Detection and Characterization of Subvisible Aggregates of Monoclonal IgG in Serum

Purpose To detect and characterize the aggregation of therapeutic monoclonal antibodies in undiluted biological fluids. Methods Fluorescently labeled subvisible IgG aggregates formed by applying either heat stress or by pH-shift were investigated immediately after addition to human serum, and after 24 h. Unstressed and stressed IgG formulations were analyzed by fluorescence single particle tracking, confocal laser scanning microscopy and flow cytometry. Results Unstressed formulations remained free from subvisible aggregates in serum, whereas heat-stressed and pH-shift stressed formulations showed dissimilar aggregation behaviors. The aggre-gation profile of the heat-stressed formulation diluted in serum remained practically the same as the one diluted in buffer, even after the 24 h incubation period. The pH-shift stressed formula-tion had strikingly smaller and more numerous subvisible aggre-gates immediately after dilution in serum compared to buffer. These aggregates became noticeably larger in both diluents after 24 h, but in serum they appeared to be formed by other types of constituents than the labeled protein itself. Conclusion These results show that subvisible therapeutic protein aggregates may undergo changes in number, type and size distribution upon contact with human serum. This empha-sizes the importance of analytical strategies for monitoring aggregation in undiluted biological fluids