Basic fibroblast growth factor (bFGF) and human immunodeficiency virus type 1 (HIV-1) Tat protein synergize in inducing angiogenic Kaposi's sarcoma-like lesions in mice. Synergy is due to Tat, which enhances endothelial cell growth and type-IV collagenase expression in response to bFGF mimicking extracellular matrix proteins. The bFGF, extracellular Tat and Tat receptors are present in HIV-1-associated KS, which may explain the higher frequency and aggressiveness of this form compared to classical Kaposi's sarcoma where only bFGF is present.

277 transactivator proteins of human retroviruses may mediate both viral and cellular effects. However, the events associated with the release, the uptake, and the biological effects of extracellular Tat are not yet well understood. In this study, we investigated whether during acute infection of T cells by HIV-1, Tat is released at concentrations sufficient to stimulate HIV-1 gene expression in a paracrine fashion and the events associated with the release of biologically active protein by cells transfected with the tat gene. As the Tat-containing supematants from both HIV-1-infected and Tat-transfected cells stimulate maximal AIDS-KS cell growth but only low levels of HIV-1 gene expression, we analyzed the kinetics of dose-response for these activities. This analysis was done by using recombinant purified Tat protein in assays of AIDS-KS cell growth, LTR-directed gene expression, and viral replication. Since the nuclear uptake of Tat is a prerequisite for transactivation, we also determined the concentration of exogenous protein necessary to detect nuclear-localized Tat with AIDS-KS cells. The results from these studies suggest that different pathways mediate the cellular and viral effects of extracellular Tat protein. MATERIALS AND METHODS Cell cultures. The T-cell lines H9 and Jurkat, the epithelial cell line COS-1, and HeLa-CD4+ cells containing a Tatdefective HIV-1 provirus (HLM1 cell line) have all been previously described (14, 44). Primary cell cultures derived from KS lesions of patients with AIDS were established and cultured as previously described (14, 16, 37, 38, 46). HIV-1 infection. H9 or Jurkat cells (106/ml) were infected by a cell-free method (14) with HIV-1 (IIIB isolate), as

Kaposi's sarcoma (KS) is a proliferative disease of vascular origin particularly frequent in HIV-1-infected homosexual men (AIDS-KS) and characterized by proliferating spindleshaped cells, angiogenesis, and inflammatory cell infiltration. Previous work has suggested that KS spindle cells are of endothelial cell origin and that chronic immune activation via the release of inflammatory cytokines may cooperate with basic fibroblast growth factor (bFGF) and the HIV-1 Tat protein in the induction and progression of AIDS-KS. Invest. 1995Invest. .95:1723Invest. -1734

The human immunodeficiency virus (HIV) type 1 Tat protein plays a key role in the life cycle of the virus and in pathogenesis and is highly conserved among HIV subtypes. On the basis of this and of safety, immunogenicity, and efficacy findings in monkeys, Tat is being tested as a vaccine in phase 1 trials. Here, we evaluated the incidence and risk of progression to advanced HIV disease by anti-Tat serostatus in a cohort of 252 HIV-1 seroconverters. The risk of progression was lower in the anti-Tat-positive subjects than in the anti-Tat-negative subjects. Progression was faster in the persistently anti-Tat-negative subjects than in the transiently anti-Tat-positive subjects, and no progression was observed in the persistently anti-Tat-positive subjects.

We determined immune cross-recognition and the degree of Tat conservation in patients infected by local human immunodeficiency virus (HIV) type 1 strains. The data indicated a similar prevalence of total and epitope-specific anti-Tat IgG in 578 serum samples from HIV-infected Italian (n=302), Ugandan (n=139), and South African (n=137) subjects, using the same B clade Tat protein that is being used in vaccine trials. In particular, anti-Tat antibodies were detected in 13.2%, 10.8%, and 13.9% of HIV-1-infected individuals from Italy, Uganda, and South Africa, respectively. Sequence analysis results indicated a high similarity of Tat from the different circulating viruses with BH-10 Tat, particularly in the 1-58 amino acid region, which contains most of the immunogenic epitopes. These data indicate an effective cross-recognition of a B-clade laboratory strain-derived Tat protein vaccine by individuals infected with different local viruses, owing to the high similarity of Tat epitopes.

Tat is an early regulatory protein that plays a major role in human HIV-1 replication and AIDS pathogenesis, and therefore, it represents a key target for the host immune response. In natural infection, however, Abs against Tat are produced only by a small fraction (∼20%) of asymptomatic individuals and are rarely seen in progressors, suggesting that Tat may possess properties diverting the adaptive immunity from generating humoral responses. Here we show that a Th1-type T cell response against Tat is predominant over a Th2-type B cell response in natural HIV-1 infection. This is likely due to the capability of Tat to selectively target and very efficiently enter CD1a-expressing monocyte-derived dendritic cells (MDDC), which represent a primary target for the recognition and response to virus Ag. Upon cellular uptake, Tat induces MDDC maturation and Th1-associated cytokines and β-chemokines production and polarizes the immune response in vitro to the Th1 pattern through the transcriptional activation of TNF-α gene expression. This requires the full conservation of Tat transactivation activity since neither MDDC maturation nor TNF-α production are found with either an oxidized Tat, which does not enter MDDC, or with a Tat protein mutated in the cysteine-rich region (cys22 Tat), which enters MDDC as the wild-type Tat but is transactivation silent. Consistently with these data, inoculation of monkeys with the native wild-type Tat induced a predominant Th1 response, whereas cys22 Tat generated mostly Th2 responses, therefore providing evidence that Tat induces a predominant Th1 polarized adaptive immune response in the host.

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Kaposi's sarcoma (KS) is the most frequent tumor of HIV-1-infected individuals (AIDS-KS). Typical features of KS are proliferating spindle-shaped cells, considered to be the tumor cells of KS, and endothelial cells forming blood vessels. Basic fibroblast growth factor (bFGF), a potent angiogenic factor, is highly expressed by KS spindle cells in vivo and after injection in nude mice it induces vascular lesions closely resembling early KS in humans. Similar lesions are induced by inoculating nude mice with cultured spindle cells from AIDS-KS lesions (AIDS-KS cells) which produce and release bFGF. Here we show that phosphorothioate antisense (AS) oligonucleotides directed against bFGF mRNA (ASbFGF) inhibit both the growth of AIDS-KS cells derived from different patients and the angiogenic activity associated with these cells, including the induction of KS-like lesions in nude mice. These effects are due to the block of the production of bFGF which is required by AIDS-KS cells to enter the cell cycle and which, after release, mediates angiogenesis. The effects of ASbFGF are specific, dose dependent, achieved at low (0.1-1 ,uM), nontoxic, oligomer concentrations, and are reversed by the addition of bFGF to the cells, suggesting that ASbFGF oligomers are promising drug candidates for KS therapy. (J. Clin. Invest. 1994.