Induction of Protective Immunity to Anthrax Lethal Toxin with a Nonhuman Primate Adenovirus-Based Vaccine in the Presence of Preexisting Anti-Human Adenovirus Immunity

Abstract

) that a single administration of a recombinant serotype 5 adenovirus (Ad) vector expressing anthrax protective antigen (PA) provides rapid protection against anthrax lethal toxin challenge. However, approximately 35 to 50% of humans have preexisting neutralizing antibodies against Ad5. This study assesses the hypothesis that a recombinant adenovirus vaccine based on the nonhuman primate-derived serotype AdC7, against which humans do not have immunity, expressing PA (AdC7PA) will protect against anthrax lethal toxin even in the presence of preexisting anti-Ad5 immunity. Naive and Ad5-immunized BALB/c mice received (intramuscularly) 10 8 to 10 11 particle units (PU) of AdC7PA, Ad5PA (a human serotype Ad5-based vector expressing a secreted form of PA), or AdNull (an Ad5 vector with no transgene). Robust anti-PA immunoglobulin G and neutralizing antibodies were detected by 2 to 4 weeks following administration of AdC7PA to naive or Ad5 preimmunized mice, whereas low anti-PA titers were detected in Ad5-preimmunized mice following administration of Ad5PA. To assess protection in vivo, naive or mice previously immunized against Ad5 were immunized with AdC7PA or Ad5PA and then challenged with a lethal intravenous dose of Bacillus anthracis lethal toxin. Whereas Ad5PA protected naive mice against challenge with B. anthracis lethal toxin, Ad5PA was ineffective in mice that were previously immunized against Ad5. In contrast, AdC7PA functioned effectively not only to protect naive mice but also to protect Ad5-preimmunized mice, with 100% survival after lethal toxin challenge. These data suggest the nonhuman-based vector AdC7PA is an effective vaccine for the development of protective immunity against B. anthracis and importantly functions as a "sero-switch" base for an adenovirus vaccine to function in the context of preexisting anti-Ad immunity.

Protective immunity against botulism provided by a single dose vaccination with an adenovirus-vectored vaccine

“…The cells were incubated at 37°C until the negative wells exhibited 90% cytopathic effect. The neutralizing antibody titer was determined to be the highest dilution wells showing <50% cytopathic effect as previously described [34][35][36].…”

“…Anti-adenovirus neutralizing antibodies were determined according to previously described methods with some modifications [34][35][36]. Briefly, AD293 cells (Stratagene, CA) were seeded in 96-well plates at a density of 10 4 cells/well in 200 μl of Eagle's minimum essential medium (EMEM) containing 10% FBS, 2 mM glutamine, 50 U of penicillin per ml, and 50 μg of streptomycin per ml and incubated at 37°C, 5% CO 2 overnight.…”

Changing the adenovirus fiber for retaining gene delivery efficacy in the presence of neutralizing antibodies

“…34,35 A hexon-switch experiment would help understand whether anti-fiber NAbs are unique with regard to sero-switching for efficacy, or whether the same might be true for any anti-capsid NAb. 36 Moreover, completely non-Ad5 serotypes might be useful, 13,28,37,38 if the appealing attributes of Ad5 (for example, high gene expression, in vivo stability, easy production, safety) can be retained. This should not be taken for granted, as Ad5 has become the single most popular gene therapy vector because of these attributes, and there is no guarantee that they would apply to other serotypes.…”

“…11,12 Because viral serotypes were classically identified based on a lack of cross-reacting antibodies, it is logical that a different serotype can overcome NAb. 13 Moreover, it has been shown that even small changes in the Ad5 fiber knob can allow escape from preexisting capsid-specific NAb. [14][15][16][17] Although further serological studies are definitely needed, it seems that full neutralization requires NAb against all major capsid proteins, such as hexon, penton and fiber, and there may be synergism between them.…”

Assessment of Genetic Shielding for Adenovirus Vectors

“…With respect to utilizing different serotypes, Ad11 and Ad35, to which the human population has a lower prevalence of neutralizing antibodies, have been investigated as alternative vectors to those of Ad5 [1,[5][6][7]. However, other human serotypes such as Ad6 [8], Ad19a [9,10] and Ad41 [11], and adenovirus serotypes from other species are *Address correspondence to this author at the VectorLogics, Inc. 550 11th Street South, Birmingham, Alabama 35294, USA; Tel: (205) 933-8378; Fax: (205) 933-5836; E-mail: ikovesdi@vectorlogics.com also being considered [12][13][14][15][16] as means to overcome preexisting Ad5 immunity. It is also likely that the development of humoral and cellular immune responses against these alternate serotypes will eventually occur.…”