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

Area of Science:

• Immunology
• Microbiology
• Vaccinology

Background:

• Cryptococcosis is often severe in CD4+ T cell deficient individuals.
• A previously developed Cryptococcus neoformans Δsgl1 mutant vaccine, rich in sterylglucosides (SGs) and with a normal capsule (GXM), confers protection.
• The immune mechanism behind this protection, especially during CD4+ T cell deficiency, was unclear.

Purpose of the Study:

• To elucidate the immune mechanism conferring host protection against Cryptococcus neoformans infection during CD4+ T cell deficiency.
• To investigate the role of specific cytokines (IFNγ, IL-17A) and immune cells (γδ T cells, TLR2) in the vaccine-induced protection.

Main Methods:

• Mice were vaccinated with C. neoformans Δsgl1 mutant and challenged with wild-type (WT) C. neoformans.
• Cytokine production (IFNγ, IL-17A) and T cell populations (γδ T cells) were analyzed.
• Experiments involved cytokine neutralization, T cell depletion, and the use of Toll-like receptor 2 knockout (TLR2-/-) mice.
• Ex vivo assays assessed γδ T cell stimulation by different vaccine mutants.

Main Results:

• Mice vaccinated with Δsgl1 produced IFNγ and IL-17A, crucial for protection, even without CD4+ T cells.
• Protection was lost upon neutralization of IFNγ or IL-17A, or in mice lacking γδ T cells.
• Ex vivo γδ T cells produced IFNγ and IL-17A upon stimulation with Δsgl1 vaccine, dependent on sterylglucosides (SGs) and capsule (GXM).
• This stimulation required Toll-like receptor 2 (TLR2) and was impaired in TLR2-/- mice, which also lacked protection.

Conclusions:

• Sterylglucosides (SGs) in the C. neoformans Δsgl1 vaccine likely act as adjuvants for the capsule (GXM).
• This combination stimulates γδ T cells to produce protective cytokines IFNγ and IL-17A via TLR2.
• This immune mechanism remains effective even in the absence of CD4+ T cells, offering a potential strategy for cryptococcosis vaccination.