This paper presents an imaging capillary isoelectric focusing (CIEF) assay for the determination of the identity, stability, and isoform distribution of a murine monoclonal antibody (MU-B3). The experiments were conducted using a Convergent Bioscience iCE280 instrument. The optimum carrier ampholyte composition that gave the best peak separation was found to be 25% Pharmalyte pH 3-10 and 75% Pharmalyte pH 5-8. The antibody gave a highly reproducible CIEF profile with three major peaks having average isoelectric point (pI) values of 6.83, 6.99, and 7.11. Intraday and interday reproducibility of pI values was found to be within RSD of 0.5%. The CIEF profile was also the same, with an alternate column cartridge and alternate batches of methyl cellulose. A plot of peak areas versus MU-B3 concentration was linear (R2 = 0.995) up to a concentration of 0.5 mg/mL in the sample solution. Peak area measurements were reproducible to within 7% RSD. The CIEF profiles of two other antibodies were distinctly different from the profile of MU-B3, showing that the assay is specific. After a sample of MU-B3 was subjected to heat stress by exposure to heat at 55 degrees C for 4 h, its CIEF profile was altered with extra peaks appearing at lower pI values, indicating that the assay could be used to monitor stability. The result of the heat stress experiment was also confirmed with a parallel slab-gel IEF analysis of the antibody sample before and after application of the heat stress. The results of this work suggest that imaging CIEF can be used for product testing under a quality control environment. The assay can be used for pI profiling of proteins and for monitoring structural changes (deamidation, glycosylation, etc.) during the manufacturing process and upon storage.
Fc fusion proteins are a new emerging class of molecules for immune-targeted delivery of therapeutic proteins. Biophysical and bioanalytical characterization is critical for clinical development and delivery of therapeutic proteins. Here we report molecular and functional characterization of a recombinant human fusion protein Mutant IL-15/Fc. MutIL-15/Fc has a molecular weight of ~95kDa as determined by multi-angle laser light scattering with online size exclusion chromatography and migrated at a faster rate (lower retention time) in gel filtration column. The kinetics of binding of MutIL-15/Fc to Fcγ receptor is best fitted in a bivalent modal with KD1 5 μM and KD2 9 μM determined by surface plasmon resonance (BIAcore®). N-glycoprofiling analysis revealed extensive glycosylation of MutIL-15/Fc. The Fc and IL-15 components in the MutIL-15/Fc are detected using the dual mode ELISA. The HT-2 cell proliferation inhibition assay is qualified as a quantitative in vitro marker functional assay. Molecular state changes associated with forced stress analyzed by SEC-MALS resulted in changes in bioactivity and Fc:Fcγ receptor interaction affinity. These data provide a systematic approach to molecular and functional characterization of the MutIL-15/Fc to establish product consistency and stability monitoring during storage and under drug delivery conditions.
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