Enhancement of DNA tumor vaccine efficacy by gene gun–mediated codelivery of threshold amounts of plasmid-encoded helper antigen

Abstract

Nucleic acid-based vaccines are effective in infectious disease models but have yielded disappointing results in tumor models when tumor-associated selfantigens are used. Incorporation of helper epitopes from foreign antigens into tumor vaccines might enhance the immunogenicity of DNA vaccines without increasing toxicity. However, generation of fusion constructs encoding both tumor and helper antigens may be difficult, and resulting proteins have unpredictable physical and immunologic properties. Furthermore, simultaneous production of equal amounts of highly immunogenic helper and weakly immunogenic tumor antigens in situ could favor development of responses against the helper antigen rather than the antigen of interest. We assessed the ability of 2 helper antigens (␤-galactosidase or fragment C of tetanus toxin) encoded by one plasmid to augment responses to a self-antigen (lymphomaassociated T-cell receptor) encoded by a separate plasmid after codelivery into skin by gene gun. This approach allowed ad- IntroductionPlasmid-encoded antigens have been used to induce immune responses in experimental animals and humans for more than a decade. Plasmid-based nucleic acid vaccines are attractive because of simplicity, low cost, and safety, but suboptimal immunogenicity and limited efficacy against certain pathogens and tumors have limited their utility. A variety of strategies have been developed to enhance DNA vaccine efficacy. These approaches include:(1) modification of DNA vaccines to include improved expression plasmids 1 or incorporation of viral vectors 2 ; (2) modifications of cDNA sequences encoding antigen to enhance antigenicity, 3 codon adjustments to optimize transcription, 1,4 or generation of string-ofepitope constructs incorporating selected subunits of antigens 5,6 ; (3) improved delivery systems, including methods for more efficient in vivo transfection of host cells, such as in vivo electroporation 6 or gene gun 7 ; and (4) the use of adjuvants. 8 Adjuvants include conventional adjuvants, such as Freund adjuvant, and the more recently developed chemically defined ("molecular") adjuvants. The latter are intended to enhance immune responses while avoiding, or at least significantly reducing, adverse effects associated with conventional adjuvants.Entities with a wide variety of biologic effects have been used as chemically defined adjuvants for DNA vaccines, including biologic response modifiers such as cytokines (eg, granulocytemacrophage colony-stimulating factor [GM-CSF] 9 ) and costimulatory molecules 10,11 as well as monoclonal antibodies (mAbs) that block undesired or trigger desired pathways, such as anti-CD40 12 or anti-CD137. 13 An alternative strategy involves codelivery of "helper antigens" (ie, foreign antigens that induce strong T-cell responses) with weak antigens of interest. Helper antigens are selected based on their high immunogenicity and enhance responses to weaker antigens via incompletely characterized bystander effects. Proteins previously used as helper antigens include keyh...

Vaccination Using Gene-Gun Technology

“…Higher doses of co-delivered pro-apoptotic molecules to increase immunogenicity result in premature host cell death and thereby reduce the immunogenicity of the vaccine [ 27 , 28 ]. The co-delivery of large amounts of helper-antigens (designed to trigger a "bystander" CD4 helper response) can lead to immunodominance of the helper antigen thus not providing the desired adjuvant effect [ 18 ]. However, gene gun vaccination permits the rapid and straight-forward comparison of multiple ratios of antigen-molecular adjuvant without the need for cloning different plasmids.…”

“…This facilitates the testing of immunomodulatory molecules ("mix-and-match") and allows the adjustment of differential expression levels by simply changing the ratio of plasmids used. This turned out to be crucial when using plasmid-encoded helper antigens or the co-delivery of pro-apoptotic molecules [ 18 ].…”

Transcriptional IL-15-directed in vivo DC targeting DNA vaccine

“…Weak immunogenicity of DNA vaccines is a major obstacle to current DNA vaccine development and may be responsible for the ineffective vaccination in humans (1-3). Many strategies have been designed and tested to overcome this problem including administration of DNA encoding cytokines, chemokines, costimulatory molecules, survival factor or helper Ag (4-8), injection of mAb (9), addition of chemical adjuvant (10), enhancement of Ag expression (11), improvement of DNA delivery (12) and modification of Ag (3, 13). …”

Hepatitis B Surface Antigen-based Vaccines for Human Neoplastic Disease

“…DNA vaccines are cheap to produce and are effective at inducing CTL responses in animal models (Rath et al, 2005;Payette et al, 2006;Muthumani et al, 2008b;Laddy et al, 2009;Leitner et al, 2009). There are successful clinical trials of DNA vaccines such as HBsAg-DNA vaccine for HBV infection in humans (Roy et al, 2000a;Wang et al, 2004;Drape et al, 2006;Jones et al, 2009) and DNA vaccines are licensed for protection of fish against viral infections (Lorenzen & LaPatra, 2005) and horses against west nile virus (Powell, 2004).…”

“…In the production of large quantities of clinical grade DNA for immunisation a number of specific hurdles can be expected (reviewed in Prazeres et al, 1999). The excessive amount of DNA required when delivered by conventional needle has led to the development of new techniques such as gene gun delivery (Frelin et al, 2003;Trimble et al, 2003;Kamili et al, 2004;Leitner et al, 2009) in which DNA is coated onto gold particles which are fired into the skin using a high pressure gas. The gold particles transverse the basal membrane transfecting cells which prime the immune system.…”