Absence of detectable viremia in plasma and peripheral blood mononuclear cells from smallpox vaccinees: implications for blood safety.

BACKGROUND: Mass smallpox vaccination with live vaccinia virus has been considered as a preventive measure to counter bioterrorism involving smallpox. This has raised concerns about the possibility of vaccinia virus being transmitted from vaccinated blood donors to recipients. The results of this study could be used to define an appropriate deferral period for blood donors (vaccinated against smallpox) to ensure safety of the blood supply. STUDY DESIGN AND METHODS: A procedure was developed to culture vaccinia virus from plasma and peripheral blood mononuclear cells (PBMNCs) of vaccinees enrolled in three smallpox vaccine clinical trials. A total of 665 plasma and PBMNC samples were obtained from 95 vaccinated subjects. RESULTS: Vaccinia viremia was not detected by virus culture from plasma and PBMNC samples of healthy vaccinees 3 to 56 days after vaccination under our assay conditions. Plasma viremia assay had a sensitivity of approximately 66 plaque-forming units per mL with a Vero cell culture assay. CONCLUSION: The results of this study present evidence that in the case of mass vaccination, the risk of transmission of vaccinia virus by blood transfusion would likely be low.

Development and evaluation of HIV-1 subtype RNA panels for the standardization of HIV-1 NAT assays.

Multiple nucleic acid-based techniques (NAT) have been implemented for testing blood and plasma donors for HIV-1 RNA which may be detected at an earlier stage of infection when HIV antigen or antibody is absent or below the limit of detection of current assays. The available NAT assays are based on different technologies. In order to evaluate the performance of nucleic acid-based techniques (NAT assays) and to allow accurate comparisons of results from different assays, it is essential to have well characterized specimens with known copy numbers as a standard. For this purpose, a comprehensive study was conducted to develop two HIV-1 RNA reference panels. The first (Panel 1) was prepared using a single specimen from the HIV-1 group M subtype B and consists of panel members with a wide range of HIV-1 RNA copy numbers. Panel 2 consists of 26 members representing HIV-1 group M subtypes A, C, D, E, F, G and groups O and N. For accurate determination of HIV-1 RNA copy numbers of each member of Panel 2, they were analyzed using various testing platforms/technologies available through the cooperation of five independent laboratories participating in the study. A consensus value for HIV RNA copy number was assigned to each member of Panel 2 based on statistical analysis of the data provided by the participants. Both panels could serve as reference panels to be used by manufacturers of HIV NAT tests to evaluate the sensitivity limits of their assays.

Computerized morphometric analysis of pathological prion protein deposition in scrapie-infected hamster brain.

Transmissible spongiform encephalopathies (TSEs or prion diseases) are characterized by a constellation of typical though variable pathological changes in the brain. Deposition of disease-associated abnormal prion protein (PrP(Sc)) is the pathological feature of TSEs most consistent and accessible for quantification. However, the evaluation of PrP(Sc) deposits detected by immunohistochemical techniques has been traditionally based on arbitrarily assigned semiquantitative scores. This approach is limited by its subjectivity and bias, yielding considerable variability. In this study, we used MetaMorph 6.1 image analysis software for quantitative analysis of immunostained PrP(Sc) deposits in the CNS of hamsters infected with the 263K strain of scrapie agent. Computerized morphometric analysis (CMA) allowed unambiguous detection of even minimal amounts of immunostained PrP(Sc). CMA values for intensity of staining and area stained correlated well with semiquantitative scores, providing reproducible quantitative data and objective criteria for analyzing PrP(Sc) deposition. CMA provides a simple and reliable method for improved and consistent diagnosis of TSEs that may also be used to quantify other immunostained biomarkers.

The clearance of viruses and transmissible spongiform encephalopathy agents from biologicals.

The viral and transmissible spongiform encephalopathy (TSE) safety of therapeutics of biological origin (biologicals) is greatly influenced by the nature and degree of variability of the source material and by the mode of purification. Plasma-derived and recombinant DNA products currently have good viral safety records, but challenges remain. In general, large enveloped viruses are easier to remove from biologicals than small 'naked' viruses. Monoclonal antibodies and recombinant DNA biopharmaceuticals are derived from relatively homogeneous source materials and purified by multistep schemes that are robust and amenable to scientific analysis and engineering improvement. Viral clearance is more challenging for blood and cell products, as they are complex and labile. Source selection (e.g. country of origin, deferral for CJD risk factors) currently occupies the front line for ensuring that biologicals are free of TSE agents, but robust methods for their clearance from products are under development.

The rat-based neurovirulence safety test for the assessment of mumps virus neurovirulence in humans: an international collaborative study.

Because of the highly neurotropic and neurovirulent properties of wild-type mumps viruses, most national regulatory organizations require neurovirulence testing of virus seeds used in the production of mumps vaccines. Such testing has historically been performed in monkeys; however, some data suggest that testing in monkeys does not necessarily discriminate among the relative neurovirulent risks of mumps virus strains. To address this problem, a collaborative study was initiated by the National Institute for Biological Standards and Control in the United Kingdom and the Food and Drug Administration in the United States, to test a novel rat-based mumps virus neurovirulence safety test. Results indicate that the assay correctly assesses the neurovirulence potential of mumps viruses in humans and is robust and reproducible.

Mouse neurotoxicity test for vaccinia-based smallpox vaccines.

The only US FDA licensed smallpox vaccine, Dryvax, was associated with rare but serious neurological adverse events. After smallpox was eradicated in the United States, mass vaccination ceased in 1971. As counter-bioterrorism/biowarfare measures, new smallpox vaccines are now being investigated. However, there are no established pre-clinical neurotoxicity assays with which to evaluate these new vaccines prior to licensure. Here we report the development and initial characterization of a small animal neurotoxicity assay for vaccinia-based smallpox vaccines using Dryvax virus as a reference vaccine strain and the neuroadapted Western Reserve (WR) strain as a neurotoxic positive control. In neonatally inoculated mice, the WR strain produced significantly greater and more rapid onset of mortality than the Dryvax vaccine reference. Expression of virus antigen in neural cells and infectious virus replication in the brain was also significantly different between the two strains. In addition, the appearance of high titer virus antibody correlated with the clearance of virus from brain. With further validation, this assay incorporating a licensed vaccine reference standard and positive control strain may provide important pre-clinical neurotoxicity data on new vaccinia-based smallpox vaccine strains.