Evaluation of Protective Immune Response Induced by a DNA Vaccine Encoding GRA8 against Acute Toxoplasmosis in a Murine Model

Co-Immunization with DNA Vaccines Expressing SABP1 and SAG1 Proteins Effectively Enhanced Mice Resistance to Toxoplasma gondii Acute Infection

Toxoplasma gondii (T. gondii) has many intermediate hosts, obligately invades nucleated cells, and seriously threatens human and animal health due to a lack of effective drugs and vaccines. Sialic acid-binding protein 1 (SABP1) is a novel invasion-related protein that, like surface antigen 1 (SAG1), is found on the plasma membrane of T. gondii. To investigate the immunogenicity and protective efficacy of DNA vaccines expressing SABP1 and SAG1 proteins against T. gondii acute infection, the recombinant plasmids pVAX1-SABP1 and pVAX1-SAG1 were produced and administered intramuscularly in Balb/c mice. Serum antibody levels and subtypes, lymphocyte proliferation, and cytokines were used to assess immunized mice's humoral and cellular immune responses. Furthermore, the ability of DNA vaccines to protect mice against T. gondii RH tachyzoites was tested. Immunized mice exhibited substantially higher IgG levels, with IgG2a titers higher than IgG1. When the immune group mice's splenocytes were stimulated with T. gondii lysate antigen, Th1-type cytokines (IL-12p70, IFN-γ, and IL-2) and Th2-type cytokine (IL-4) increased significantly. The combined DNA vaccine significantly increased the immunized mouse survival compared to the control group, with an average death time extended by 4.33 ± 0.6 days (p < 0.0001). These findings show that DNA vaccines based on the SABP1 and SAG1 genes induced robust humoral and cellular immunity in mice, effectively protecting against acute toxoplasmosis and potentially serving as a viable option for vaccination to prevent T. gondii infection.

Toxoplasma gondii vaccine candidates: a concise review

Toxoplasma gondii is an obligate intracellular parasite that causes toxoplasmosis. It has been shown that the severity of symptoms depends on the functioning of the host immune system. Although T. gondii infection typically does not lead to severe disease in healthy people and after infection, it induces a stable immunity, but it can contribute to severe and even lethal Toxoplasmosis in immunocompromised individuals (AIDS, bone marrow transplant and neoplasia). The antigens that have been proposed to be used in vaccine candidate in various studies include surface antigens and secretory excretions that have been synthesized and evaluated in different studies. In some studies, secretory antigens play an important role in stimulating the host immune response. Various antigens such as SAG, GRA, ROP, ROM, and MAG have been from different strains of T. gondii have been synthesized and their protective effects have been evaluated in animal models in different vaccine platforms including recombinant antigens, nanoparticles, and DNA vaccine. Four bibliographic databases including Science Direct, PubMed Central (PMC), Scopus, and Google Scholar were searched for articles published up to 2020.The current review article focuses on recent studies on the use and usefulness of recombinant antigens, nanoparticles, and DNA vaccines.

Insight into the current Toxoplasma gondii DNA vaccine: a review article

INTRODUCTION

Toxoplasma gondii (T.gondii) is a widespread protozoan with significant economic losses and public health importance. But so far, the protective effect of reported DNA-based vaccines fluctuates widely, and no study has demonstrated complete protection.

AREAS COVERED

This review provides an inclusive summary of T. gondii DNA vaccine antigens, adjuvants, and some other parameters. A total of 140 articles from 2000 to 2021 were collected from five databases. By contrasting the outcomes of acute and chronic challenges, we aimed to investigate and identify viable immunological strategies for optimum protection. Furthermore, we evaluated and discussed the impact of several parameters on challenge outcomes in the hopes of developing some recommendations to assist better future horizontal comparisons among research.

EXPERT OPINION

In the coming five years of research, the exploration of vaccine cocktails combining invasion antigens and metabolic antigens with genetic adjuvants or novel DNA delivery methods may offer us desirable protection against this multiple stage of life parasite. In addition to finding a better immune strategy, developing better in silico prediction methods, solving problems posed by variables in practical applications, and gaining a more profound knowledge of T.gondii-host molecular interaction is also crucial towards a successful vaccine.

Evaluation of anti-tick efficiency in rabbits induced by DNA vaccines encoding Haemaphysalis longicornis lipocalin homologue

Haemaphysalis longicornis is an obligate haematophagous ectoparasite, transmitting a variety of pathogens, which brings great damage to human health and animal husbandry development. Lipocalins (LIP) are a family of proteins that transport small hydrophobic molecules and also involve in immune regulation, such as the regulation of cell homeostasis, inhibiting the host's inflammatory response and resisting the contractile responses in host blood vessels. Therefore, it is one of the candidate antigens for vaccines. Based on previous studies, we constructed the recombinant plasmid pcDNA3.1-HlLIP of LIP homologue from H. longicornis (HlLIP). ELISA results showed that rabbits immunized with pcDNA3.1-HlLIP produced higher anti-rHlLIP antibody levels compared with the pcDNA3.1 group, indicating that pcDNA3.1-HlLIP induced the humoral immune response of host. Adult H. longicornis infestation trial in rabbits demonstrated that the engorgement weight, oviposition and hatchability of H. longicornis fed on rabbits immunized with pcDNA3.1-HlLIP decreased by 7.07%, 14.30% and 11.70% respectively, compared with that of the pcDNA3.1 group. In brief, DNA vaccine of pcDNA3.1-HlLIP provided immune protection efficiency of 30% in rabbits. This study demonstrated that pcDNA3.1-HlLIP can partially protect rabbits against H. longicornis, and it is possible to develop a new candidate antigen against ticks.

REVIEW OF DNA VACCINE APPROACHES AGAINST THE PARASITE TOXOPLASMA GONDII

Toxoplasma gondii is an apicomplexan parasite that affects both humans and livestock. Transmitted to humans through ingestion, it is the second-leading cause of foodborne illness-related death. Currently, there exists no approved vaccine for humans or most livestock against the parasite. DNA vaccines, a type of subunit vaccine which uses segments of the pathogen's DNA to generate immunity, have shown varying degrees of experimental efficacy against infection caused by the parasite. This review compiles DNA vaccine efforts against Toxoplasma gondii, segmenting the analysis by parasite antigen, as well as a review of concomitant adjuvant usage. No single antigenic group was consistently more effective within in vivo trials relative to others.

A systematic review on the role of GRA proteins of Toxoplasma gondii in host immunization

Toxoplasma gondii is a widespread obligatory intracellular parasite infecting humans and most of all other warm-blooded animals. Currently there is no any accepted vaccine for prevention of T. gondii infection. Many studies are focused on using of various excretory secretory antigens (ESA); and among them dense granule antigens (GRAs) being involved in parasite survival, virulence and replication processes, are considered as one of the predominant vaccine candidates. The aim of this systematic review is to prepare more comprehensive understanding of these antigens to reduce T. gondii infection in humans and animals. English databases, including PubMed, Science Direct, Google Scholar, Scopus, ISI Web of Science were systematically searched and papers evaluating GRA antigens published until June 2019 were selected. Evaluation of selected publications revealed that GRA4 and GRA7 substantially increased survival time of the experimental animals. It is noticeable that the maximum reduction in cyst burden was observed in BALB/c mice vaccinated with combination of GRA3, GRA7 and M2AP antigens (93.5%). GRA6 and GRA10 have shown high immunogenicity and GRA1 and 2 are important for virulence and induction of immune responses. This review will be helpful for researchers to conduct more effective studies in the field of immunization against T. gondii infection.