Vaccination with RecombinantCryptococcusProteins in Glucan Particles Protects Mice against Cryptococcosis in a Manner Dependent upon Mouse Strain and Cryptococcal Species

Abstract

Development of a vaccine to protect against cryptococcosis is a priority given the enormous global burden of disease in at-risk individuals. Using glucan particles (GPs) as a delivery system, we previously demonstrated that mice vaccinated with crude Cryptococcus-derived alkaline extracts were protected against lethal challenge with Cryptococcus neoformans and Cryptococcus gattii. The goal of the present study was to identify protective protein antigens that could be used in a subunit vaccine. Using biased and unbiased approaches, six candidate antigens (Cda1, Cda2, Cda3, Fpd1, MP88, and Sod1) were selected, recombinantly expressed in Escherichia coli, purified, and loaded into GPs. Three mouse strains (C57BL/6, BALB/c, and DR4) were then vaccinated with the antigen-laden GPs, following which they received a pulmonary challenge with virulent C. neoformans and C. gattii strains. Four candidate vaccines (GP-Cda1, GP-Cda2, GP-Cda3, and GP-Sod1) afforded a significant survival advantage in at least one mouse model; some vaccine combinations provided added protection over that seen with either antigen alone. Vaccine-mediated protection against C. neoformans did not necessarily predict protection against C. gattii. Vaccinated mice developed pulmonary inflammatory responses that effectively contained the infection; many surviving mice developed sterilizing immunity. Predicted T helper cell epitopes differed between mouse strains and in the degree to which they matched epitopes predicted in humans. Thus, we have discovered cryptococcal proteins that make promising candidate vaccine antigens. Protection varied depending on the mouse strain and cryptococcal species, suggesting that a successful human subunit vaccine will need to contain multiple antigens, including ones that are species specific.

Helper T‐cell responses and pulmonary fungal infections

“…Vaccination with glucan particles loaded with calnexin peptide was capable of eliciting protective immunity against both B. dermatitidis and Coccidioides posadasii experimental pulmonary infection, demonstrating the potential for vaccination strategies promoting calnexin‐specific T‐cell responses to protect against multiple endemic fungal infections. Various strategies, including recombinant proteins in glucan particles, engineered attenuated strains and alkaline extracts have shown promise in vaccination against experimental murine Cryptococcus infections …”

Glucuronoxylomannan in theCryptococcusspecies capsule as a target for CAR+T-cell therapy

“…Recently, a research group used a vaccination strategy to control cryptococcosis using glucan particles as a delivery system to carry protective protein antigens from C. neoformans or C. gattii . This approach induced CD4 + T-cell responses in the lungs of vaccinated mice, providing partial protection after challenge with C. neoformans or C. gattii [35]. These studies demonstrated that polarization of adaptive immune cells is critical to an appropriate immune response against cryptococcosis.…”

Vaccines and Protective Immune Memory against Cryptococcosis

“…[59][60][61][62][63][64] More recently, the following strains have been constructed using the gene-targeting approach and used for immunization: C. neoformans interferon-γ (IFN-γ)expressing strain (H99γ); ZNF2 overexpression strain; ∆sgl1 strain; ∆cda1/2/3 strain; ∆cap59 strain; and C. gattii ∆cap60 strain. 14,53,[65][66][67][68] Interestingly, all groups immunized with C. neoformans recombinants had significantly improved survival rates when challenged with highly virulent C. gattii as well as with C. neoformans. Thus, it appears that these immunizations are cross-reactive to C. neoformans and C. gattii infection.…”

“…49,50) Both crude and single recombinant MPs have been used as vaccine antigens, and it was found that those vaccines significantly improved survival rates and decreased fungal burdens when challenged with C. neoformans and highly virulent C. gattii. 21,[51][52][53][54][55][56] C. neoformans culture filtrate antigen (CneF) is a crude antigen containing GXM, GalXM, and MPs, and MPs can be enriched from the culture filtrate via concanavalin A (ConA) affinity columns. 21,57) The following MPs have been identified as protective vaccine antigens: chitin deacetylase (Cda1, Cda2, also known as MP98 and Cda3); and a 25-kDa chitin deacetylase homologue (d25).…”

“…Superoxide dismutase (Sod1) was identified as the protective vaccine antigen that was the most abundant protein in the mild alkaline extract of C. neoformans acapsular mutant ∆cap59. 53,54) It was demonstrated that vaccination with the cytoplasmic proteins significantly prolonged survival times and reduced the fungal burden after the infection challenge with highly virulent C. gattii. 52,54) 3.4.…”