title: Conditional lethality yields a new vaccine strain of Listeria monocytogenes for the induction of cell-mediated immunity.
abstract: Listeria monocytogenes is a gram-positive intracellular pathogen that can enter phagocytic and nonphagocytic cells and colonize their cytosols. Taking advantage of this property to generate an intracellular vaccine delivery vector, we previously described a mutant strain of L. monocytogenes, Deltadal Deltadat, which is unable to synthesize cell wall by virtue of deletions in two genes (dal and dat) required for d-alanine synthesis. This highly attenuated strain induced long-lived protective systemic and mucosal immune responses in mice when administered in the transient presence of d-alanine. We have now increased the usefulness of this organism as a vaccine vector by use of an inducible complementation system that obviates the need for exogenous d-alanine administration. The strain expresses a copy of the Bacillus subtilis racemase gene under the control of a tightly regulated isopropyl-beta-d-thiogalactopyranoside (IPTG)-inducible promoter present on a multicopy plasmid. This bacterium demonstrates strict dose-dependent growth in the presence of IPTG. After removal of inducer, bacterial growth ceased within two replication cycles. Following infection of mice in the absence of IPTG or d-alanine, the bacterium survived in vivo for less than 3 days. Nevertheless, a single immunization elicited a state of long-lasting protective immunity against wild-type L. monocytogenes and induced a subset of effector listeriolysin O-specific CD11a(+) CD8(+) T cells in spleen and other tissues that was strongly enhanced after secondary immunization. This improved L. monocytogenes vector system may have potential use as a live vaccine against human immunodeficiency virus, other infectious diseases, and cancer.
authors.affiliation: 203C Johnson Pavilion, 3610 Hamilton Walk, Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
authors.forename: Zhongxia
authors.initials: Z
authors.lastname: Li
authors.forename: Xinyan
authors.initials: X
authors.lastname: Zhao
authors.forename: Darren E
authors.initials: DE
authors.lastname: Higgins
authors.forename: Fred R
authors.initials: FR
authors.lastname: Frankel
mesh_terms: D000411:Alanine Racemase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001428:Bacterial Vaccines / Q000276:immunology* / Q000494:pharmacology; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D005347:Fibroblasts / Q000382:microbiology; D007111:Immunity, Cellular / Q000187:drug effects / Q000276:immunology; D008089:Listeria monocytogenes / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000276:immunology*; D008088:Listeriosis / Q000276:immunology / Q000517:prevention & control; D051379:Mice; D009154:Mutation
chemical_list: D001428:Bacterial Vaccines; D000411:Alanine Racemase