For antiretoviral efficacy studies, plasma HIV RNA is a suitable study endpoint that is likely to predict a decreased risk for AIDS progression and death. Because greater and more sustained reductions in HIV RNA appear to confer greater reductions in clinical risk, maintaining maximal suppression of plasma HIV RNA, particularly below the limits of assay quantification, appears to be a rigorous benchmark for assessing the efficacy of antiretroviral regimens.

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The gene encoding Bacillus anthracis protective antigen (PA) was modified by site-directed mutagenesis, subcloned into baculovirus and vaccinia virus plasmid transfer vectors (pAcYMl and pSC-1l, respectively), and inserted via homologous recombinations into baculovirus Autographa californica nuclear polyhedrosis virus or vaccinia virus (strains WR and Connaught). Expression of PA was detected in both systems by immunofluorescence assays with antisera from rabbits immunized with B. anthracis PA. Western blot (immunoblot) analysis showed that the expressed product of both systems was slightly larger (86 kilodaltons) than B. anthracis-produced PA (83.5 kilodaltons). Analysis of trypsin digests of virus-expressed and authentic PA suggested that the size difference was due to the presence of a signal sequence remaining with the virus-expressed protein. Immunization of mice with either recombinant baculovirus-infected Spodoptera frugiperda cells or with vaccinia virus recombinants elicited a high-titer, anti-PA antibody response.

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We previously described the cloning and expression of the protective antigen (PA) gene of Bacillus anthracis in both vaccinia virus and a baculovirus. The antigenicity of the PA products was characterized. PA expressed by the recombinant vaccinia viruses elicited a partial protective immune response against a lethal B. anthracis spore challenge in guinea pigs and mice. The WR strain vaccinia virus recombinant (WR-PA) protected 60% of male mice and 50% of guinea pigs. WR-PA elicited high anti-PA antibody titers in mice but not in guinea pigs. Connaught strain vaccinia virus recombinanits failed to protect any immunized animals. PA purified from baculovirus recombinant-infected cultures plus adjuvant partially protected male CBA/J mice and completely protected female Hartley guinea pigs from challenge. Both the recombinant and nonrecombinant PA preparations combined with adjuvant elicited high anti-PA antibody titers in Hartley guinea pigs and CBA/J mice. These data demonstrate that the recombinant baculovirus-and vaccinia virus-produced PAs were immunogenic in both guinea pigs and mice, that the baculovirus-PA recombinant was a useful source of immunogenic PA, and that vaccinia virus-PA recombinants may be feasible live anthrax vaccine candidates worthy of consideration for further development as live vaccines.

SUMMARYThe Flaviviridae include almost 70 viruses, nearly half of which have been associated with human disease. These viruses are among the most important arthropod-borne viruses worldwide and include dengue, yellow fever, and Japanese encephalitis viruses. Morbidity and mortality caused by these viruses vary, but collectively they account for millions of encephalitis, hemorrhagic fever, arthralgia, rash, and fever cases per year. Most of the members of this family are transmitted between vertebrate hosts by arthropod vectors, most commonly mosquitoes or ticks. Transmission cycles can be simple or complex depending on the hosts, vectors, the virus, and the environmental factors affecting both hosts and viruses. Replication of virus in invertebrate hosts does not seem to result in any significant pathology, which suggests a close evolutionary relationship between virus and vector. Another example of this relationship is the ability of these viruses to grow in invertebrate ceil culture, where replication usually results in a steady state, persistent infection, often without cytopathic effect. Yields of virus from insect cell culture vary but are generally similar to yields in vertebrate cells. Replication kinetics are comparable between insect and vertebrate ceil lines, despite differences in incubation temperature. Both vertebrate and insect cell culture systems continue to play a significant role in flavivirus isolation and the diagnosis of disease caused by these agents. Additionally, these culture systems permit the study of flavivirus attachment, penetration, replication, and release from cells and have been instrumental in the production and characterization of live-attenuated vaccines. Both vertebrate and insect cell culture systems will continue to play a significant role in basic and applied flavivirus research in the future.