Recombinant vaccines of a CD4+ T-cell epitope promote efficient control of Paracoccidioides brasiliensis burden by restraining primary organ infection

Paracoccidioidomycosis (PCM) is an infectious disease endemic to South America, caused by the thermally dimorphic fungi Paracoccidioides. Currently, there is no effective human vaccine that can be used in prophylactic or therapeutic regimes. We tested the hypothesis that the immunogenicity of the immunodominant CD4+ T-cell epitope (P10) of Paracoccidioides brasiliensis gp43 antigen might be significantly enhanced by using a hepatitis B virus-derived particle (VLP) as an antigen carrier. This chimera was administered to mice as a (His)6-purified protein (rPbT) or a replication-deficient human type 5 adenoviral vector (rAdPbT) in an immunoprophylaxis assay. The highly virulent Pb18 yeast strain was used to challenge our vaccine candidates. Fungal challenge evoked robust P10-specific memory CD4+ T cells secreting protective Th-1 cytokines in most groups of immunized mice. Furthermore, the highest level of fungal burden control was achieved when rAdPbT was inoculated in a homologous prime-boost regimen, with 10-fold less CFU recovering than in non-vaccinated mice. Systemic Pb18 spreading was only prevented when rAdPbT was previously inoculated. In summary, we present here VLP/P10 formulations as vaccine candidates against PCM, some of which have demonstrated for the first time their ability to prevent progression of this pernicious fungal disease, which represents a significant social burden in developing countries.
Author summary Human paracoccidioidomycosis (PCM) represents a serious public health issue due to its disabling sequelae in working-age people and mortality rates (8th among chronic infectious parasitic diseases in endemic countries and first among mycoses in Brazil). Although antifungal drugs have been widely used and provide clinical improvement for patients, the long duration of treatments (commonly from 6 to 12 months) has contributed to non-compliance and worsening of the disease in many cases. Induction of protective immune responses (either prophylactic or immune-therapeutic) remains the most cost-effective approach against most infectious agents. Members of our group have previously reported the protective properties of P10, a peptide contained in Paracoccidioides brasiliensis gp43 antigen, against PCM. However, the magnitude of the CD4+ T-cell responses elicited lacked the capacity of completely protecting experimental animals. We demonstrate here that immunogenic virus-like particles (VLP) carrying multiple copies of P10 peptide substantially improve P10-related cellular immunity in mice. This was particularly true when an adenoviral immunization vector expressed the chimeric VLP. Moreover, VLP/P10 formulations were capable of controlling the host fungal burden and prevented fungal systemic dissemination. The efficacy of diverse VLP/P10 formulations in murine PCM showed at least one promising candidate vaccine against human PCM.