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Infection and Immunity, January 2000, p. 54-63, Vol. 68, No. 1
Institute for Biological Sciences, National
Research Council of Canada, Ottawa, Ontario, Canada K1A 0R6
Received 1 July 1999/Returned for modification 26 August
1999/Accepted 19 October 1999
Ether glycerolipids extracted from various archaeobacteria were
formulated into liposomes (archaeosomes) possessing strong adjuvant
properties. Mice of varying genetic backgrounds, immunized by different
parenteral routes with bovine serum albumin (BSA) entrapped in
archaeosomes (~200-nm vesicles), demonstrated markedly enhanced serum
anti-BSA antibody titers. These titers were often comparable to those
achieved with Freund's adjuvant and considerably more than those with
alum or conventional liposomes
(phosphatidylcholine-phosphatidylglycerol-cholesterol, 1.8:0.2:1.5
molar ratio). Furthermore, antigen-specific immunoglobulin G1 (IgG1),
IgG2a, and IgG2b isotype antibodies were all induced. Association of
BSA with the lipid vesicles was required for induction of a strong
response, and >80% of the protein was internalized within most
archaeosome types, suggesting efficient release of antigen in vivo.
Encapsulation of ovalbumin and hen egg lysozyme within archaeosomes
showed similar immune responses. Antigen-archaeosome immunizations also
induced a strong cell-mediated immune response: antigen-dependent
proliferation and substantial production of cytokines gamma interferon
(Th1) and interleukin-4 (IL-4) (Th2) by spleen cells in vitro. In
contrast, conventional liposomes induced little cell-mediated immunity,
whereas alum stimulated only an IL-4 response. In contrast to alum and
Freund's adjuvant, archaeosomes composed of Thermoplasma
acidophilum lipids evoked a dramatic memory antibody response to
the encapsulated protein (at ~300 days) after only two initial
immunizations (days 0 and 14). This correlated with increased
antigen-specific cell cycling of CD4+ T cells: increase in
synthetic (S) and mitotic (G2/M) and decrease in resting
(G1) phases. Thus, archaeosomes may be potent vaccine carriers capable of facilitating strong primary and memory humoral, and
cell-mediated immune responses to the entrapped antigen.
0019-9567/0/$04.00+0
Archaeosome Vaccine Adjuvants Induce Strong Humoral,
Cell-Mediated, and Memory Responses: Comparison to Conventional
Liposomes and Alum
*
Corresponding author. Mailing address: Institute for
Biological Sciences, National Research Council of Canada, 100 Sussex Dr., Room 3016, Ottawa, Ontario, Canada K1A 0R6. Phone: (613) 991-6371. Fax: (613) 952-9092. E-mail: lakshmi.krishnan{at}nrc.ca.
National Research Council of Canada publication no. 40403.
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