considerably reduced, leading to higher recovered yields at the elution
stage, and thus higher productivity. Information related to
these DoE optimisation studies will be reported subsequently.
The crude supernatants of all three monoclonal human IgGs were
diluted 5-fold with a higher ionic strength, pH 8.0, buffer to
achieve a final concentration of 25 mM Tris and 600 mM Na3citrate
as the loading and wash buffer. No evidence for ‘‘salting out’’ of the
humanised monoclonal antibodies was observed under the experimental
conditions with the 600 mM Na3citrate employed in these
studies. Gradient elution was achieved using a buffer of lower pH
and without salt present (Buffer B: 25 mM MES, pH 5.0). In order
to readily allow a comparison of the capture efficiency and elution
recoveries of the three different mAbs with the same adsorbent,
the same volume of sample was loaded onto columns of identical
dimensions packed with the same amount of the 40-TerPSEA adsorbent
at the same linear flow velocity in each case, with the volume
chosen to achieve overload conditions based on the previously
determined static binding capacities.
Although the overall protein mass balance for the different
humanised mAb isotypes in the combined breakthrough, wash
and eluted fractions in each case was high, i.e. >95%, it was evident
from the these results, e.g. Figs. 4–7 respectively, that whilst selectivity
between the monomeric mAb and other components present
in the loaded sample was achieved, breakthrough of the monomeric
mAb occurred at the load and wash stages of up to ca 15%,
depending of the mAb isotype examined. Fig. 4A shows the chromatographic
profile for the humanised IgG1 mAb supernatant
run on the 40-TerPSEA adsorbent. All fractions as well as the original
sample were analysed by SDS-PAGE (Fig. 4B), demonstrating
that this mAb was largely confined to the eluted peak fractions
with only a very limited extent of breakthrough under the loading
conditions employed. It can also be noted that the elution profiles