DNA vaccination with genes encoding Toxoplasma gondii antigens ROP5 and GRA15 induces protective immunity against toxoplasmosis in Kunming mice

Abstract

Objectives: To evaluate the protective efficacy of a DNA vaccine encoding Toxoplasma gondii rhoptry protein 5 (ROP5) and GRA15 antigens. Methods: We constructed eukaryotic plasmids expressing pVAX-ROP5 and pVAX-GRA15, and measured the immune responses to these DNA vaccines. Results: Kunming mice immunized with pVAX-ROP5 or pVAX-GRA15 showed significantly increased serum IgG2a titers; Th1 responses association with the production of IFN-γ, IL-2, IL12 p40 and IL-12 p70; cell-mediated cytotoxic activity with increased frequencies of IFN-γ secreting CD8⁺ T cells (CD8⁺ IFN-γ+ T cells), as well as prolonged survival time (19.4 ± 4.9 days for ROP5; 17.8 ± 3.8 days for GRA15) and brain cyst reduction (57.4% for ROP5; 65.9% for GRA15) compared to control mice. Co-administration with pVAX-ROP5 and pVAX-GRA15 boosted the cellular and humoral immune responses, and significantly increased cyst reduction (79%) and prolonged the survival of immunized mice (22.7 ± 7.2 days). Conclusion: Co-immunization of pVAX-ROP5 and pVAX-GRA15 increase the protective efficacy.

Keywords:

• DNA vaccine
• GRA15
• Kunming mice
• protective immunity
• ROP5
• Toxoplasma gondii
• toxoplasmosis

Financial & competing interests disclosure

The study was approved by the animal ethics committee of the Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences (Approval No, LVRIAEC2012-009). Project support was provided by the National Natural Science Foundation of China (Grant Nos. 31230073 and 31172316), the international science and technology cooperation project of Gansu province (Gran No. 1204WCGA023), and the Science Fund for Creative Research Groups of Gansu Province (Grant No. 1210RJIA006) The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Key issues

• Vaccination with Toxoplasma gondii rhoptry protein 5 (ROP5) and or GRA15 DNA vaccine induced specific humoral and cellular responses associated with increased frequencies of IFN-γ parameters analyzed in CD8⁺ T-cell compartments (CD8⁺ IFN-γ+ T cells).

• Significant production of IFN-γ, IL-2, IL12 p40 and IL-12 p70 associated with a Th1 type response was observed after DNA vaccination.

• DNA vaccination resulted in a significantly prolonged survival time of immunized mice.

• Significant reduction in brain cyst number was observed after vaccination.

• Co-administration with pVAX-ROP5 and pVAX-GRA15 boosted the cellular and humoral immune responses and thus the protective efficacy.

• Both T. gondii ROP5 and pVAX-GRA15 are potential vaccine candidates against both acute and chronic T. gondii infection and co-injection of pVAX-ROP5 and pVAX-GRA15 could increase the protective efficacy.

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