Antibody titer threshold predicts anti-candidal vaccine efficacy even though the mechanism of protection is induction of cell-mediated immunity.

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.