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Vaccination with the recombinant N terminus of the candidal adhesin Als3p (rAls3p-N) protects mice from lethal candidemia. Candidal Als3p also is structurally similar to the microbial surface components recognizing adhesive matrix molecule adhesin, clumping factor, from Staphylococcus aureus. To determine the potential for cross-kingdom vaccination, we immunized mice with rAls3p-N or negative control proteins and challenged them via the tail vein with S. aureus or other gram-positive or gram-negative pathogens. The rAls3p-N vaccine, but neither tetanus toxoid nor a related Als protein (Als5p), improved the survival of vaccinated mice subsequently infected with multiple clinical isolates of S. aureus, including methicillin-resistant strains. The rAls3p-N vaccine was effective against S. aureus when combined with aluminum hydroxide adjuvant. However, the vaccine did not improve the survival of mice infected with other bacterial pathogens. Vaccinated, infected mice mounted moderated type 1 immune responses. T lymphocyte-deficient mice were more susceptible to S. aureus infection, but B lymphocyte-deficient mice were not. Furthermore, T but not B lymphocytes from vaccinated mice mediated protection in adoptive transfer studies. The passive transfer of immune serum was not protective. These data provide the foundation for cross-kingdom vaccine development against S. aureus and Candida, which collectively cause 200,000 bloodstream infections resulting in >/=40,000 to 50,000 deaths annually in the United States alone.

We previously reported that vaccination with Freund's adjuvant plus the recombinant N-terminus of the candidal adhesin, Als3p (rAls3p-N), protects mice from disseminated candidiasis. Here we report that the rAls3p-N vaccine is effective when combined with aluminum hydroxide adjuvant. Antibody titers of > or =1:6400 accurately predicted protection from infection. Nevertheless, neither B lymphocytes nor serum from immunized animals transferred protection to vaccine-naive animals. In contrast, CD3(+), CD4(+), or CD8(+) T lymphocytes from immunized animals transferred protection, and the vaccine was efficacious in IL-4-deficient mice but not in IFN-gamma-deficient mice. These data have significant implications for the development and interpretation of vaccine surrogate markers.

Commensal and pathogenic states of Candida albicans depend on cell surface-expressed adhesins, including those of the Als family. Mature Als proteins consist of a 300-residue N-terminal region predicted to have an immunoglobulin (Ig)-like fold, a 104-residue conserved Thr-rich region (T), a central domain of a variable number of tandem repeats (TR) of a 36-residue Thr-rich sequence, and a heavily glycosylated C-terminal Ser/Thr-rich stalk region, also of variable length (N. K. Gaur and S. A. Klotz, Infect. Immun. 65: 5289-5294, 1997). Domain deletions in ALS5 were expressed in Saccharomyces cerevisiae to excrete soluble protein and for surface display. Far UV circular dichroism indicated that soluble Ig-T showed a single negative peak at 212 nm, consistent with previous data indicating that this region has high beta-sheet content with very little alpha-helix. A truncation of Als5p with six tandem repeats (Ig-T-TR(6)) gave spectra with additional negative ellipticity at 200 nm and, at 227 to 240 nm, spectra characteristic of a structure with a similar fraction of beta-sheet but with additional structural elements as well. Soluble Als5p Ig-T and Ig-T-TR(6) fragments bound to fibronectin in vitro, but the inclusion of the TR region substantially increased affinity. Cellular adhesion assays with S. cerevisiae showed that the Ig-T domain mediated adherence to fibronectin and that TR repeats greatly increased cell-to-cell aggregation. Thus, the TR region of Als5p modulated the structure of the Ig-T region, augmented cell adhesion activity through increased binding to mammalian ligands, and simultaneously promoted fungal cell-cell interactions.