Toxicological Safety Evaluation of DNA Plasmid Vaccines against HIV-1, Ebola, Severe Acute Respiratory Syndrome, or West Nile Virus Is Similar Despite Differing Plasmid Backbones or Gene-Inserts

U.S. Public Health Service, Vaccine Production Program, NIH/NIAID/Vaccine Research Center, Bethesda, Maryland 20892-7628, USA.
Toxicological Sciences (Impact Factor: 3.85). 07/2006; 91(2):620-30. DOI: 10.1093/toxsci/kfj170
Source: PubMed


The Vaccine Research Center has developed a number of vaccine candidates for different diseases/infectious agents (HIV-1, Severe Acute Respiratory Syndrome virus, West Nile virus, and Ebola virus, plus a plasmid cytokine adjuvant-IL-2/Ig) based on a DNA plasmid vaccine platform. To support the clinical development of each of these vaccine candidates, preclinical studies were performed to screen for potential toxicities (intrinsic and immunotoxicities). All treatment-related toxicities identified in these repeated-dose toxicology studies have been confined primarily to the sites of injection and seem to be the result of both the delivery method (as they are seen in both control and treated animals) and the intended immune response to the vaccine (as they occur with greater frequency and severity in treated animals). Reactogenicity at the site of injection is generally seen to be reversible as the frequency and severity diminished between doses and between the immediate and recovery termination time points. This observation also correlated with the biodistribution data reported in the companion article (Sheets et al., 2006), in which DNA plasmid vaccine was shown to remain at the site of injection, rather than biodistributing widely, and to clear over time. The results of these safety studies have been submitted to the Food and Drug Administration to support the safety of initiating clinical studies with these and related DNA plasmid vaccines. Thus far, standard repeated-dose toxicology studies have not identified any target organs for toxicity (other than the injection site) for our DNA plasmid vaccines at doses up to 8 mg per immunization, regardless of disease indication (i.e., expressed gene-insert) and despite differences (strengths) in the promoters used to drive this expression. As clinical data accumulate with these products, it will be possible to retrospectively compare the safety profiles of the products in the clinic to the results of the repeated-dose toxicology studies, in order to determine the utility of such toxicology studies for signaling potential immunotoxicities or intrinsic toxicities from DNA vaccines. These data build on the biodistribution studies performed (see companion article, Sheets et al., 2006) to demonstrate the safety and suitability for investigational human use of DNA plasmid vaccine candidates for a variety of infectious disease prevention indications.

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Available from: Rebecca L Sheets, Oct 08, 2014
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    • "Mean spleen weights were increased after three doses of either vaccine, which corresponded in some animals with enlargements of the white pulp, due to generation or growth of germinal centers. This effect likely resulted from immune activation of the secondary lymphoid organs by the vaccines, which has also been observed in other preclinical studies (Sheets et al. 2006; Speijers et al. 1988). It is less likely that local virus replication in these organs has caused the increased spleen weights, as no clear relationship between increased spleen weights, enlargements of the white pulp and the presence of viral RNA in the spleens could be established. "
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    • "Unlike the live hybrid viral systems or attenuated vaccines, DNA vaccines do not demonstrate reactogenicity, pathogenicity, or genetic instability. DNA vaccines have low allergenicity because of their high purity and low antigenic load [5]. It is hypothesized that cytotoxic T lymphocytes (CTLs) are capable of protecting the host against HIV infection because they kill HIV-infected cells before they can produce new virions [6] and, furthermore, because they release chemokines that inhibit HIV infection [7]. "
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