Efficient Generation of Mucosal and Systemic Antigen-Specific CD8⁺T-Cell Responses following Pulmonary DNA Immunization

Abstract

Although mucosal CD8؉ T-cell responses are important in combating mucosal infections, the generation of such immune responses by vaccination remains problematic. In the present study, we evaluated the ability of plasmid DNA to induce local and systemic antigen-specific CD8 ؉ T-cell responses after pulmonary administration. We show that the pulmonary delivery of plasmid DNA formulated with polyethyleneimine (PEI-DNA) induced robust systemic CD8 ؉ T-cell responses that were comparable in magnitude to those generated by intramuscular (i.m.) immunization. Most importantly, we observed that the pulmonary delivery of PEI-DNA elicited a 10-fold-greater antigen-specific CD8؉ T-cell response in lungs and draining lymph nodes of mice than that of i.m. immunization. The functional evaluation of these pulmonary CD8؉ T cells revealed that they produced type I cytokines, and pulmonary immunization with PEI-DNA induced lung-associated antigen-specific CD4 ؉ T cells that produced higher levels of interleukin-2 than those induced by i.m. immunization. Pulmonary PEI-DNA immunization also induced CD8 ؉ T-cell responses in the gut and vaginal mucosa. Finally, pulmonary, but not i.m., plasmid DNA vaccination protected mice from a lethal recombinant vaccinia virus challenge. These findings suggest that pulmonary PEI-DNA immunization might be a useful approach for immunizing against pulmonary pathogens and might also protect against infections initiated at other mucosal sites. Since establishing that antigen-specific CD8ϩ T-cell populations in mucosal sites may confer protection against intracellular pathogens that initiate infections at mucosal surfaces, vaccine strategies have been explored for eliciting cellular immune responses in mucosal tissues (40). Studies have been done to evaluate the immunogenicity of vaccines delivered to a variety of mucosal surfaces, including those of the nose, intestine, rectum, and vagina. These studies have shown that immunization at mucosal sites can induce larger numbers of antigen-specific CD8 ϩ T cells in mucosal tissues than parenteral immunization (3).Particular attention has focused on the lungs as a target for mucosal immunization. The lungs are an important mucosal portal of entry for pathogens. They are also a readily accessed mucosal site for the delivery of immunogens that might induce diverse mucosal immune responses. Pulmonary immunization strategies have been shown to generate potent Th1 responses and protective immunity against respiratory challenge with pathogens in several animal models (4,29,32,37,38).Because of the ease of generating vaccine constructs and the ability to administer repeated inoculations of the same vector, DNA immunization remains a promising vaccination strategy for eliciting cellular immune responses. Only a limited number of studies have been done to evaluate the immunogenicity of DNA vaccines following pulmonary delivery (4, 32). Although the importance of CD8 ϩ T lymphocytes in eradicating mucosal infections has been well established, it has not been determin...

Enhancement of plasmid DNA immunogenicity with linear polyethylenimine

“…Previous studies have shown that intramuscular delivery of PEI-DNA complexes reduced DNA expression from that observed following intramuscular delivery of DNA alone [24,38]. This decrease in DNA expression may explain the reduced immunogenicity of PEI-DNA complexes when delivered by the intramuscular route.…”

“…PEI is superior to other nonmicrobial transfection agents because of its ability to protect DNA from degradation [18], to escape intracellular endosomal lysis [19] and to efficiently deliver DNA into the nucleus of cells [20]. Formulation with PEI polymers has been employed in DNA-and siRNAbased immunotherapy against cancer [21,22] and in vaccination studies targeting different infectious agents [10,23,24].…”

“…Still, complexation of PEI to DNA did enhance the priming of plasmid DNA, as demonstrated by improved boost responses. Recent studies have also suggested that the adjuvant effect of PEI can be observed with pulmonary delivery [24]. Other novel delivery routes, such as intradermal or oral delivery, should be explored to determine the best approach to harness the profound effect of polymer adjuvants on the immunogenicity of plasmid DNA vaccine constructs.…”

“…PEI is superior to other nonmicrobial transfection agents because of its ability to protect DNA from degradation [18], to escape intracellular endosomal lysis [19] and to efficiently deliver DNA into the nucleus of cells [20]. Formulation with PEI polymers has been employed in DNA-and siRNAbased immunotherapy against cancer [21,22] and in vaccination studies targeting different infectious agents [10,23,24].In the present study, we have evaluated the physicochemical characteristics of a series of PEI polymers and have assessed associations between particular characteristics of these polymers and their ability to facilitate in vivo DNA expression and enhanced adaptive immune responses. Moreover, we have examined plasmid DNA constructs formulated with these various PEI polymers for their ability to generate immune responses under conditions that maximize the immunogenicity of these PEI-DNA complexes.…”

An enhanced immune response against G250, induced by a heterologous DNA prime-protein boost vaccination, using polyethyleneimine as a DNA vaccine adjuvant

“…PEI is superior to other non-microbial transfection agents because of its ability to protect DNA from degradation (15), to escape intracellular endosomal lysis, and to efficiently deliver DNA into the cell nucleus (16). Formulation with PEI polymers has been employed in DNA and siRNA (small interfering RNA)-based cancer immunotherapies (17) and in vaccination studies targeting infectious agents (18). In the present study, pVAX1, a Food and Drug Administration-approved plasmid vector, was used as the carrier of G250 DNA, and combined with the synthetic PEI.…”