Kaposi's sarcoma (KS) is the leading neoplasm of AIDS patients, and HIV infection is known to be a major risk factor for its development. However, KS can occur in the absence of HIV infection and the risk of KS development varies widely even among HIV-infected patients, with homosexual men with AIDS being 20 times more likely to develop KS than AIDS-afflicted children or hemophiliacs. These and other data strongly suggest that a sexually transmitted agent or co-factor may be involved in KS pathogenesis. Recently, DNA sequences corresponding to the genome of a novel member of the herpesvirus family have been identified within AIDS-KS biopsies, and several reports indicate that these sequences are also present in all forms of HIV-negative KS. These and other findings suggest this new agent, referred to as KS-associated herpesvirus (KSHV) or human herpesvirus 8 (HHV8), as a candidate for the putative etiologic cofactor. However, the role of this agent in KS remains hotly debated. Further progress in understanding its biology has been severely hampered by the lack of a cell culture system for virus growth. Here we report the development of a system for the lytic growth of this virus in a latently infected B cell line and present the first ultrastructural visualization of the virus. This system will facilitate the detailed study of the molecular biology of viral replication, the testing of antiviral drugs and the development of diagnostic tests for viral infection.

The ribonucleoside analog ribavirin (1-beta-D-ribofuranosyl-1,2, 4-triazole-3-carboxamide) shows antiviral activity against a variety of RNA viruses and is used in combination with interferon-alpha to treat hepatitis C virus infection. Here we show in vitro use of ribavirin triphosphate by a model viral RNA polymerase, poliovirus 3Dpol. Ribavirin incorporation is mutagenic, as it templates incorporation of cytidine and uridine with equal efficiency. Ribavirin reduces infectious poliovirus production to as little as 0. 00001% in cell culture. The antiviral activity of ribavirin correlates directly with its mutagenic activity. These data indicate that ribavirin forces the virus into 'error catastrophe'. Thus, mutagenic ribonucleosides may represent an important class of anti-RNA virus agents.

Kaposi sarcoma (KS) is the leading neoplasm of HIV-infected patients and is also found in several HIV-negative populations. Recently, DNA sequences from a novel herpesvirus, termed KS-associated herpesvirus (KSHV), or human herpesvirus 8 (HHV-8) have been identified within KS tissue from both IHlV-positive and HIV-negative cases; infection with this agent has been proposed as a possible factor in the etiology or pathogenesis ofthe tumor. Here we have examined the pattern of KSHV/HHV-8 gene expression in KS and find it to be highly restricted. We identify and characterize two small transcripts that represent the bulk of the virus-specific RNA transcribed from over 120 kb of the Kaposi sarcoma (KS) is the most common neoplasm occurring in patients with AIDS (1). The lesion is histologically complex, containing proliferating spindle-shaped cells thought to be of endothelial origin, as well as infiltrating mononuclear cells, plasma cells, and abundant slit-like neovascular spaces. Although HIV infection is a major risk factor for KS development, epidemiologic studies suggest that it cannot be the sole determinant of KS risk and that other cofactors, possibly sexually transmitted, play an important role in the etiology of the tumor (2). For example, HIV-positive male homosexuals are at least 20-fold more likely to develop KS than HIVinfected children or hemophiliacs. In addition, KS occurs in several clinical settings in the absence of HIV infection (1). These and other observations have prompted a search for other viral agents that might be implicated in KS pathogenesis. Recently, DNA sequences of a novel member of the herpesvirus family, termed KS-associated herpesvirus (KSHV) or human herpesvirus 8 (HHV-8), have been regularly identified in KS tumors from both HI V-positive (3-5) and HI V-negative (6-9) patients. This agent has been proposed as a candidate for the presumed etiologic cofactor in KS (3, 10), but definitive evidence for a causal role in KS is lacking. As a first step toward understanding the molecular nature of the association between KS and KSHV/HHV-8, we have examined the nature of viral gene expression in KS tissue. Our studies reveal that viral gene expression is dramatically restricted in the tumor. Detailed characterization of the major viral transcripts produced in infection reveals them to be highly unusual RNAs quite distinct from those found in infection by related herpesviruses. These observations suggest that most infected cells in a KS lesion are latently infected, with lytic growth restricted to no more than a small subpopulation of cells, and bear importantly on potential roles for antiviral chemotherapy. MATERIALS AND METHODSViral Gene Expression Screen. Genomic DNA was extracted from an AIDS-associated pulmonary KS lesion using previously described methods (11) and was partially digested with SauIIIA. Restriction fragments from 10 to 20 kb were gelpurified and cloned into the bacteriophage vector Lambda FIX II (Stratagene). The initial probes used to screen the library were...