Research Insights

Cryptococcal meningoencephalitis (CME) is responsible for more than 15% of the total deaths of AIDS patients. The disease claims hundreds of thousands of lives each year, with global mortality rates of ~70% despite antifungal therapies. Unfortunately, there is no vaccine clinically available for cryptococcosis. The challenges of preventing and treating this fungal disease motivate our investigation of cryptococcal pathways that can induce a strong protective host response. The encapsulated fungus Cryptococcus neoformans is known to undergo yeast-to-filament morphological transition. We previously showed that morphotype of this fungus has a profound effect on its interaction with various hosts. In mammalian models of cryptococcosis, the yeast form is pathogenic while the filamentous form is not. We established that the transcription factor Znf2, which drives filamentous growth, is a powerful anti-virulence regulator. Cryptococcal cells overexpressing ZNF2 (ZNF2oe) are avirulent and elicit strong and long-lasting protective immunity, which serves as an effective vaccine against subsequent lethal challenges. Importantly, we showed that once mice are vaccinated with ZNF2oe cells, their CD4+ T cells are dispensable for protection at the time of fungal challenge (mimic people with HIV prior to AIDS). Furthermore, vaccination with ZNF2oe cells even in hosts with pre- existing CD4+ T cell deficiency is also protective against cryptococcosis (mimic AIDS patients). These findings are important because the majority of cryptococcosis patients are AIDS patients with low CD4+ T cell counts, and our preclinical studies suggest that cryptococcal vaccines could be effective in these individuals. The long-term goal of this project is to characterize the filamentation pathway and explore it for therapeutics (e.g. vaccines). We have made significant progress in establishing the link between morphotype, virulence and immunity, and discovered multiple regulators required for both Znf2-directed filamentation and Znf2-induced host immunity. Recently, we also identified mutations that block Znf2’s function in filamentation, but do not affect its ability to induce host protective effects. These findings provide a unique opportunity to pinpoint cryptococcal factors associated with host protective effect of Znf2. Because ZNF2oe in both heat- inactivated and live cells provides host protection, we predicted that extracellular components of ZNF2oe cells are important protective immunogens. Consistently, host protection elicited by ZNF2oe cells depends on the capsule where extracellular antigens are localized. Additionally, our preliminary data revealed that some antigens are secretory proteins including several glycosylphosphatidylinositol (GPI)-anchored glycoproteins. Capitalizing on these discoveries and our expertise in mRNA lipid nanoparticle (mRNA-LNP) technology, we aim to (1) define cryptococcal factors that are important for Znf2’s anti-virulence effect; (2) identify immunogens that elicit protective host responses; and (3) use selected immunogens to develop mRNA-LNP or recombinant protein vaccines against cryptococcosis.

Funder: National Institutes of Health 

Amount: $2,828,534 

PI: Xiaorong Lin, Franklin College of Arts and Sciences, Department of Microbiology