Johan Fransson

Human framework adaptation of a mouse anti-human IL-13 antibody.

Humanization of a potent neutralizing mouse anti-human IL-13 antibody (m836) using a method called human framework adaptation (HFA) is reported. HFA consists of two steps: human framework selection (HFS) and specificity-determining residue optimization (SDRO). The HFS step involved generation of a library of m836 antigen binding sites combined with diverse human germline framework regions (FRs), which were selected based on structural and sequence similarities between mouse variable domains and a repertoire of human antibody germline genes. SDRO consisted of diversifying specificity-determining residues and selecting variants with improved affinity using phage display. HFS of m836 resulted in a 5-fold loss of affinity, whereas SDRO increased the affinity up to 100-fold compared to the HFS antibody. Crystal structures of Fabs in complex with IL-13 were obtained for m836, the HFS variant chosen for SDRO, and one of the highest-affinity SDRO variants. Analysis of the structures revealed that major conformational changes in FR-H1 and FR-H3 occurred after FR replacement, but none of them had an evident direct impact on residues in contact with IL-13. Instead, subtle changes affected the V(L)/V(H) (variable-light domain/variable-heavy domain) interface and were likely responsible for the 5-fold decreased affinity. After SDRO, increased affinity resulted mainly from rearrangements in hydrogen-bonding pattern at the antibody/antigen interface. Comparison with m836 putative germline genes suggested interesting analogies between natural affinity maturation and the engineering process that led to the potent HFA anti-human IL-13 antibody.

Characterization of a high-affinity human antibody with a disulfide bridge in the third complementarity-determining region of the heavy chain.

Disulfide bridges are common in the antigen‐binding site from sharks (new antigen receptor) and camels (single variable heavy‐chain domain, VHH), in which they confer both structural diversity and domain stability. In human antibodies, cysteine residues in the third complementarity‐determining region of the heavy chain (CDR‐H3) are rare but naturally encoded in the IGHD germline genes. Here, by panning a phage display library designed based on human germline genes and synthetic CDR‐H3 regions against a human cytokine, we identified an antibody (M3) containing two cysteine residues in the CDR‐H3. It binds the cytokine with high affinity (0.4 nm), recognizes a unique epitope on the antigen, and has a distinct neutralization profile as compared with all other antibodies selected from the library. The two cysteine residues form a disulfide bridge as determined by mass spectrometric peptide mapping. Replacing the cysteines with alanines did not change the solubility and stability of the monoclonal antibody, but binding to the antigen was significantly impaired. Three‐dimensional modeling and dynamic simulations were employed to explore how the disulfide bridge influences the conformation of CDR‐H3 and binding to the antigen. On the basis of these results, we envision that designing human combinatorial antibody libraries to contain intra‐CDR or inter‐CDR disulfide bridges could lead to identification of human antibodies with unique binding profiles. Copyright

Structural insights into humanization of anti-tissue factor antibody 10H10

ABSTRACT Murine antibody 10H10 raised against human tissue factor is unique in that it blocks the signaling pathway, and thus inhibits angiogenesis and tumor growth without interfering with coagulation. As a potential therapeutic, the antibody was humanized in a two-step procedure. Antigen-binding loops were grafted onto selected human frameworks and the resulting chimeric antibody was subjected to affinity maturation by using phage display libraries. The results of humanization were analyzed from the structural perspective through comparison of the structure of a humanized variant with the parental mouse antibody. This analysis revealed several hot spots in the framework region that appear to affect antigen binding, and therefore should be considered in human germline selection. In addition, some positions in the Vernier zone, e.g., residue 71 in the heavy chain, that are traditionally thought to be crucial appear to tolerate amino acid substitutions without any effect on binding. Several humanized variants were produced using both short and long forms of complementarity-determining region (CDR) H2 following the difference in the Kabat and Martin definitions. Comparison of such pairs indicated consistently higher thermostability of the variants with short CDR H2. Analysis of the binding data in relation to the structures singled out the ImMunoGeneTics information system® germline IGHV1-2*01 as dubious owing to two potentially destabilizing mutations as compared to the other alleles of the same germline and to other human germlines.

Homology modeling and structure-based design improve hydrophobic interaction chromatography behavior of integrin binding antibodies

ABSTRACT Monoclonal antibody (mAb) candidates from high-throughput screening or binding affinity optimization often contain mutations leading to liabilities for further development of the antibody, such as aggregation-prone regions and lack of solubility. In this work, we optimized a candidate integrin α11-binding mAb for developability using molecular modeling, rational design, and hydrophobic interaction chromatography (HIC). A homology model of the parental mAb Fv region was built, and this revealed hydrophobic patches on the surface of the complementarity-determining region loops. A series of 97 variants of the residues primarily responsible for the hydrophobic patches were expressed and their HIC retention times (RT) were measured. As intended, many of the computationally designed variants reduced the HIC RT compared to the parental mAb, and mutating residues that contributed most to hydrophobic patches had the greatest effect on HIC RT. A retrospective analysis was then performed where 3-dimentional protein property descriptors were evaluated for their ability to predict HIC RT using the current series of mAbs. The same descriptors were used to train a simple multi-parameter protein quantitative structure-property relationship model on this data, producing an improved correlation. We also extended this analysis to recently published HIC data for 137 clinical mAb candidates as well as 31 adnectin variants, and found that the surface area of hydrophobic patches averaged over a molecular dynamics sample consistently correlated to the experimental data across a diverse set of biotherapeutics.