Background: An antagonistic anti-PCSK9 antibody exhibits target-mediated clearance, resulting in a dose-dependent PK. Results: Engineering of an antibody with pH-sensitive binding to PCSK9 decreases target-mediated clearance, resulting in increased PK and efficacy in vivo. Conclusion: pH-sensitive anti-PCSK9 antibodies are excellent candidates for therapeutic development. Significance: pH-sensitive antibodies may enable less frequent or lower dosing of antibodies hampered by target-mediated clearance and high antigen load.

No abstract

No abstract

(2015) The neonatal Fc receptor (FcRn) binds independently to both sites of the IgG homodimer with identical affinity, mAbs, 7:2, 331-343, DOI: 10.1080DOI: 10. /19420862.2015 To link to this article: https://doi.org/10. 1080/19420862.2015 The neonatal Fc receptor (FcRn) is expressed by cells of epithelial, endothelial and myeloid lineages and performs multiple roles in adaptive immunity. Characterizing the FcRn/IgG interaction is fundamental to designing therapeutic antibodies because IgGs with moderately increased binding affinities for FcRn exhibit superior serum half-lives and efficacy. It has been hypothesized that 2 FcRn molecules bind an IgG homodimer with disparate affinities, yet their affinity constants are inconsistent across the literature. Using surface plasmon resonance biosensor assays that eliminated confounding experimental artifacts, we present data supporting an alternate hypothesis: 2 FcRn molecules saturate an IgG homodimer with identical affinities at independent sites, consistent with the symmetrical arrangement of the FcRn/Fc complex observed in the crystal structure published by Burmeister et al. in 1994. We find that human FcRn binds human IgG1 with an equilibrium dissociation constant (K D ) of 760 § 60 nM (N D 14) at 25 C and pH 5.8, and shows less than 25% variation across the other human subtypes. Human IgG1 binds cynomolgus monkey FcRn with a 2-fold higher affinity than human FcRn, and binds both mouse and rat FcRn with a 10-fold higher affinity than human FcRn. FcRn/IgG interactions from multiple species show less than a 2-fold weaker affinity at 37 C than at 25 C and appear independent of an IgG's variable region. Our in vivo data in mouse and rat models demonstrate that both affinity and avidity influence an IgG's serum half-life, which should be considered when choosing animals, especially transgenic systems, as surrogates.

4-1BB (CD137, TNFRSF9) is an inducible costimulatory receptor expressed on activated T cells. Clinical trials of two agonist antibodies, utomilumab (PF-05082566) and urelumab (BMS-663513), are ongoing in multiple cancer indications, and both antibodies demonstrate distinct activities in the clinic. To understand these differences, we solved structures of the human 4-1BB/4-1BBL complex, the 4-1BBL trimer alone, and 4-1BB bound to utomilumab or urelumab. The 4-1BB/4-1BBL complex displays a unique interaction between receptor and ligand when compared with other TNF family members. Furthermore, our ligand-only structure differs from previously published data. Utomilumab, a ligand-blocking antibody, binds 4-1BB between CRDs 3 and 4. In contrast, urelumab binds 4-1BB CRD-1, away from the ligand binding site. Finally, cell-based assays demonstrate utomilumab is a milder agonist than urelumab. Collectively, our data provide a deeper understanding of the 4-1BB signaling complex, providing a template for future development of next generation 4-1BB targeted biologics.