AIDS-like disease following mucosal infection of pig-tailed macaques with SIVsmmPBj14

In vivo inactivation of Nef ITAM motif of chimeric simian/human immunodeficiency virus SHIVsbg-YE correlates with absence of increased virulence in Chinese rhesus macaques

SHIVsbg, expressing Vpu, Tat, Rev, and Env proteins of HIV-1 Lai, was shown to be infectious for rhesus macaques. In this study, we mutated SHIVsbg Nef amino acids 17-18 from RQ to YE, conferring to SHIVsbg-YE the ability to replicate in vitro in unstimulated macaque PBMC. Juvenile macaques inoculated intravenously or orally with SHIVsbg-YE developed persistent infection. All macaques lost weight during the first 17 weeks but recovered afterward. All animals developed a strong HIV-specific humoral immune response. Viruses isolated 2 years postinoculation lost the ability to replicate in unstimulated macaque PBMC. Point mutations or 33-bp-wide deletions in the nef ITAM motif were responsible for this phenotype and correlated with clinical improvement of the infected macaques. These data demonstrate that the ITAM domain is inactivated in animals developing an acute antiviral immune response and may be detrimental to viral replication, perhaps by interfering with other well-conserved functions of SIV Nef protein.

Relationship of lymphoid lesions to disease course in mucosal feline immunodeficiency virus type C infection

Feline immunodeficiency virus (FIV) infection typically has a prolonged and variable disease course in cats, which can limit its usefulness as a model for human immunodeficiency virus infection. A clade C FIV isolate (FIV-C) has been associated with high viral burdens and rapidly progressive disease in cats. FIV-C was transmissible via oral-nasal, vaginal, or rectal mucosal exposure, and infection resulted in one of three disease courses: rapid, conventional/slow, or regressive. The severity of the pathologic changes paralleled the disease course. Thymic depletion was an early lesion and was correlated with detection of FIV RNA in thymocytes by in situ hybridization. The major changes in thymic cell populations were depletion of p55+/S100+ dendritic cells, CD3- cells, CD4+/CD8- cells, and CD4+/CD8+ cells and increases in apoptosis, CD45R+ B cells, and lymphoid follicles. In contrast to thymic depletion, peripheral lymphoid tissues often were hyperplastic. Mucosally transmitted FIV-C is thymotropic and induces a spectrum of lymphoid lesions and disease mirroring that seen with the human and simian immunodeficiency virus infections.

Short- and long-term clinical outcomes in rhesus monkeys inoculated with a highly pathogenic chimeric simian/human immunodeficiency virus

A highly pathogenic simian/human immunodeficiency virus (SHIV), SHIV(DH12R), isolated from a rhesus macaque that had been treated with anti-human CD8 monoclonal antibody at the time of primary infection with the nonpathogenic, molecularly cloned SHIV(DH12), induced marked and rapid CD4(+) T cell loss in all rhesus macaques intravenously inoculated with 1.0 50% tissue culture infective dose (TCID(50)) to 4.1 x 10(5) TCID(50)s of virus. Animals inoculated with 650 TCID(50)s of SHIV(DH12R) or more experienced irreversible CD4(+) T lymphocyte depletion and developed clinical disease requiring euthanasia between weeks 12 and 23 postinfection. In contrast, the CD4(+) T-cell numbers in four of five monkeys receiving 25 TCID(50)s of SHIV(DH12R) or less stabilized at low levels, and these surviving animals produced antibodies capable of neutralizing SHIV(DH12R). In the fifth monkey, no recovery from the CD4(+) T cell decline occurred, and the animal had to be euthanized. Viral RNA levels, subsequent to the initial peak of infection but not at peak viremia, correlated with the virus inoculum size and the eventual clinical course. Both initial infection rate constants, k, and decay constants, d, were determined, but only the latter were statistically correlated to clinical outcome. The attenuating effects of reduced inoculum size were also observed when virus was inoculated by the mucosal route. Because the uncloned SHIV(DH12R) stock possessed the genetic properties of a lentivirus quasispecies, we were able to assess the evolution of the input virus swarm in animals surviving the acute infection by monitoring the emergence of neutralization escape viral variants.

Progress and challenges in therapies for AIDS in nonhuman primate models

Efforts to develop animal models for human immunodeficiency virus type-1 (HIV-1) vaccine testing have focused on lentivirus infection of nonhuman primates. A long-term goal of this primate research is to utilize the models to understand the mechanisms of pathogenesis leading to AIDS. Because the time to disease is compressed relative to HIV infection in humans, therapeutic strategies and compounds can be tested in nonhuman primate models in a shorter time frame and under more controlled conditions than are possible in many clinical studies. Recent interventive studies in primates using antiviral drugs or passive immune globulin (IgG) have demonstrated that multiple log reductions in plasma virus can be achieved and sustained, with accompanying health benefits. Information gained about timing and dosage may be of utility in designing clinical studies. The development of reliable and predictable animal models for effective therapies and vaccines against AIDS remains a critical priority for primate research.

Rectal transmission of human immunodeficiency virus type 1 to chimpanzees

Inoculation of chimpanzees with human immunodeficiency virus type 1 (HIV-1) has been used as a model system to define mechanisms of pathogenesis and to test protective efficacy of candidate HIV-1 vaccines. In most of these studies, the animals were inoculated intravenously. However, because HIV-1 is transmitted primarily across mucosal surfaces, future evaluations of vaccines should employ mucosal routes for administering infectious virus to immunized animals. To develop a model of rectal transmission of HIV-1, chimpanzees were exposed without trauma to 4 different HIV-1 strains at doses ranging from 200 to 10,000 TCIDs. Infection, characterized by seroconversion and repeated isolation of virus from lymphocytes, was established in 1 of 5 animals. This animal was sequentially inoculated with a subtype B and then an E strain and was infected with both strains. The results show that rectal exposure of adult chimpanzees to cell-free HIV-1 was not an efficient mode of transmission in this cohort.

Genital infection of female chimpanzees with human immunodeficiency virus type 1

To develop an animal model for mucosal HIV-1 infection, adult chimpanzees were inoculated without trauma by depositing the virus inoculum at the entrance to the cervical canal with a rigid catheter to which flexible tubing was attached. By this procedure, persistent infections were established in some chimpanzees with various infectious doses of either cell-associated HIV-1LAI(IIIB) (peripheral blood mononuclear cells from an infected chimpanzee) or with cell-free HIV-1 strains representing subtypes B and E, but not with a subtype A strain. Although some animals did not become infected until after the second or third cervicovaginal exposure, one chimpanzee was clearly infected after one exposure by several criteria, including virus isolation, but this animal did not seroconvert. A second chimpanzee appeared to be resistant to infection despite repeated mucosal exposures at irregular intervals. However, lymphocytes from both of these animals exhibited low-level proliferative responses to HIV-1 but not SIV antigens. Despite these apparently abortive or latent infections, after exposure to HIV-1 by the intravenous route, both animals developed systemic infections and seroconverted. Overall, 8 of 10 chimpanzees were infected systemically after one to three cervicovaginal exposures to HIV-1LAI(IIIB). The results indicate that (1) HIV-1 productive infection of female chimpanzees by the cervicovaginal route generally requires more than one exposure, just as with humans; (2) low level infections without seroconversion can be established after mucosal exposure to HIV; and (3) vaccine efficacy studies involving a single virus challenge of immunized chimpanzees by the cervicovaginal route probably will not be possible.

Loss of the SIVsmmPBj14 phenotype and nef genotype during long-term survival of macaques infected by mucosal routes

The ability of the simian immunodeficiency virus SIVsmmPBj14 (SIV-PBj14) to activate and induce proliferation of quiescent peripheral blood lymphocytes from macaques is an in vitro correlate of its acutely lethal in vivo phenotype. SIV-PBj14 differs from other SIV strains by encoding tyrosine at amino acid 17 (Y17) in Nef, which generates an activation motif important for signal transduction. Although intravenous inoculation of pig-tailed macaques with SIV-PBj14 uniformly leads to death within 2 weeks, inoculation by mucosal routes results in persistent infections that progress to AIDS. In the present study, we determined whether viruses in long-term survivors retained not only the Nef Y17 residue but also the biologic properties associated with rapid disease-and death. Viruses reisolated at early and late times after mucosal infection of macaques with SIV-PBj14 were tested in vivo for acute lethality and in vitro for the ability to replicate in and induce activation and proliferation of quiescent macaque lymphocytes. In addition, the coding sequence for the first 55 amino acids in Nef was amplified from proviral DNA or plasma virion RNA by PCR or RT-PCR, respectively, and nucleotide sequences were obtained. The results showed that the majority of the quasispecies that persisted as disease progressed not only lost biological properties unique to SIV-PBj14, but also lost through mutation either Y17 or Y28 in Nef, which together were part of the activation motif. In the case of Y17, these mutations were stepwise to histidine then arginine, the amino acid encoded in this position in other SIV strains. We conclude, therefore, that replicative properties of the acutely lethal virus provide no selective advantage during long-term infections with SIV-PBj14 and that disruption of the activation motif in Nef is associated with loss of the acutely lethal phenotype.

SIV/DeltaB670 transmission across oral, colonic, and vaginal mucosae in the macaque

The primary mode of human immunodeficiency virus (HIV) transmission worldwide is by exposure to the virus at vaginal, rectal, and oral mucosal surfaces. To understand HIV/simian immunodeficiency virus (SIV) transmission events at mucosal portals of entry, we used the SIV-macaque model to determine if mucosal surfaces function as barriers and select for particular viral genotypes. Rhesus macaques were inoculated intravaginally, intracolonically, intrarectally, or orally with the complex primary viral isolate SIV/DeltaB670. Peripheral blood mononuclear cells, collected within the first two weeks postinoculation, were cloned and sequenced from all infected macaques. In the majority of the animals analyzed, multiple genotypes were identified, independent of the route of infection. These findings suggest that the mucosal barrier may play a minor role in the genotypic selection observed during sexual transmission of HIV and emphasize the need to evaluate the viral diversity present within the mucosal secretions of chronically infected individuals.