Optimization of DNA vaccination immune responses in dairy cows: effect of injection site and the targeting efficacy of antigen-bCTLA-4 complex

Recent advances in antigen targeting to antigen-presenting cells in veterinary medicine

Advances in antigen targeting in veterinary medicine have gained traction over the years as an alternative approach for diseases that remain a challenge for traditional vaccines. In addition to the nature of the immunogen, antigen-targeting success relies heavily on the chosen receptor for its direct influence on the elicited response that will ensue after antigen uptake. Different approaches using antibodies, natural or synthetic ligands, fused proteins, and DNA vaccines have been explored in various veterinary species, with pigs, cattle, sheep, and poultry as the most frequent models. Antigen-presenting cells can be targeted using a generic approach, such as broadly expressed receptors such as MHC-II, CD80/86, CD40, CD83, etc., or focused on specific cell populations such as dendritic cells or macrophages (Langerin, DC-SIGN, XCR1, DC peptides, sialoadhesin, mannose receptors, etc.) with contrasting results. Interestingly, DC peptides show high specificity to DCs, boosting activation, stimulating cellular and humoral responses, and a higher rate of clinical protection. Likewise, MHC-II targeting shows consistent results in enhancing both immune responses; an example of this strategy of targeting is the approved vaccine against the bovine viral diarrhea virus in South America. This significant milestone opens the door to continuing efforts toward antigen-targeting vaccines to benefit animal health. This review discusses the recent advances in antigen targeting to antigen-presenting cells in veterinary medicine, with a special interest in pigs, sheep, cattle, poultry, and dogs.

Antigen targeting to APC: from mice to veterinary species

Antigen delivery to receptors expressed on antigen presenting cells (APC) has shown to improve immunogenicity of vaccines in mice. An enhancement of cytotoxic T lymphocyte (CTL), helper T cell or humoral responses was obtained depending on the type of APC and the surface molecule targeted. Although this strategy is being also evaluated in livestock animals with promising results, some discrepancies have been found between species and pathogens. The genetic diversity of livestock animals, the different pattern of expression of some receptors among species, the use of different markers to characterize APC in large animals and sometimes the lack of reagents make difficult to compare results obtained in different species. In this review, we summarize the data available regarding antigen targeting to APC receptors in cattle, sheep and pig and discuss the results found in these animals in the context of what has been obtained in mice.

Protective immune response against Toxoplasma gondii elicited by a recombinant DNA vaccine with a novel genetic adjuvant

Previous immunological studies from our laboratory have demonstrated the potential role of Toxoplasma gondii antigens SAG1 and GRA2 as vaccine candidates. To further evaluate the vaccine's effects, a series of recombinant DNA vaccines pVAX1-SAG1, pVAX1-GRA2 and pVAX1-SAG1-GRA2, termed pSAG1, pGRA2 and pSAG1-GRA2, respectively, were constructed. A plasmid pVAX1-S/PreS2, termed pSPreS2 encoding hepatitis B virus (HBV) surface antigen (HBsAg) S and PreS2 as a novel genetic adjuvant, was also constructed. The expression abilities of those DNA plasmids were examined in HFF cells by Western blotting. Then BALB/c mice were intramuscularly immunized with DNA plasmids and followed by challenging with the highly virulent T. gondii RH strain. The results demonstrated that the recombinant DNA vaccine pSAG1-GRA2 was capable of eliciting high levels of antibodies, a Th1 type of immune response with significant production of IFN-γ and low levels of IL-4 or IL-10 in BALB/c mice, and partial protection against the acute phase of toxoplasmosis as compared to pSAG1, pGRA2 and controls. In addition, the adjuvant pSPreS2 formulated with DNA vaccine induced a Th1 type of immune response and therefore might be a novel genetic adjuvant to DNA vaccine for further investigation.

Insulin antibodies with pulmonary delivery of insulin

BACKGROUND AND METHODS

Delivery of insulin to the deep lung presents unique challenges to the body's mucosal defense system. Pulmonary mucosal defense has the ability to discriminate between self and non-self antigens and has the potential for induction of immunologic tolerance. Published data concerning the immunogenicity of inhaled human insulin in drug trials will be reviewed, and data regarding the possible adverse effects of anti-insulin antibody development will be presented. Examination of the immunologic safety of inhaled human insulin will include discussion of comparator studies, factors affecting immunogenicity, the effects of insulin immunity on glycemic control and pulmonary function, and the relationship of insulin antibodies to dose requirements, pharmacodynamics, and hypoglycemia.

CONCLUSIONS

Inhaled human insulin, whether formulated as a powder or liquid, has been shown to be more immunogenic than comparator insulins given by subcutaneous routes; however, adverse effects of antibody formation have not been demonstrated.

Protective immune responses to a multi-gene DNA vaccine against Staphylococcus aureus

To investigate the strategy of using a multivalent polyprotein DNA vaccine against Staphylococcus aureus, a series of plasmids was used to immunize mice followed by infectious challenge. The plasmid vaccines expressed Clumping factor A (Clfa), fibronectin binding protein A (FnBPA) and the enzyme Sortase (Srt) as single proteins or combined as a polyprotein. All animals produced a mixed Th1 and Th2 response including functional antigen-specific, mostly IgG2a antibodies, sustained production of IFN-gamma and a predominantly CD8+ T-cell response. Upon challenge with a virulent S. aureus isolate (Sa042), after 21 days, 55% of the multi-gene vaccinated mice survived infection compared to only 15% of the control groups. Vaccinated mice showed no signs of arthritis when challenged with the less virulent "Newman" strain that caused reactive arthritis in the controls. The results suggest that a multi-gene polyprotein-expressing nucleic acid vaccine alone produces a combined Th1 and Th2 response that can contribute to protection against the complex pathogenesis of S. aureus.

DNA immunization of dairy cows with the clumping factor A of Staphylococcus aureus

Blocking the primary stages of Staphylococcus aureus infection, specifically the bacterial adhesion to cell and the colonization of the mucosal surface, may be the most effective strategy for preventing infections. Clumping factor A (ClfA) is considered to be one of the most important adhesions factors of S. aureus to host cells. The present study describes the immune response of dairy cattle to a DNA vaccine against ClfA and evaluates the ability of specific genetic adjuvants, targeting sequences (granulocyte macrophage colony-stimulating factor and cytotoxic T lymphocyte antigen-4) and transporter molecules (chitosan and copolymer) to modify the immune response of cows. The results show that vaccination of cows with fibrinogen-binding region A induced a strong and specific antibody response to ClfA in comparison with a control group injected with the pCI vector alone. Although the co-expression of both genetic adjuvants and the addition copolymer transporter did not augment the overall antibody response, these approaches decreased the number of non-responsive cows. Chitosan was the only factor that did not enhance the immune response. Three months after the last DNA immunization, three cows from each of the pGM-CSF, internal ribosomal entry site (IRES), pCTLA and pCI groups were injected with 200 microg of recombinant ClfA protein in incomplete Freund's adjuvant. A strong humoral response was observed in all groups following this protein boost, with the response occurring slightly earlier in DNA-primed protein boost cows. Sera and milk samples taken from cows after the second DNA injection or after the protein boost (sera only) were analyzed for their ability to block adherence and increase phagocytosis. Pre-incubation of S. aureus with sera or milk from vaccinated cows significantly reduced the pathogen's ability to adhere to MAC-T cells relative to the sera and milk samples from the pCI-injected control cows. Similarly, pools of sera and milk from vaccinated cows increased phagocytosis of S. aureus by neutrophils. After the protein boost, sera were more efficient promoters of phagocytosis, reflecting the higher anti-ClfA antibody level of these sera. DNA-prime/protein boost regimes combined with molecular adjuvants appeared to be effective in generating a strong immune response to S. aureus antigens in cattle.

Successful parallel development and integration of a plasmid-based biologic, container/closure system and electrokinetic delivery device

We have developed three major technologies that allow plasmid-based products to be used for large-scale vaccination or therapeutic protein applications. Our team has integrated these components into one complete, cost-effective, easy-to-use system capable of rapid implementation under field conditions. The proprietary manufacturing process uses a lysis method and membrane-based chromatography to rapidly produce large-scale batches of plasmid. Plasmid doses are filled into the Becton-Dickinson Uniject container/closure system. The Uniject adapts to the electrode array of our constant current electrokinetic device, such that the plasmid is delivered in the area of tissue defined by the electrodes. Thus, plasmid uptake and expression levels are dramatically improved. This is the first completely integrated delivery system for plasmid-based products.

Strategies for improved formulation and delivery of DNA vaccines to veterinary target species

Interest in DNA immunization of animals continues, despite the fact that immune responses induced by DNA vaccines are generally lower than those elicited by conventional vaccines. In attempts to enhance the immune response to DNA vaccines, individuals have tried a variety of immune modulators, cytokines, and costimulatory molecules, but these only boost immune responses marginally. These results clearly demonstrate that the major challenge to improving DNA-based vaccines is to improve the transfection efficiency. Gene gun and electroporation can increase transfection and improve immune responses significantly, but these technologies have not yet advanced to the stage of routine use in livestock. Hopefully, transfection efficiency can be increased further in a user-friendly manner to ensure that the benefits of using DNA vaccines become a reality.