Gardiquimod Nanoemulsion Targets Cutaneous Leishmaniasis Lesions Reducing Systemic Toxicity and Parasite Burden

Cutaneous leishmaniasis (CL) remains difficult to treat because Leishmania parasites persist within dermal macrophages and suppress their microbicidal activity, promoting chronic infection. Toll-like receptor (TLR) agonists can restore macrophage effector functions, but their therapeutic use is limited by systemic toxicity. Here, we developed a lipid-based nanoemulsion (NE) for the systemic delivery of the TLR7 agonist gardiquimod (GDQM) to improve macrophage targeting and reduce off-target inflammatory effects. Following intravenous administration, GDQM-NEs efficiently accumulated in dermal lesions and significantly reduced systemic cytokine release compared with free GDQM, resulting in an improved safety profile. Importantly, nanoencapsulation preserved GDQM antileishmanial activity achieving an approximately 2-log reduction in parasite burden. Treatment induced both Th1-associated cytokines (IFN-γ and IL-12p70) and regulatory responses, including IL-10 production and FoxP3⁺ regulatory T-cell expansion. Despite efficient lesion accumulation, CD86 upregulation was detected in macrophages from draining lymph nodes (dLNs) but not at the lesion site, indicating limited local macrophage activation. These findings indicate that GDQM-NEs effectively overcome major delivery and safety barriers associated with systemic TLR7 agonist administration, whereas the lesion microenvironment and TLR-driven regulatory mechanisms remain key constraints on therapeutic efficacy. Combining TLR agonists with strategies that counteract these local suppressive pathways may further enhance treatment outcomes in CL.