Suppression of simian immunodeficiency virus replication by human immunodeficiency virus type 1 trans-dominant negative rev mutants

A therapeutic SIV DNA vaccine elicits T-cell immune responses, but no sustained control of viremia in SIVmac239-infected rhesus macaques

The immunologic and virologic outcome of therapeutic DNA-vaccines administered during antiretroviral therapy (ART) using electroporation with or without (interleukin) IL-2 treatment was evaluated in the SIVmac239/macaque model. Rhesus macaques inoculated with pathogenic SIVmac239 were treated with ART [(R(-9-(2-phosphonomethoxypropyl) adenine) (PMPA), FTC, Zerit] from weeks 13 to 41 postinfection (wpi). Group 1 (n = 7) received ART only, groups 2 and 3 (each n = 6) additionally received SIVmac239-derived gp140Env, GagPol, and TatRevNef plasmids by in vivo electroporation at 22, 26, 30, and 34 wpi, and group 3 also IL-2 for 14 days after each vaccination. Endpoints evaluated were viral load, Gag(181189)-specific CD8+ T-cell responses in MamuA01+ animals, lymphoproliferative responses, and CD4 T-cell counts. Viremia in all animals dropped below 200 RNA copies/ml during ART. Frequencies of Gag(181189)-specific CD8+ T cells prior to ART were detectable in all three groups (1.27-3.01%) and increased significantly (p < 0.01) postvaccination with maximum responses after the fourth immunization (0.2% versus 3.49-7.15%). Gag(181189)-specific CD8+ T-cell frequencies increased post-ART cessation in all groups and remained at significantly higher levels (p < 0.001) until the end of the study (75 wpi) in both groups of vaccinated animals. Lymphoproliferative responses were detected against Gag in a limited number of animals after vaccination and post-ART. However, plasma RNA viral loads rebounded after ART termination to similar levels in all three groups, but remained below 10(5) copies/ml until the end of the study, which could be a late effect of the triple drug therapy.

A rhesus macaque rhadinovirus related to Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 encodes a functional homologue of interleukin-6

The rhesus rhadinovirus strain 17577 (RRV strain 17577) genome is essentially colinear with human herpesvirus 8 (HHV8)/Kaposi's sarcoma-associated herpesvirus (KSHV) and encodes several analogous open reading frames (ORFs), including the homologue of cellular interleukin-6 (IL-6). To determine if the RRV IL-6-like ORF (RvIL-6) is biologically functional, it was expressed either transiently in COS-1 cells or purified from bacteria as a glutathione S-transferase (GST)-RvIL-6 fusion and analyzed by IL-6 bioassays. Utilizing the IL-6-dependent B9 cell line, we found that both forms of RvIL-6 supported cell proliferation in a dose-dependent manner. Moreover, antibodies specific to the IL-6 receptor (IL-6R) or the gp130 subunit were capable of blocking the stimulatory effects of RvIL-6. Reciprocal titrations of GST-RvIL-6 against human recombinant IL-6 produced a more-than-additive stimulatory effect, suggesting that RvIL-6 does not inhibit but may instead potentiate normal cellular IL-6 signaling to B cells. These results demonstrate that RRV encodes an accessory protein with IL-6-like activity.

Reduction in SIV replication in rhesus macaques infused with autologous lymphocytes engineered with antiviral genes

Simian immunodeficiency virus (SIV) infection of nonhuman primates is one of the most relevant animals models of HIV infection in humans. To test a potential anti-HIV gene therapy strategy in this model, CD4-enriched lymphocytes from three rhesus macaques were subjected to retrovirally mediated gene transfer with a vector expressing an antisense tat/rev gene. This group of animals and three control macaques were subsequently infected with SIVmac239. Blood and lymph nodes from all macaques were sampled for more than a year to monitor the progress of infection. Although all animals became infected, the animals that received the lymphocytes engineered with the antisense vector demonstrated a significant reduction in viral load in both peripheral blood and lymph nodes, had sustained numbers of CD4+ cells, and exhibited little disruption of lymph node architecture.

DNA immunization of mice against SIVmac239 Gag and Env using Rev-independent expression plasmids

Simian immunodeficiency virus (SIV) structural gene expression, including gag and env, strictly depends on the interaction of the viral posttranscriptional regulator Rev with its target RNA, the Rev-responsive element (RRE). A small RNA element, termed the constitutive transport element (CTE), located in the 3' portion of simian retrovirus 1 (SRV-1) mRNA, can efficiently substitute for the human immunodeficiency virus (HIV) Rev-RRE interaction, and thus render HIV expression and replication Rev independent. We tested the ability of the SRV-1 CTE to drive the expression of SIVmac239 env and gag from subgenomic constructs designed for possible use in vaccine trials. In vitro expression studies showed that when the SRV-1 sequence is coupled to the SIV gag and env mRNAs, it functions in an orientation-dependent fashion, and leads to strong expression of SIV Gag and Env in human and monkey cell lines; levels of CTE-mediated protein expression were similar to those obtained with a functional Rev-RRE system. On the other hand, in murine fibroblast-like cells, SIV Gag and Env were expressed from constructs at relatively high levels even in the absence of Rev-RRE; nevertheless, their expression was increased by the presence of the SRV-1 CTE. As reported previously for HIV, the murine cell lines appeared to be defective for Rev-RRE activity, and required overexpression of Rev to induce a Rev response. Intramuscular injection of the gag-CTE and env-CTE constructs in BALB/c mice resulted in the expression of the corresponding mRNAs, and the production of anti-Gag and anti-Env antibodies, thus suggesting that these vectors might be used for genetic immunization approaches.

In vitro T lymphopoiesis: a model system for stem cell gene therapy for AIDS

Stable introduction of therapeutic genes into hematopoietic stem cells has the potential to reconstitute immunity in individuals with HIV infection. However, many important questions regarding the safety and efficacy of this approach remain unanswered and may be addressed in a non-human primate model. To facilitate evaluation of expression of foreign genes in T cells derived from transduced hematopoietic progenitor cells, we have established a culture system that supports the differentiation of rhesus macaque and human CD34+ bone marrow derived cells into mature T cells. Thymic stromal monolayers were prepared from the adherent cell fraction of collagenase digested fetal or neonatal thymus. After 10-14 days, purified rhesus CD34+ bone marrow-derived cells cultured on thymic stromal monolayers yielded CD3+CD4+CD8+, CD3+CD4+CD8-, and CD3+CD4-CD8+ cells. Following stimulation with mitogens, these T cells derived from CD34+ cells could be expanded over 1,000-fold and maintained in culture for up to 20 weeks. We next evaluated the ability of rhesus CD34+ cells transduced with a retroviral vector containing the marker gene neo to undergo in vitro T cell differentiation. CD34+ cells transduced in the presence of bone marrow stroma and then cultured on rhesus thymic stroma resulted in T cells containing the retroviral marker gene. These studies should facilitate both in vitro and in vivo studies of hematopoietic stem cell therapeutic strategies for AIDS.

Nuclear transport of human immunodeficiency virus type 1, visna virus, and equine infectious anemia virus Rev proteins: identification of a family of transferable nuclear export signals

The human immunodeficiency virus type 1 Rev trans activator binds directly to unspliced viral mRNA in the nucleus and activates its transport to the cytoplasm. In additon to the sequences that confer RNA binding and nuclear localization, Rev has a carboxy-terminal region, the activation domain, whose integrity is essential for biological activity. Because it has been established that Rev constitutively exits and reenters the nucleus and that the activation domain is required for nuclear exit, it has been proposed that Rev's activation domain is a nuclear export signal (NES). Here, we used microinjection-based assays to demonstrate that the activation domain of human immunodeficiency virus type 1 Rev imparts rapid nuclear export after its transfer to heterologous substrates. NES- mediated export is specific, as it is sensitive both to inactivation by missense mutation and to selective inhibition by an excess of the wild-type, but not mutant, activation domain peptide. Examination of the Rev trans activators of two nonprimate lentiviruses, visna virus and equine infectious anemia virus, revealed that their activation domains are also potent NESs. Taken together, these data demonstrate that nuclear export can be determined by positively acting peptide motifs, namely, NESs, and suggest that Rev proteins activate viral RNA transport by providing export ribonucleoproteins with specific information that targets them to the cytoplasm.