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

Abstract

IntroductionPlasmid DNA vaccines are a promising modality for immunization against a variety of infectious agents because they are safe, readily scalable, and easy distributed. Plasmid DNA vaccine vectors can elicit CD8 ϩ cytotoxic T lymphocytes (CTLs), CD4 ϩ T helper cell immune responses, as well as humoral immune responses. Nonetheless, the utility of DNA immunogens has been limited by their failure to elicit sufficiently potent immune responses. 1 One potential explanation for the limited immunogenicity of plasmid DNA is that vaccine antigen expression is generated at only transient and at low levels. 1 Immune-mediated destruction of antigen-producing muscle fibers appears to play a significant role in limiting vaccine antigen expression. Clearance of antigen-expressing myocytes has been shown to be dependent both on the immunogenicity of the antigen and the presence of a functional immune system. 2,3 However, the cell types responsible for this destruction remain to be determined. We have shown that damping of plasmid DNA vaccine antigen expression in vivo occurs coincident with the emergence of major histocompatibility complex (MHC) class I-restricted T-cell responses. In addition, we observed that vaccine antigen expression persists in Fas receptor knockout mice, suggesting a role in this process for T cell-mediated apoptosis via the Fas/FasL pathway. 3 Based on these data, we hypothesized that CD8 ϩ T cells mediated vaccine antigen clearance through Fas-dependent apoptosis. Alternatively, other studies have suggested that the limited antigen expression in this setting may be a result of antibody-dependent cell-mediated cytotoxicity or complement-mediated lysis. 4 In addition to adaptive immune responses, innate immune responses, such as those mediated by macrophages and NK cells, have also been implicated as potential contributors to the destruction of antigenproducing myocytes. 5,6 In the present study, we investigated the cell types responsible for antigen clearance in plasmid DNA vaccinated mice. We used an In Vivo Imaging System (IVIS), which enabled us to measure antigen expression in vivo precisely, without serial killing of the animals. Using knockout (KO) mice and antibodydepletion experiments, we investigated the relative contribution of NK cells, macrophages, CD8 ϩ T cells, and CD4 ϩ T cells to the damping of antigen expression in vaccinated animals. Surprisingly, we observed that CD4 ϩ T cells were both necessary and sufficient to mediate plasmid DNA vaccine antigen clearance. These findings demonstrate a central role for CD4 ϩ T cells in vaccine antigen clearance. Methods Animals and immunizationsSix-to 8-week-old wild-type C57BL/6, C57BL/6.␤2 M KO, C57BL/ 6.MHC II KO, Rag1 KO, and NK-function-deficient beige mice (C57BL/6-Lyst bg7-9 ) were purchased from The Jackson Laboratory (Bar Harbor, ME). All animals were housed and maintained in accordance with the Guide for the Care and Use of Laboratory Animals, 10 and all studies and procedures were reviewed and approved by the Institutional Animal...

Non-classical Natural Killer T Cells Modulate Plasmid DNA Vaccine Antigen Expression and Vaccine-elicited Immune Responses by MCP-1 Secretion after Interaction with a β2-Microglobulin-independent CD1d

“…2D). Together with earlier findings that DNA antigen clearance is ␤2m-independent (22), these findings suggest that the type II NKT mediate this function.…”

“…Thus, the model seems to create an environment that favors the immune potentiating function, rather than the suppressive function of NKT cells. We have previously shown that these CD4 ϩ T cells clear plasmid DNA antigen expression though a MHC class II-restricted Fas/FasL-dependent mechanism, and that depletion of CD4 ϩ T cells leads to a reduction in the plasmid DNA antigen-specific CD8 ϩ T cell immune response (22). Therefore, the NKT-cell enhanced CD4 ϩ helper cells might also be responsible for the increase of the plasmid DNA antigen-specific CD8 ϩ T cell immune response.…”

Treatment with anti-FasL antibody preserves memory lymphocytes and virus-specific cellular immunity in macaques challenged with simian immunodeficiency virus

“…We also know that Fas/FasL interactions reduce CD8 ϩ T-cell responses to plasmidencoded antigens by destroying the transfected antigenpresenting cell. 17,18 The superior ELISPOT responses in our study suggest that interfering with the Fas/FasL interaction protected these antigen-specific cells from destruction. Preservation of CCR5 ϩ CD4 T cells upon anti-FasL treatment did not result in any increase in viral replication.…”

“…Plasmid DNA immunization of mice triggered a response by class II-restricted CD4 ϩ T cells that expressed FasL and killed the transfected antigenpresenting cells. 17 When plasmid DNA immunizations were performed in Fas Ϫ/Ϫ mice 17 or class II Ϫ/Ϫ mice, 18 the damping of CD8 ϩ T-cell responses was not observed. The damping effect was independent of perforin expression and depended only on Fas/FasL interactions.…”

Modulation of Plasmid DNA Vaccine Antigen Clearance by Caspase 12 RNA Interference Potentiates Vaccination

“…The reduction of vaccine antigen expression in vivo in mice vaccinated i.m. with plasmid DNA is temporally correlated with local accumulation of T cells in the muscle and involves an apoptotic Fas/FasL-dependent process (8,10). Therefore, we coadministered plasmid DNA vaccine and plasmid DNAs encoding the antiapoptotic proteins BCL-xl, BCL-2, X-linked inhibitor of apoptosis protein (XIAP), or dominant negative (dn) mutants of caspase 9 (dnCasp9) and caspase 8 (dn-Casp8) to evaluate their abilities to augment the immunogenicity of a plasmid DNA immunogen.…”