Vaccine 22 (2004) 4326–4331 Dendritic cells infected by recombinant modified vaccinia virus Ankara retain immunogenicity in vivo despite in vitro dysfunction Shahriar Behboudi a,∗ , Anne Moore a , Sarah C. Gilbert b , Claire L. Nicoll a , Adrian V.S. Hill a,b a Nuffield Department of Clinical Medicine, John Radcliffe Hospital, University of Oxford, Headington, Oxford OX3 9DU, UK b Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK Received 8 September 2003; accepted 19 April 2004 Abstract The administration of recombinant vaccinia virus Ankara (MVA) encoding a CTL epitope (pb9) from a malaria antigen induced activation and maturation of splenic dendritic cells (DCs) in vivo. In contrast, incubation of immature dendritic cells (iDCs) with the MVA, in vitro, resulted in down-regulation of MHC class I molecules and reduced their T-cell stimulatory ability. However, the ability of the infected DC to induce an antigen-specific CTL response, in vivo, remained intact. Furthermore, the administration of recombinant MVA-infected DC, but not pb9 peptide-pulsed DC, boosted and expanded the anti-pb9 CTL response that was primed by pb9 peptide-pulsed DC. These data indicate that despite the ability of poxviruses to impair DC maturation in vivo, the important ability of MVA to boost CD8 T-cell response in vivo is mediated at the level of the infected dendritic cells. © 2004 Elsevier Ltd. All rights reserved. Keywords: Dendritic cells; Vaccination; Viral vector 1. Introduction Dendritic cells (DCs) are the most potent antigen present- ing cells of the immune system and are crucial to the initiation of a CD8 T-cell lymphocyte response (CTL) to pathogens and tumours. DC exist in two different stages of differentiation: immature and mature. Immature DC express low levels of sur- face molecules such as CD80, CD86, CD40 and MHC class II and have low T-cell stimulatory capacity. Several stimulatory agents such as pro-inflammatory cytokines and viral or bacte- rial products can trigger DC activation and maturation which is defined by up-regulation of co-stimulatory molecules, an increase in the level of IL-12 production and improved capac- ity to stimulate T cells [1,2]. Several vaccination protocols have been applied to target DC and thereby generate a potent immune response to pathogens or tumour antigens. In addi- ∗ Corresponding author. Present address: Institute of Hepatology, University College London, 69–75 Chenies Mews, London WC1E 6HX, UK. Tel.: +44 20 7679 6517; fax: +44 20 7380 0405. E-mail address: s.bedhoudi@ucl.ac.uk (S. Behboudi). tion, DCs have been generated in vitro and re-administered to stimulate a specific, MHC class I-restricted, CTL response. It has been shown that DC pulsed with MHC class I-binding peptides derived from tumour antigens initiate a relatively strong CTL response in patients with cancer [3,4]. There are, however, limitations to the use of DC pulsed with MHC class I-binding peptides. There is induction of a CTL response against the administered DC, resulting in failure of DC to boost the CTL response against the CTL epitope [5]. Vaccinia virus, the prototype poxvirus, is a highly im- munogenic virus and has successfully been used as a vaccine to eradicate smallpox. However, it has been suggested that the infection of DC, in vitro, by vaccinia virus induces DC dysfunction [6]. It has been shown that recombinant vaccinia virus expressing antigens derived from other pathogens in- duces a protective CTL response. It is yet unclear how modi- fied vaccinia Ankara virus (MVA) can induce a CTL response [7], without perturbation of DC function. In this study, we show that the infection of DC with MVA induces DC dys- function in vitro but that the administration of the infected DC induces a potent CTL response in vivo. Furthermore, we 0264-410X/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.vaccine.2004.04.029