Background: Although unique DNA sequences related to gammaherpesviruses have been found in Kaposi's sarcoma lesions, it is uncertain whether this DNA encodes a virus that is able to reproduce. Methods: We isolated and propagated a filterable agent whose DNA sequences were found to be identical to those of the Kaposi's sarcoma-associated herpesvirus (KSHV). We obtained early-passage spindle cells from skin lesions of patients with the acquired immunodeficiency syndrome (AIDS) who had Kaposi's sarcoma and cultured them with cells of the human embryonal-kidney epithelial-cell line 293. We characterized the virus according to its effects on cellular morphology and viral replication and its appearance on electron microscopy. Results: KSHV was cytotoxic to 293 cells and was detected by the polymerase chain reaction (PCR) in infected cells but not uninfected ones. Cytotoxicity and positive PCR signals were consistently maintained with viral titers of 1 million per milliliter or higher for about 20 serial infections of 293 cells. The viral copy number was relatively low (1 to 10 copies per cell). Viral replication was confirmed by Southern blot analysis of DNA isolated from the enriched nuclear fraction of infected cells and by a semiquantitative PCR using dilutions of the lysates of infected cells to detect the 233-bp viral DNA fragment originally described in association with Kaposi's lesions. Electron microscopy revealed herpesvirus-like particles in about 1 percent of cells from infected cultures, as compared with none in cells from uninfected cultures. Conclusions: A herpesvirus with DNA sequences identical to those of KSHV can be propagated from skin lesions of patients with AIDS-associated Kaposi's sarcoma.
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