Affinity separation using an Fv antibody fragment-"smart" polymer conjugate.

Poly(N-isopropylacrylamide), or PNIPAAm, is considered a "smart" polymer because it sharply precipitates when heated above a critical temperature, about 32 degrees C in water, and redissolves when cooled. Conjugates made of PNIPAAm and IgG antibodies also exhibit the same critical temperature behavior. Interestingly, antigens that are complexed with these conjugates can also be phase-separated along with the conjugates. In this work, we conjugated PNIPAAm for the first time to the immunoglobulin Fv fragment, the smallest fragment of an antibody that still retains the antigenic affinity of the whole antibody. For our studies, we used an Fv fragment that strongly binds hen egg white lysozyme (HEL). The purified Fv fragment-polymer conjugate precipitated at the same temperature as did the pure polymer. After addition of the conjugate to a mixture containing HEL and after thermal separation of the conjugate at 37 degrees C, the amount of HEL in solution was reduced by as much as 80%. We were able to demonstrate the reversibility of the separation through three cycles of precipitation and dissolution. It was also possible to recover free HEL by thermal separation of the conjugate in the presence of an eluant, 50 mM diethylamine. The conjugate can then be recycled for second use. In conclusion, immunoseparations can be performed using smart polymer conjugates made with just the variable domains of an antibody. Unlike whole antibodies, fragments of antibodies can be produced in Escherichia coli, allowing easier genetic engineering of the antibody and tailoring of the conjugate.

Characterization of humanized antibodies secreted by Aspergillus niger.

Two different humanized immunoglobulin G1(kappa) antibodies and an Fab' fragment were produced by Aspergillus niger. The antibodies were secreted into the culture supernatant. Both light and heavy chains were initially synthesized as fusion proteins with native glucoamylase. After antibody assembly, cleavage by A. niger KexB protease allowed the release of free antibody. Purification by hydrophobic charge induction chromatography proved effective at removing any antibody to which glucoamylase remained attached. Glycosylation at N297 in the Fc region of the heavy chain was observed, but this site was unoccupied on approximately 50% of the heavy chains. The glycan was of the high-mannose type, with some galactose present, and the size ranged from Hex(6)GlcNAc(2) to Hex(15)GlcNAc(2). An aglycosyl mutant form of antibody was also produced. No significant difference between the glycosylated antibody produced by Aspergillus and that produced by mammalian cell cultures was observed in tests for affinity, avidity, pharmacokinetics, or antibody-dependent cellular cytotoxicity function.