Protective efficacy of a recombinant vaccinia virus in vaccinia-immune mice

Influenza vaccines and vaccination strategies in birds

Although it is well accepted that the present Asian H5N1 panzootic is predominantly an animal health problem, the human health implications and the risk of human pandemic have highlighted the need for more information and collaboration in the field of veterinary and human health. H5 and H7 avian influenza (AI) viruses have the unique property of becoming highly pathogenic (HPAI) during circulation in poultry. Therefore, the final objective of poultry vaccination against AI must be eradication of the virus and the disease. Actually, important differences exist in the control of avian and human influenza viruses. Firstly, unlike human vaccines that must be adapted to the circulating strain to provide adequate protection, avian influenza vaccination provides broader protection against HPAI viruses. Secondly, although clinical protection is the primary goal of human vaccines, poultry vaccination must also stop transmission to achieve efficient control of the disease. This paper addresses these differences by reviewing the current and future influenza vaccines and vaccination strategies in birds.

PREPS and L-particles: a new approach to virus-like particle vaccines

Conventional virus-like particles are usually composed of a single structural protein which spontaneously assembles into particles. L-particles, a little-known type of virus-like particle, are produced as part of the natural infectious process of many, if not all, alpha-herpesviruses. L-particles lack the nucleocapsid present in the infectious virion but contain all of the virus envelope and tegument proteins. L-particles contain no virus DNA and are noninfectious, though they are biologically competent, since they are capable of delivering viral envelope and tegument proteins to cells. When cells are infected with herpes simplex virus Type 1 under conditions where viral DNA synthesis is blocked, previral DNA replication enveloped particles are produced. These are similar to L-particles, but differ slightly in protein composition. This article reviews the available data regarding these vaccine candidates and explores the wide-ranging potential applications, including vaccine candidates against infectious diseases and cancer, as well as a protein delivery vector.

Preexisting immunity to poliovirus does not impair the efficacy of recombinant poliovirus vaccine vectors

Recombinant viruses are attractive candidates for the development of novel vaccines. A number of viruses have been engineered as vaccine vectors to express antigens from other pathogens or tumors. Inoculation of susceptible animals with this type of recombinant virus results in the induction of both humoral and cellular immune responses directed against the foreign antigens. A general problem to this approach is that existing immunity to the vector can diminish or completely abolish the efficacy of the viral vector. In this study, we investigated whether poliovirus recombinants are capable of inducing effective immunity to the foreign antigen in previously vaccinated animals. Antipoliovirus immunity was induced in susceptible mice by intraperitoneal immunization with live poliovirus. Immunized mice developed antibodies directed against capsid proteins that effectively neutralized poliovirus in vitro and protected animals from a lethal challenge with a high dose of pathogenic poliovirus. To test whether preexisting immunity reduces the efficacy of vaccination with recombinant poliovirus, immunized mice were inoculated with a recombinant poliovirus expressing the C-terminal half of chicken ovalbumin (Polio-Ova). Animals developed ovalbumin-specific antibodies and cytotoxic T lymphocytes (CTL). While the antibody titers observed in preimmune and naive mice were similar, the overall CTL response appeared to be reduced in preimmune mice. Importantly, vaccination with Polio-Ova was able to effectively protect preimmune mice against lethal challenge with a tumor expressing the antigen. Thus, preexisting immunity to poliovirus does not compromise seriously the efficacy of replication-competent poliovirus vaccine vectors. These results contrast with those observed for other viral vaccine vectors and suggest that preexisting immunity does not equally affect the vaccine potential of individual viral vectors.

The effect of pre-existing adenovirus-specific immunity on immune responses induced by recombinant adenovirus expressing glycoprotein D of bovine herpesvirus type 1

We investigated whether pre-existing adenovirus-specific immunity influenced the development of immunity to a foreign antigen expressed by recombinant adenovirus. Active adenovirus-specific immunity was induced in cotton rats by i.n. administration of wild type human adenovirus type 5 (HAd5) two weeks before immunisation with a HAd5 vector expressing the glycoprotein D (gD) of bovine herpesvirus type 1 (gD-dE3 recombinant adenovirus). Active adenovirus-specific immunity inhibited gD-specific immune responses, following either i.n. or gastrointestinal immunisation with gD-dE3. An inhibitory effect was present even if infection with HAd5 and immunisation with gD-dE3 were 13 weeks apart. Passive transfer of adenovirus specific antibodies to cotton rats one day before immunisation, however, did not significantly inhibit gD-specific immune responses induced by i.n. immunisation with gD-dE3. Repeated administration of an adenovirus vector, therefore, may have a limited ability to deliver antigen, while passive immunity to adenovirus may not interfere with the success of immunisation.

Induction of antigen-presenting capacity in tumor cells upon infection with non-replicating recombinant vaccinia virus encoding murine MHC class II and costimulatory molecules

The possibility of inducing antigen-presenting capacity in cells normally lacking such capacity, currently represents a major goal in vaccine research. To address this issue we attempted to generate 'artificial' APC able to stimulate CD4+ T cell responses when tumor cells were infected with a single, recombinant, vaccinia virus (rVV) containing the two genes encoding murine MHC class II I-Ak and a third gene encoding the murine B7-1 (mB7-1) costimulatory molecule. To minimize the cytopathic effect and to improve safety, in view of possible in vivo applications, we made this rVV replication incompetent by Psoralen and long wave UV treatment. Tumor cells infected with rVV encoding I-Ak alone, pulsed with hen egg white lysozyme peptide (HEL46-61), induced IL-2 secretion by an antigen-specific T hybridoma. Tumor cells infected with the rVV encoding mB7-1 provided costimulation for activating resting CD4+ T cells in the presence of ConA. Tumor cells infected with the rVV encoding I-Ak and mB7-1, and pulsed with chicken ovotransferrin peptide (conalbumin133-145), induced a significantly higher response in a specific Th2 cell clone (D10.G4.1) as compared to cells infected with rVV encoding I-Ak molecules only. Thus, this replication incompetent rVV represents a safe, multiple gene, vector system able to confer in one single infection step effective APC capacity to non-professional APCs.