Plasmid DNA Vaccine-Elicited Cellular Immune Responses Limit In Vivo Vaccine Antigen Expression through Fas-Mediated Apoptosis

ABSTRACTThe magnitude of the immune responses elicited by plasmid DNA vaccines might be limited, in part, by the duration of vaccine antigen expressionin vivo. To explore strategies for improving plasmid DNA vaccine efficacy, we studied the apoptotic process in myocytes of mice vaccinated intramuscularly. We found that after vaccination, the proapoptotic protein caspase 12 (Casp12) was upregulated in myocytes coincident with the loss of vaccine antigen expression. To harness this observation to improve plasmid DNA vaccine efficacy, we used RNA interference technology, coadministering plasmid DNA expressing a short hairpin RNA (shRNA) of Casp12 with plasmid DNA vaccine constructs. This treatment with shRNA Casp12, administered twice within the first 10 days following vaccine administration, increased antigen expression 7-fold, the antigen-specific CD8+T cell immune response 6-fold, and antigen-specific antibody production 5-fold. This study demonstrates the critical role for Casp12 in plasmid DNA vaccine-induced immune responses and shows that increased antigen expression mediated by down-modulation of Casp12 can be used to potentiate vaccine efficacy.

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CD4+ T lymphocytes mediate in vivo clearance of plasmid DNA vaccine antigen expression and potentiate CD8+ T-cell immune responses

Blood ◽

10.1182/blood-2008-06-165803 ◽

2008 ◽

Vol 112 (12) ◽

pp. 4585-4590 ◽

Cited By ~ 20

Author(s):

Ralf Geiben-Lynn ◽

John R. Greenland ◽

Kwesi Frimpong-Boateng ◽

Nico van Rooijen ◽

Avi-Hai Hovav ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Dna Vaccine ◽

Plasmid Dna ◽

Cd4 T Cells ◽

Antigen Expression ◽

Cd8 T Cell ◽

Vaccine Antigen ◽

Cell Immune Response ◽

Plasmid Dna Vaccine

Abstract There is evidence that the limited immunogenicity of plasmid DNA vaccines is the result, at least in part, of the rapid clearance of vaccine antigen expression by antigen-specific immune responses. However, the cell types responsible for the clearance of plasmid DNA vaccine antigens are not known. Here we demonstrate that macrophages, NK cells, and CD8+ T cells did not significantly contribute to the DNA antigen clearance but CD4+ T cells played the crucial role in attenuating plasmid DNA vaccine antigen expression. Adoptive transfer experiments demonstrate that CD4+ T cells facilitated DNA vaccine antigen clearance in a Fas/FasL-dependent manner. Furthermore, we show that depletion of CD4+ T cells prevented the clearance of vaccine antigen and the appearance of a CD8+ T-cell immune response. Inoculation of major histocompatibility complex class II KO mice with the plasmid DNA led to persistent antigen expression and abolition of a CD8+ T-cell immune response. Importantly, the prolongation of antigen expression by disrupting the CD4+ T-cell Fas/FasL myocytes signaling led to a 3- to 5-fold increase of antigen-specific CD8+ T-cell responses. These data demonstrate a dominant role of CD4+ T cell–mediated cytotoxicity in plasmid DNA vaccine antigen clearance.

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