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Journal of Virology, November 2000, p. 9987-9993, Vol. 74, No. 21
Center for Blood Research, Harvard Medical
School, Boston Massachusetts 02115,1 and
Department of Microbiology, University of Pennsylvania School
of Medicine, Philadelphia, Pennsylvania 191042
Received 2 March 2000/Accepted 8 August 2000
Induction of cell-mediated immunity may be essential for an
effective AIDS vaccine. Listeria monocytogenes is an
attractive bacterial vector to elicit T-cell immunity to human
immunodeficiency virus (HIV) because it specifically infects monocytes,
key antigen-presenting cells, and because natural infection originates
at the mucosa. Immunization with recombinant L. monocytogenes has been shown to protect mice from lymphocytic
choriomeningitis virus, influenza virus, and tumor inoculation.
L. monocytogenes expressing HIV gag elicits
sustained high levels of Gag-specific cytotoxic T lymphocytes (CTLs) in
mice. We have examined the ability of Listeria to infect
human monocytes and present HIV antigens to CD8 T lymphocytes of
HIV-infected donors to induce a secondary T-cell immune response. Using
this in vitro vaccination protocol, we show that L. monocytogenes expressing the HIV-1 gag gene
efficiently provides a strong stimulus for Gag-specific CTLs in
HIV-infected donor peripheral blood mononuclear cells.
Listeria expressing Nef also elicits a secondary in vitro anti-Nef CTL response. Since L. monocytogenes is a
pathogen, before it can be seriously considered as a human vaccine
vector, safety concerns must be addressed. We therefore have produced a
highly attenuated strain of L. monocytogenes that requires
D-alanine for viability. The recombinant bacteria are
attenuated at least 105-fold. We show that when these
hyperattenuated bacteria are engineered to express HIV-1 Gag, they are
at least as efficient at stimulating Gag-specific human CTLs in vitro
as wild-type recombinants. These results suggest that attenuated
Listeria is an attractive candidate vaccine vector to
induce T-cell immunity to HIV in humans.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Induction of Human Immunodeficiency Virus
(HIV)-Specific CD8 T-Cell Responses by Listeria
monocytogenes and a Hyperattenuated Listeria Strain
Engineered To Express HIV Antigens

*
Corresponding author. Mailing address: Center for Blood
Research, 800 Huntington Ave., Boston, MA 02115. Phone: (617) 278-3381. Fax: (617) 278-3493. E-mail:
lieberman{at}cbr.med.harvard.edu.
Present address: Department of Immunology, Corixa Corporation,
Seattle, WA 98104.
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