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Infection and Immunity, September 1998, p. 4299-4304, Vol. 66, No. 9
Departments of Microbiology and Oral Biology,
University of Alabama at Birmingham, Birmingham, Alabama 35294
Received 22 December 1997/Returned for modification 7 April
1998/Accepted 23 June 1998
Liposomes appear to be a promising oral antigen delivery system for
the development of vaccines against infectious diseases, although their
uptake efficiency by Peyer's patches in the gut and the subsequent
induction of mucosal immunoglobulin A (IgA) responses remain a major
concern. Aiming at targeted delivery of liposomal immunogens, we have
previously reported the conjugation via a thioether bond of the
GM1 ganglioside-binding subunit of cholera toxin (CTB) to
the liposomal outer surface. In the present study, we have investigated
the effectiveness of liposomes containing the saliva-binding region
(SBR) of Streptococcus mutans AgI/II adhesin and possessing
surface-linked recombinant CTB (rCTB) in generating mucosal (salivary,
vaginal, and intestinal) IgA as well as serum IgG responses to the
parent molecule, AgI/II. Responses in mice given a single oral dose of
the rCTB-conjugated liposomes were compared to those in mice given one
of the following unconjugated liposome preparations: (i) empty
liposomes, (ii) liposomes containing SBR, (iii) liposomes containing
SBR and coadministered with rCTB, and (iv) liposomes containing SBR
plus rCTB. Three weeks after the primary immunization, significantly
higher levels of mucosal IgA and serum IgG antibodies to AgI/II were
observed in the rCTB-conjugated group than in mice given the
unconjugated liposome preparations, although the latter mice received a
booster dose at week 9. The antibody responses in mice immunized with
rCTB-conjugated liposomes persisted at high levels for at least 6 months, at which time (week 26) a recall immunization significantly
augmented the responses. In general, mice given unconjugated liposome
preparations required one or two booster immunizations to develop a
substantial anti-AgI/II antibody response, which was more prominent in
the group given coencapsulated SBR and rCTB. These data indicate that
conjugation of rCTB to liposomes greatly enhances their effectiveness
as an antigen delivery system. This oral immunization strategy should be applicable for the development of vaccines against oral, intestinal, or sexually transmitted diseases.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Effectiveness of Liposomes Possessing
Surface-Linked Recombinant B Subunit of Cholera Toxin as an Oral
Antigen Delivery System
*
Corresponding author. Mailing address: The University
of Alabama at Birmingham, Department of Microbiology, 845 19th St.
South, BBRB 258/5, Birmingham, AL 35294-2170. Phone: (205) 934-3470. Fax: (205) 934-1426. E-mail:
sue_michalek{at}micro.microbio.uab.edu.
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