Vaccine 22 (2004) 1249–1259 Partial protection against infectious bursal disease virus through DNA-mediated vaccination with the VP2 capsid protein and chicken IL-2 genes Diane J. Hulse ∗ , Carlos H. Romero Department of Pathobiology, University of Florida, 2015 SW 16th Ave. Gainesville, FL 32611, USA Received 28 May 2003; received in revised form 3 September 2003; accepted 12 September 2003 Abstract Several DNA vaccination experiments were performed to determine the protective capability of a plasmid DNA molecule encoding the VP2 capsid protein gene of infectious bursal disease virus (IBDV) injected into chickens in the presence or absence of chicken interleukin 2 (IL-2) plasmid DNA. The results of these experiments indicate that partial protection against IBDV can be achieved by using the VP2 gene of IBDV as a DNA vaccine. Furthermore, the simultaneous injection of chicken IL-2 plasmid DNA significantly increased the protection after challenge with the virulent strain. It was also found that immunological tolerance may have been induced in one of the chicken experiments by vaccination with plasmid DNA. © 2003 Elsevier Ltd. All rights reserved. Keywords: DNA Vaccination; IBDV; Chicken interleukin 2 1. Introduction Infectious bursal disease virus (IBDV) causes an impor- tant disease of young chickens which targets the bursa of Fabricius [14]. Virulent IBDV destroys developing B lym- phocytes, reducing the peripheral pool of B cells available to respond against infections, thus leaving the chickens immunosuppressed. Chickens worldwide are constantly ex- posed to IBDV, suffering infections that cost the poultry industry billions of dollars in losses. IBDV is classified within the Birnaviridae family [4]. The double stranded RNA genome is comprised of two segments: Segment A and Segment B [1]. The larger open reading frame, Segment A, encodes for a long polypeptide repre- sented as N-VPX-VP4-VP3-C [1]. The precursor polypro- tein is processed by a series of post-translational proteolytic cleavage steps to yield mature virion proteins [2,11]. VPX is further processed by VP4, the viral protease, to produce VP2. VP2 is considered to be the major host-protective anti- gen, and at least two neutralizing epitopes were found to be located on this peptide [2,3,8]. Therefore, VP2 is of major interest in the development of new vaccines against IBDV. Chickens infected with IBDV develop a strong anti-IBDV neutralizing antibody response which is critical for disease ∗ Corresponding author. E-mail address: diane.hulse@stjude.org (D.J. Hulse). recovery [17]. Because of this, vaccination against IBDV has been focused primarily on developing strong humoral immune responses. However, recent studies looking at the importance of T-cells in IBDV pathogenesis have shown that cell-mediated immunity may be more important in IBDV in- fections than previously thought [19]. Replication of IBDV in the bursa of Fabricius is accompanied by a large infil- tration of CD4+ and CD8+ T-cells in this organ [15,24]. Rautenschlein et al. [19] found that T-cells in the bursa of Fabricius during IBDV infection affect pathogenesis in two ways: By limiting viral replication and by promoting bursal tissue damage and recovery, possibly through the release of inflammatory cytokines and cell-mediated cytotoxicity. Immunization with DNA-based plasmids has been suc- cessfully attempted in chickens for a variety of infectious diseases including influenza, Newcastle disease, and IBD [5,9,20,21,27]. DNA vaccines can be delivered into the host by several routes, the most common being by intramuscular injection [28]. The exact mechanism of DNA up-take by cells is poorly understood and, therefore, it is not known why muscle cells seem to be the most efficient target cell transfected [27]. Antigen expressed from DNA injection is displayed to the cell surface in association with major his- tocompatibility complex class I (MHC-I) molecules, similar to what occurs during natural viral infection [10]. As vacci- nation with DNA results in the antigen being processed and presented in the context of MHC-I, one of the potentially 0264-410X/$ – see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.vaccine.2003.09.021