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

Abstract

We previously reported that administration of Cryptococcus neoformans Δsgl1 mutant vaccine, accumulating sterylglucosides (SGs) and having normal capsule (GXM), protects mice from a subsequent infection even during CD4+ T cells deficiency, a condition commonly associated with cryptococcosis. Here, we studied the immune mechanism that confers host protection during CD4+T deficiency. Mice receiving Δsgl1 vaccine produce IFNγ and IL-17A during CD4+ T (or CD8+ T) deficiency, and protection was lost when either cytokine was neutralized. IFNγ and/or IL-17A are produced by γδ T cells, and mice lacking these cells are no longer protected. Interestingly, ex vivo γδ T cells are highly stimulated in producing IFNγ and/or IL-17A by Δsgl1 vaccine, but this production was significantly decreased when cells were incubated with C. neoformans Δcap59/Δsgl1 mutant, accumulating SGs but lacking GXM. GXM modulates toll-like receptors (TLRs), including TLR2. Importantly, neither Δsgl1 nor Δcap59/Δsgl1 stimulate IFNγ or IL-17A production by ex vivo γδ T cells from TLR2−/− mice. Finally, TLR2−/− animals do not produce IL-17A in response to Δsgl1 vaccine and were no longer protected from WT challenge. Our results suggest that SGs may act as adjuvants for GXM to stimulate γδ T cells in producing IFNγ and IL-17A via TLR2, a mechanism that is still preserved upon CD4+ T deficiency.

Targeting Sterylglucosidase A to Treat Aspergillus fumigatus Infections

“…In our previous studies, we found that C. neoformans Δ sgl1 and A. fumigatus Δ sgla are potent immune stimulators, and for C. neoformans Δ sgl1 , we showed that this immune activation is controlled by Toll-like receptor 2 (TLR2) on γ/δ T cells ( 28 ). Thus, both Cn Δ sgl1 and Af Δ sgla are exciting vaccine candidates, because they are highly effective in preventing a secondary infection either as live-attenuated or as heat-killed vaccines.…”

Promising whole‐cell vaccines against cryptococcosis

“…The γδ T cells appear to recognize C. neoformans directly via TLR2 and produce IFNγ and IL‐17A. Stimulation of γδ T cells with sgl1∆ containing a larger amount of SGs releases larger amounts of IFNγ and IL‐17A than stimulation with H99 or sgl1∆/cap59∆ (sgl1∆ lacking capsule), and the production is markedly reduced in γδ T cells lacking TLR2 23 . CAP59 is an essential gene for the biosynthesis of glucuronoxylomannan (GXM), the main component of capsules, and CAP59 ‐deficient strains lose GXM 46 .…”

“…Stimulation of γδ T cells with sgl1Δ containing a larger amount of SGs releases larger amounts of IFNγ and IL-17A than stimulation with H99 or sgl1Δ/ cap59Δ (sgl1Δ lacking capsule), and the production is markedly reduced in γδ T cells lacking TLR2. 23 CAP59 is an essential gene for the biosynthesis of glucuronoxylomannan (GXM), the main component of capsules, and CAP59deficient strains lose GXM. 46 TLR2 recognizes cryptococcal GXM; 47 thus, the authors indicated that the γδ T cells would not be able to recognize sgl1Δ and would not be activated under conditions lacking TLR2 or the absence of GXM.…”

“…46 TLR2 recognizes cryptococcal GXM; 47 thus, the authors indicated that the γδ T cells would not be able to recognize sgl1Δ and would not be activated under conditions lacking TLR2 or the absence of GXM. 23 Indeed, CBA/J mice immunized with sgl1Δ/cap59Δ succumb to H99 challenge, 20 and the live vaccine using sgl1Δ is ineffective in TLR2-deficient mice challenged with H99. 23 The vaccine-induced γδ T cells could be an innate source for producing IFNγ and IL-17A in the early phase of infection, which could lead to Th1 and Th17 responses in the later phase of infection.…”

“…23 Indeed, CBA/J mice immunized with sgl1Δ/cap59Δ succumb to H99 challenge, 20 and the live vaccine using sgl1Δ is ineffective in TLR2-deficient mice challenged with H99. 23 The vaccine-induced γδ T cells could be an innate source for producing IFNγ and IL-17A in the early phase of infection, which could lead to Th1 and Th17 responses in the later phase of infection. The production of IFNγ and IL-17A and the infiltration of neutrophils in the lungs are required for the protection by this immunization, and the sgl1Δ-immunized mice become unable to resist H99 challenge when given neutralization or depletion antibodies including 1A8 (Ly6G), 17F3 (IL-17A), and XMG1.2 (IFNγ).…”