Recently, the Intellectual Property Court of the Supreme People's Court rendered a final judgment in an administrative case concerning the invalidation of an invention patent, holding that where the improvement of an invention on the use of a monoclonal antibody over the prior art lies in the selective reduction of specific amino acid residues, and where, under the international nomenclature rules for monoclonal antibodies, whether individual amino acid residues in the sequence are in oxidised or reduced form ordinarily does not affect their naming, then, absent further corroborating evidence, the mere fact that a monoclonal antibody in the prior art bears the same name as the invention is insufficient to establish that the prior art disclosed the patented product and the patented technical solution formed by the selective reduction of specific amino acid residues. On that basis, the court ruled to maintain the patent right at issue as valid.

The case concerns an invention patent entitled “Selective reduction of cysteine residues in IL-17 antibodies”, whose patentee is Nuo X Co., a Swiss company. Claim 1 of the patent reads: “1. Use of a purified preparation of secukinumab antibody in the manufacture of a medicament for treating immune-mediated inflammation, wherein the cysteine at position 97 of the light chain of the secukinumab antibody is selectively reduced, wherein the content of intact secukinumab in the preparation as measured by sodium dodecyl sulfate capillary electrophoresis (CE-SDS) is at least 90%, and wherein the activity level of secukinumab in the preparation as measured by cystamine-CEX is at least 90%.” In response to the request for invalidation of the patent right filed by Liu X-li, the China National Intellectual Property Administration issued Decision No. 568432 on the examination of the request for invalidation, maintaining the patent right as valid. Dissatisfied, Liu X-li brought an action before the Beijing Intellectual Property Court, requesting revocation of the challenged decision and an order that the China National Intellectual Property Administration make a fresh decision. The Beijing Intellectual Property Court rendered administrative judgment (2024) Jing 73 Xing Chu No. 15057, dismissing Liu X-li's claims. Dissatisfied, Liu X-li lodged an appeal.

In the second instance, the Supreme People's Court held as follows. First, as recorded in the specification of the patent, the feature in claim 1 that “the cysteine at position 97 of the light chain of the secukinumab antibody is selectively reduced” means that, without reducing the conserved cysteine residues of the antibody, the cysteine at position 97 of the light chain of the secukinumab antibody (CysL97) is reduced so that it exists in the form of a thiol group “-SH”. The structure of an antibody is determined by, among other things, its amino acid sequence and the modified forms of the amino acids; cysteine residues in a monoclonal antibody sequence may be in an oxidised or a reduced state, and therefore “selectively reduced” does not mean that this technical feature is merely a process feature — its limitation on the state of the cysteine residue also constitutes a limitation on the structure of the antibody. The secukinumab preparation described in claim 1 is homogeneous with respect to the attribute that the cysteine at position 97 of the light chain is in the reduced state. Although Evidence 1 records that the antibody AIN457 is secukinumab, the cysteine at position 97 contained in secukinumab may be in either the oxidised or the reduced state, and its state is not uniquely determined.

Second, although Evidence 1 records that “the activity of secukinumab as measured by cystamine-CEX was maintained at 98% to 99% (data not shown)”, a person skilled in the art would understand from its contents that what was measured was the activity-retention result in a product stability test. Because a stability test focuses on the change in the product before and after storage, the statement that the activity of secukinumab was maintained at 98% to 99% refers to the change in the activity of secukinumab after storage relative to that before storage, and not to an absolute value of activity. In other words, if the activity value of the original secukinumab was 50%, then where the activity value after storage is also close to 50%, the ratio of the activity value of the later product to that of the earlier product may likewise be 98% to 99%, but this does not mean that the activity value of secukinumab is 98% to 99%. Accordingly, the figure of “activity maintained at 98% to 99%” recorded in Evidence 1 cannot be compared with the absolute activity value described in the patent, and no similarity in activity and/or structure between the two can be inferred.

Finally, the relevant records in Evidence 1 do not make it possible to determine the oxidation-reduction state of the cysteine at position 97 of the light chain of secukinumab, whereas the preparation method of the patent mainly involves selectively reducing the cysteine at position 97 of the light chain of the secukinumab antibody to generate a thiol group. The activity referred to in the patent denotes the reduced state of CysL97, and the cystamine-CEX activity ratio therein refers to the ratio of the level of cystamine derivatisation of reduced CysL97 in the secukinumab preparation to the theoretical maximum cystamine derivatisation content in the secukinumab preparation. Therefore, Evidence 1 does not disclose the technical feature in claim 1 of the patent that “the cysteine at position 97 of the light chain of the secukinumab antibody is selectively reduced”, and claim 1 of the patent is therefore novel over Evidence 1.

On the basis of an accurate understanding of the patented technical solution and of what the prior art disclosed, this case takes into account the course of technological development and the technical routes in the biopharmaceutical field, respects the research-and-development patterns and innovation models of monoclonal antibody technology, and maintains the patent right at issue as valid in accordance with the law. It effectively protects the innovation achievements of biopharmaceutical research and development enterprises, better incentivises the research and development of innovative biopharmaceuticals, and conveys the judicial philosophy of protecting and encouraging innovation and of according equal protection to Chinese and foreign parties.

Source: Intellectual Property Court of the Supreme People's Court | Date of original: 20 August 2026 | Original link: https://ipc.court.gov.cn/zh-cn/news/view-6000.html