Combination treatment with intralesional cidofovir and viral-DNA vaccination cures large cottontail rabbit papillomavirus-induced papillomas and reduces recurrences

We used the cottontail rabbit papillomavirus (CRPV) New Zealand White rabbit model to test a combination treatment of large established papillomas with intralesional cidofovir and DNA vaccination to cure sites and reduce recurrences. Intralesional 1% (wt/vol) (0.036 M) cidofovir treatment of rabbit papillomas led to elimination, or "cure," of the papillomas over a 6- to 8-week treatment period (N.D. Christenson, M.D. Pickel, L.R. Budgeon, and J.W. Kreider, Antivir. Res. 48:131-142, 2000). However, recurrences at periods from 1 to 8 weeks after treatment cessation were observed at approximately 50% of cured sites. DNA vaccinations with CRPV E1, E2, E6, and E7 were initiated either after or at the time of intralesional treatments, and the recurrence rates were observed. When DNA vaccinations were started after intralesional cures, recurrence rates were similar to those of vector-vaccinated rabbits. A small proportion of recurrent sites subsequently regressed (4 out of 10, or 40%) in the vaccinated group versus no regression of recurrences in the vector-immunized group (0 out of 19, or 0%), indicating partial effectiveness. In contrast, when DNA vaccinations were conducted during intralesional treatments, a significant reduction of recurrences (from 10 out of 19, or 53%, of sites in vector-immunized rabbits to 3 out of 20, or 15%, of sites in viral-DNA-immunized rabbits) was observed. DNA vaccination without intralesional treatments had a minimal effect on preexisting papillomas. These data indicated that treatment with a combination of antiviral compounds and specific immune stimulation may lead to long-term cures of lesions without the ensuing problem of papilloma recurrence.