Recombinant Adenovirus Vector Infection of Human Dendritic Cells

IntroductionRecombinant Adenoviruses (rAd) are widely used as gene delivery vectors in gene therapy and vaccination (Hall et al., 2010, Liu, 2010).These replication incompetent vectors have established safety in humans and possess a number of advantages, such as that high viral titres can be produced efficiently.Several different human rAd types are being intensively investigated in clinical trials for their usefulness.In addition, there is an ever-expanding body of literature covering basic virology of Ad and interactions with host immune and other cells.It is important to understand how rAd vectors interact with specific cells of the immune system in order to improve their clinical efficacy.In particular, studies on the interaction of rAd and professional antigen presenting cells (pAPC), which specialize in recognizing pathogens and initiating a cascade of events that lead to specific immunity, are highly relevant.The most potent type of pAPC are dendritic cells (DC) that possess a unique ability to prime adaptive immune responses (Palucka & Banchereau, 1999, Palucka et al., 2010).rAd vectors likely contact DC early following inoculation and thus these cells may play a major role in regulating immunity towards the vector itself and encoded transgenes.This chapter will include a review of the current literature on the interactions between DC and rAd vectors reported by ourselves and others, in addition to a presentation of novel data.We will first summarize the phenotype and function of specific human DC subsets and methods to isolate or differentiate DC, which are crucial tools to study the interplay of DC and rAd vectors in physiologically relevant systems.Further, we will discuss basic virological aspects of rAd including vector generation and cellular receptor usage among different rAd species.While a multitude of receptors have been described for rAd, we will focus on those relevant for DC.In addition to how rAd vectors bind and infect DC, the extent by which different rAd types infect different DC subsets will be examined.Finally we will give an overview of the functional response of DC to rAd vectors, including maturation, cytokine production, and antigen presentation.Understanding how human DC sense and respond to rAd vectors will assist in guiding the use of these gene delivery vehicles in their many different clinical applications. Human dendritic cells2.1 Function in innate and adaptive immunity DC participate centrally in the initiation of immune responses towards foreign antigen and in this way link the innate and adaptive arms of the immune system (Palucka & Banchereau, www.intechopen.comViral Gene Therapy 150 1999).During the steady state, DC have an immature phenotype, possess high endocytic capacity, and express a diverse array of pathogen recognition receptors (PRR) to sense extracellular and intracellular foreign antigen.Recognition of specific viral nucleic acid signatures by cytosolic and endosomal PRR enables DC to initiate downstream signalling cascades that lead to phenotypic maturation and production of cytokines such as type-1 interferons (IFN) (Pichlmair & Reis e Sousa, 2007).DC activation is also characterized by upregulation of chemokine receptors that facilitate their migration from the periphery to the spleen or lymph nodes, the primary sites for presentation of antigens, to activate antigennaïve T lymphocytes.The morphological and phenotypic changes that occur upon maturation endow DC with a notable capacity to activate lymphocytes in an antigen specific manner (Steinman & Witmer, 1978).Specifically, DC have a unique capacity to present foreign peptides on MHC (major histocompatibility complex) I and II to activate both cytotoxic CD8+ T cells and helper CD4+ T cells, respectively.In addition to efficient induction of antigen-specific T cell responses, DC are also becoming increasingly appreciated for their role in shaping the function of innate immune cells such as NK cells (Medzhitov, 2007).Since DC have a multifaceted role in both innate and adaptive immunity, they likely respond to and influence the efficacy of rAd vector administration.While DC may facilitate the induction of systemic immunity towards vector transgenes, local immune responses may in contrast blunt the desired effect of the delivered gene.Part of the diversity in DC function is attributable to the presence of distinct DC subsets present in blood and other tissues. Overview of DC subsets, phenotype, and functionHuman DC are classified into subsets based on characteristics such as surface phenotype, anatomical location, cytokine and maturation profiles, and the capacity to present antigen to activate antigen specific lymphocytes.In this section, we will describe the phenotypes and functions of subsets of DC derived from human blood and skin. Blood DC subsetsHuman DC from blood can be broadly separated into three distinct subsets: plasmacytoid DC (pDC) and two types of myeloid DC (mDC) (Ueno et al., 2011, Ziegler-Heitbrock et al., 2010) (Table I).These subsets are distinguished by their unique expression of different blood DC antigens (BDCA) (Dzionek et al., 2000, Palucka et al., 2010).mDC are CD1c+ (BDCA-1+), while pDC co-express CD303 (BDCA-2) and CD304 (BDCA-4) (Table I).Another recently identified mDC subset expressing CD141+ (BDCA-3) is notably adept at presenting exogenous foreign peptides on MHC I molecules, in a process termed cross-presentation (Bachem et al., 2010, Crozat et al., 2010, Jongbloed et al., 2010, Poulin et al., 2010).Because there is very limited data on the interaction of rAd vectors and the CD141+ mDC subsets this chapter will focus on pDC and CD1c+ mDC.While mDC and pDC are similar in that they share several classical DC functions, such as mechanisms for efficient uptake of antigen, expression of PRR, ability to phenotypically mature, migrate and activate naïve T cells, they also differ in a number of critical aspects.For example, their expression repertoire of PRR differs.mDC express toll like receptors (TLR) 1 through 8, and 10 whereas pDC express TLR 7 and 9. mDC are generally considered more potent antigen presenting cells, while pDC specialize in the production of rapid and copious type-1 IFN (IFNα/β) and may thus have a particularly important role in viral immunity (Liu, 2005).Both pDC and mDC are also defined as being mostly CD14-(Fig.1).A surrogate for DC of myeloid lineage may www.intechopen.com