Active and Passive Immunization with rHyr1p-N Protects Mice against Hematogenously Disseminated Candidiasis

Guanpingsheng Luo,Ashraf S Ibrahim,Yue Fu,Samuel W French,John E Edwards,Marta Feldmesser

doi:10.1371/journal.pone.0025909

Abstract

We previously reported that Candida albicans cell surface protein Hyr1 encodes a phagocyte killing resistance factor and active vaccination with a recombinant N-terminus of Hyr1 protein (rHyr1p-N), significantly protects immunocompetent mice from disseminated candidiasis. Here we report the marked efficacy of rHyr1p-N vaccine on improving the survival and reducing the fungal burden of disseminated candidiasis in both immunocompetent and immunocompromised mice using the FDA-approved adjuvant, alum. Importantly, we also show that pooled rabbit anti-Hyr1p polyclonal antibodies raised against 8 different peptide regions of rHyr1p-N protected mice in a hematogenously disseminated candidiasis model, raising the possibility of developing a successful passive immunotherapy strategy to treat this disease. Our data suggest that the rabbit anti-Hyr1p antibodies directly neutralized the Hyr1p virulence function, rather than enhanced opsonophagocytosis for subsequent killing by neutrophil in vitro. Finally, the rHyr1p-N vaccine was protective against non-albicans Candida spp. These preclinical data demonstrate that rHyr1p-N is likely to be a novel target for developing both active and passive immunization strategies against Candida infections.

Highlights

Candida species, the third most common cause of healthcareassociated bloodstream infections [1] causes approximately 60,000 cases of hematogenously disseminated candidiasis per year in the United States [2], resulting in billions of dollars of healthcare expenditures
Consistent with our previous mouse IgG data [12], we found that F(ab9) 2 fragments prepared from anti-Hyr1p antibodies but not those prepared from control antibodies were able to restore HL-60 derived neutrophil killing of the HYR1 conditional expressing strain to levels equivalent to that of the suppressing strain (Figure 4D)
C. albicans vaccine development has focused on using cell surface components [18,19], peptides derived from cell wall proteins as immunogens [20], or on antibodies targeting cell surface components [21,22]

Summary

Introduction

The third most common cause of healthcareassociated bloodstream infections [1] causes approximately 60,000 cases of hematogenously disseminated candidiasis per year in the United States [2], resulting in billions of dollars of healthcare expenditures. Because of the rising incidence of life-threatening candidiasis and high treatment failure rates, more effective prophylactic and therapeutic strategies are needed. HYR1 belongs to the IFF gene family of C. albicans, which includes 12 members [9]. It encodes a cell surface glycosylphosphatidylinositol (GPI)-anchored protein that is expressed during hyphal formation [10,11]. We showed that Hyr1p mediated C. albicans resistance to phagocyte killing in vitro and contributed higher fungal burden in organs rich in phagocytes (e.g. liver and spleen) [12]. We found that autonomous HYR1 expression reversed the hyper-susceptibility to phagocyte-mediated killing of a bcr null mutant of C. albicans in vitro [12]. Our study showed that a vaccine based on the recombinant N terminus of Hyr1p (rHyr1p-N) markedly improved survival of immunocompetent mice challenged intravenously with C. albicans when mixed with either Freund’s or alum as an adjuvant [12]

Methods

Results

Conclusion