Immune Protection of Nonhuman Primates against Ebola Virus with Single Low-Dose Adenovirus Vectors Encoding Modified GPs

Abstract

BackgroundEbola virus causes a hemorrhagic fever syndrome that is associated with high mortality in humans. In the absence of effective therapies for Ebola virus infection, the development of a vaccine becomes an important strategy to contain outbreaks. Immunization with DNA and/or replication-defective adenoviral vectors (rAd) encoding the Ebola glycoprotein (GP) and nucleoprotein (NP) has been previously shown to confer specific protective immunity in nonhuman primates. GP can exert cytopathic effects on transfected cells in vitro, and multiple GP forms have been identified in nature, raising the question of which would be optimal for a human vaccine.Methods and FindingsTo address this question, we have explored the efficacy of mutant GPs from multiple Ebola virus strains with reduced in vitro cytopathicity and analyzed their protective effects in the primate challenge model, with or without NP. Deletion of the GP transmembrane domain eliminated in vitro cytopathicity but reduced its protective efficacy by at least one order of magnitude. In contrast, a point mutation was identified that abolished this cytopathicity but retained immunogenicity and conferred immune protection in the absence of NP. The minimal effective rAd dose was established at 1010 particles, two logs lower than that used previously.ConclusionsExpression of specific GPs alone vectored by rAd are sufficient to confer protection against lethal challenge in a relevant nonhuman primate model. Elimination of NP from the vaccine and dose reductions to 1010 rAd particles do not diminish protection and simplify the vaccine, providing the basis for selection of a human vaccine candidate.

How Ebola and Marburg viruses battle the immune system

“…Nucleoprotein alone provided incomplete protection in monkeys infected with MARV, whereas viral glycoprotein by itself (or admixed with nucleoprotein) prevented illness and death in six out of six infected animals 4 . Similarly, the first successes in protecting non-human primates against ZEBOV were with a vaccine containing glycoprotein; subsequent studies showed glycoprotein by itself to be sufficient 64,65 , and there are no published data to indicate that there are any other proteins capable of protecting non-human primates against ZEBOV in the absence of glycoprotein.…”

“…Put most simply, higher doses of vaccine seem to evoke greater total immune responses, along with a protection that is more rapidly acquired and more complete than that obtained with replication-defective vaccines given at much lower doses. A recent report with a recombinant adenovirus that expresses the ZEBOV glycoprotein, in which the minimal protective dose of 10 10 particles is described as a 'low dose' , affirms that protection is dependent on the vaccine dose 65 , and might explain why repliconbased vaccines given at much lower doses have not been uniformly successful 67 and DNA vaccines have been only partially effective 79 . Live vesicular stomatitis virus (VSV) 64 or parainfluenza virus 80,81 recombinants, which show considerable promise in protecting non-human primates from filoviral infection, presumably generate high amounts of viral glycoprotein antigen in vivo.…”

Managing Potential Laboratory Exposure to Ebola Virus by Using a Patient Biocontainment Care Unit1

“…An effective vaccine would reduce inherent hazards in working with these viruses. There have been some recent developments with virus-vectored vaccines with and without naked DNA vaccine priming (29)(30)(31). A phase I human study of such a vaccine is ongoing (32).…”

Ebola vaccines in clinical trial: The promising candidates

“…The rAd5-based Ebola vaccine encoding both the GPs of the EBOV (Kikwit 1995) and SUDV subspecies, which demonstrated a 100% protection in previously assessed NHPs challenging models. 24 31 healthy adults were allocated randomly to receive intramuscular injection of either rAd5-based Ebola vaccine at 2 £ 10 9 vp, or 2 £ 10 10 vp or placebo. The results showed that this rAd5-based Ebola vaccine was able to elicit both specific humoral and cellular immune responses, and the most common adverse reaction is mild and short-lived headache.…”