The long circulating half-life of serum albumin, the most abundant protein in mammalian plasma, derives from pH-dependent endosomal salvage from degradation, mediated by the neonatal Fc receptor (FcRn). Using yeast display, we identified human serum albumin (HSA) variants with increased affinity for human FcRn at endosomal pH, enabling us to solve the crystal structure of a variant HSA/FcRn complex. We find an extensive, primarily hydrophobic interface stabilized by hydrogen-bonding networks involving protonated histidines internal to each protein. The interface features two key FcRn tryptophan side chains inserting into deep hydrophobic pockets on HSA that overlap albumin ligand binding sites. We find that fatty acids (FAs) compete with FcRn, revealing a clash between ligand binding and recycling, and that our high-affinity HSA variants have significantly increased circulating half-lives in mice and monkeys. These observations open the way for the creation of biotherapeutics with significantly improved pharmacokinetics.

IL-1 is a key inflammatory and immune mediator in many diseases, including dry-eye disease, and its inhibition is clinically efficacious in rheumatoid arthritis and cryopyrin-associated periodic syndromes. To treat ocular surface disease with a topical biotherapeutic, the uniqueness of the site necessitates consideration of the agent's size, target location, binding kinetics, and thermal stability. Here we chimerized two IL-1 receptor ligands, IL-1β and IL-1Ra, to create an optimized receptor antagonist, EBI-005, for topical ocular administration. EBI-005 binds its target, IL-1R1, 85-fold more tightly than IL-1Ra, and this increase translates to an ∼100-fold increase in potency in vivo. EBI-005 preserves the affinity bias of IL-1Ra for IL-1R1 over the decoy receptor (IL-1R2), and, surprisingly, is also more thermally stable than either parental molecule. This rationally designed antagonist represents a unique approach to therapeutic design that can potentially be exploited for other β-trefoil family proteins in the IL-1 and FGF families.T he IL-1 cytokines (IL-1α and IL-1β) are master mediators of inflammatory responses (1). IL-1β also regulates immune function through its role in T helper 17 (Th17) cell differentiation and maintenance (2, 3). IL-1 action has been implicated in numerous human diseases, including rheumatoid arthritis, MuckleWells syndrome, gout, type 2 diabetes, and stroke (4). Several natural mechanisms directly oppose the actions of IL-1, including a soluble and cell surface decoy receptor (IL-1R2), a natural antagonist (IL-1Ra), and a soluble signaling receptor (IL-1R1) (5). Therapeutics that block IL-1 based on these mechanisms have been developed (6-8).Recently, a nonoptimized formulation of anakinra (methionyl-IL-1Ra; Kineret) was shown to provide clinical benefit in dry-eye disease (DED) (9). Moderate to severe DED is a chronic inflammatory condition of the corneal surface that results in pain, discomfort, and epitheliopathy (as measured by fluorescein staining). Inability to maintain a proper tear film over the cornea (owing to a variety of etiologies) results in desiccating stress, which drives an inflammatory cascade (10, 11). IL-1 plays a central role in the initiation and maintenance of this cascade, as well as in the pain mediated by the corneal neural plexus. IL-1α and IL-1β protein are elevated in the lacrimal gland, tears, and the ocular surface in all forms of dry-eye disease (12), and their mRNA is increased in both humans and in rodent disease models (13,14). Genetic ablation of IL-1R1, the primary receptor for IL-1α and IL-1β, can block the development of corneal staining in a Sjögren syndrome corneal epitheliopathy model (15), and topically administered anakinra can improve surface epithliopathy in a mouse dry-eye model (14). IL-1β is essential for Th17 cell differentiation and maintenance, and Th17 cells are likely the main effector cells that induce epithelial damage (2, 3). Genetic and pharmacologic studies have shown that IL-1β mediates, and IL-1Ra blocks, normal, inflamm...

Advances in single-use technologies can enable greater speed, flexibility, and a smaller footprint for multi-product production facilities, such as at a contract manufacturer. Recent efforts in the area of cell line and media optimization have resulted in bioreactor productivities that exceed 8 g/L in fed-batch processes or 25 g/L in high-density cell culture processes. In combination with the development of single-use stirred tank bioreactors with larger working volumes, these intensified upstream processes can now be fit into a single-use manufacturing setting. Contrary to these upstream advances, downstream single-use technologies have been slower to follow, mostly limited by low capacity, high cost, and poor scalability. In this study we describe a downstream process based solely on single-use technologies that meets the challenges posed by expression of a mAb (IgG(1)) in a high-density suspension culture of PER.C6 cells. The cell culture harvest was clarified by enhanced cell settling (ECS) and depth filtration. Precipitation was used for crude purification of the mAb. A high capacity chromatographic membrane was then used in bind/elute mode, followed by two membranes in flow-through (FT) mode for polishing. A proof of concept of the entire disposable process was completed for two different scales of the purification train.

in Wiley InterScience (www.interscience.wiley.com).Both a new method for measuring protein ion exchange kinetics and new data for the adsorption of three different proteins in anionic agarose gels are described. The gels were prepared as spherical particles to determine chemical and structural properties and the macroscopic protein adsorption behavior, and as thin slabs supported in a microfluidics chip to observe transient concentration profiles with a light microscope. The combination of these approaches provides deeper insight in the nature of protein transport mechanisms than previously possible. The adsorption of cytochrome c, myoglobin, and hemoglobin was studied macroscopically and microscopically. Although all proteins exhibited similarly favorable adsorption isotherms, adsorption kinetics, and concentration profiles were quantitatively and qualitatively different. Cytochrome c was adsorbed very quickly and resulted in diffuse concentration profiles, while myoglobin adsorbed much more slowly and resulted in sharp fronts. Hemoglobin exhibited lower rates with diffuse profiles at higher pH and sharp fronts at lower pH. In general, the shape of the profiles appeared to be correlated with the binding strength. Reversibly bound proteins yielded diffuse profiles, while irreversibly bound proteins exhibited sharp advancing fronts, indicating that protein-surface interactions play a major role in the nature of the transport mechanism.

in Wiley InterScience (www.interscience.wiley.com).The adsorption kinetics of myoglobin in charged gels of varying agarose content have been measured macroscopically, through batch uptake experiments, and microscopically, using light microscopy with gels supported in microfluidics chips. The apparent effective pore diffusivities, determined by fitting either set of rate data to the shrinking core model, were greater than the free solution diffusivity and concentrationdependent. Moreover, the microscopically derived concentration profiles were qualitatively different from the predicted ones. Therefore, a new model taking into account an assumed favorable partitioning of the protein in the pore liquid is proposed to describe the adsorption kinetics. The new model yields effective pore diffusivities that are in approximate agreement with the values determined chromatographically under nonbinding conditions and with hindered diffusion theory. In addition, it predicts concentration profiles in the gel that are consistent with those observed microscopically. The overall increase in mass transfer is attributed to the favorable partitioning of the protein in the pores at low ionic strength, which results in a greater diffusional driving force.