Editing DNA vaccine (section)

=== Cytokine modulation ===

An effective vaccine must induce an appropriate immune response for a given pathogen. DNA vaccines can polarise T-cell help towards TH1 or TH2 profiles and generate CTL and/or antibody when required. This can be accomplished by modifications to the form of antigen expressed (i.e. intracellular vs. secreted), the method and route of delivery or the dose.<ref name=Feltquate1997 /><ref name=References1996 /><ref name=Cardoso1996>{{cite journal | vauthors = Cardoso AI, Blixenkrone-Moller M, Fayolle J, Liu M, Buckland R, Wild TF | title = Immunization with plasmid DNA encoding for the measles virus hemagglutinin and nucleoprotein leads to humoral and cell-mediated immunity | journal = Virology | volume = 225 | issue = 2 | pages = 293–299 | date = November 1996 | pmid = 8918915 | doi = 10.1006/viro.1996.0603 | doi-access = free }}</ref><ref name=Sato1996>{{cite journal | vauthors = Sato Y, Roman M, Tighe H, Lee D, Corr M, Nguyen MD, Silverman GJ, Lotz M, Carson DA, Raz E | display-authors = 6 | title = Immunostimulatory DNA sequences necessary for effective intradermal gene immunization | journal = Science | volume = 273 | issue = 5273 | pages = 352–354 | date = July 1996 | pmid = 8662521 | doi = 10.1126/science.273.5273.352 | s2cid = 9333197 | bibcode = 1996Sci...273..352S }}</ref><ref name=Weiss2000>{{cite journal | vauthors = Weiss R, Leitner WW, Scheiblhofer S, Chen D, Bernhaupt A, Mostböck S, Thalhamer J, Lyon JA | display-authors = 6 | title = Genetic vaccination against malaria infection by intradermal and epidermal injections of a plasmid containing the gene encoding the Plasmodium berghei circumsporozoite protein | journal = Infection and Immunity | volume = 68 | issue = 10 | pages = 5914–5919 | date = October 2000 | pmid = 10992502 | pmc = 101554 | doi = 10.1128/IAI.68.10.5914-5919.2000 }}</ref> It can also be accomplished by the co-administration of plasmid DNA encoding immune regulatory molecules, i.e. cytokines, [[lymphokine]]s or co-stimulatory molecules. These "genetic [[adjuvants]]" can be administered as a:
* mixture of 2 plasmids, one encoding the immunogen and the other encoding the cytokine
* single bi- or polycistronic vector, separated by spacer regions
* plasmid-encoded [[Fusion protein|chimera]], or fusion protein
In general, co-administration of pro-inflammatory agents (such as various [[interleukins]], [[tumor necrosis factor]], and GM-CSF) plus TH2-inducing cytokines increase antibody responses, whereas pro-inflammatory agents and TH1-inducing cytokines decrease humoral responses and increase cytotoxic responses (more important in viral protection). Co-stimulatory molecules such as [[CD80|B7-1]], [[CD86|B7-2]] and [[CD154|CD40L]] are sometimes used.

This concept was applied in topical administration of pDNA encoding [[Interleukin 10|IL-10]].<ref name=Daheshia1997 /> Plasmid encoding B7-1 (a ligand on APCs) successfully enhanced the immune response in tumour models. Mixing plasmids encoding GM-CSF and the circumsporozoite protein of ''P. yoelii'' (PyCSP) enhanced protection against subsequent challenge (whereas plasmid-encoded PyCSP alone did not). It was proposed that GM-CSF caused dendritic cells to present antigen more efficiently and enhance IL-2 production and TH cell activation, thus driving the increased immune response.<ref name=Weiss1998 /> This can be further enhanced by first priming with a pPyCSP and pGM-CSF mixture, followed by boosting with a recombinant [[Poxviridae|poxvirus]] expressing PyCSP.<ref name=Sedegah2000>{{cite journal | vauthors = Sedegah M, Weiss W, Sacci JB, Charoenvit Y, Hedstrom R, Gowda K, Majam VF, Tine J, Kumar S, Hobart P, Hoffman SL | display-authors = 6 | title = Improving protective immunity induced by DNA-based immunization: priming with antigen and GM-CSF-encoding plasmid DNA and boosting with antigen-expressing recombinant poxvirus | journal = Journal of Immunology | volume = 164 | issue = 11 | pages = 5905–5912 | date = June 2000 | pmid = 10820272 | doi = 10.4049/jimmunol.164.11.5905 | doi-access = free }}</ref> However, co-injection of plasmids encoding GM-CSF (or IFN-γ, or IL-2) and a fusion protein of ''[[Plasmodium chabaudi|P. chabaudi]]'' [[Apicomplexan life cycle|merozoite surface protein]] 1 (C-terminus)-hepatitis B virus surface protein (PcMSP1-HBs) abolished protection against challenge, compared to protection acquired by delivery of pPcMSP1-HBs alone.<ref name=Wunderlich2000 />

The advantages of genetic adjuvants are their low cost and simple administration, as well as avoidance of unstable [[recombinant cytokine]]s and potentially toxic, "conventional" adjuvants (such as [[alum]], [[calcium phosphate]], monophosphoryl lipid A, [[cholera]] toxin, cationic and mannan-coated liposomes, [[QS21]], [[carboxymethyl cellulose]] and [[ubenimex]]).<ref name=Robinson2000 /><ref name=Lewis1999 /> However, the potential toxicity of prolonged cytokine expression is not established. In many commercially important animal species, cytokine genes have not been identified and isolated. In addition, various plasmid-encoded cytokines modulate the immune system differently according to the delivery time. For example, some cytokine plasmid DNAs are best delivered after immunogen pDNA, because pre- or co-delivery can decrease specific responses and increase non-specific responses.<ref name=Barouch1998>{{cite journal | vauthors = Barouch DH, Santra S, Steenbeke TD, Zheng XX, Perry HC, Davies ME, Freed DC, Craiu A, Strom TB, Shiver JW, Letvin NL | display-authors = 6 | title = Augmentation and suppression of immune responses to an HIV-1 DNA vaccine by plasmid cytokine/Ig administration | journal = Journal of Immunology | volume = 161 | issue = 4 | pages = 1875–1882 | date = August 1998 | doi = 10.4049/jimmunol.161.4.1875 | pmid = 9712056 | s2cid = 36488254 | url = http://www.jimmunol.org/cgi/content/abstract/161/4/1875 | doi-access = free }}</ref>