There is numerous evidence that glycosylation attached to the Fc fragment may, despite its very limited structural variability, be used by the immune system to fine-tune an immune response

There is numerous evidence that glycosylation attached to the Fc fragment may, despite its very limited structural variability, be used by the immune system to fine-tune an immune response. higher efficacy of therapeutic antibodies lacking the core fucose and also suggest a unique mechanism by which the immune system can regulate antibody-mediated effector functions. Keywords:immunoglobulin, afucosylation, antibody effector function, X-ray crystallography Antibodies are central mediators of the immune system, with IgG being the most dominant immunoglobulin. Upon binding of IgG/antigen complexes to membrane-bound Fc receptors (FcRs) a cellular immune response is triggered. Multiple factors regulate such immune response. First, different IgG subclasses bind with different affinities to a given FcR. Second, NU6300 different FcRs are heterogeneous in terms of ligand specificity, expression pattern, and triggered effector functions. Furthermore, posttranslational modifications, in particular glycosylation, of both antibodies and Fc receptors modulate the affinity of their interactions (1,2). Glycosylation of the Fc region of human IgGs occurs at a conserved N-glycosylation site within the CH2 domain, where glycans are linked to asparagine 297 (Asn297). The carbohydrate chain attached at this site is usually comprised of a complex-type heptasaccharide core made up of N-acetylglucosamine (GlcNAc) and mannose, and followed by variable addition of galactose, sialic acid, fucose, as well as bisecting GlcNAc NU6300 residues. NU6300 The attached glycans play a crucial role for the function of immunoglobulins (1). It is well described that a- or deglycosylated IgGs are almost completely devoid of all Fc-mediated immune effector functions as a result of drastically reduced binding to FcRs or to proteins of the complement system (3), although Fc carbohydrates are not directly in contact with FcRs (4). By incrementally truncating the Fc-oligosaccharides, it was shown that the decreased interactions with FcRs result from increased conformational changes in the Mmp11 individual CH2 domains and from a closed Fc conformation generated through a mutual approach of both CH2 domains (5). Changes outside the oligosaccharide core can also modulate the affinity to various Fc receptors and proteins of the complement system and in some cases have been associated with various pathological conditions. For example, murine agalactosylated IgG has a slightly higher affinity toward the activating FcRIII, whereas the affinity to the inhibiting FcRIIb receptor is reduced, which may explain the enhanced proportion of this glycoform in an autoimmune setting (6). In contrast, Fc-oligosaccharide sialylation, shown to reduce binding to Fc receptors and in addition facilitate binding to the lectin specific Icam-3 grabbing nonintegrin-related 1 (SIGN-R1), has been associated with an anti-inflammatory activity of immunoglobulins (7,8). A further modification consists in the attachment of a fucose residue in an 1,6-linkage to the first GlcNAc of Fc-oligosaccharide core (core fucosylation). Removal of core fucose selectively and significantly increases binding affinity to FcRIII and leads to enhanced cellular immune effector functions, such as antibody-dependent cellular cytotoxicity (ADCC) both in vitro (9) and in vivo (10). Fc-FcRIII interactions and ADCC can be highly relevant to the biological activity NU6300 of therapeutic anticancer antibodies (11,12), thus this type of Fc-oligosaccharide modification has been the focus of much research during the last decade. In particular, NU6300 a next generation of anticancer antibodies carrying afucosylated glycoforms (13,14) is currently in clinical development; the most advanced among these is the glycoengineered CD20 antibody obinutuzumab (GA101), currently in phase II/III clinical trials for treatment of non-Hodgkins lymphoma and chronic lymphocytic leukemia (15,16). Because the Fc fucose residue does not come into contact with the FcRIII polypeptide (4), both the large impact of this modification in the affinity of the interaction as well as.