SELECTIVE PRECIPITATION OF INTERLEUKIN-4 USING HYDROPHOBIC ION-PAIRING - A METHOD FOR IMPROVED ANALYSIS OF PROTEINS FORMULATED WITH LARGE EXCESSES OF HUMAN SERUM-ALBUMIN

In order to ensure the stability of protein pharmaceuticals, human ser um albumin (HSA) is often added as an excipient, frequently in large e xcess. This makes chromatographic analysis of the stability of the act ive protein difficult. In the case of interleukin-4 (IL-4), separation from HSA can be achieved to some degree by size exclusion chromatogra phy, but some I-ISA co-elutes with the IL-4. Hydrophobic ion pairing p rovides a method for selective precipitation of IL-4 from HSA. Hydroph obic ion pairing involves the electrostatic interaction of ionic deter gents with oppositely charged polypeptides. Even when HSA is present i n fifty-fold excess (w/w), the resulting precipitate contains greater than 70% of the IL-4. Selective precipitation with SDS produces enhanc ements in IL-4 over HSA of more than 2000-fold. This approach permits subsequent facile analysis of IL-4 by conventional reverse phase HPLC.