Multivalent Smallpox DNA Vaccine Delivered by Intradermal Electroporation Drives Protective Immunity in Nonhuman Primates Against Lethal Monkeypox Challenge

To evaluate new vaccines when human efficacy studies are not possible, the FDA's "Animal Rule" requires well-characterized models of infection. Thus, in the present study, the early pathogenic events of monkeypox infection in nonhuman primates, a surrogate for variola virus infection, were characterized. Cynomolgus macaques were exposed to aerosolized monkeypox virus (10 5 PFU). Clinical observations, viral loads, immune responses, and pathological changes were examined on days 2, 4, 6, 8, 10, and 12 postchallenge. Viral DNA (vDNA) was detected in the lungs on day 2 postchallenge, and viral antigen was detected, by immunostaining, in the epithelium of bronchi, bronchioles, and alveolar walls. Lesions comprised rare foci of dysplastic and sloughed cells in respiratory bronchioles. By day 4, vDNA was detected in the throat, tonsil, and spleen, and monkeypox antigen was detected in the lung, hilar and submandibular lymph nodes, spleen, and colon. Lung lesions comprised focal epithelial necrosis and inflammation. Body temperature peaked on day 6, pox lesions appeared on the skin, and lesions, with positive immunostaining, were present in the lung, tonsil, spleen, lymph nodes, and colon. By day 8, vDNA was present in 9/13 tissues. Blood concentrations of interleukin 1ra (IL-1ra), IL-6, and gamma interferon (IFN-␥) increased markedly. By day 10, circulating IgG antibody concentrations increased, and on day 12, animals showed early signs of recovery. These results define early events occurring in an inhalational macaque monkeypox infection model, supporting its use as a surrogate model for human smallpox. IMPORTANCEBioterrorism poses a major threat to public health, as the deliberate release of infectious agents, such smallpox or a related virus, monkeypox, would have catastrophic consequences. The development and testing of new medical countermeasures, e.g., vaccines, are thus priorities; however, tests for efficacy in humans cannot be performed because it would be unethical and field trials are not feasible. To overcome this, the FDA may grant marketing approval of a new product based upon the "Animal Rule," in which interventions are tested for efficacy in well-characterized animal models. Monkeypox virus infection of nonhuman primates (NHPs) presents a potential surrogate disease model for smallpox. Previously, the later stages of monkeypox infection were defined, but the early course of infection remains unstudied. Here, the early pathogenic events of inhalational monkeypox infection in NHPs were characterized, and the results support the use of this surrogate model for testing human smallpox interventions.

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confidence: 99%

Sequence of Pathogenic Events in Cynomolgus Macaques Infected with Aerosolized Monkeypox Virus

Tree

Hall

Pearson

et al. 2015

“…In humans, plasmid DNA vaccines have been shown to be safe and well tolerated in thousands of volunteers (14,41,48); however, their strong immunogenicity observed in smaller animals does not transfer to primates, including humans. Thus, the potency of DNA vaccines in humans must be significantly improved for the vaccines to become a practical and commercially attractive health care tool.The use of in vivo electroporation (EP) was shown to improve DNA transfection into cells at the site of injection and to promote local inflammation, thereby increasing the immunogenicity of DNA vaccines (7,18,37,39). Safety and tolerability of intramuscular (i.m.)…”

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confidence: 99%

“…The use of in vivo electroporation (EP) was shown to improve DNA transfection into cells at the site of injection and to promote local inflammation, thereby increasing the immunogenicity of DNA vaccines (7,18,37,39). Safety and tolerability of intramuscular (i.m.)…”

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confidence: 99%

Superior Induction of T Cell Responses to Conserved HIV-1 Regions by Electroporated Alphavirus Replicon DNA Compared to That with Conventional Plasmid DNA Vaccine

Knudsen

Mbewe-Mvula

Rosario

et al. 2012

f Vaccination using "naked" DNA is a highly attractive strategy for induction of pathogen-specific immune responses; however, it has been only weakly immunogenic in humans. Previously, we constructed DNA-launched Semliki Forest virus replicons (DREP), which stimulate pattern recognition receptors and induce augmented immune responses. Also, in vivo electroporation was shown to enhance immune responses induced by conventional DNA vaccines. Here, we combine these two approaches and show that in vivo electroporation increases CD8 ؉ T cell responses induced by DREP and consequently decreases the DNA dose required to induce a response. The vaccines used in this study encode the multiclade HIV-1 T cell immunogen HIVconsv, which is currently being evaluated in clinical trials. Using intradermal delivery followed by electroporation, the DREP.HIVconsv DNA dose could be reduced to as low as 3.2 ng to elicit frequencies of HIV-1-specific CD8 ؉ T cells comparable to those induced by 1 g of a conventional pTH.HIVconsv DNA vaccine, representing a 625-fold molar reduction in dose. Responses induced by both DREP.HIVconsv and pTH.HIVconsv were further increased by heterologous vaccine boosts employing modified vaccinia virus Ankara MVA.HIVconsv and attenuated chimpanzee adenovirus ChAdV63.HIVconsv. Using the same HIVconsv vaccines, the mouse observations were supported by an at least 20-fold-lower dose of DNA vaccine in rhesus macaques. These data point toward a strategy for overcoming the low immunogenicity of DNA vaccines in humans and strongly support further development of the DREP vaccine platform for clinical evaluation. " N aked" DNA constitutes an attractive vaccine platform for delivery of pathogen-or cancer-derived immunogens. Three veterinary DNA vaccines have been licensed for use in dogs, salmon, and horses, demonstrating that DNA vaccines are capable of inducing protective immunity (8, 48). In humans, plasmid DNA vaccines have been shown to be safe and well tolerated in thousands of volunteers (14,41,48); however, their strong immunogenicity observed in smaller animals does not transfer to primates, including humans. Thus, the potency of DNA vaccines in humans must be significantly improved for the vaccines to become a practical and commercially attractive health care tool.The use of in vivo electroporation (EP) was shown to improve DNA transfection into cells at the site of injection and to promote local inflammation, thereby increasing the immunogenicity of DNA vaccines (7,18,37,39). Safety and tolerability of intramuscular (i.m.) and intradermal (i.d.) DNA EP were demonstrated in both preclinical and clinical settings (28,49,51). Although the i.m. delivery route has been more extensively studied, i.d. EP offers an attractive route of delivery due to the characteristics of the skin, with many resident antigen-presenting cells such as Langerhans and dermal dendritic cells. Intradermal EP is also considerably less painful, and any possible residual pain may be further controlled by topical anesthetics (38,48).The D...

“…Thus, a well-defined animal model using monkeypox virus should mimic the natural course of smallpox disease. Macaques have been used at various stages of smallpox vaccine and antiviral research (16,(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36), and in each case the route of infection, dose, and choice of challenge strain have been key factors in determining whether the macaque model of monkeypox resembles human clinical variola virus infection.…”

Section: Discussionmentioning

confidence: 99%

Assessment of the Protective Effect of Imvamune and Acam2000 Vaccines against Aerosolized Monkeypox Virus in Cynomolgus Macaques

Hatch

Graham

Bewley

et al. 2013

122

To support the licensure of a new and safer vaccine to protect people against smallpox, a monkeypox model of infection in cynomolgus macaques, which simulates smallpox in humans, was used to evaluate two vaccines, Acam2000 and Imvamune, for protection against disease. Animals vaccinated with a single immunization of Imvamune were not protected completely from severe and/or lethal infection, whereas those receiving either a prime and boost of Imvamune or a single immunization with Acam2000 were protected completely. Additional parameters, including clinical observations, radiographs, viral load in blood, throat swabs, and selected tissues, vaccinia virus-specific antibody responses, immunophenotyping, extracellular cytokine levels, and histopathology were assessed. There was no significant difference (P > 0.05) between the levels of neutralizing antibody in animals vaccinated with a single immunization of Acam2000 (132 U/ml) and the prime-boost Imvamune regime (69 U/ml) prior to challenge with monkeypox virus. After challenge, there was evidence of viral excretion from the throats of 2 of 6 animals in the prime-boost Imvamune group, whereas there was no confirmation of excreted live virus in the Acam2000 group. This evaluation of different human smallpox vaccines in cynomolgus macaques helps to provide information about optimal vaccine strategies in the absence of human challenge studies.