Noncovalent interactions between immunoglobulin polypeptide chains. Stability to dissociation by denaturants

In-capillary (electrophoretic) digestion-reduction-separation: A smart tool for middle-up analysis of mAb

Comprehensive characterization of physicochemical properties of monoclonal antibodies (mAbs) is a critical process to ensure their quality, efficacy, and safety. For this purpose, mAb analysis at different levels (bottom-up, middle-up) is a common approach that includes rather complex multistep sample preparation (reduction, digestion). To ensure high analysis performance, the development of fully integrated methodologies is highly valuable. Capillary zone electrophoresis is a particularly well-adapted technique for the multistep implementation of analytical strategies from sample preparation to detection. This feature was employed to develop novel integrated methodologies for the analysis of mAb at the middle-up level. Multiple in-line reactions (simultaneous reduction and digestion) were performed for the first time in the separation capillary. Tris (2-carboxyethyl) phosphine hydrochloride (TCEP) was used as an effective reducing agent under a broad pH range and IdeS (Immunoglobulin degrading enzyme from Streptococcus) as a highly specific enzyme for mAb digestion. Transverse diffusion of laminar flow profile (TDLFP) was applied for reactants mixing. Both in-line sample preparation and separation parameters were optimized under non-denaturing and denaturing conditions. The developed in-line methodologies provided good reproducibility and higher peak efficiencies comparing with off-line assays. They were successfully applied to different mAbs.

Kinetic mechanism of controlled Fab-arm exchange for the formation of bispecific immunoglobulin G1 antibodies

Bispecific antibodies (bsAbs) combine the antigen specificities of two distinct Abs and demonstrate therapeutic promise based on novel mechanisms of action. Among the many platforms for creating bsAbs, controlled Fab-arm exchange (cFAE) has proven useful based on minimal changes to native Ab structure and the simplicity with which bsAbs can be formed from two parental Abs. Despite a published protocol for cFAE and its widespread use in the pharmaceutical industry, the reaction mechanism has not been determined. Knowledge of the mechanism could lead to improved yields of bsAb at faster rates as well as foster adoption of process control. In this work, a combination of Förster resonance energy transfer (FRET), nonreducing SDS-PAGE, and strategic mutation of the Ab hinge region was employed to identify and characterize the individual steps of cFAE. Fluorescence correlation spectroscopy (FCS) was used to determine the affinity of parental (homodimer) and bispecific (heterodimer) interactions within the C_H3 domain, further clarifying the thermodynamic basis for bsAb formation. The result is a clear sequence of events with rate constants that vary with experimental conditions, where dissociation of the K409R parental Ab into half-Ab controls the rate of the reaction.

Hamster-to-rat bone marrow xenotransplantation and humoral graft vs. host disease

Bone marrow transplantation (BMT) may induce tolerance across xenogeneic barriers. We have established a xenogeneic BMT model where hamster BM is transplanted into splenectomized LEW rat recipients resulting in high levels of engraftment. Unfortunately, graft vs. host disease (GVHD) with severe dermatitis developed in all rat recipients. We were successful in treating or preventing the dermatitis of this xenogeneic GVHD by the use of the T-cell suppressant tacrolimus. However, this compound did not prevent the development of a fatal liver injury in the rat recipients. This study was designed to elucidate the pathogenesis of this liver injury appearing in T-cell suppressed rat recipients of hamster BM. Splenectomized and irradiated (10 Gy) LEW rats received 300 x 106 unfractionated hamster BM cells. These BMT recipients were divided in 3 groups: Group I recipients (n = 8) did not receive further immunosuppression. Group II animals (n = 10) received tacrolimus 1 mg/kg/d for 7 d. Group III recipients (n = 6) were given the same daily dose of tacrolimus on a long-term basis. Chimerism was detected by flow cytometry. Cytotoxicity of recipient's sera against rat and hamster lymph node cells was measured by complement-dependent cytotoxicity (CDC) test. Immunofluorescence was used to detect hamster antirat antibodies on several recipient organs. In Group I, 2 out of 8 animals engrafted (25%) and survived for a median of 21 d showing the severe dermatitis characteristic of GVHD. In group II (n = 10), 9/10 rat recipients engrafted (90%) and survival was increased to a median of 53.7 days. However, these surviving recipients developed fatal GVHD not different from that observed in Group I recipients. All animals in Group III (n = 6) engrafted and did not show the characteristic dermatitis of GVHD. Their survival, however, was shortened to a median of 30.3 d by a severe liver injury. This injury was characterized by hepatocyte necrosis in zones 1 and 2 with polymorphonuclear (PMN) cell infiltration. Deposits of hamster immunoglobulins were present around the necrotic areas and in the portal veins. Moreover, antirat antibodies appeared in the circulation. These antibodies were sensitive to dithiothreitol (DTT) treatment indicating that they were of the IgM class. This study shows that xenogeneic GVHD may have a dual presentation in the hamster-to-rat model: a classical cellular GVHD not distinct to the allogeneic one and a humoral GVHD affecting solely the recipient liver. The degree of humoral injury is potentiated by T-cell suppression.

Multistep denaturation and hierarchy of disulfide bond cleavage of a monoclonal antibody

A humanized, monoclonal antibody of the IgG4 class was treated with SDS at room temperature. Analysis using SDS-PAGE revealed the progressive formation of a series of denaturation intermediates, of increasing apparent molecular weights. The detectable species migrated with apparent molecular weights of 137, 152, 162, 182, 196, and 210 kDa. Antibody not incubated in SDS had an apparent molecular weight of 137 kDa, while boiling in SDS provoked the immediate conversion of all antibody to the slowest migrating form (210 kDa). A study designed to test if all rungs of the ladder were equally cleavable by mild treatment with mercaptoethanol revealed small amounts of a novel form, and conditions were devised to generate large amounts of this novel form. The novel form, before full denaturation, migrated at the position of unheated, intact antibody (137 kDa), while full denaturation in SDS converted the novel form to a species migrating at about 190 kDa. The novel form, before full denaturation, was identified as HHL ***L, where the asterisks indicate noncovalent binding of one light chain to HHL. This noncovalent complex remains intact during SDS-PAGE. The novel form, after full denaturation, was identified as HHL. This study, with earlier studies, reveals that different pathways of reductive cleavage are taken by different antibodies, and that the most sensitive disulfide bond is different for different antibodies. Our results on antibody denaturation serve as a warning to those who use two-dimensional gels for the analysis of antibodies.

Immunological identity of the small subunit of HL-A antigens and beta2-microglobulin and its turnover on the cell membrane

A number of immunological methods have been employed to show that the small subunit of HL-A antigens, isolated either after papain treatment or after solubilization with detergent, is identical to beta(2)-microglobulin, a protein previously isolated from human urine and shown to be homologous in structure to constant region domains of immunoglobulins. Moreover, quantitative data indicate virtually total identity between the small subunit of HL-A antigens and beta(2)-microglobulin. Studies of the turnover of labeled HL-A antigens from the lymphocyte surface indicate that the two subunits turn over at similar rates, although only the small subunit could be detected in the culture medium. The significance of these observations is discussed.