Extended blood half-life of monomethoxypolyethylene glycol-conjugated hen lysozyme is a key parameter controlling immunological tolerogenicity

The blood half-life of a protein is prolonged by conjugating a protein with a linear amphiphilic polymer, monomethoxypolyethylene glycol (mPEG). The c onjugation gives a protein immunotolerogenicity; hence, it is likely that t he long half-life is crucial for the tolerogenicity. We prepared a toleroge nic mPEG conjugate of hen egg lysozyme (mPEG(1.5)-HEL), which is conjugated 1.5-fold the molecular weight of mPEG against that of HEL, and evaluated t he relationship between in vivo stability and the tolerogenicity. mPEG(1.5) -HEL retained immunogenicity to prime HEL-specific T cell and antibody resp onses and had a long blood half-life, more than 27 times that of native HEL . The tolerant state was maintained as long as mPEG(1.5)-HEL was detected i n sera. With a decrease in the blood mPEG(1.5)-HEL level, the tolerant stat e returned gradually to the responsive state; however, reinjection of mPEG( 1.5)-HEL again restored the tolerance. Thus, the extended blood half-life o f HEL by mPEG conjugation is probably vital for establishing and maintainin g the tolerant states.