CTLA-4 Antisense Oligonucleotide Contributes to Enhanced Immunogenicity of an Adjuvanted Recombinant Sporothrix spp. Enolase Antigen

Background/Objectives: Sporotrichosis is an emerging zoonotic subcutaneous fungal infection with limited therapeutic options, highlighting the need for improved immunomodulatory strategies. CTLA-4 is an inhibitory immune checkpoint that negatively regulates T-cell activation. In this study, we evaluated whether a CTLA-4 antisense oligonucleotide (CTLA-4 ASO) is associated with enhanced immune responses to an adjuvanted recombinant Sporothrix sp. enolase antigen (rSsEno) formulation. Methods: CTLA-4 ASO uptake, cytotoxicity, and gene-silencing activity were assessed in murine splenocytes in vitro. BALB/c mice were immunized with rSsEno formulated with Montanide Gel 01, either alone or in combination with 5 µg CTLA-4 ASO. Antigen-specific serum antibody responses were quantified by ELISA. Splenocytes from immunized mice were restimulated with enolase, and cytokine production (IFN-γ, IL-2, IL-17, and TNF-α) was measured using Cytometric Bead Array (CBA). Results: CTLA-4 ASO was efficiently internalized by splenocytes and was associated with reduced expression of CTLA-4 without detectable cytotoxicity in vitro. Mice receiving the ASO-supplemented formulation developed significantly higher anti-enolase antibody titers compared to those immunized with adjuvant alone. Upon antigen restimulation, splenocytes from ASO-treated mice produced higher levels of IFN-γ, IL-2, TNF-α, and IL-17, consistent with an enhanced recall response characterized by a mixed Th1/Th17 cytokine profile. Conclusions: CTLA-4 ASO was associated with an enhanced recall response characterized by a mixed Th1/Th17 cytokine profile. These findings suggest a potential immunomodulatory effect of CTLA-4 targeting. Further studies incorporating dose optimization, infection challenge models, and appropriate sequence controls are required to determine the specificity and relevance of these effects for protective immunity against sporotrichosis.