T 0159/17 (Chimeric antibodies/ABLEXIS) 25-01-2021

Article 123(2) EPC

1. The present main request is derived from the auxiliary request 1 underlying the decision under appeal. The examining division acknowledged that the claimed subject-matter had a basis in the application as filed, and pointed in particular to Figures 4A, 4B and 4C, and the passage on page 27, lines 9 to 12 of the application (see first two paragraphs under the heading "Auxiliary Request 1" on page 21 of the decision under appeal).

2. The board is satisfied that the subject-matter of the amended claims according to the present main request does not extend beyond the content of the application as filed (Article 123(2) EPC). A mouse cell as defined in amended claim 1 has a basis in claims 1, 8 and 14 combined with the disclosure in the passage on page 27, lines 9 to 12 of the application as filed. Basis for dependent claims 2 to 5 is found in, respectively, claims 3, 2, 4 and 13 of the application as filed.

3. The method of independent claim 6 has a basis in claims 15 and 28 of the application as filed.

4. Basis for the knock-in mouse of independent claim 7 is found in claims 77, 85 and 105 combined with the disclosure in the passage on page 27, lines 9 to 12 of the application as filed. Dependent claim 8 is based on claim 79 of the application as filed.

5. Chimeric antibodies according to claims 9 and 10 have a basis in claim 106 of the application as filed which refers to, inter alia, claims 77, 85 and 105.

6. Basis for claim 11 is found in claim 107 of the application as filed. Claims 12 and 13 have a basis in, respectively, claim 118 and the passage on page 39, lines 4 and 5 of the application as filed.

7. No objections under Article 84 EPC concerning the auxiliary request 1 then on file were raised in the decision under appeal. In view of the amendments introduced into the claims, the board is satisfied that the requirements of Article 84 EPC are fulfilled.

Articles 83 and 54 EPC

8. In the decision under appeal, the examining division did not raise any objections of lack of sufficient disclosure, and acknowledged novelty over document (4) (see second paragraph from the bottom of page 21 of the decision under appeal). In view of the documents on file, the board sees no reason to raise any objections in this respect of its own motion.

Article 56 EPC

9. In the decision under appeal, document (4) was considered to be the closest state of the art for the subject-matter of the auxiliary request 1 then on file. In the examining division's view, the passage from page 42, line 20 to page 44, line 30 of document (4) clearly emphasized that fully human antibodies are not optimal, and that murine Fc regions are crucial for maturation and affinity of chimeric antibodies comprising a humanized variable region. However, the examining division acknowledged that neither the passage in question nor document (4) as a whole suggested or showed that antibodies with a constant region comprising a human CH1-upper hinge-middle hinge segment combined with murine CH2 and CH3 regions would be effective "... and provide chimeric antibodies with optimal characteristics" (see third paragraph on page 23 of the decision under appeal).

10. In the board's view, the same applies with respect to chimeric antibodies produced by a cell as defined in present claim 1, the constant region of which comprises a human CH1-upper hinge segment combined with murine CH2 and CH3 regions.

11. In the passage from page 43, line 27 to page 44, line 3 of document (4), it is stated that:

"The mouse will create antibodies that are human (VDJ/VJ)-mouse constant region, which will have the following benefits over the previously available HuMAb mice that produce totally human antibodies. Antibodies generated by the new mouse will retain murine Fc regions which will interact more efficiently with the other components of the mouse B cell receptor complex, including the signalling components required for appropriate B cell differentiation (such as Iga and Igb). Additionally, the murine Fc regions will be more specific than human Fc regions in their interactions with Fc receptors on mouse cells, complement molecules, etc. These interactions are important for a strong and specific immune response, for the proliferation and maturation of B cells, and for the affinity maturation of antibodies".

12. As apparent from this passage, the mouse described in document (4) has in its genome a chimeric locus that includes gene segments encoding the human variable region and the (complete) murine constant region. However, document (4) does not teach or even suggest a mouse having a chimeric locus as defined in claim 1 in which part of the constant region, namely the CH1 domain and the upper hinge region are human, while the CH2 and CH3 domains remain murine.

13. According to the present application, the technical effect associated with this difference is that the "... antibodies produced by the knock-in animals of the present invention do not exhibit the reduction or loss of activity and potency seen in antibodies from other chimeric antibody producing animals when the human V region is appended to a human C region to make a fully human antibody ..." (see page 19, lines 25 to 28 of the application as filed).

14. In view of these statements, the examining division formulated the objective technical problem to be solved starting from document (4) as the provision of "... means of generating in transgenic mouse, in response to an undefined antigen, chimeric humanized antibodies that [, when further humanized,] would retain affinity and specificity without eliciting an immune response" (see page 22, first paragraph of the decision).

15. The examining division found that, since the purported technical effect had not been demonstrated, the problem of retaining affinity when the generated chimeric antibodies are further humanized could not be considered to have been solved. Consequently, "... the (speculative) inclusion of human CH1, upper and middle hinge gene segments into the gene locus is just a design option that the skilled person may contemplate when trying to further humanize the chimeric constant region ..." (see fourth paragraph on page 23 of the decision under appeal).

16. It is a fact that, while the examples of the present application describe engineering a murine Ig loci by incorporation of large bacterial artificial chromosomes (BACs) into embryonic stem cells in order to generate chimeric antibodies comprising a human CH1-upper hinge domain and murine CH2 and CH3 domains (see e.g. Example 8), there is no experimental evidence in the application that the generated antibodies, when further humanized, do not suffer from a reduction or loss of activity and potency.

17. However, the disclosure of experimental data or results in the application as filed, while highly desirable, is not always required to establish that the claimed subject-matter solves the objective technical problem, in particular in the absence of substantiated doubts (see decision T 578/06 of 29 June 2011, points 13 to 15 of the Reasons). According to the established jurisprudence of the boards of appeal, the assessment of inventive step is to be made on the basis of the information in the application as filed, and on account of the common general knowledge available to the skilled person at the effective date of the application. Experimental evidence submitted after the filing date to support that the claimed subject-matter solves the problem, can be taken into account if it is already credible from the disclosure in the application as filed that the problem is indeed solved (see, inter alia, decisions T 578/06, supra, and T 716/08 of 19 August 2010).

18. In the present case, the examining division did not substantiate its doubts about the suitability of the claimed invention to solve the formulated technical problem. The board sees no reason to consider the purported technical effect underlying the present invention as merely speculative, because it is not implausible, in the light of the common general knowledge available to the person skilled in the art at the effective date, that chimeric antibodies comprising a human CH1-upper hinge domain and murine CH2 and CH3 domains, when further humanized, may retain their activity and potency.

19. Under these circumstances, the experimental data submitted by the appellant as Annexes A and B to its statement of grounds of appeal can be accepted as evidence for a technical effect associated with the combination in the chimeric locus of a human CH1-upper hinge gene segment and a murine CH2-CH3 gene segment.

20. As apparent from Annex A, an antibody specific for human CD115 generated from a hybridoma obtained by immunizing transgenic mice harbouring in their genome a chimeric locus as defined in claim 1 (human V-D-J-CH1-upper hinge and murine middle hinge-CH2-CH3), when converted to a fully human antibody of three different isotypes (IgG1, IgG2 and IgG4), binds to CD115 with the same affinity as the chimeric human-murine antibody (see Table 1) and exhibits potency identical to the parental chimeric human-mouse antibody (see Table 2). Similarly, chimeric anti-IL-8 antibodies generated by mice having a chimeric locus as defined in claim 1, when fully humanized, retain the same affinity as the parental antibody (see Table 3 in Annex B).

21. In view of this experimental evidence, the board acknowledges that the objective technical problem as defined in the decision under appeal (see paragraph 14 above) is solved by the claimed invention.

22. Hence, the sole issue that remains to be decided is whether or not, starting from the chimeric locus having a human variable region and a murine constant region described in document (4), it was obvious to a person skilled in the art seeking to generate fully human antibodies that retain the affinity and potency of the chimeric parental antibodies, to modify the locus by replacing the murine CH1 and upper hinge gene segment with its human counterpart.

23. Document (6) addresses the same problem as the present invention, namely the decrease in affinity or other characteristics when the chimeric antibodies produced in transgenic mice are humanized (see paragraph [0011]). The solution proposed in document (6) is to replace the murine sequences that encode one or more of the murine heavy chain constant regions (e.g. the murine alpha region, the murine Cgamma3, Cgamma1, Cgamma2b and Cgamma2a region set, and/or the epsilon heavy chain constant region) or murine light chain constant regions, preferably CLkappa or CLlambda, by a human constant region (see paragraph [0014]).

24. Document (6) does not specifically teach or even suggest to replace the murine constant region CH1-upper hinge gene segment by the human counterpart, while retaining the murine CH2-CH3 gene segment. Thus, a person skilled in the art starting from document (4) could not arrive at the claimed invention by applying the teachings of document (6).

25. Document (5) describes expression vectors used for screening of mouse Fab libraries. The individual clones encode a hybrid antibody constant region that includes murine and human constant regions; in particular, a vector with partial human heavy chain constant region CH1 plus partial human hinge region is described (see paragraph [0029]).

26. As apparent from paragraphs [0004] and [0005] of document (5), the problem addressed by the vectors described therein, namely the relatively poor expression of murine antibodies in a host cell like, e.g., E. coli compared to the level of expression of a similar human-derived antibody, clearly differs from the problem solved by the present invention. The use of such expression vectors is said to greatly increase expression compared to the expression of murine Fabs that include a fully murine constant region (see second sentence in paragraph [0022]). Hence, the board fails to see why a person skilled in the art trying to solve the problem of retaining affinity and potency when chimeric human-murine antibodies are further humanized, would have considered the teaching in document (5) of a hybrid human-murine constant region.

27. Documents (10) and (11) are scientific articles published by the same research group which provide experimental data supporting the hypothesis that the constant region may affect the secondary structure of the antigen binding site, thus accounting for variations in specificity of the antibody (see Abstract of document (10)). Particular attention is given to two regions of the CH1 domain because of their ability to form hydrogen bonds and, consequently, affect the segmental flexibility of the antibody (see paragraph bridging pages 13924 and 13925 of document (10)).

28. The board shares the appellant's view that neither document (10) nor document (11) provides a clear pointer to the particular chimeric locus defined in claim 1. Even if the skilled person, in view of the teachings of these documents, might have considered replacing the murine CH1 domain by the human counterpart, he/she would not have any reasonable expectation of success in providing human-murine chimeric antibodies that, after being fully humanized, retain the specificity and potency of the parental antibody.

29. In view of the above, the board concludes that the mouse cell of claim 1 involves an inventive step. The same applies to the method of producing it (claim 6), a knock-in mouse obtainable from the cell (claim 7), chimeric antibodies produced by the cell (claim 9) and their uses (claims 11 to 13).