Protected biopolymers for oral administration and methods of using same

A method for protecting a cytokine regulatory agent from degradation in the gastrointestinal system, comprising forming a complex comprising an ion-exchange resin and an oppositely charged cytokine regulatory agent (CRA) having the amino acid sequence

• X.sub.1 -X.sub.2 -(D)Phe-Arg-(D)Trp-X.sub.3, wherein ##STR10## H, COCH.sub.3, or absent;
• ##STR11## H, His or COCH.sub.3 ;
• and ##STR12## or R.sub.5 ;
• wherein Y is O, H.sub.2 or S;
• R.sub.1 is H, COCH.sub.3, C.sub.2 H.sub.5, CH.sub.2 Ph, COPh, COO-t-butyl, COOCH.sub.2 Ph, CH.sub.2 CO-(polyethylene glycol) or A;
• R.sub.2 is H, COCH.sub.3, C.sub.2 H.sub.5 or CH.sub.2 Ph;
• R.sub.3 is a linear alkyl group having 1 to 6 carbon atoms or a branched or cyclic alkyl group having 3 to 6 carbon atoms;
• R.sub.4 is (CH.sub.2).sub.m --CONH.sub.2, (CH.sub.2).sub.m --CONHR.sub.1 or (CH.sub.2).sub.m --CONHA;
• R.sub.5 is OH, OR.sub.3, NH.sub.2, SH, NHCH.sub.3, NHCH.sub.2 Ph or A;
• and R.sub.6 is H or R.sub.3 ;
• and wherein "Ph" is C.sub.6 H.sub.5 ;
• "m" is 1, 2 or 3;
• "n" is 0, 1, 2 or 3;
• and "A" is a carbohydrate having the general formula ##STR13## whereby the therapeutic activity of the CRA is protected in the gastrointestinal system against enzymes.