Killed Saccharomyces cerevisiae protects against lethal challenge of Cryptococcus grubii.

Heat-killed Saccharomyces cerevisiae (HKY) vaccination protects mice against aspergillosis, coccidioidomycosis, mucormycosis, or candidiasis. We studied HKY protection against murine cryptococcosis. Once weekly subcutaneous HKY doses (S, 6 × 10(7); 2S, 1.2 × 10(8); 3S, 2.4 × 10(8)) began 28 (×3), 35 (×4), or 42 (×6) days prior to intravenous Cryptococcus grubii infection. Survival through 28 days, and CFU in the organs of survivors, were compared to saline-vaccinated controls. In the initial experiment, S, S×4, or 2S reduced brain CFU; liver or spleen CFU was reduced by S×4 or 2S. In a more lethal second experiment, 2S×6, 2S, or 3S×4 improved survival, and HKY regimens reduced CFU in the brain, liver, or spleen, with 2S×6, 2S, or 3S×4 most efficacious. Dose size appears more important than the number of doses: Regimens >S were superior, and 2S and 2S×6 were equivalent. 2S and 3S were equivalent, suggesting doses >2S do not provide additional protection. HKY protects against Cryptococcus, supporting components of HKY as a basis for the development of a panfungal vaccine.

Saccharomyces as a vaccine against systemic aspergillosis: 'the friend of man' a friend again?

The mortality of clinical Aspergillus infections necessitates consideration of the utility of a vaccine. We have found that Saccharomyces species can act as a protective vaccine against a lethal systemic Aspergillus infection, and describe experiments optimizing a subcutaneous regimen with killed yeast. Three injections of 2.5 mg given a week apart, 2 weeks prior to challenge, consistently, significantly, provided survival protection and reduction of infection in organs in survivors. The protection was independent of the strain of Saccharomyces, and possibly even the species, and could be demonstrated in several inbred (including C'-deficient) and outbred mouse strains. The protective moiety(ies) appeared to reside in the cell wall and was resistant to 100 °C, but not to protease or formalin. Alum potentiated the protection. The protection was comparable or superior to that of several Aspergillus-specific preparations described in the literature. Other studies have indicated that heat-killed Saccharomyces can protect against infection with at least three other fungal genera, raising the possibility of development of a panfungal vaccine, and such a vehicle has been studied in clinical trials, without dose-limiting toxicity.