SgtrCypB Formulated with Freund's Adjuvant Confers Protective Immunity Against S. globosa and Partial Cross-Protection Against S. schenckii Infections in Mice.

Sporothrix globosa is the predominant cause of sporotrichosis in China, highlighting the need for effective vaccine strategies. Cyclophilins from pathogenic microorganisms have emerged as potential vaccine antigens. We previously generated a high-yield, high-purity recombinant truncated S. globosa cyclophilin B protein (SgtrCypB) retaining its functional domain. Here, BALB/c mice were immunized subcutaneously with SgtrCypB alone or formulated with Freund's adjuvant to evaluate immunogenicity. Only the adjuvant-formulated vaccine induced a high antibody titer (1:51,200). Then, the infection-challenge experiments compared the SgtrCypB formulated with Freund's adjuvant and PBS formulated with Freund's adjuvant groups. Following challenge, SgtrCypB plus adjuvant reduced cutaneous lesion size (0.6 vs. 1.0 cm at week 1) without significantly affecting ulcer incidence. In systemic S. globosa infection, vaccination increased survival to 90% versus 40% in controls and reduced organ fungal burdens. Partial cross-protection was observed against S. schenckii, with 60% versus 20% survival and lower fungal burdens in the kidneys and lungs. Protection against C. albicans was minimal. These findings identify SgtrCypB as a promising protective antigen against S. globosa and S. schenckii and support further evaluation with clinically applicable adjuvants.