• Vaccine Name: Smallpox DNA Vaccine
• Target Pathogen: Variola virus
• Target Disease: Smallpox
• Vaccine Ontology ID: VO_0004096
• Type: DNA
• A27L gene engineering:
  • Type: Protein
  • Description:
  • Detailed Gene Information: Click Here.
• A33R from Monkeypox virus (strain: Zaire-96-I-16) gene engineering:
  • Type: Protein
  • Description:
  • Detailed Gene Information: Click Here.
• B5R from Monkeypox virus (strain: Zaire-96-I-16) gene engineering:
  • Type: Protein
  • Description: (Hooper et al., 2004)
  • Detailed Gene Information: Click Here.
• L1R from Monkeypox virus Zaire-96-I-16 gene engineering:
  • Type: Protein
  • Description:
  • Detailed Gene Information: Click Here.
• Preparation: The 4pox DNA vaccine contained two IMV-specific genes (L1R and A27L) and two EEV-specific genes (A33R and B5R) (Hooper et al., 2004).
• Virulence: (Hooper et al., 2004)
• Description: DNA vaccine strategies have been investigated in animal models. A DNA vaccine composed of 4 vaccinia virus genes protected rhesus macaques from severe disease, with the animals exhibiting mild clinical and laboratory abnormalities, after challenge with a lethal dose of monkeypox virus. When vaccinated with a single gene (L1R), macaques developed severe, but not fatal, disease. Heterologous prime-boost strategies have also been evaluated. Priming BALB/c mice with DNA vaccine resulted in greater immune responses after boosting with live vaccinia virus compared with controls (Parrino et al., 2006).

Human Response

• Host Strain: rhesus macaque (Macaca mulata)
• Vaccination Protocol: The challenge experiment included 4 groups: group 1 consisted of 3 monkeys vaccinated with the 4pox DNA vaccine, group 2 consisted of 2 monkeys vaccinated with the L1R DNA vaccine, group 3 (negative controls) consisted of 3 monkeys vaccinated with a Hantaan virus DNA vaccine, and group 4 (positive controls) consisted of 2 monkeys vaccinated with the human smallpox vaccine (Dryvax). The L1R DNA vaccine was tested to determine the degree to which vaccination with a single immunogen eliciting IMV-neutralizing antibodies could confer protection. The DNA vaccines were administered by gene gun. Five weeks before challenge, all monkeys, except the monkeys vaccinated with Dryvax and one of the negative controls, were vaccinated with new preparations of the same DNA vaccine they had received 1-2 years earlier. This booster vaccination was administered to affirm that immunological memory had been elicited by the initial vaccination series and to ensure robust responses to the DNA vaccines with the intent to prove concepts rather than explore minimal requirements for protection. Based on the dosing experiments, a dose of 2 x 10^7 PFU was chosen for the vaccine evaluation experiment. Vaccinated monkeys were challenged with MPOV-Z79 by i.v. injection into the right or left saphenous vein. At 2-day intervals, whole-blood, serum, and throat swab samples were collected, and rectal temperature, pulse, and blood oxygen saturation were measured (Hooper et al., 2004).
• Persistence: Gene gun vaccination with the 4pox DNA vaccine or the L1R DNA vaccine elicited a memory response that was maintained for at least a year and up to 2 years (Hooper et al., 2004).
• Side Effects: Although VACV is highly immunogenic and is known to confer long-lasting protective immunity to smallpox, the adverse events associated with the present smallpox vaccine (i.e., Dryvax) pose a significant obstacle to successful vaccination campaigns. Adverse events historically associated
  with VACV range from the nonserious (e.g., fever, rash, headache, pain, and fatigue) to life threatening (e.g., eczema vaccinatum, encephalitis, and progressive vaccinia). Serious adverse events that are not necessarily causally associated with vaccination, including myocarditis and/or myopericarditis, have been reported during past and present smallpox vaccination programs. Several adverse cardiac events reported in the first 4 months of the 2003 civilian and military vaccination campaigns prompted the CDC to revise their recommendations for exclusion of potential smallpox recipients to include those persons with heart disease or several other conditions. In addition, identifying protective immunogens might allow the development of a subunit smallpox vaccine that affords protection with negligible adverse events (Hooper et al., 2004).
• Efficacy: Monkeys vaccinated with the 4pox DNA vaccine were protected not only from lethal monkeypox but also from severe disease. This is the first demonstration that vaccination with a combination of VACV immunogens, rather than the whole infectious virus, is sufficient to protect NHPs against any poxvirus disease (Hooper et al., 2004).
• Description: Much of the threat posed by orthopoxviruses could be eliminated by vaccination; however, because the smallpox vaccine is a live orthopoxvirus vaccine administered to the skin, the vaccine itself can pose a serious health risk. The present study demonstrates that monkeys vaccinated with a DNA vaccine consisting of four vaccinia virus genes (L1R, A27L, A33R, and B5R) were protected from severe disease after an otherwise lethal challenge with monkeypox virus. Animals vaccinated with a single gene (L1R), which encodes a target of neutralizing antibodies, developed severe disease but survived. This is the first demonstration that a subunit vaccine approach to smallpox-monkeypox immunization is feasible (Hooper et al., 2004).

Mouse Response

• Host Strain: BALB/c
• Vaccination Protocol: Adult (16–23 g) female BALB/c mice were vaccinated in the skin of the thigh using an Easy Vax™ DNA vaccine delivery system to deliver the vaccine plasmids on weeks 0, 3, and 8. Anesthetized mice were scarified by placing 10 μl of PBS containing live VACV on the tail. A 26 gauge 5/8" needle was used to scratch the tail to facilitate infection/vaccination. A lesion (pock) at the site of scarification on d 10 indicated successful vaccination. Mice were anesthetized and weighed before i.n. injection of 50 μl of PBS containing 2 × 10^6 pfu of VACV strain IHD-J using a plastic pipette tip. After challenge, mice were observed and weighed daily for 3 weeks (Hooper et al., 2006).
• Persistence: (Hooper et al., 2006)
• Side Effects: There are several drawbacks to the current anthrax vaccines including nonserious and serious adverse events that make the vaccine contraindicated in large segments of the population (e.g., persons who are immunodeficient, immunosuppressed, pregnant, breastfeeding, or have history of cardiac disease), and because this vaccine results in a localized skin infection containing infectious virus (i.e. pock), the infection can spread to other sites on the body (e.g. ocular autoinoculation) or to persons who come in close contact with the vaccinee. Identification of the genes associated with protective immunity and, conversely, the genes associated with adverse events unrelated to dissemination or transmission will be important for characterizing the next-generation smallpox vaccines and for engineering future smallpox vaccines (Hooper et al., 2006).
• Efficacy: Mice vaccinated with the 4pox DNA vaccine using the Easy Vax™ device were completely protected from i.n. challenge with >10 LD50 of VACV, strain IHD-J (Hooper et al., 2006).
• Description: The enhanced immunogenicity of DNA vaccines delivered by gene gun likely involves the direct introduction of plasmid DNA to cells in the skin, including specialized antigen-presenting cells (APCs). While the gene gun has yielded among the most promising immune responses for a DNA vaccine thus far, there is the possibly that all of the criteria required for successful product development will not be satisfied. Hence, it is important to continue to evaluate alternative technologies that might better facilitate the development of licensed human vaccines. Alternative means of delivering DNA vaccines under investigation include the use of electric field technologies. Electroporation is a process whereby cells are transiently permeabilized by high-intensity electric field pulses. The present study tests a novel device capable of targeting electroporation to the dermis using a microneedle array. The plasmid DNA is dried onto the tips of the microneedles, which are inserted into the skin where the DNA dissolves in interstial fluid and is then transfected into the surrounding cells by electroporation (Hooper et al., 2006).