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Infection and Immunity, February 2004, p. 1181-1183, Vol. 72, No. 2
0019-9567/04/$08.00+0 DOI: 10.1128/IAI.72.2.1181-1183.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Needle-Free Skin Patch Vaccination Method for Anthrax
Gary R. Matyas,1* Arthur M. Friedlander,2 Gregory M. Glenn,3 Stephen Little,2 Jianmei Yu,3 and Carl R. Alving1
Department of Membrane Biochemistry, Walter Reed Army Institute of Research, Silver Spring, Maryland 20910,1
U.S. Army Medical Research Institute of Infectious Diseases, Fort Detrick, Frederick, Maryland 21702,2
Iomai Corporation, Gaithersburg, Maryland 208783
Received 15 August 2003/
Returned for modification 7 November 2003/
Accepted 14 November 2003

ABSTRACT
Three immunizations of mice with recombinant protective antigen
(rPA) by transcutaneous immunization (TCI) induced long-term
neutralizing antibody titers that were superior to those obtained
with aluminum-adsorbed rPA. In addition, rPA alone exhibited
adjuvant activity for TCI. Forty-six weeks after completion
of TCI, 100% protection was observed against lethal anthrax
challenge.

INTRODUCTION
Transcutaneous immunization (TCI) is a procedure that relies
on application of antigen and associated adjuvant onto the outer
layer of the skin and subsequent delivery to underlying Langerhans
cells that serve as antigen-presenting cells (
4). A variety
of adjuvants have shown effectiveness in stimulating immunity
by TCI, but the most widely used and most effective adjuvants
have been members of the ADP-ribosylating bacterial exotoxins,
such as cholera toxin or heat-labile enterotoxin (HLT) from
Escherichia coli (
13).
Two days prior to immunization, hair was shaved on the backs of female A/J mice (12 weeks old) purchased from the Jackson Laboratory (Bar Harbor, Maine). Recombinant protective antigen (rPA; 20 µg) (Monoclonal Antibody/Recombinant Protein Production Facility-Science Applications International Corporation, National Cancer Institute-Frederick Cancer Research and Development Center) was mixed with the indicated doses of HLT in phosphate-buffered saline (purchased from Berna Biotech, Bern, Switzerland) and applied to gauze patches placed on the backs of mice overnight. The backs were shaved 1 to 2 days prior to application of the patch. The site was hydrated with saline-soaked gauze and mildly abraded by being brushed 10 times with emery paper (GE Medical Systems, Milwaukee, Wis.) prior to patch application. Control groups consisted of HLT alone, rPA alone, or intramuscular (i.m.) immunization with 10 µg of rPA mixed with aluminum hydroxide (0.1 mg of Al3+ Rehydrogel HPA; Reheis Inc., Berkeley Heights, N.J.). Animals were bled, and sera were assayed for rPA antibodies by enzyme-linked immunosorbent assay (ELISA), as described previously (7, 9). Antiserum neutralization of Bacillus anthracis lethal toxin cytotoxicity was determined by measuring the viability of 6 x 104 J774A.1 cells in the presence of lethal toxin (100 ng of PA/ml plus 50 ng of lethal factor/ml) (10). At week 50, the mice were challenged subcutaneously with 1,000 50% lethal doses (LD50) of B. anthracis Sterne strain spores (1).
As shown in Fig. 1A, over a period of 47 weeks 100% of mice immunized with rPA by TCI with HLT as an adjuvant responded with strong antibody titers after applications of vaccine at 0, 2, and 4 weeks. All of the mice responded briskly even after a single immunization. During the 43 weeks after the last immunization the titers initially rose further and then declined gradually (less than a log) to the end of the observation period. A similar pattern, except for a more rapid rise in titer at 4 weeks, was obtained after control i.m. injection with rPA adsorbed to aluminum hydroxide (Fig. 1B).
At the end of 47 weeks, ELISA antibody titers of mice that received
different amounts of HLT as an adjuvant were measured (Fig.
2A). Maximal adjuvant activity of the HLT was reached even with
0.4 µg of HLT, and the antibody titer was not significantly
increased with higher amounts of HLT. Figure
2A also illustrates
the interesting finding that rPA by itself, not previously known
as an adjuvant for inducing antibodies, had significant activity
without additional adjuvant for induction of antibodies to PA
by TCI. The strength of immunization with rPA alone was less
than that observed after TCI with rPA combined with HLT as an
additional adjuvant, and as shown in Fig.
2B, neutralizing antibody
titers were much lower when HLT was not present. Neutralizing
antibody titers of aluminum-adsorbed rPA were also much lower
than those observed after TCI with rPA and HLT.
As shown in Table
1, at every level of HLT employed, TCI resulted
in 100% protection 46 weeks after the last immunization following
lethal challenge at week 50 with
B. anthracis spores. The protection
by TCI was identical to the protection observed after i.m. injection
with aluminum-adsorbed rPA, which served as a positive control.
The negative-control group that received no immunization confirmed
that the challenge employed was 100% lethal. It is noteworthy
that immunization with rPA alone, where rPA was used as an antigen
without additional adjuvant, also resulted in 100% protection.
From these data it is evident that, under the conditions employed,
TCI resulted in protective immunity that was at least equivalent
to that obtained after i.m. immunization with aluminum-adsorbed
antigen. Furthermore, if neutralizing antibody titers were important
for protection, as previously suggested (
12), TCI would be expected
to be a stronger immunization strategy. These data are consistent
with the previous observation that anti-PA immunoglobulin G
(IgG) is a significant in vitro correlate of survival after
lethal challenge with inhalational anthrax (
10).
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TABLE 1. Survival of mice challenged by subcutaneous injection with 1,000 LD50 of B. anthracis Sterne strain spores
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The present anthrax vaccines that are licensed in the United
States and United Kingdom have been subjected to criticisms
for numerous real or perceived suboptimal features and for frequency
of adverse events (
8). The vaccines are incompletely characterized
and are also difficult to characterize; they are locally reactogenic
like other aluminum-containing vaccines, and the dose schedule
is long (
2,
8). Aluminum adjuvants have the limitations of being
associated with occasional severe local reactions such as erythema,
IgE induction, contact hypersensitivity, and granulomatous inflammation,
and they are not biodegradable and remain at the site of injection
for up to a year (
6). Subcutaneous nodules that can last for
weeks are often found after subcutaneous injection of aluminum-containing
vaccines, including the U.S. licensed anthrax vaccine (
6,
11).
Although aluminum adjuvants are usually viewed as relatively
safe, large-scale vaccination might gain better acceptance if
a less reactogenic potent adjuvant were used along with an improved
immunization strategy.
The TCI vaccine strategy proposed in this study utilizes a recombinant protein (rPA), lacks aluminum adjuvant, is administered without injection, uses a potent adjuvant (HLT) that has a good safety record when administered with TCI in humans (3, 5), induces specific antibody titers that are at least equivalent to those observed after i.m. injection of aluminum-adsorbed rPA, and causes long-lived (at least 47 weeks) protective immunity against lethal (1,000-LD50) anthrax challenge.

ACKNOWLEDGMENTS
We acknowledge the excellent technical assistance of Elaine
Morrison for her work with the laboratory animals.
Research was conducted in compliance with the Animal Welfare Act and other federal statutes and regulations relating to animals and experiments involving animals and adheres to principles stated in the Guide for the Care and Use of Laboratory Animals, National Research Council publication, 1996 edition.
This work was performed under a Cooperative Research and Development Agreement between Walter Reed Army Institute of Research, Silver Spring, Md., and Iomai Corporation, Gaithersburg, Md. Funding for the study was provided by the Biological Defense Research Program, U.S. Army Medical Research and Materiel Command, Fort Detrick, Md., and Iomai Corporation.
The information contained herein reflects the views of the authors and should not be construed to represent those of the Department of the Army or the Department of Defense.

FOOTNOTES
* Corresponding author. Mailing address: Department of Membrane Biochemistry, Walter Reed Army Institute of Research, 503 Robert Grant Ave., Silver Spring, MD 20910-7500. Phone: (301) 319-9477. Fax: (301) 319-9035. E-mail:
gary.matyas{at}na.amedd.army.mil.

Editor: A. D. O'Brien

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Infection and Immunity, February 2004, p. 1181-1183, Vol. 72, No. 2
0019-9567/04/$08.00+0 DOI: 10.1128/IAI.72.2.1181-1183.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
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