Three Models of Vaccination Strategies Against Cryptococcosis in Immunocompromised Hosts Using Heat-Killed Cryptococcus neoformans Δsgl1

Abstract

Vaccines are one of the greatest medical accomplishments to date, yet no fungal vaccines are currently available in humans mainly because opportunistic mycoses generally occur during immunodeficiencies necessary for vaccine protection. In previous studies, a live, attenuated Cryptococcus neoformans Δsgl1 mutant accumulating sterylglucosides was found to be avirulent and protected mice from a subsequent lethal infection even in absence of CD4+ T cells, a condition most associated with cryptococcosis (e.g., HIV). Here, we tested three strategies of vaccination against cryptococcosis. First, in our preventative model, protection was achieved even after a 3-fold increase of the vaccination window. Second, because live C. neoformans Δsgl1-vaccinated mice challenged more than once with WT strain had a significant decrease in lung fungal burden, we tested C. neoformans Δsgl1 as an immunotherapeutic. We found that therapeutic administrations of HK C. neoformans Δsgl1 post WT challenge significantly improves the lung fungal burden. Similarly, therapeutic administration of HK C. neoformans Δsgl1 post WT challenge resulted in 100% or 70% survival depending on the time of vaccine administration, suggesting that HK Δsgl1 is a robust immunotherapeutic option. Third, we investigated a novel model of vaccination in preventing reactivation from lung granuloma using C. neoformans Δgcs1. Remarkably, we show that administration of HK Δsgl1 prevents mice from reactivating Δgcs1 upon inducing immunosuppression with corticosteroids or by depleting CD4+ T cells. Our results suggest that HK Δsgl1 represents a clinically relevant, efficacious vaccine that confers robust host protection in three models of vaccination against cryptococcosis even during CD4-deficiency.

Vaccination with Live or Heat-Killed Aspergillus fumigatus Δ sglA Conidia Fully Protects Immunocompromised Mice from Invasive Aspergillosis

“…Overall, these data show that 1 dose of HK A. fumigatus Δ sglA conidia was sufficient to confer complete host protection in corticosteroid-treated mice and induce protective host immunity necessary to clear the WT strain from the lungs. These data also confirmed the results of previous studies in which an HK C. neoformans Δ sgl1 strain completely protected immunocompromised mice from a lethal WT challenge ( 33 ), suggesting that an HK vaccine formulation enriched in SGs could be a valuable option for protecting individuals at risk of developing invasive cryptococcosis and aspergillosis.…”

“…But this should not be a problem because only one administration of either the autoclaved or boiled Δ sglA conidia was sufficient for complete protection of the host. This was not observed in studies using HK C. neoformans Δ sgl1 conidia, where 2 doses of HK conidia were necessary to obtain 100% protection, while 1 dose conferred 70% protection in immunodeficient mice ( 33 ).…”

“…We recently reported that mice immunized with 2 doses of heat-killed (HK) C. neoformans Δ sgl1 were completely protected from a lethal WT challenge ( 33 ). Because the administration of A. fumigatus Δ sglA conferred complete host protection against the WT strain, we then wanted to assess the efficacy of the HK A. fumigatus Δ sglA mutant in inducing host protection.…”

“…We previously reported that Cryptococcus neoformans Δ sgl1 , a mutant strain that accumulates sterylglucosides (SGs) due to the deletion of the sterylglucosidase-encoding gene ( SGL1 ), was avirulent in a mouse model of infection and conferred complete host protection against a subsequent lethal challenge with the wild type (WT) in several models of immunosuppression ( 29 , 30 ). SGs are immunomodulatory glycolipids with a wide array of applications (reviewed in reference 31 ) but were only recently shown to protect immunocompromised mice from lethal infection with C. neoformans , possibly functioning as potent adjuvants for fungal antigens ( 29 , 32 , 33 ). Moreover, in vivo treatments with Sgl1 inhibitors restricted WT C. neoformans infection to the lungs ( 34 ).…”

Vaccine protection by Cryptococcus neoformans Δsgl1 is mediated by γδ T cells via TLR2 signaling

“…We observed complete (100%) host protection, suggesting that C. neoformans Δ sgl1 mutant can be used as a live, attenuated vaccine 32 . Subsequent studies showed that C. neoformans Δ sgl1 provided complete host protection even during CD4 + T cell deficiency 41 , 42 . We also identified that in order to be protective, C. neoformans Δ sgl1 must display on its surface certain antigenic capsular components, such as glucuronoxylomannan (GXM), because a mutant strain accumulating SGs but lacking the capsule (Δ cap59 Δ sgl1 ) was no longer protective 36 , suggesting that SGs may act as an adjuvant to GXM.…”