CpG oligodeoxynucleotide ligand potentiates the activity of the pVAX1-Sj26GST

Abstract

Schistosomiasis is considered one of the most important neglected tropical diseases and remains a major public health problem in endemic countries. Toll-like receptor (TLR) ligands have been investigated as potential vaccine adjuvants for tumor and virus immunotherapy. However, few TLR ligands affecting schistosoma vaccines have been characterized. In this study, we evaluated a TLR9 ligand (CpG oligodeoxynucleotide 1826, CpG) as an adjuvant for a partially protective DNA vaccine encoding a 26-kDa glutathione S-transferase of Schistosoma japonicum (pVAX1-Sj26GST). Vaccination with pVAX1-Sj26GST in combination with CpG inhibited Treg immunosuppressive function, upregulated the production of interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-4, IL-10, IL-2 and IL-6, and decreased CD4⁺CD8⁺Foxp3⁺ expression in vitro, which may contribute to the escape from Treg-mediated suppression during vaccination, allowing expansion of antigen-specific T cells against pathogens. In conclusion, our data demonstrated that selective TLR ligand combination may increase protective efficacy against schistosomiasis, which may synergistically antagonize Treg-mediated suppression.

Keywords: CpG oligodeoxynucleotide ligand; pVAX1-Sj26GST; vaccine.

Figure 1.

Combination with CpG inhibited the CD4⁺CD25⁺ Treg function in vitro. Isolated CD4⁺CD25⁻ T cells (1×10⁵/well) from naïve rats were cultured with or without CD4⁺CD25⁺ Tregs (5×10⁴/well), irradiated antigen-presenting cells (APCs) (1×10⁵/well) and 1 μg/ml anti-CD3 in 96-well plates in the presence or absence of 3 μg/ml CpG for 72 h. Proliferation was determined by measuring ³H-thymidine incorporation during the last 16 h of the experiment. Data are expressed as means ± standard deviation of three independent experiments performed in triplicate. ^*P<0.05; ^**P<0.01.

Figure 2.

Combination with CpG induced a panel of proinflammatory cytokines in a conventional in vitro suppression assay. Isolated CD4⁺CD25⁻ T cells (1×10⁵/well) from naïve rats were cultured with or without CD4⁺CD25⁺ Tregs (5×10⁴/well), irradiated APCs (1×10⁵/well) and 1 μg/ml anti-CD3 in 96-well plates in the presence or absence of 3 μg/ml CpG. Supernatants were collected after 72 h of culture and tested for (A) IFN-γ, (B) TNF-α, (C) IL-4, (D) IL-10, (E) IL-2 or (F) IL-6. Data are expressed as the means ± standard deviation from two experiments performed in triplicate wells. ^*P<0.05; ^**P<0.01; ^***P<0.001.

Figure 3.

CpG reduced the induction of Foxp3-expressing T cells in vitro. Splenocytes from naïve rats were stimulated in vitro with 3 μg/ml CpG for 48 h and were then subjected to flow cytometry analysis for Foxp3 expression in CD4⁺ T cells. P<0.05.