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Journal of Virology, December 2000, p. 11935-11949, Vol. 74, No. 24
AIDS Vaccine Program,
SAIC-Frederick,1 and Basic Research
Laboratory, National Cancer Institute,2
Frederick Cancer Research and Development Center, Frederick,
Maryland 21702-1201; Washington Regional Primate Research
Center, University of Washington, Seattle, Washington
981953; and Animal Sciences Branch,
National Cancer Institute, Bethesda, Maryland
208924
Received 15 September 1999/Accepted 21 September 2000
Molecular clones were constructed that express nucleocapsid (NC)
deletion mutant simian immunodeficiency viruses (SIVs) that are
replication defective but capable of completing virtually all of the
steps of a single viral infection cycle. These steps include production
of particles that are viral RNA deficient yet contain a full complement
of processed viral proteins. The mutant particles are ultrastructurally
indistinguishable from wild-type virus. Similar to a live attenuated
vaccine, this approach should allow immunological presentation of a
full range of viral epitopes, without the safety risks of replicating
virus. A total of 11 Macaca nemestrina macaques were
inoculated with NC mutant SIV expressing DNA, intramuscularly (i.m.) in
one study and i.m. and subcutaneously in another study. Six control
animals received vector DNA lacking SIV sequences. Only modest and
inconsistent humoral responses and no cellular immune responses were
observed prior to challenge. Following intravenous challenge with 20 animal infectious doses of the pathogenic SIV(Mne) in a long-term
study, all control animals became infected and three of four animals
developed progressive SIV disease leading to death. All 11 NC mutant
SIV DNA-immunized animals became infected following challenge but
typically showed decreased initial peak plasma SIV RNA levels compared
to those of control animals (P = 0.0007). In the
long-term study, most of the immunized animals had low or undetectable
postacute levels of plasma SIV RNA, and no CD4+ T-cell
depletion or clinical evidence of progressive disease, over more than 2 years of observation. Although a subset of immunized and control
animals were boosted with SIV(Mne) proteins, no apparent protective benefit was observed. Immunization of macaques with DNA that
codes for replication-defective but structurally complete virions
appears to protect from or at least delay the onset of AIDS after
infection with a pathogenic immunodeficiency virus. With further
optimization, this may be a promising approach for vaccine development.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Protection of Macaca nemestrina from Disease following
Pathogenic Simian Immunodeficiency Virus (SIV) Challenge:
Utilization of SIV Nucleocapsid Mutant DNA Vaccines with and
without an SIV Protein Boost
*
Corresponding author. Mailing address: AIDS Vaccine
Program, SAIC-Frederick, Frederick Cancer Research and Development
Center, Frederick, MD 21702-1201. Phone: (301) 846-1408. Fax: (301)
846-5588. E-mail: arthur{at}avpaxp1.ncifcrf.gov.
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