Column chromatography and filtration for plasma IgG with aggregate spike
Figure 3 shows the effect of column chromatography on the filterability of polyclonal plasma IgG isolated from plasma derivatives with 0.5% aggregate spike. Plasma IgG spiked with 0.5% IgG aggregate (control) had increased larger aggregate content (from 0.3% for the reference solution to 0.5%) and 7.8% dimer content (Table 2). The figure clearly shows that the 0.5% IgG aggregate spike causes a marked decrease in filterability as evidenced by achieving flux of 100 LMH at nearly 80 L/m2 for the reference, while the flux of the control had become nearly zero and the run was ended by 12 L/m2. Normal AEX processing of aggregate-spiked plasma IgG produced no aggregate removal was observed and there was no improvement in filterability.
Mixed-mode AEX1 showed more than double the throughput of the control and high aggregate removal with dimer content decreasing from 7.8% to 5.8% and larger aggregate content decreasing from 0.5% to 0%. On the other hand, while larger aggregate content was also reduced to 0% by modified CEX1 and modified CEX2 processing, dimer was not reduced markedly from the control and remained at 7.3% and 7.7%, respectively. Interestingly, modified CEX output showed significantly higher filterability than the mixed-mode AEX1 output and even exceeded the flux of the reference in the early phase of filtration (Figure 3b). Modified CEX1 and modified CEX2 both show high filterability, but modified CEX2 output shows a greater flux decay than does modified CEX1 output.