COTTONTAIL RABBIT PAPILLOMAVIRUS-L1 PROTEIN-BASED VACCINES - PROTECTION IS ACHIEVED ONLY WITH A FULL-LENGTH, NONDENATURED PRODUCT

Papillomas induced by the cottontail rabbit papillomavirus (CRPV) Prog ress at a high frequency to carcinomas. In this regard, CRPV and its t umors can serve as an animal model for highly oncogenic human papillom aviruses. We have previously shown that immunization with major struct ural protein L1 elicits neutralizing antibodies and protects rabbits f rom papilloma development (Y.-L. Lin, L. A. Borenstein, R. Selvakumar, R. Ahmed, and F. O. Wettstein, Virology 187:612-619, 1992). In this s tudy, we demonstrated that vaccination with the TrpE-L1 fusion protein not only protected rabbits from papilloma development but also preven ted latent infection. This was indicated by the failure to amplify CRP V sequences by polymerase chain reaction in biopsies from infection si tes of immunized animals. Furthermore, we showed that TrpE-Ll immuniza tion protected rabbits from papilloma formation induced by virus but n ot from that induced by viral DNA. To explore the possibility of devel oping vaccines based on Ll subfragments, we mapped the linear L1 epito pes recognized by TrpE-L1-immunized rabbits and by virus-infected rabb its resistant to superinfection. Sera from papilloma-bearing rabbits r eacted with one major epitope located at the carboxy-terminal end of L l, between amino acids (aa) 480 and 505. A second epitope, and in some animals a third one, was located in the amino-terminal region, betwee n aa 78 and 101, as well as between aa 37 and 62. Sera from TrpE-Ll-im munized animals recognized only one major epitope, located between aa 6 and 37. Immunization of rabbits with Ll subfragment fusion proteins led to seroconversion, but no neutralizing antibodies were produced an d the animals were not protected against papilloma formation. The data indicate that a successful papillomavirus vaccine must be based on im munization with full-length native L1 and that further simplification to smaller peptides containing major linear epitopes is not feasible.