Capture of proteins from mammalian cells in pilot scale using different STREAMLINE adsorbents.

This presentation compares three different expanded bed matrices. STREAMLINE rProtein A, STREAMLINE SP-XL and STREAMLINE Chelating were monitored in respect to their ability to clarify the broth, to concentrate and to purify the distinct target protein. The capture of a mouse IgG1 and a recombinant prothrombin (PT) was carried out in pilot scale using a 100-l bioreactor and STREAMLINE 100 and 200 columns, respectively. The robustness of the process was also estimated monitoring the expansion behaviour and the cell and debris concentrations during the load and in the eluat. In all cases the capture of the target proteins was comparable to conventional chromatographic systems. The purification success was mainly dependent on the selectivity of the ligand used. The affinity process resulted in a highly purified product. The ion exchanger and chelating material mainly concentrated the product. In all three cases 100 l of cell broth were successfully processed in one run. The robustness of the ion exchanger process was poor, because of strong cell matrix interaction. However, for the chelating and especially for the affinity matrix a highly reproducible process was obtained.

Estimation of cell damage in bench- and pilot-scale affinity expanded-bed chromatography for the purification of monoclonal antibodies.

The first step in downstream processing of mammalian cell culture includes the separation of the cells without cell damage to avoid the release of intracellular enzymes, which could potentially cause proteolytic degradation of the target protein and may increase the impurities for further chromatographic steps. This especially includes the reduction of host DNA for therapeutic proteins. The aim of this investigation was to examine the extent of cell damage at the bench and pilot scale using a stabilized fluidized bed (expanded bed) for direct recovery of IgG from cell culture broth. For this purpose, Streamline-25 and -200 columns containing 75 mL and 5 L of rProtein A matrix, respectively, were used. The repeated batch cultivations resulted in high cell viabilities of about 90% prior purification. The pH was gently adjusted to pH 8 before the broth was applied to the gel. In bench scale, 1 to 6 L of unclarified feed was applied to the Streamline-25 column. In pilot scale, up to 95 L was processed using the Streamline-200 column. The antibodies from 95 L of unclarified feed were recovered after approximately 1.5 h. The possible cell damage, caused either by the equipment or by the cells' passage through the expanded bed, was detected by the following assays: microscopic count of the cells using trypan blue dye exclusion to determine viability; monitoring of intracellular components (i.e., DNA concentration); activity of lactate dehydrogenase (LDH); and, finally, the particle load in the flow through and the eluate. Despite the sensitivity of hybridoma cells to shear forces, neither the high flow rate (300 to 450 cm/h) nor the passage of the cells through the expanded bed caused any relevant cell damage or clogging of the gel. Excellent DNA depletion was observed.

Pilot scale recovery of monoclonal antibodies by expanded bed ion exchange adsorption.

The aim of the investigations was to estimate the scale up properties of an efficient chromatographic first capture step for the recovery of murine IgG1 from undiluted and unclarified hybridoma cell culture broth using an ion exchange matrix in expanded bed mode. The tested new sulfopropyl-based ion exchange matrix (Streamline SP XL, Amersham Pharmacia Biotech) stands out due to its enhanced capacity compared to its precursor (Streamline SP). Defining the working pH in preliminary electrophoretic analyses (titration curve, SDS-PAGE) and small-scaled chromatographic binding studies showed, that the optimal value for the IgG purification was pH 4.6, where a co-chromatography of the medium supplement albumin (500 mg l-1, pI = 4.8) could not be avoided. Further scouting experiments dealt with the dynamic capacity of the matrix, which was evaluated by frontal adsorption analysis. In packed bed mode no break-through of the target protein was achieved even after 6.5 mg IgG per ml matrix were applied. These results could not be reproduced in expanded bed mode with cell-free supernatant, where the dynamic capacity was found to be only 1.5 mg IgG/ml SP XL. Processing cell-containing broth resulted in an additional decrease of the value down to 0.5 mg ml-1, presumably caused by the remarkable biomass adsorption to the matrix. The search for the reasons led to the examination of the hydrodynamic conditions. Buffer experiments with a tracer substance (acetone) pointed out, that the flow in expanded bed was significantly more influenced by back-mixing effects and channel formations than in packed bed. These effects could be compensated with an enhanced viscosity of the liquid phase, which was achieved by the addition of glucose. As a result of the improved hydrodynamic conditions in the expanded bed, the dynamic capacity could be increased from 0.5 to more than 4.5 mg IgG/ml matrix for the processing of cell culture broth with 400 mM glucose. Finally, the scale up from a Streamline 25 to a Streamline 200 column was performed under conditions, which proved to be optimal: 100 L of unclarified hybridoma broth were concentrated with a binding rate of 95% in less than 3.5 hours. Loading the column no break-through of the target protein was achieved. However, the eluate still contained debris and cells, which points out the major disadvantage of the method: the biomass attachment to the matrix.