Shabbir Ahmad

Vaccinia Virus Vectors with an Inactivated Gamma Interferon Receptor Homolog Gene (B8R) Are Attenuated In Vivo without a Concomitant Reduction in Immunogenicity

ABSTRACT The vaccinia virus (VV) B8R gene encodes a secreted protein with homology to the gamma interferon (IFN-γ) receptor. In vitro, the B8R protein binds to and neutralizes the antiviral activity of several species of IFN-γ, including human and rat IFN-γ; it does not, however, bind significantly to murine IFN-γ. Here we report on the construction and characterization of recombinant VVs (rVVs) lacking the B8R gene. While the deletion of this gene had no effect on virus replication in vitro, rVVs lacking the B8R gene were attenuated for mice. There was a significant decrease in weight loss and mortality in normal mice, and nude mice survived significantly longer than did controls inoculated with parental virus. This is a surprising result considering the minimal binding of the B8R protein to murine IFN-γ and its failure to block the antiviral activity of this cytokine in vitro. Such reduction in virulence could not be determined in rats, since they are considerably more resistant to VV infection than are mice. Finally, deletion of the B8R gene had no detectable effects on humoral immune responses. Mice and rats vaccinated with the rVVs showed identical humoral responses to both homologous and heterologous genes expressed by VV. This study demonstrates that the deletion of the VV B8R gene leads to enhanced safety without a concomitant reduction in immunogenicity.

Detection of antibodies to equine arteritis virus by enzyme linked immunosorbant assays utilizing GL, M and N proteins expressed from recombinant baculoviruses

Indirect enzyme linked immunosorbant assays (ELISAs) utilizing the three major structural proteins (M, N, and G(L)) of equine arteritis virus (EAV) expressed from recombinant baculoviruses were developed. A large panel of sera collected from uninfected horses, and from animals experimentally and naturally infected with EAV or vaccinated with the modified live virus vaccine against equine viral arteritis, were used to characterize the humoral immune response of horses to the three major EAV structural proteins. The data suggest that the M protein was the major target of the equine antibody response to EAV. The responses of individual animals varied and ELISAs that utilized individual EAV structural proteins were not reliable for detecting antibodies in all sera that contained neutralizing antibodies to EAV. An ELISA based on a cocktail of all three EAV structural proteins, however, was used successfully to detect antibodies in most equine sera that were positive in the standard serum neutralization assay following natural or experimental EAV infection (100% specificity, 92.3% sensitivity). In contrast, this ELISA did not reliably detect antibodies in the sera of vaccinated horses. EAV frequently causes a persistent infection in stallions and all sera from carrier stallions evaluated in this study had obvious reactivity with the N protein, whereas seropositive non-carrier stallions, mares and geldings did not respond consistently to the N protein.

Long-term sterilizing immunity to rinderpest in cattle vaccinated with a recombinant vaccinia virus expressing high levels of the fusion and hemagglutinin glycoproteins

ABSTRACT Rinderpest is an acute and highly contagious viral disease of ruminants, often resulting in greater than 90% mortality. We have constructed a recombinant vaccinia virus vaccine (v2RVFH) that expresses both the fusion (F) and hemagglutinin (H) genes of rinderpest virus (RPV) under strong synthetic vaccinia virus promoters. v2RVFH-infected cells express high levels of the F and H glycoproteins and show extensive syncytium formation. Cattle vaccinated intramuscularly with as little as 103 PFU of v2RVFH and challenged 1 month later with a lethal dose of RPV were completely protected from clinical disease; the 50% protective dose was determined to be 102 PFU. Animals vaccinated with v2RVFH did not develop pock lesions and did not transmit the recombinant vaccinia virus to contact animals. Intramuscular vaccination of cattle with 108 PFU of v2RVFH provided long-term sterilizing immunity against rinderpest. In addition to being highly safe and efficacious, v2RVFH is a heat-stable, inexpensive, and easily administered vaccine that allows the serological differentiation between vaccinated and naturally infected animals. Consequently, mass vaccination of cattle with v2RVFH could eradicate rinderpest.

Characterization of SIV-specific CD4+ T-helper proliferative responses in macaques immunized with live-attenuated SIV

Abstract: Analysis of immune responses generated by live‐attenuated simian immunodeficiency virus (SIV) strains may provide clues to the mechanisms of protective immunity induced by this approach. We examined SIV‐specific T‐helper responses in macaques immunized with the live‐attenuated SIV strains SIVmac239Δnef and SIVmac239Δ3. Optimization of the concentration and duration of antigenic stimulation resulted in the detection of relatively strong SIV‐specific proliferative responses, with peak stimulation indices of up to 84. SIV‐specific proliferative responses were mediated by CD4 + T cells and were major histocompatibility (MHC) class II restricted. Limiting dilution analysis revealed SIV‐specific T‐helper precursor frequencies of up to 96 per 106 peripheral blood mononuclear cells (PBMC). Intracellular flow‐cytometric analysis demonstrated the production of interleukin (IL)‐2, interferon (IFN)‐γ, RANTES and macrophage inhibitory protein‐1α (MIP‐1α) by T lymphocytes from SIVmac239Δnef‐vaccinated animals following SIV p55 stimulation. Induction of strong SIV‐specific T‐helper responses by live‐attenuated SIV vaccines may play a role in their ability to induce protective immunity.

Lack of Protection Against Avian Cholera by Vaccination with Recombinant P6-Like Protein from Pasteurella multocida

The gene encoding the P6-like protein of Pasteurella multocida was cloned in the baculovirus expression system. Baculovirus-expressed recombinant protein was used to parenterally immunize 6-wk-old Nicholas broad-breasted white turkeys. Turkeys developed significant antibody titers to the recombinant protein as measured by enzyme-linked immunosorbent assay. Two weeks after the last immunizing injection, vaccinated turkeys were placed in contact with turkeys infected with P. multocida strain P1059, as were nonvaccinated control birds. No differences occurred in percent mortality between the two groups. We conclude that parenterally administered recombinant P6-like protein does not protect turkeys from avian cholera.

Enhanced safety and efficacy of live attenuated SIV vaccines by prevaccination with recombinant vaccines

The only vaccines shown to be protective against intravenous challenge with virulent virus in the simian immunodeficiency virus (SIV)/macaque model are attenuated live SIVs. However, these vaccines have several disadvantages: 1) they persist indefinitely in vaccinated macaques; 2) they are pathogenic to neonatal macaques; and 3) they are lethal in some adult macaques. To enhance the safety and efficacy of these vaccines, we immunized macaques first with recombinant vaccines and then inoculated the animals with SIVΔnef. In the first experiment, preimmunized macaques advanced to disease slower than controls after challenge with virulent SIV; five animals survived for 3 years without disease and only the vaccine virus (SIVΔnef) could be isolated at this time. In the second experiment, preimmunized animals had lower virus loads and no disease compared to controls.