Vaccination against gonadotropin-releasing hormone (GnRH) using toxin receptor-binding domain-conjugated GnRH repeats

A method for the preparation of an immunogen containing multiple copies of a self-peptide in linear alignment was designed in order to overcome the di fficulty of inducing an immune response to poorly immunogenic peptide antig ens, DNA fragments encoding multiple repeats of the self-peptide were gener ated by a new technique, termed template-repeated polymerase chain reaction (TR-PCR), which could be subcloned into an expression vector for productio n of peptide repeats as an immunogen, This approach was tested by construct ing fusion proteins containing the receptor-binding domain of Pseudomonas e xotoxin A and multiple copies of the 10-residue sequence of the peptide hor mone gonadotropin-releasing hormone (GnRH), Immunization of female rabbits with the immunogen that contained the exotoxin receptor-binding domain and 12 copies of GnRH (PEIa-GnRH(12)) resulted in the generation of high-titer antibodies specific for GnRH, Although at equal molar basis of the GnRH moi ety, the immunogen that contained single copy of GnRH (PEIa-GnRH(1)) induce d low-titer anti-GnRH antibodies. These observations suggest that the prese nce of multiple peptide repeats is a keg factor in eliciting an immune resp onse. In addition, anti-GnRH, antibodies effectively neutralized GnRH activ ity in vivo, as demonstrated by the degeneration of the ovaries in the inje cted rabbits, Because anti-GnRH antibody could he functionally analogous to GnRH antagonist, which has been used to treat patients with ovarian canter , vaccination of PEIa-GnRH(12) presents a potential therapeutic application for the treatment of GnRH-sensitive ovarian cancer.