Idiotypic Intravaginal Vaccination to Protect Against Candidal Vaginitis by Secretory, Yeast Killer Toxin-like Anti-idiotypic Antibodies

The principles of idiotypic (Id) vaccination were used to immunize against vaginitis caused by Candida albicans, a widespread and sometimes intractable disease in women. To this aim, a murine mAb (KT4, IgG1) neutralizing in vitro the anti-Candida activity of a yeast killer toxin (YKT) was used as an Id vaccine to elicit Abs with toxin-like activity in a rat vaginitis model. Nonimmunized and isotype-matched, irrelevant mAb-immunized rats served as controls. An effective protection was obtained in Id-vaccinated animals, as demonstrated by a highly significant decrease in vaginal Candida CFU compared with controls. The protection was associated with rising vaginal titers of anti-idiotypic Abs (IdAb), prevalently of the IgA isotype, that were able to passively transfer the protective state to nonimmunized animals. The vaginal IdAb possessed YKT-like activity because they were able to kill in vitro the challenging fungal cells, and this killing was neutralized by the mAb KT4. Overall, these data demonstrate that secretory IdAb elicited by intravaginal Id vaccination with mAb KT4 protected the rats from the infectious challenge with Candida albicans by molecular mimicking YKT activity as its internal image.