Mechanism of Ad5 Vaccine Immunity and Toxicity: Fiber Shaft Targeting of Dendritic Cells

Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
PLoS Pathogens (Impact Factor: 8.06). 03/2007; 3(2):e25. DOI: 10.1371/journal.ppat.0030025
Source: PubMed

ABSTRACT Recombinant adenoviral (rAd) vectors elicit potent cellular and humoral immune responses and show promise as vaccines for HIV-1, Ebola virus, tuberculosis, malaria, and other infections. These vectors are now widely used and have been generally well tolerated in vaccine and gene therapy clinical trials, with many thousands of people exposed. At the same time, dose-limiting adverse responses have been observed, including transient low-grade fevers and a prior human gene therapy fatality, after systemic high-dose recombinant adenovirus serotype 5 (rAd5) vector administration in a human gene therapy trial. The mechanism responsible for these effects is poorly understood. Here, we define the mechanism by which Ad5 targets immune cells that stimulate adaptive immunity. rAd5 tropism for dendritic cells (DCs) was independent of the coxsackievirus and adenovirus receptor (CAR), its primary receptor or the secondary integrin RGD receptor, and was mediated instead by a heparin-sensitive receptor recognized by a distinct segment of the Ad5 fiber, the shaft. rAd vectors with CAR and RGD mutations did not infect a variety of epithelial and fibroblast cell types but retained their ability to transfect several DC types and stimulated adaptive immune responses in mice. Notably, the pyrogenic response to the administration of rAd5 also localized to the shaft region, suggesting that this interaction elicits both protective immunity and vector-induced fevers. The ability of replication-defective rAd5 viruses to elicit potent immune responses is mediated by a heparin-sensitive receptor that interacts with the Ad5 fiber shaft. Mutant CAR and RGD rAd vectors target several DC and mononuclear subsets and induce both adaptive immunity and toxicity. Understanding of these interactions facilitates the development of vectors that target DCs through alternative receptors that can improve safety while retaining the immunogenicity of rAd vaccines.

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Available from: Rebecca L Sheets, Aug 12, 2015
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    • "In fact, we have found that the toxicity profiles are quite similar and consistent, although Ad35 may be slightly less reactogenic systemically at the doses tested. This is consistent with our recent report in which we demonstrated that even when the fiber shaft of Ad5 vectors are modified to eliminate binding to the primary CAR or the secondary integrin RGD receptor or are switched with the fiber shaft of Ad35 (which utilizes CD46 as a receptor), they retain their ability to transfect, through a heparin-sensitive receptor, several dendritic cell and mononuclear cell subtypes, and they retain their pyrogenicity (Cheng et al., 2007), inducing both adaptive immunity and toxicity (pyrogenicity). "
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    ABSTRACT: Thesis (Ph.D.)--University of Rochester. School of Medicine and Dentistry. Dept. of Microbiology and Immunology, 2007. Helper-free herpes simplex virus type-1 (HSV-1) amplicon vectors are replicationdefective, “gutless” plasmid-based gene transfer vectors that possess compelling advantages as potential vaccine delivery platforms. These advantages include: a favorable safety profile due to the lack of expression of virally-encoded immunomodulatory genes, the capacity to encode large amounts of foreign DNA and a broad host cell tropism - including the ability to directly transduce antigen presenting cells such as dendritic cells. Previous work from our laboratory has shown that a single injection of a helper-free HSV-1 amplicon vector can elicit potent and durable immune responses to an encoded HIV antigen, even in the face of preexisting immunity to HSV. The focus of this thesis was a three-pronged examination of the hypothesis that it might be possible to maximize HSV-1 amplicon vector-induced immune responses to encoded HIV-1 antigens by further optimizing antigen design and vector delivery strategies. As an initial focus, amplicons encoding a modified HIV-1 clade C Env antigen were generated and tested, in vivo, to determine whether addition of an immunodominant CTL tag had any effect on the antigen-specific CD8+ T cell response. This study showed that immunization of mice with an amplicon vector encoding the tagged envelope protein elicited potent and detectable cellular immune responses. Planned follow-up experiments on the immune response to amplicon vectors encoding multiple Env antigens were abandoned when other investigators published similar studies. The second focus of the thesis was a determination of whether the volume of buffer (and the associated route of delivery)in which a fixed dose of amplicon encoding a model HIV-1 antigen (gp120) is delivered might affect the CD8+T-cell immune response to amplicon encoded antigens. The underlying rationale was that a larger inoculum volume might result in higher levels of non-specific immune activation due to minor tissue damage, and more broad dissemination of the vector. This study revealed that the inoculum volume had a minimal effect on the measured immune response to either recombinant adenovirus serotype 5 (rAd5) or HSV-1 amplicon vectors encoding a model HIV-1 antigen. The third focus of this thesis was a multilayered examination of the magnitude and quality of CD4+ and CD8+ T-cell immune responses elicited by a heterologous prime boost regimen combining HSV-1 amplicon and rAd5 vectors that encoded the same HIV-1 antigen (gp120). A careful comparison of the magnitude and quality of the T cell response that was elicited, at acute and late time points, following immunization with HSV-1 amplicon and rAd5 vectors showed that HSV-1 amplicon vectors and rAd5 vectors that encoded gp120 from the same transcriptional regulatory element elicited primary T cell responses that were similar both in magnitude and quality. In contrast, HSV-1 amplicon vectors that incorporated different promoter elements upstream of gp120 elicited qualitatively and quantitatively distinct antigenspecific T cell response profiles. Further, the heterologous combination of a rAd5 vector prime and a HSV-1 amplicon vector boost was found to yield the best combination of cellular immune response magnitude and quality. Taken together, these findings point the way forward to novel and more effective use of the HSV-1 amplicon vector system for HIV-1 vaccine development.
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