Toward new viral vaccines for man

Replicating vectors for gene therapy of cancer: risks, limitations and prospects

There are good theoretical arguments for exploring the use of replicating gene-transfer vectors for human cancer therapy. Such vectors should be derived from weakly pathogenic human viruses with initially broad tissue tropism. Coat protein engineering and promoter engineering might be used successfully to narrow the tropism of the vector, enhancing its ability to target tumour cells. Killing of uninfected 'bystander' tumour cells could be achieved through prodrug activation by a vector-encoded enzyme. Rapid elimination of infused vector particles by circulating antiviral antibody would limit access to tumour deposits after repeated administration, but might be circumvented by the use of infectious nucleic acid which is poorly imunogenic [64]. This putative therapeutic strategy is illustrated in Figure 1.

Effects of hydrostatic pressure on a membrane-enveloped virus: high immunogenicity of the pressure-inactivated virus

A new approach to the preparation of antiviral vaccines relying on the inactivation of the virus particle by hydrostatic pressure is described. The enveloped virus vesicular stomatitis virus was utilized as a model; a pressure of 260 MPa applied for 12 h reduced infectivity by a factor of 10(4), and the antibodies against pressurized material were as effective as those against the intact virus when measured by their neutralization titer. Fluorescence measurements indicate that application of pressure results in perturbations of the particle interactions that permit binding of specific molecular probes. Electron microscopy showed that the membrane of the pressurized virus was partially preserved, presenting the spike pattern of the membrane G protein. Unlike the icosahedral viruses, dissociation into smaller particles was not observed, but a constant change in the morphology was the presence of a bulge in the surface of the pressurized virus, indicating a displacement of the capsid subunits, retained under the lipid and protein membrane.

A comparison of T cell responses to glycoprotein B (gB-1) of herpes simplex virus type 1 and its non-glycosylated precursor protein, pgB-1

The ability of non-glycosylated precursor glycoprotein B (pgB) to induce T cell responses in herpes simplex virus (HSV) infected mice was compared with fully glycosylated glycoprotein B (gB) and with whole virus. pgB was as effective as gB in priming for virus- and glycoprotein-specific T cells. pgB could also re-stimulate virus or glycoprotein primed cells in vitro as efficiently as gB. In addition, priming with pgB protected mice against a lethal challenge with HSV type 1 (HSV-1) and could induce the early in vivo production of IL-2 and IL-3 in infected mice. In all of these responses, pgB was as effective as gB. Thus, the carbohydrate side chains on gB do not appear to be necessary for T cell recognition of this protein.

Protection from herpes simplex virus type 1 lethal and latent infections by secreted recombinant glycoprotein B constitutively expressed in human cells with a BK virus episomal vector

The herpes simplex virus type 1 (HSV-1) glycoprotein B (gB-1) gene, deleted of 639 nucleotides that encode the transmembrane anchor sequence and reconstructed with the extramembrane and intracytoplasmic domains, was cloned under control of the Rous sarcoma virus long terminal repeat in the episomal replicating vector pRP-RSV, which contains the origin of replication and early region of the human papovavirus BK as well as a cDNA for a mutant mouse dihydrofolate reductase that is resistant to methotrexate. gB-1 (0.15 to 0.25 pg per cell per 24 h) was constitutively secreted into the culture medium of pRP-RSV-gBs-transformed human 293 cells. Treatment of transformed cells with methotrexate at high concentrations (0.6 to 6 microM) increased gB-1 production 10- to 100-fold, because of an amplification of the episomal recombinant. Mice immunized with secreted gB-1 produced HSV-1- and HSV-2-neutralizing antibodies and were protected against HSV-1 lethal, latent, and recurrent infections. Constitutive expression of secreted gB-1 in human cells may establish a system to develop diagnostic material and a subunit vaccine for HSV infections.

Viral-bacterial synergistic interaction in respiratory disease

In the present review we have identified how viruses can alter the host's susceptibility to bacterial infections by altering both environmental conditions in the lung which favor bacterial replication as well as by suppressing the host's defense mechanisms which prevent clearance of the bacteria. In many instances, these interactions are extremely complex but similar for many viruses. If the virus can overcome the initial host defense mechanisms, which include local antibody and mucus, the virus initiates tissue damage as a result of direct replication within the epithelial cells lining the mucosal surfaces of the respiratory tract. As a result of virus infection, the host cells respond by producing a variety of mediators including various types of interferons, which can alter both virus replication and host response. Replication also produces by-products of virus infection capable of initiating an inflammatory process, which in turn, through release of other mediators, can further modify lung defense mechanisms and encourage bacterial adherence and growth. The bacterium, in turn, releases chemotactic factors which encourage infiltration of specific effector cells into the lung. These effector cells can cause tissue damage and immunopathology, which encourage rapid bacterial growth and may result in death of the animal. In order to be able to control this complicated scenario, it is important either to prevent the initial infection with viruses or to reduce the degree of immunosuppression, so that bacterial clearance can occur rapidly before microcolony formation and extensive lung damage occur. Once a large amount of bacterial replication and lung damage is present, the use of antibiotics is generally of limited value. A schematic illustration of the complexity of the various interactions and counteractions occurring during virus--bacterial synergistic interactions is presented in Fig. 1.