requirements of CDR sequence disclosure and working example persisted.

Kaisha: Humanized Antibody Claims Follow Suit

This brings us to Kaisha, where the PAB reversed the examiner’s rejection of humanized antibody claims on Sloan-Kettering grounds. In Kaisha, the PAB cited the Supreme Court of Canada case Whirlpool Corp v Camco Inc [7], which asserted that the skilled person is thought to be reasonably diligent in keeping up with advances in the field to which the patent relates and the common general knowledge of skilled workers undergoes continuous evolution and growth. The PAB emphasized that the evolution of the common general knowledge is an important factor for assessing whether the disclosure is sufficient to enable a skilled person to practice the invention as claimed without displaying inventive ingenuity or undertaking undue experimentation as of the relevant date. With that in mind, the PAB distinguished Kaisha from Sloan-Kettering by reasoning that while the Sloan-Kettering application was filed in 1990, the Kaisha application was filed in 2002 and published in 2003, such that there has been “a significant evolution” of the common general knowledge possessed by the skilled person during the interval [8].

By applying this reasoning to Kaisha, the PAB noted the advances made in the state of the art of antibody-related technology and found that there was sufficient disclosure and enablement, thereby reversing the examiner’s rejections [9]. The PAB extended the holding in Immunex that monoclonal antibodies could be patentable in the absence of a working example to Kaisha’s humanized antibody claims [10]. Further, the PAB explicitly stated that Sloan-Kettering “cannot impose a rigid rule” that sequence information of the CDRs of humanized antibodies must be provided to meet disclosure and enablement requirements [11].

Moving Forward

Kaisha is welcoming news for applicants who have for years been facing Sloan-Kettering based objections during examination. A narrow reading of Kaisha would lead one to conclude that the decision only impacts “humanized” antibodies, but that would overlook a key point made by the PAB – patent examination should keep up with the continuous evolution of the state of the art and the common general knowledge possessed by the skilled person. Rigid assessment during examination without factoring in advances in technological knowledge as exhibited by the Institut Pasteur and Sloan-Kettering approaches would be a disservice to pioneering applicants who have made sufficient disclosure in view of the state of the art at the relevant date.