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

Abstract

24Cryptococcal meningitis (CM) causes high rates of HIV-related mortality, yet Cryptococcus 25 factors influencing patient outcome are not well understood. Pathogen-specific traits, such as the 26 strain genotype and degree of antigen shedding, are associated with clinical outcome but the 27 underlying biology remains elusive. In this study, we examined factors determining disease 28 outcome in HIV-infected cryptococcal meningitis patients infected with C. neoformans strains 29 with the same multi-locus sequence type. Both patient mortality and survival were observed 30 during infections with the same sequence type. Disease outcome did not correlate with 31 underlying patient immune deficiencies. Patient mortality was associated with higher antigen 32 levels, fungal burden in the CSF, and low CSF fungal clearance. Virulence of a subset of clinical 33 strains with the same sequence type were analyzed using the mouse inhalation model of 34 cryptococcosis. We showed a strong correlation between human and mouse mortality rates, 35 demonstrating the mouse inhalation model recapitulates human infection. Similar to human 36 infection, the ability to multiply in vivo, demonstrated by high fungal burden in the lung and 37 brain tissues, was associated with mouse mortality. Mortality rate was not associated with single 38 C. neoformans virulence factors in vitro or in vivo; rather, a trend in mortality rate correlated 39 with a suite of traits. These observations show that genotype similarities between C. neoformans 40 strains do not necessarily translate into similar virulence either in the mouse model or in human 41 patients. In addition, our results show that in vitro assays do not fully reproduce in vivo 42 conditions that influence C. neoformans virulence. 44Cryptococcus neoformans is a fungal pathogen that causes disease mainly in 45 immunocompromised patients such as individuals living with HIV/AIDS or receiving organ 46 transplants. The availability of antiretroviral therapy has reduced AIDS-related mortality, 47 however deaths due to cryptococcal meningitis (CM) have plateaued with C. neoformans still 48 causing 15 % of all AIDS-related deaths globally (1, 2). Mortality rates due to Cryptococcus 49 infection varies by region from 70% in low-income countries to 20-40% of all infected patients 50 in high-income countries (2). Although differences in mortality rates between high-and low-51 income countries can be linked to sub-optimal antifungal treatments in low-income countries (3), 52 variations in mortality rates between patient groups receiving similar treatments and residing in 53 the same region of the world are observed (1,(4)(5)(6). Mortality is a measure influenced by many 54 intrinsic host and pathogen factors (as well as host-pathogen interaction factors). Thus, we need 55 better proxies to understand C. neoformans pathogenesis in patients and identify factors 56 determining clinical outcome. 57Although C. neoformans pathogenesis in the mouse model of cryptococcosis has been 58 extensively studied, the...