Abstract
Signaling through the Fas/Apo-1/CD95 death receptor is known to affect virus-specific cell-mediated immune (CMI) responses. We tested whether modulating the Fas-apoptotic pathway can enhance immune responses to DNA vaccination or lymphocytic choriomeningitis virus (LCMV) infection. Mice were electroporated with plasmids expressing a variety of pro- or anti-apoptotic molecules related to Fas signaling and then either LCMV-infected or injected with plasmid DNA expressing SIV or HIV antigens. Whereas Fas or FasL knockout mice had improved CMI, down-regulation of Fas or FasL by shRNA or antibody failed to improve CMI and was accompanied by increases in regulatory T cells (Treg). Two “adjuvant” plasmids were discovered that significantly enhanced plasmid immunizations. The adjuvant effects of Fas-associated death domain (FADD) and of cellular FLICE-inhibitory protein (cFLIP) were consistently accompanied by increased effector memory T lymphocytes and increased T cell proliferation. This adjuvant effect was also observed when comparing murine infections with LCMV-Armstrong and its persisting variant LCMV-Clone 13. LCMV-Armstrong was cleared in 100% of mice nine days after infection, while LCMV-Clone 13 persisted in all mice. However, half of the mice pre-electroporated with FADD or cFLIP plasmids were able to clear LCMV-Clone 13 by day nine, and, in the case of cFLIP, increased viral clearance was accompanied by higher CMI. Our studies imply that molecules in the Fas pathway are likely to affect a number of events in addition to the apoptosis of cells involved in immunity.
Highlights
New developments in DNA injection technology have improved efficacy for vaccination, adjuvant delivery and gene therapy
It has been shown that Fas signaling negatively regulates DNA vaccine potency in studies with Fas or FasL KO mice [13,14]
Since we showed that both cellular FLICE-inhibitory protein (cFLIP) and Fas-associated death domain (FADD) were capable of improving cellular immune responses to SIVmac Gag and HIVBal gp140, we asked whether they could influence virus infection in vivo
Summary
New developments in DNA injection technology have improved efficacy for vaccination, adjuvant delivery and gene therapy. DNA vaccines are increasingly attractive for preventing or even treating infectious diseases and cancers, despite a history of low immunogenicity during human clinical trials [1,2,3]. The recent licensure of four veterinary DNA vaccines [2], and new advances in DNA vaccine technology, especially electroporation [5], have prompted many new clinical trials for infectious diseases, e.g., malaria, HIV, HPV, and cancer, e.g., melanoma, prostate cancer and breast cancer [2]. Best et al [6] showed that electroporation-mediated intramuscular delivery of HPV DNA vaccine induces better immunity than epidermal gene gun-mediated particle delivery. Hirao et al [7] compared the Merck adenovirus serotype 5 (Ad5) SIV vaccine with an optimized electroporation-delivered SIV DNA vaccine in macaques, and concluded that the DNA vaccine induced much better cellular immune responses than did the Ad5 vector. The Ad5 immunization failed to boost following the first immunization while DNA responses were continually boosted with all four immunizations demonstrating a major advantage of the electroporated DNA
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