No abstract

An open reading frame (ORF) with homology to interleukin-10 (IL-10) has been identified in rhesus cytomegalovirus (RhCMV). The IL-10-like protein is generated from a multispliced, polyadenylated early gene transcript encompassing part of the corresponding UL111A ORF of human CMV (HCMV). Immunological analyses confirm expression of the IL-10-like protein both in tissue culture and in RhCMV-infected rhesus macaques. Conserved ORFs were subsequently identified in human, baboon, and African green monkey CMV, and a fully processed transcript has been mapped in fibroblasts infected with the Towne strain of HCMV. The conservation of this previously unrecognized ORF suggests that the protein may play an essential role in primate CMV persistence and pathogenesis.

Congenital human cytomegalovirus (HCMV) infection has long been recognized as a threat to the developing fetus, even though studies have shown that only a subset of congenital infections results in clinical signs of disease. Among the estimated 8000 children who develop sequelae from congenital CMV infection each year in the United States alone, most suffer permanent developmental defects within the central nervous system. Because there is currently no approved vaccine for HCMV, and anti-HCMV drugs are not administered to gravid women with congenital infection because of potential toxicity to the fetus, there is a clear clinical need for effective strategies that minimize infection in the mother, transplacental transmission of the virus, and/or fetal disease. Animal models provide a method to understand the mechanisms of HCMV persistence and pathogenesis, and allow for testing of novel strategies that limit prenatal infection and disease. The rhesus macaque model is especially well suited for these tasks because monkeys and humans share strong developmental, immunological, anatomical, and biochemical similarities due to their close phylogenetic relationship. This nonhuman primate model provides an invaluable system to accelerate the clinical development of promising new therapies for the treatment of human disease. This review addresses salient findings with the macaque model as they relate to HCMV infection and potential avenues of discovery, including studies of intrauterine CMV infection. The complexity of the natural history of HCMV is discussed, along with the ethical and logistical issues associated with studies during pregnancy, the recent contributions of animal research in this field of study, and future prospects for increasing our understanding of immunity against HCMV disease.

Human cytomegalovirus (HCMV) possesses low pathogenic potential in an immunocompetent host. In the immunosuppressed host, however, a wide spectrum of infection outcomes, ranging from asymptomatic to life threatening, can follow either primary or nonprimary infection. The variability in the manifestations of HCMV infection in immunosuppressed individuals implies that there is a threshold of host antiviral immunity that can effectively limit disease potential. We used a nonhuman primate model of CMV infection to assess the relationship between CMV disease and the levels of developing anti-CMV immunity. Naive rhesus macaques were inoculated with rhesus cytomegalovirus (RhCMV) followed 2 or 11 weeks later by inoculation with pathogenic simian immunodeficiency virus SIVmac239. Two of four monkeys inoculated with SIV at 2 weeks after inoculation with RhCMV died within 11 weeks with simian AIDS (SAIDS), including activated RhCMV infection. Neither animal had detectable anti-SIV antibodies. The other two animals died 17 and 27 weeks after SIV inoculation with either SAIDS or early lymphoid depletion, although no histological evidence of activated RhCMV was observed. Both had weak anti-SIV antibody titers. RhCMV antibody responses for this group of monkeys were significantly below those of control animals inoculated with only RhCMV. In addition, all animals of this group had persistent RhCMV DNA in plasma and high copy numbers of RhCMV in tissues. In contrast, animals that were inoculated with SIV at 11 weeks after RhCMV infection rarely exhibited RhCMV DNA in plasma, had low copy numbers of RhCMV DNA in most tissues, and did not develop early onset of SAIDS or activated RhCMV. SIV antibody titers were mostly robust and sustained in these monkeys. SIV inoculation blunted further development of RhCMV humoral responses, unlike the normal pattern of development in control monkeys following RhCMV inoculation. Anti-RhCMV immunoglobulin G levels and avidity were slightly below control values, but levels maintained were higher than those observed following SIV infection at 2 weeks after RhCMV inoculation. These findings demonstrate that SIV produces long-lasting insults to the humoral immune system beginning very early after SIV infection. The results also indicate that anti-RhCMV immune development at 11 weeks after infection was sufficient to protect the host from acute RhCMV sequelae following SIV infection, in contrast to the lack of protection afforded by only 2 weeks of immune response to RhCMV. As previously observed, monkeys that were not able to mount a significant immune response to SIV were the most susceptible to SAIDS, including activated RhCMV infection. Rapid development of SAIDS in animals inoculated with SIV 2 weeks after RhCMV inoculation suggests that RhCMV can augment SIV pathogenesis, particularly during primary infection by both viruses.

To determine whether live-attenuated feline immunodeficiency virus (FIV) proviral DNA will induce protective immunity, a plasmid clone constructed with a FIV provirus containing a deletion in the viral accessory gene vif (FIV-pPPR-Deltavif) was inoculated as proviral DNA into four cats by the intramuscular route. After 43 weeks, these cats were boosted with the same proviral plasmid. Analysis of peripheral blood mononuclear cells at several time points after the primary and booster inoculations revealed no detectable virus or proviral DNA. At 6 weeks after the booster, immunized cats and additional naive control cats were challenged with a cell-free preparation of the infectious biological isolate FIV-PPR by the intraperitoneal route. Virus was detected after challenge in unvaccinated control cats but not in any of the FIV-pPPR-Deltavif-immunized cats. Both FIV Gag- and Env-specific cytotoxic T lymphocyte (CTL) activities were detected in peripheral blood cells of control cats after challenge infection, whereas only one of four cats immunized with FIV-pPPR-Deltavif DNA exhibited a measurable CTL response to Env following challenge. Although anti-Gag antibodies were not detected after both proviral DNA inoculation and challenge, anti-Env antibodies were found in FIV-pPPR-Deltavif-immunized cats after vaccination as well as after challenge. These findings indicate that inoculation with FIV-pPPR-Deltavif proviral DNA induced resistance to challenge with infectious FIV and that a vif deletion mutant may provide a relatively safe attenuated lentiviral vaccine.