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Infection and Immunity, June 2001, p. 3897-3905, Vol. 69, No. 6
Malaria Program, Naval Medical Research
Center, Silver Spring, Maryland 20910-75001;
Department of Molecular Microbiology and Immunology, School of
Public Health, The Johns Hopkins University, Baltimore, Maryland
212052; Department of Microbiology and
Immunology, University of Maryland, Baltimore, Maryland
212013; and Henry M. Jackson Foundation
for the Advancement of Military Medicine, Rockville, Maryland
208524
Received 13 December 2000/Returned for modification 29 January
2001/Accepted 19 March 2001
The gene encoding the 60-kDa heat shock protein of Plasmodium
yoelii (PyHsp60) was cloned into the VR1012 and VR1020 mammalian expression vectors. Groups of 10 BALB/c mice were immunized
intramuscularly at 0, 3, and 9 weeks with 100 µg of PyHsp60 DNA
vaccine alone or in combination with 30 µg of pmurGMCSF. Sera from
immunized mice but not from vector control groups recognized P. yoelii sporozoites, liver stages, and infected erythrocytes in an
indirect fluorescent antibody test. Two weeks after the last
immunization, mice were challenged with 50 P. yoelii
sporozoites. In one experiment the vaccine pPyHsp60-VR1012 used in
combination with pmurGMCSF gave 40% protection (Fisher's exact test;
P = 0.03, vaccinated versus control groups). In a
second experiment this vaccine did not protect any of the immunized
mice but induced a delay in the onset of parasitemia. In neither
experiment was there any evidence of a protective effect against the
asexual erythrocytic stage of the life cycle. In a third experiment
mice were primed with PyHsp60 DNA, were boosted 2 weeks later with
2 × 103 irradiated P. yoelii sporozoites,
and were challenged several weeks later. The presence of PyHsp60 in the
immunization regimen did not lead to reduced blood-stage infection or
development of parasites in hepatocytes. PyHsp60 DNA vaccines were
immunogenic in BALB/c mice but did not consistently, completely protect
against sporozoite challenge. The observation that in some of the
PyHsp60 DNA vaccine-immunized mice there was protection against
infection or a delay in the onset of parasitemia after sporozoite
challenge deserves further evaluation.
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.6.3897-3905.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Immunogenicity and Protective Efficacy of a
Plasmodium yoelii Hsp60 DNA Vaccine in BALB/c Mice

*
Corresponding author. Mailing address: Celera Genomics,
45 West Gude Dr., Rockville, MD 20850. Phone: (240) 453-3580. Fax: (240) 452-4580. E-mail: stephen.hoffman{at}celera.com.
Present address: BIOGENESIS
Immunovirología, Facultad de
Medicina, Universidad de Antioquia, A.A. 1226, Medellín, Colombia.
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