Role of Sterylglucosidase 1 (Sgl1) on the pathogenicity of Cryptococcus neoformans: potential applications for vaccine development.

Antonella Rella,Amir M Farnoud,Visesato Mor,Nicholas Carpino,Achraf A Shamseddine,Elitza Ivanova,Maria T Montagna,Chiara Luberto,Maurizio Del Poeta,Ashutosh Singh

doi:10.3389/fmicb.2015.00836

Abstract

Cryptococcosis caused by Cryptococcus neoformans and Cryptococcus gattii affects a large population and is a cause of significant morbidity and mortality. Despite its public health burden, there are currently no vaccines against cryptococcosis and new strategies against such infections are needed. In this study, we demonstrate that C. neoformans has the biochemical ability to metabolize sterylglucosides (SGs), a class of immunomodulatory glycolipids. Genetic manipulations that eliminate cryptococccal sterylglucosidase lead to the accumulation of SGs and generate a mutant strain (Δsgl1) that is non-pathogenic in the mouse models of cryptococcosis. Interestingly, this mutant strain acts as a vaccine strain and protects mice against cryptococcosis following infection with C. neoformans or C. gattii. The immunity induced by the Δsgl1 strain is not CD4+ T-cells dependent. Immunocompromised mice, which lack CD4+ T-cells, are able to control the infection by Δsgl1 and acquire immunity against the challenge by wild-type C. neoformans following vaccination with the Δsgl1 strain. These findings are particularly important in the context of HIV/AIDS immune deficiency and suggest that the Δsgl1 strain might provide a potential vaccination strategy against cryptococcosis.

Highlights

Cryptococcus is an opportunistic fungal pathogen and the causative agent of the disease cryptococcosis
Plasmid, and Culture Conditions The fungal strains used in this study were C. neoformans (Cn) var. grubii strain H99 wild-type (WT) and C. gattii strain R265 and Saccharomyces cerevisiae YIR007W mutant (Sc YIR) derived from BY4741
The plasmid pCR II-TOPO 4.0 kb was used for cloning, and pYES2/CT was used for expression of Cn 5607 in Sc YIR

Summary

Introduction

Cryptococcus is an opportunistic fungal pathogen and the causative agent of the disease cryptococcosis. Infections caused by Cryptococcus neoformans and Cryptococcus gattii lead to more than 600000 deaths per year (Park et al, 2009), especially among immunocompromised individuals. Despite its significant public health burden, no vaccines currently exist in the clinic for cryptococcosis (or other fungal infections Nanjappa and Klein, 2014). Experimental vaccines have been developed using the glucuronoxylomannan (GXM) capsule bound to tetanus toxoid (Devi et al, 1991; Casadevall et al, 1992; Devi, 1996), these formulations have not been translated to the clinic and have suffered from drawbacks such as inducing detrimental antibodies in mice (Casadevall and Pirofski, 2005; Datta and Pirofski, 2006). Recent attempts in the mouse models of cryptococcosis have been focused on the use of genetically engineered C. neoformans strains that generate cytokines (Wormley et al, 2007; Wozniak et al, 2011) or protein preparations from C. gattii administered prior to infection (Chaturvedi et al, 2014).

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Conclusion