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Journal of Virology, October 2001, p. 9731-9740, Vol. 75, No. 20
Laboratory of Infectious Diseases, National
Institute of Allergy and Infectious Diseases, National Institutes of
Health, Bethesda, Maryland 20892
Received 1 May 2001/Accepted 24 July 2001
A recombinant live attenuated dengue virus type 4 (DEN4) vaccine
candidate, 2A
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.20.9731-9740.2001
Chemical Mutagenesis of Dengue Virus Type 4 Yields
Mutant Viruses Which Are Temperature Sensitive in Vero Cells or Human
Liver Cells and Attenuated in Mice
30, was found previously to be generally well tolerated
in humans, but a rash and an elevation of liver enzymes in the serum
occurred in some vaccinees. 2A
30, a non-temperature-sensitive (non-ts) virus, contains a 30-nucleotide deletion (
30)
in the 3' untranslated region (UTR) of the viral genome. In the present study, chemical mutagenesis of DEN4 was utilized to generate
attenuating mutations which may be useful in further attenuation of the
2A
30 candidate vaccine. Wild-type DEN4 2A virus was grown in Vero
cells in the presence of 5-fluorouracil, and a panel of 1,248 clones were isolated. Twenty ts mutant viruses were identified
that were ts in both simian Vero and human liver HuH-7
cells (n = 13) or only in HuH-7 cells
(n = 7). Each of the 20 ts mutant viruses possessed an attenuation phenotype, as indicated by restricted replication in the brains of 7-day-old mice. The complete nucleotide sequence of the 20 ts mutant viruses identified nucleotide
substitutions in structural and nonstructural genes as well as in the
5' and 3' UTRs, with more than one change occurring, in general, per mutant virus. A ts mutation in the NS3 protein (nucleotide
position 4995) was introduced into a recombinant DEN4 virus possessing the
30 deletion, thereby creating rDEN4
30-4995, a recombinant virus which is ts and more attenuated than rDEN4
30 virus
in the brains of mice. We are assembling a menu of attenuating
mutations that should be useful in generating satisfactorily attenuated recombinant dengue vaccine viruses and in increasing our understanding of the pathogenesis of dengue virus.
*
Corresponding author. Mailing address: LID, NIAID, NIH,
Bldg. 7, Room 100, 7 Center Dr. MSC 0720, Bethesda, MD 20892. Phone: (301) 402-7751. Fax: (301) 496-8312. E-mail:
jblaney{at}niaid.nih.gov.
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