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Journal of Virology, October 1999, p. 8356-8363, Vol. 73, No. 10
New England Regional Primate Research Center,
Harvard Medical School, Southborough, Massachusetts
01772-91024; Primedica, Worcester,
Massachusetts 016081; Duke University
Medical Center, Department of Surgery, Durham, North Carolina
277102; and AIDS Vaccine Program,
SAIC
Received 3 May 1999/Accepted 9 July 1999
We examined the ability of a live, attenuated deletion mutant of
simian immunodeficiency virus (SIV), SIVmac239
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Protection by Live, Attenuated Simian
Immunodeficiency Virus against Heterologous Challenge
Frederick, NCI
Frederick Cancer Research and Development
Center, Frederick, Maryland 217013
3, which is missing
nef and vpr genes, to protect against challenge
by heterologous strains SHIV89.6p and SIVsmE660. SHIV89.6p is a
pathogenic, recombinant SIV in which the envelope gene has been
replaced by a human immunodeficiency virus type 1 envelope gene; other
structural genes of SHIV89.6p are derived from SIVmac239. SIVsmE660 is
an uncloned, pathogenic, independent isolate from the same primate
lentivirus subgrouping as SIVmac but with natural sequence variation in
all structural genes. The challenge with SHIV89.6p was performed by the
intravenous route 37 months after the time of vaccination. By the
criteria of CD4+ cell counts and disease, strong protection
against the SHIV89.6p challenge was observed in four of four vaccinated
monkeys despite the complete mismatch of env sequences.
However, SHIV89.6p infection was established in all four previously
vaccinated monkeys and three of the four developed fluctuating viral
loads between 300 and 10,000 RNA copy equivalents per ml of plasma 30 to 72 weeks postchallenge. When other vaccinated monkeys were
challenged with SIVsmE660 at 28 months after the time of vaccination,
SIV loads were lower than those observed in unvaccinated controls but
the level of protection was less than what was observed against
SHIV89.6p in these experiments and considerably less than the level of
protection against SIVmac251 observed in previous experiments. These
results demonstrate a variable level of vaccine protection by live,
attenuated SIVmac239
3 against heterologous virus challenge and
suggest that even live, attenuated vaccine approaches for AIDS will
face significant hurdles in providing protection against the natural
variation present in field strains of virus. The results further
suggest that factors other than anti-Env immune responses can be
principally responsible for the vaccine protection by live, attenuated SIV.
*
Corresponding author. Mailing address: New England
Regional Primate Research Center, Harvard Medical School, One Pine Hill Dr., Box 9102, Southborough, MA 01772-9102. Phone: (508) 624-8042. Fax:
(508) 624-8190. E-mail:
ronald_desrosiers{at}hms.harvard.edu.
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