Enhanced Precision of Circular Dichroism Spectral Measurements Permits Detection of Subtle Higher Order Structural Changes in Therapeutic Proteins.

Protein higher order structure (HOS) is an essential quality attribute to ensure protein stability and proper biological function. Protein HOS characterization is performed during comparability assessments for product consistency as well as during forced degradation studies for structural alteration upon stress. Circular dichroism (CD) spectroscopy is a widely used technique for measuring protein HOS, but it remains difficult to assess HOS with a high degree of accuracy and precision. Moreover, once spectral changes are detected, interpreting the differences in terms of specific structural attributes is challenging. Spectral normalization by the protein concentration remains one of the largest sources of error and reduces the ability to confidently detect differences in CD spectra. This work develops a simple method to enhance the precision of the CD spectral measurements through normalization of the CD spectra by the protein concentration determined directly from the CD measurement. This method is implemented to successfully detect small CD spectral changes in multiple forced degradation studies as well as comparability assessments during biologics drug development. Furthermore, the interpretation of CD spectral changes in terms of HOS differences are provided based on orthogonal data in conjunction with structural insights gained through in silico homology modeling of the protein structure.

Generation and characterization of human anti-human IL-21 neutralizing monoclonal antibodies.

Interleukin-21 (IL-21) is a type I four-helical bundle cytokine that exerts a variety of significant effects on many hematopoietic cells, including T and B lymphocytes and natural killer cells. IL-21 is produced predominantly by CD4+ T cells and natural killer T cells and, when aberrantly overexpressed, appears to play important roles in a wide variety of autoimmune disorders. To generate potential therapeutic reagents capable of inhibiting IL-21 for clinical use, we immunized human immunoglobulin transgenic mice with IL-21 and then identified and cloned a panel of human anti-human IL-21 binding monoclonal antibodies. IL-21 neutralizing and IL-21-binding, non-neutralizing antibodies were assigned to distinct epitope "bins" based on surface plasmon resonance competition studies. The most potent neutralizing antibodies had extremely high (sub pM) affinity for IL-21 and were able to block IL-21 activity in various biological assays using either an IL-21R-transfected pre-B-cell line or primary human B cells, and their neutralizing activity was, in some cases, superior to that of a soluble form of the high affinity heterodimeric IL-21 receptor. Characterization of this panel of IL-21 antibodies provided the basis for the selection of a therapeutic candidate antibody capable of inhibiting IL-21 activity for the treatment of autoimmune and inflammatory diseases.

Generation of a high-affinity Fcgamma receptor by Ig-domain swapping between human CD64A and CD16A.

A recombinant soluble version of the human high-affinity receptor for IgG, rh-FcgammaRIA or CD64A, was expressed in mammalian cells and purified from their conditioned media. As assessed by circular dichroism, size exclusion chromatography and dynamic light scattering, incubation of rh-FcgammaRIA at 37 degrees C resulted in time-dependent formation of soluble aggregates caused by protein unfolding and loss of native structure. Aggregate formation was irreversible, temperature-dependent and was independent of rh-FcgammaRIA concentration. Aggregated rh-FcgammaRIA lost its ability to inhibit immune complex precipitation and failed to bind to IgG-Sepharose. Addition of human IgG1 to rh-FcgammaRIA prior to incubation at 37 degrees C blocked the formation of rh-FcgammaRIA aggregates. Production of soluble monomeric rh-FcgammaRIA was limited by aggregate formation during cell culture. Substitution of the membrane distal D1 Ig domain of FcgammaRIA with the D1 Ig domain of FcgammaRIIIA or CD16A resulted in a chimeric receptor, FcgammaR3A1A, with enhanced temperature stability. Relative to native rh-FcgammaRIA, FcgammaR3A1A exhibited less aggregation in Chinese hamster ovary cell-conditioned media or when purified receptor was incubated for up to 24 h at 37 degrees C. Both receptors bound to immobilized human IgG1 with high affinity and were equipotent at blockade of immune complex-mediated cytokine production from cultured mast cells. Equivalent dose-dependent reductions in edema and neutrophil infiltration in the cutaneous Arthus reaction in mice were noted for rh-FcgammaRIA and FcgammaR3A1A. These data demonstrate that the D1 Ig domains of FcgammaRIA and FcgammaRIIIA are functionally interchangeable and further suggest that the chimeric receptor FcgammaR3A1A is an effective inhibitor of type III hypersensitivity in mice.

Engineering of stable bispecific antibodies targeting IL-17A and IL-23.

Bispecific antibodies (bsAbs) present an attractive opportunity to combine the additive and potentially synergistic effects exhibited by combinations of monoclonal antibodies (mAbs). Current challenges for engineering bsAbs include retention of the binding affinity of the parent mAb or antibody fragment, the ability to bind both targets simultaneously, and matching valency with biology. Other factors to consider include structural stability and expression of the recombinant molecule, both of which may have significant impact on its development as a therapeutic. Here, we incorporate selection of stable, potent single-chain variable fragments (scFvs) early in the engineering process to assemble bsAbs for therapeutic applications targeting the cytokines IL-17A/A and IL-23. Stable scFvs directed against human cytokines IL-23p19 and IL-17A/A were isolated from a human Fab phage display library via batch conversion of panning output from Fabs to scFvs. This strategy integrated a step for shuffling V regions during the conversion and permitted the rescue of scFv molecules in both the V(H)V(L) and the V(L)V(H) orientations. Stable scFvs were identified and assembled into several bispecific formats as fusions to the Fc domain of human IgG1. The engineered bsAbs are potent neutralizers of the biological activity of both cytokines (IC(50) < 1 nM), demonstrate the ability to bind both target ligands simultaneously and display stability and productivity advantageous for successful manufacture of a therapeutic molecule. Pharmacokinetic analysis of the bsAbs in mice revealed serum half-lives similar to human mAbs. Assembly of bispecific molecules using stable antibody fragments offers an alternative to reformatting mAbs and minimizes subsequent structure-related and manufacturing concerns.

A dual-targeting PDGFRbeta/VEGF-A molecule assembled from stable antibody fragments demonstrates anti-angiogenic activity in vitro and in vivo.

Targeting angiogenesis is a promising approach to the treatment of solid tumors and age-related macular degeneration (AMD). Inhibition of vascularization has been validated by the successful marketing of monoclonal antibodies (mAbs) that target specific growth factors or their receptors, but there is considerable room for improvement in existing therapies. Combination of mAbs targeting both the VEGF and PDGF pathways has the potential to increase the efficacy of anti-angiogenic therapy without the accompanying toxicities of tyrosine kinase inhibitors and the inability to combine efficiently with traditional chemotherapeutics. However, development costs and regulatory issues have limited the use of combinatorial approaches for the generation of more efficacious treatments. The concept of mediating disease pathology by targeting two antigens with one therapeutic was proposed over two decades ago. While mAbs are particularly suitable candidates for a dual-targeting approach, engineering bispecificity into one molecule can be difficult due to issues with expression and stability, which play a significant role in manufacturability. Here, we address these issues upstream in the process of developing a bispecific antibody (bsAb). Single-chain antibody fragments (scFvs) targeting PDGFRbeta and VEGF-A were selected for superior stability. The scFvs were fused to both termini of human Fc to generate a bispecific, tetravalent molecule. The resulting molecule displays potent activity, binds both targets simultaneously, and is stable in serum. The assembly of a bsAb using stable monomeric units allowed development of an anti-PDGFRB/VEGF-A antibody capable of attenuating angiogenesis through two distinct pathways and represents an efficient method for rapid engineering of dual-targeting molecules.

Comparison of the ability of wild type and stabilized human IgG(4) to undergo Fab arm exchange with endogenous IgG(4)in vitro and in vivo.

Fab arm exchange by a stabilized anti-IL-31 IgG(4)S228P monoclonal antibody (mAb) was studied using physiologically relevant antibody concentrations and thiol exchange conditions, and directly compared to that of matched wild type IgG(4) (IgG(4)wt) and IgG(1) control antibodies. In vitro arm exchange between the test mAbs and a purified IgG(4)wt exchange partner was monitored using capillary isoelectric focusing and a size-exclusion peak shift assay. Arm exchange between the test mAbs and IgG exchange partners with unknown specificity was monitored using only the shift assay. Studies were performed using single isotype human and mouse mAbs, unfractionated human, mouse, and cynomolgus monkey IgG, and human serum as the sources of the exchange partners. In vitro studies using human serum demonstrated that anti-IL-31 IgG(4)S228P did not undergo significant Fab arm exchange with endogenous human IgG(4) whereas anti-IL-31 IgG(4)wt underwent rapid and extensive Fab arm exchange. The in vitro results were corroborated by in vivo studies in which mice were injected with a mixture of either form of the test mAb and an excess of non-specific human IgG(4) exchange partner.