Inhibition of Candida albicans adhesion by recombinant human antibody single‐chain variable fragment specific for Als3p

The Candida albicans adhesin, Als3p, was identified as a potential cognate antigen for previously described human antibody fragments [single‐chain variable fragment (scFv)] based on similarity of the binding pattern of the scFv to the distribution of this protein on the hyphal surface. Although all scFv bound avidly to wild type, scFv3 showed no detectable binding via immunofluorescence assay to strain 1843, containing a homozygous deletion of ALS3 . Binding to the ALS3 reintegrant strain, 2322, was preserved, and scFv3 also bound to Saccharomyces cerevisiae expressing ALS3 . Other scFv retained binding to 1843, but with a markedly altered pattern. To determine if scFv3 could interfere with Als3p function, adhesion assays were conducted using human epithelial or endothelial cells as target. Treatment of wild‐type C. albicans with scFv3 reduced adhesion of the fungus to both cell types to levels comparable to the als3 Δ/ als3 Δ mutant. These experiments confirm that phage display is a viable method to isolate human scFv specific to an antigen implicated in C. albicans virulence, and that the scFv interfere with adhesion to human cells. The altered pattern of immunostaining with other scFv that retain binding to the als3 Δ/ als3 Δ mutant suggest that Als3p may also have a role in structural organization of the C. albicans cell surface.