Closely related Cryptococcus neoformans strains possess differential virulence both in humans and the mouse inhalation model

Cryptococcal meningitis (CM) causes high rates of HIV-related mortality, yet Cryptococcus factors influencing patient outcome are not well understood. Pathogen-specific traits, such as the strain genotype and degree of antigen shedding, are associated with clinical outcome but the underlying biology remains elusive. In this study, we examined factors determining disease outcome in HIV-infected cryptococcal meningitis patients infected with C. neoformans strains with the same multi-locus sequence type. Both patient mortality and survival were observed during infections with the same sequence type. Disease outcome did not correlate with underlying patient immune deficiencies. Patient mortality was associated with higher antigen levels, fungal burden in the CSF, and low CSF fungal clearance. Virulence of a subset of clinical strains with the same sequence type were analyzed using the mouse inhalation model of cryptococcosis. We showed a strong correlation between human and mouse mortality rates, demonstrating the mouse inhalation model recapitulates human infection. Similar to human infection, the ability to multiply in vivo, demonstrated by high fungal burden in the lung and brain tissues, was associated with mouse mortality. Mortality rate was not associated with single C. neoformans virulence factors in vitro or in vivo; rather, a trend in mortality rate correlated with a suite of traits. These observations show that genotype similarities between C. neoformans strains do not necessarily translate into similar virulence either in the mouse model or in human patients. In addition, our results show that in vitro assays do not fully reproduce in vivo conditions that influence C. neoformans virulence.