Vaccination with Replication-Deficient Recombinant Adenoviruses Encoding the Main Surface Antigens ofToxoplasma gondiiInduces Immune Response and Protection Against Infection in Mice

Abstract

We have generated recombinant adenoviruses encoding three genetically modified surface antigens (SAGs) of the parasite Toxoplasma gondii, that is, AdSAG1, AdSAG2, and AdSAG3. Modifications included the removal of their glycosylphosphatidylinositol (GPI) anchoring motifs and, in some cases, the exchange of the native signal peptide for influenza virus hemagglutinin signal sequence. Adenovirus immunization of BALB/c mice elicited potent antibody responses against each protein, displaying a significant bias toward a helper T cell type 1 (Th1) profile in animals vaccinated with AdSAG1. Furthermore, the presence of parasite-specific IFN-gamma-producing T cells was analyzed by proliferation assays and enzyme-linked immunospot assays in the same animals. Splenocytes from immunized mice secreted IFN-gamma after in vitro stimulation with tachyzoite lysate antigen or with a fraction enriched for membrane-purified GPI-anchored proteins (F3) from the T. gondii tachyzoite surface. Epitopes recognized by CD8+ T cells were identified in SAG1 and SAG3, but not SAG2, sequences, although this protein also induced a specific response. We also tested the capacity of the immune responses detected to protect mice against a challenge with live T. gondii parasites. Although no protection was observed against tachyzoites of the highly virulent RH strain, a significant reduction in cyst loads in the brain was observed in animals challenged with the P-Br strain. Thus, up to 80% of the cysts were eliminated from animals vaccinated with a mixture of the three recombinant viruses. Because adenoviruses seemed capable of inducing Th1-biased protective immune responses against T. gondii antigens, other parasite antigens should be tested alone or in combination with those described here to further develop a protective vaccine against toxoplasmosis.

Complex interactions with several arms of the complement system dictate innate and humoral immunity to adenoviral vectors

“…Relative to their use in vaccine development, Ad-based vaccines have recently shown great promise in a number of applications that require elicitation of robust immune responses, such as combined humoral and cellular immune responses. [1][2][3][4][5][6] We have recently focused on Ad interactions with the complement system, and how these interactions may shape these important Ad-induced immune responses. Bars represent mean ± s.d.…”

“…More dramatically, recent demonstrations confirm the high efficacy and safe use of recombinant Ad (rAd)-based vaccines in infectious and acquired disease applications, including human immunodeficiency virus (HIV)-AIDS, Ebola, toxoplasmosis, H5N1 influenza and cancer. [1][2][3][4][5][6] Despite this widespread utility, little information is available regarding the mechanisms as to why rAds can elicit robust adaptive immune responses (both humoral and cellular). Although we, and others, have recently implicated intracellular signaling systems as mediating several important aspects of this response (that is, Ad interactions with the Toll-like receptor (TLR) system), it is also clear that instantaneous interactions of rAds with the extracellular pathogensensing complement system may also be significantly modulating these intracellular responses.…”

Parasite Stage–Specific Recognition of EndogenousToxoplasma gondii–Derived CD8+T Cell Epitopes

“…Published reports of T. gondii specific CD8 + T cell responses are based on studies where animals were vaccinated mostly with major parasite protein, the surface antigens (SAG1-3). The resulting CD8 + T cells responded to either parasite lysate or to peptide restimulation in vitro ([11, 12, 13, 14] and references therein). Whether these potential SAG epitopes are generated in the course of a natural infection is not known.…”

Long-Term Humoral and Cellular Immune Responses Elicited by a Heterologous Plasmodium vivax Apical Membrane Antigen 1 Protein Prime/Adenovirus Boost Immunization Protocol

“…Our previous work has shown that homologous prime/boost protocols that use this vector to immunize mice are effective against Leishmania spp. (43), Toxoplasma gondii (10), or Trypanosoma cruzi (31) infections; they are all highly dependent on the induction of T-cell immunity for protection. Parasite-specific antibodies were also induced in all those animals.…”