Cryptococcus neoformans Δsgl1 Vaccination Requires Either CD4+ or CD8+ T Cells for Complete Host Protection

Abstract

Cryptococcus neoformans is a fungal pathogen causing life-threatening meningoencephalitis in susceptible individuals. Fungal vaccine development has been hampered by the fact that cryptococcosis occurs during immunodeficiency. We previously reported that a C. neoformans mutant (Δsgl1) accumulating sterylglucosides (SGs) is avirulent and provides complete protection to WT challenge, even under CD4+ T cell depletion, an immunodeficient condition commonly associated with cryptococcosis. We found high levels of SGs in the lungs post-immunization with Δsgl1 that decreased upon fungal clearance. Th1 cytokines increased whereas Th2 cytokines concurrently decreased, coinciding with a large recruitment of leukocytes to the lungs. Depletion of B or CD8+ T cells did not affect either Δsgl1 clearance or protection from WT challenge. Although CD4+ T cell depletion affected clearance, mice were still protected indicating that clearance of the mutant was not necessary for host protection. Protection was lost only when both CD4+ and CD8+ T cells were depleted, highlighting a previously unexplored role of fungal-derived SGs as an immunoadjuvant for host protection against cryptococcosis.

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

“…Prior studies in our lab have shown that C. neoformans Δ sgl1 induces a proinflammatory lung cytokine environment with robust effector cell recruitment to the lungs as well as confers complete host protection to lethal WT challenge under immunodeficiencies most associated with cryptococcosis (e.g., lacking CD4 + T cells) ( 52 ). Interestingly, we found that protection required SGs in combination to the immunosuppressive glucuronoxylomannan (GXM)-based capsule since an acapsular mutant strain (Δ cap59 Δ sgl1 ) was no longer protective ( 53 ) nor induce a protective cytokine response to ex vivo stimulated γδ T cells (T.G.…”

Three models of vaccination strategies against cryptococcosis in immunocompromised hosts using heat-killedCryptococcus neoformansΔsgl1

“…Since we have previously reported that either CD4 + or CD8 + T cells are required for C. neoformans Δ sgl1 -mediated host protection [52], we hypothesized that repeated immunization with this HK mutant dose may negate the negative facets of HK vaccination and promote stronger adaptive T cell-mediated immunity as seen with other HK mutant vaccine studies [55, 56]. We tested this hypothesis by administering two subsequent doses of 5x10 7 HK C .…”

“…Sheridan, and M. Del Poeta, submitted for publication). In those studies, we showed that the lung fungal burden at days 45, 75, and 105 post WT challenge was nearly identical at all timepoints, and histopathology at these timepoints displayed a decreased percentage of inflamed lung tissue and increased formation isolated nodules of contained yeast cells [52]. In this study, we found for the first time that vaccination with two subsequent doses of HK C. neoformans Δ sgl1 results in a significant decrease of lung fungal burden compared to live C. neoformans Δ sgl1 -vaccination for both immunocompetent and CD4-deficient mice ( Fig.…”

“…With regards to our vaccine, we aimed to test the rigor and robustness of C. neoformans Δ sgl1 in the preventative model of vaccination via functional alterations to our experimental design. Since T cell mediated immunity is a well-established keystone of anti-cryptococcal immunity [60, 61] as well as the need for either CD4 + or CD8 + T cells for C. neoformans Δ sgl1 protection [52], these alterations focused upon memory T cells. The first alteration involved a 3- fold increase in the time between vaccination and WT challenge, where vaccination began 90 days prior to WT challenge for both live and HK C. neoformans Δ sgl1 .…”

“…Prior studies in our lab have shown that C. neoformans Δ sgl1 induces a proinflammatory lung cytokine environment with robust effector cell recruitment to the lungs as well as confers complete host protection to lethal WT challenge under immunodeficiencies most associated with cryptococcosis (e.g., lacking CD4 + T cells) [52]. Interestingly, we found that protection required SGs in combination to the immunosuppressive glucuronoxylomannan (GXM)-based capsule since an acapsular mutant strain (Δ cap59 Δ sgl1 ) was no longer protective [53] nor induce aprotective cytokine response to ex vivo stimulated γ δ T cells (T.G.…”