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Clinical and Vaccine Immunology, July 2007, p. 926-928, Vol. 14, No. 7
1071-412X/07/$08.00+0 doi:10.1128/CVI.00450-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Mary Hoelscher,1,
Jessica A. Belser,1
Chong Wang,1
Lakshmi Jayashankar,1
Zhu Guo,1
Ross H. Durland,2
Jacqueline M. Katz,1 and
Suryaprakash Sambhara1*
Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia 30333,1 Altea Therapeutics, Tucker, Georgia 300842
Received 20 November 2006/ Returned for modification 9 March 2007/ Accepted 30 April 2007
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Since late 2003, the World Health Organization has reported over 300 laboratory-confirmed cases of human H5N1 virus infection that resulted in over 180 deaths, primarily due to the direct transmission of the virus from infected birds to humans (25). If H5N1 viruses acquire the capacity for sustained human-to-human transmission, a pandemic may be inevitable. Vaccination against influenza virus is the most important public health measure that helps to protect against the annual morbidity and mortality associated with seasonal influenza virus outbreaks. However, the protection conferred by the currently licensed influenza virus vaccines, which offer protection against three circulating human strains, namely, H1N1, H3N2, and B, will not provide protection against H5N1 strains, as the protection induced by annual vaccines is subtype specific. Development of a vaccine against highly pathogenic H5N1 strains poses a number of challenges, such as containment, evaluation of its immunogenicity, the ability to meet the demand, and assurance of an uninterrupted supply of embryonated eggs. The use of vaccines produced by egg-independent technologies, such as tissue culture-derived vaccines and DNA vaccines, may provide a safer approach, but these methods of production are still in the experimental stages (1, 9, 14). Hence, attempts to develop a vaccine against pandemic avian influenza viruses were largely directed toward a recombinant hemagglutinin (rHA)-based approach or an inactivated subunit vaccine. These vaccines were derived from a surrogate nonpathogenic H5N3 virus or inactivated vaccines based on H5N1 reassortant vaccine strains that were generated by plasmid-based reverse genetics technology and that bore the N1 and genetically attenuated H5 glycoproteins and internal genes from A/Puerto Rico/8/34, a strain that grows at a high yield in embryonated eggs. However, when these vaccines were evaluated in humans, they all performed far below expectations, even at high antigen doses (5, 18, 23, 24), perhaps due to the poor immunogenicity of the avian HA.
In the event of a pandemic, effective mass immunization worldwide will require the development of not only more immunogenic and dose-sparing vaccines but also improved vaccine delivery technologies (19). Since a majority of pathogens enter the body through the skin or mucosal surfaces, the skin and mucosa have well-developed pathogen sensors and defenses, including an extensive network of resident professional antigen-presenting cells (3, 13, 22). The primary antigen-presenting cell type found in the epidermis, the Langerhans cell (LC), is a bone marrow-derived dendritic cell. After antigen capture, the activated LCs migrate to the draining lymph node, where they orchestrate potent systemic immune responses. Thus, a route of delivery through the skin offers a potential alternative to the traditional routes through injection for the development of more effective vaccines against pandemic strains. The stratum corneum, the outermost layer of skin, is an effective barrier to the penetration of fluids, large molecules, particles, and microbes. Hence, to deliver the antigen, disruption of this barrier is an absolute requirement. A variety of techniques (such as disruption of the stratum corneum by intradermal injection, by taper stripping, or with sand paper and the use of topical application, ultrasound, microneedles, hydration, and the gene gun) have been shown to deliver antigen through the skin and to generate immune responses with various degrees of success (10, 15, 16, 21). Glenn et al. (6) extended their seminal findings on the transcutaneous delivery of vaccines with adjuvants in BALB/c mice to humans with several phase I human clinical trials (7, 8). In the case of influenza virus, it has been shown that sparing of the vaccine dose can be achieved by the intradermal delivery of a seasonal influenza virus vaccine (2, 12). The translational nature of the studies described above substantiate the usefulness of the mouse model, despite the architectural differences, such as the location of melanocytes, between human skin and mouse skin.
In the present study we evaluated a novel needle-free transdermal patch delivery technology, the PassPort system. Transdermal immunization by use of the PassPort system creates 80 micropores within a 1-cm2 area with a disposable filament attached to an applicator applying an electrical current. This area is covered with a disposable liquid reservoir patch containing the relevant vaccine formulation (4). For transdermal immunization, the abdomens of mice were shaved (
2 cm2), with care taken not to breach the integrity of the skin, 48 h prior to application of the patch. Using the PassPort system, we immunized three groups of female BALB/c mice (10 mice per group; ages, 10 to 12 weeks; Charles River Laboratories, Wilmington, MA) with 3 µg of baculovirus-expressed H5 rHA protein from the A/Hong Kong/156/97 (H5N1; HK/156) virus (Protein Sciences Corporation, Meriden, CT) either alone or with one of two adjuvants: 25 µg of CpG oligodeoxynucleotide (CpG ODN; TCCATGACGTTCCTGATCGT), a Toll-like receptor 9 (TLR9) ligand obtained from GENSET Corp. (La Jolla, CA), or 30 µg of R-848 (resiquimod hydrochloride), a TLR7 ligand purchased from GL Synthesis (Worcester, MA). The fourth group of mice was immunized transdermally with 3 µg of bovine serum albumin (BSA) as a negative control. A fifth group was immunized by intraperitoneal (i.p.) injection of 106 50% egg infective doses (EID50s) of A/DK/Singapore-Q/F119-3/97 (Dk/Sing), an avian influenza H5N3 virus with low pathogenicity, as a positive control. Patches from the transdermally immunized groups were removed after overnight application. After two booster immunizations given at 4-week intervals, sera were collected 3 weeks after the final immunization to assess the development of HK/156 virus-specific hemagglutination-inhibition (HI) antibody by using horse red blood cells, as described previously (20). As shown in Table 1, transdermal immunization with H5HA elicited HI titers that were significant (P < 0.05) compared to the titers obtained for the negative control group immunized transdermally with BSA. Compared to results for the H5HA group, the use of CpG ODN, but not R-848, significantly increased the HI titers (P < 0.05) to levels comparable to those in animals immunized by i.p. injection of live virus.
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TABLE 1. TLR9 ligand (CpG ODN) but not TLR7 ligand (R-848) enhances the immunogenicity of transdermally delivered H5 HA
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6% of their body weight (Fig. 1B) and survived the lethal H5N1 infection, whereas mice vaccinated transdermally with BSA lost an average of >20% of their body weight and succumbed to the H5N1 infection by day 8 postinfection.
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FIG. 1. Transdermal immunization with H5HA plus CpG ODN (a TLR9 ligand) as the adjuvant completely protects mice against morbidity following challenge with a lethal H5N1 virus. Groups of BALB/c mice were immunized transdermally with 3 µg of H5HA protein alone ( ) or with the H5HA protein with 25 µg of CpG ODN ( ) or 30 µg of R-848 ( ). Control animals were immunized transdermally with 3 µg of BSA ( ) or i.p. with 106 EID50s of A/DK/Singapore-Q/F119-3/97 influenza virus (). After two booster immunizations with the same formulation delivered at intervals of 4 weeks, five mice per group were challenged intranasally with 10 LD50s (A) or 50 LD50s (B) of HK/483 virus in 50 µl PBS while they were under light anesthesia. Individual mice were monitored for clinical signs and changes in body weight every day for 14 days. Error bars represent the standard errors of the means.
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Published ahead of print on 9 May 2007. ![]()
S.G. and M.H. contributed equally to the present study. ![]()
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