Effects of novel vaccine/adjuvant complexes on the protective immunity against Eimeria acervulina and transcriptome profiles

Vaccines against chicken coccidiosis with particular reference to previous decade: progress, challenges, and opportunities

Chicken coccidiosis is an economically significant disease of commercial chicken industry accounting for losses of more than £10.4 billion (according to 2016 prices). Additionally, the costs incurred in prophylaxis and therapeutics against chicken coccidiosis in developing countries (for instance Pakistan according to 2018 prices) reached US $45,000.00 while production losses for various categories of chicken ranges 104.74 to US $2,750,779.00. The infection has been reported from all types of commercial chickens (broiler, layer, breeder) having a range of reported prevalence of 7-90%. The concern of resistance towards major anticoccidials has provided a way forward to vaccine research and development. For prophylaxis of chicken coccidiosis, live virulent, attenuated, ionophore tolerant strains and recombinant vaccines have been extensively trialed and commercialized. Eimeria antigens and novel vaccine adjuvants have elicited the protective efficacy against coccidial challenge. The cost of production and achieving robust immune responses in birds are major challenges for commercial vaccine production. In the future, research should be focused on the development of multivalent anticoccidial vaccines for commercial poultry. Efforts should also be made on the discovery of novel antigens for incorporation into vaccine designs which might be more effective against multiple Eimeria species. This review presents a recap to the overall progress against chicken Eimeria with particular reference to previous decade. The article presents critical analysis of potential areas for future research in chicken Eimeria vaccine development.

A potent novel vaccine adjuvant based on straight polyacrylate

A structure-activity study was conducted to identify the structural characteristics underlying the adjuvant activity of straight (i.e. non-crosslinked) polyacrylate polymers (PAAs) in order to select a new PAA adjuvant candidate for future clinical development. The study revealed that the adjuvant effect of PAA was mainly influenced by polymer size (Mw) and dose. Maximal effects were obtained with large PAAs above 350 kDa and doses above 100 μg in mice. Small PAAs below 10 kDa had virtually no adjuvant effect. HPSEC analysis revealed that PAA polydispersity index and ramification had less impact on adjuvanticity. Heat stability studies indicated that residual persulfate could be detrimental to PAA stability. Hence, this impurity was systematically eliminated by diafiltration along with small Mw PAAs and residual acrylic acid that could potentially affect product safety, potency and stability. The selected PAA, termed SPA09, displayed an adjuvant effect that was superior to that of a standard emulsion adjuvant when tested with CMV-gB in mice, even in the absence of binding to the antigen. The induced immune response was dominated by strong IFNγ, IgG2c and virus neutralizing titers. The activity of SPA09 was then confirmed on human cells via the innate immune module of the human MIMIC® system.

•

Straight polyacrylate (350 kDa < Mw < 650 kDa; termed SPA09) is a strong adjuvant easy to formulate with vaccine antigens

•

SPA09 induces Th-1 type immune responses in mice, dominated by strong IFN-γ, IgG2c and virus neutralizing titers

•

SPA09 can activate human antigen presenting cells when tested via the innate immune module (PTE) of the human MIMIC® system

•

SPA09 constitutes a straightforward new adjuvant candidate for future clinical development

Promising Plant-Derived Adjuvants in the Development of Coccidial Vaccines

Coccidial parasites cause medical and veterinary diseases worldwide, frequently leading to severe illness and important economic losses. At present, drugs, chemotherapeutics and prophylactic vaccines are still missing for most of the coccidial infections. Moreover, the development and administration of drugs and chemotherapeutics against these diseases would not be adequate in livestock, since they may generate unacceptable residues in milk and meat that would avoid their commercialization. In this scenario, prophylactic vaccines emerge as the most suitable approach. Subunit vaccines have proven to be biologically safe and economically viable, allowing researchers to choose among the best antigens against each pathogen. However, they are generally poorly immunogenic and require the addition of adjuvant compounds to the vaccine formulation. During the last decades, research involving plant immunomodulatory compounds has become an important field of study based on their potential pharmaceutical applications. Some plant molecules such as saponins, polysaccharides, lectins and heat shock proteins are being explored as candidates for adjuvant/carriers formulations. Moreover, plant-derived immune stimulatory compounds open the possibility to attain the main goal in adjuvant research: a safe and non-toxic adjuvant capable of strongly boosting and directing immune responses that could be incorporated into different vaccine formulations, including mucosal vaccines. Here, we review the immunomodulatory properties of several plant molecules and discuss their application and future perspective as adjuvants in the development of vaccines against coccidial infections.

Identification of Molecular Signatures from Different Vaccine Adjuvants in Chicken by Integrative Analysis of Microarray Data

The present study compared the differential functions of two groups of adjuvants, Montanide incomplete Seppic adjuvant (ISA) series and Quil A, cholesterol, dimethyl dioctadecyl ammonium bromide, and Carbopol (QCDC) formulations, in chicken by analyzing published microarray data associated with each type of vaccine adjuvants. In the biological function analysis for differentially expressed genes altered by two different adjuvant groups, ISA series and QCDC formulations showed differential effects when chickens were immunized with a recombinant immunogenic protein of Eimeria. Among the biological functions, six categories were modified in both adjuvant types. However, with respect to “Response to stimulus”, no biological process was modified by the two adjuvant groups at the same time. The QCDC adjuvants showed effects on the biological processes (BPs) including the innate immune response and the immune response to the external stimulus such as toxin and bacterium, while the ISA adjuvants modified the BPs to regulate cell movement and the response to stress. In pathway analysis, ISA adjuvants altered the genes involved in the functions related with cell junctions and the elimination of exogenous and endogenous macromolecules. The analysis in the present study could contribute to the development of precise adjuvants based on molecular signatures related with their immunological functions.

Biological characteristics of Chinese precocious strain of eimeria acervulina and its immune efficacy against different field strains

In this study, the biologic characteristics of one experimental precocious strain of Eimeria acervulina and seven field isolates from different geographic locations in China were compared, and the immune efficacy of two precocious strains against coccidiosis in chickens was assessed to explore their potential use as coccidiosis vaccines. All the different strains were purified by single oocyst separation and their monospecificity was confirmed using E acervulina-specific PCR assays. The average sizes of E. acervulina oocysts were 18.28-20.19 X 14.09-14.79 microm and the shape indexes were from 1.28 to 1.40. The prepatent periods ranged from 93 to 115 hr, except for the Heyuan precocious strain (HYP; 75 hr). Chickens infected with Huadu field strain (GHD) produced the highest oocyst output whereas HYP induced the lowest level. When inoculated with 50,000 sporulated oocysts or more, the average weight gains of infected chickens were reduced, with apparent clinical symptoms. To assess the immunogenicity of precocious strains HYP and Baoding (BDP), birds were orally immunized and challenged with seven different field strains of E. acervulina. Body weight gain, fecal oocyst output, and gut lesion scores were compared to evaluate their vaccine potential. The results showed that the average body weight gains of chickens in all the vaccinated and challenged groups were higher than those of nonvaccinated and challenged groups. In general, oocyst shedding was reduced 34.39%-95.31% and gut lesion scores decreased 31.03%-86.21% compared with unvaccinated and challenged control chickens. In summary, this study indicated that the precocious strains of E. acervulina could induce a protective immune effect with various responses against coccidiosis caused by different field strains.

Identification and molecular characterization of microneme 5 of Eimeria acervulina

In the present study, the microneme 5 gene of Eimeria acervulina (E. acervulina) (EaMIC5) was cloned and characterized. Specific primers for the rapid amplification of cDNA ends (RACE) were designed based on the expressed sequence tag (EST, GenBank Accession No. EH386430.1) to amplify the 3'- and 5'-ends of EaMIC5. The full length cDNA of this gene was obtained by overlapping the sequences of 3'- and 5'-extremities and amplification by reverse transcription PCR. Sequence analysis revealed that the open reading frame (ORF) of EaMIC5 was 336 bp and encoded a protein of 111 amino acids with 12.18 kDa. The ORF was inserted into pET-32a (+) to produce recombinant EaMIC5. Using western blotting assay, the recombinant protein was successfully recognized by the sera of chicks experimentally infected with E. acervulina, while the native protein in the somatic extract of sporozoites was as well detected by sera from rats immunized with the recombinant protein of EaMIC5. Immunofluorescence analysis using antibody against recombinant protein EaMIC5 indicated that this protein was expressed in the sporozoites and merozoites stages of E. acervulina. Animal challenge experiments demonstrated that the recombinant protein of EaMIC5 could significantly increase the average body weight gains, decrease the mean lesion scores and the oocyst outputs of the immunized chickens, and presented anti-coccidial index (ACI) more than 160. All the above results suggested that the EaMIC5 was a novel E. acervulina antigen and could be an effective candidate for the development of a new vaccine against this parasite.

Evaluation of Montanide™ ISA 71 VG adjuvant during profilin vaccination against experimental coccidiosis

Chickens were immunized subcutaneously with an Eimeria recombinant profilin protein plus Montanide™ ISA 70 VG (ISA 70) or Montanide™ ISA 71 VG (ISA 71) water-in-oil adjuvants, or with profilin alone, and comparative RNA microarray hybridizations were performed to ascertain global transcriptome changes induced by profilin/ISA 70 vs. profilin alone and by profilin/ISA 71 vs. profilin alone. While immunization with profilin/ISA 70 vs. profilin alone altered the levels of more total transcripts compared with profilin/ISA 71 vs. profilin alone (509 vs. 296), the latter was associated with a greater number of unique biological functions, and a larger number of genes within these functions, compared with the former. Further, canonical pathway analysis identified 10 pathways that were associated with genes encoding the altered transcripts in animals immunized with profilin/ISA 71 vs. profilin alone, compared with only 2 pathways in profilin/ISA 70 vs. profilin alone. Therefore, ISA 71 was selected as a candidate adjuvant in conjunction with profilin vaccination for in vivo disease protection studies. Vaccination with profilin/ISA 71 was associated with greater body weight gain following E. acervulina infection, and decreased parasite fecal shedding after E. maxima infection, compared with profilin alone. Anti-profilin antibody levels were higher in sera of E. maxima- and E. tenella-infected chickens vaccinated with profilin/ISA 71 compared with profilin alone. Finally, the levels of transcripts encoding interferon-γ, interleukin (IL)-2, IL-10, and IL-17A were increased in intestinal lymphocytes from E. acervulina-, E. maxima-, and/or E. tenella-infected chickens vaccinated with profilin/ISA 71 compared with profilin alone. None of these effects were seen in chickens injected with ISA 71 alone indicating that the adjuvant was not conferring non-specific immune stimulation. These results suggest that profilin plus ISA 71 augments protective immunity against selective Eimeria species in chickens.