Monday, October 19, 2020

CAFC parses the term "antibodies" in Immunex case

First, the relevant science. Antibodies are proteins. Like all proteins, they are composed of numerous individual amino acids chained together in a particular sequence. Antibodies are roughly Y-shaped, made of four chains—two “heavy” and two “light.” Each chain can be further divided into a “variable region” and a “constant region.” And each variable region contains three relatively small “complementarity-determining regions” (CDRs) situated at the tips of the Y. The remainder of the variable regions are the “framework regions.” Particular antibody regions have particular biological implications. For instance, it is primarily the CDRs that give an antibody its ability to bind selectively to specific targets (i.e., antigens), despite making up just a sliver of its structure. See J.A. 1501, 7042–43. To that end, an antibody’s exact amino acid sequence determines what the antibody binds to, which affects the antibody’s therapeutic usefulness. The amino acid sequence of an antibody also determines whether the human immune system recognizes and rejects it as “non-human.” Amino acid sequences that are human in origin—that is, sequences “consistent with the amino acid sequences of antibodies produced naturally by the human immune system,” see Appellant’s Br. 4—can avoid triggering immune responses. Early efforts at therapeutic antibody development started with mice. For example, researchers could inject a mouse with an antigen, the mouse would generate antibodies to the antigen, and those antibodies would be harvested. In that case, the entire amino acid sequence was murine (i.e., from mice). These antibodies, disappointingly, tended to plague patients with “undesirable and harmful immune reactions.” See Appellant’s Br. 7–8. Too much of each antibody was “mouse” in origin, to the consternation of the human immune system. Through various techniques, the proportion of an antibody that is recognized as “mouse” can be decreased. In “chimeric” antibodies, for instance, the constant regions tend to be human in origin, and the variable regions, including the CDRs, tend to be nonhuman—making the antibodies’ amino acid sequences mostly human in origin. Appellant’s Br. 8–9. In “humanized” antibodies, only the CDRs are nonhuman—the antibodies’ amino acid sequences, including the portions responsible for immune reaction, are almost entirely human in origin.1 Further, fully human antibodies can be made in which even the CDRs are human in origin.


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