Development of a protective vaccine against Leishmania depends on antigen formulation and adjuvants that induce specific immunity and long-lasting immune responses. We previously demonstrated that BALB/c mice intranasally vaccinated with a plasmid DNA encoding the p36/LACK leishmanial antigen (LACK-DNA) develop a protective immunity for up to 3 months after vaccination, which was linked with the systemic expression of vaccine mRNA in peripheral organs. In this study, LACK-DNA vaccine was associated with biocompatible chitosan microparticles cross-linked with glyceraldehyde (CMC) to boost the long-lasting immunity against the late Leishmania infantum challenge. Infection at 7 days, 3 or 6 months after vaccination resulted in significantly lower parasite loads when compared with non-vaccinated controls. Besides, LACK-DNA-chitosan vaccinated mice showed long-time protection observed after the late time point challenge. The achieved protection was correlated with an enhanced spleen cell responsiveness to parasite antigens, marked by increased proliferation and IFN-γ as well as decreased IL-10 production. Moreover, we found diminished systemic levels of TNF-α that was compatible with the better health condition observed in LACK-DNA/CMC vaccinated-infected mice. Together, our data indicate the feasibility of chitosan microparticles as a delivery system tool to extend the protective immunity conferred by LACK-DNA vaccine, which may be explored in vaccine formulations against Leishmania parasite infections.

针对利什曼原虫的保护性疫苗的开发取决于抗原制剂和诱导特异性免疫和持久免疫反应的佐剂。我们之前证明，用编码 p36/LACK 利什曼原虫抗原 (LACK-DNA) 的质粒 DNA 鼻内接种的 BALB/c 小鼠在接种疫苗后长达 3 个月内产生保护性免疫，这与外周疫苗 mRNA 的全身表达有关器官。在这项研究中，LACK-DNA 疫苗与生物相容性壳聚糖微粒与甘油醛 (CMC) 交联，以增强对晚期婴儿利什曼原虫的持久免疫力挑战。与未接种疫苗的对照组相比，接种疫苗后 7 天、3 或 6 个月的感染导致寄生虫载量显着降低。此外，LACK-DNA-壳聚糖疫苗接种的小鼠在晚期时间点攻击后表现出长期保护作用。获得的保护与增强的脾细胞对寄生虫抗原的反应相关，其标志是增殖和 IFN-γ 增加以及 IL-10 产生减少。此外，我们发现 TNF-α 的全身水平降低，这与在 LACK-DNA/CMC 接种疫苗感染的小鼠中观察到的更好的健康状况相一致。总之，我们的数据表明壳聚糖微粒作为一种传递系统工具来扩展 LACK-DNA 疫苗所赋予的保护性免疫的可行性，这可以在疫苗制剂中进行探索利什曼原虫感染。