Virus Particles in Tissue Cultures of a Human

SUMMARY-Liposarcoma cells from a malignant pleural effusion of a 60-year-old man with a liposarcoma on his right thigh were grown in vitro in medium RPMI-1640. Fifty-seven days after the initiation of the culture, multilayered foci of tightly packed, lipid-containing cells were scattered throughout most Aasks. By electron microscopic investigation, virus particles were found budding into intracytoplasmic vesicles of cells in all foci ob-served, but in none of the cells between foci or in cultures before foci had formed. The particles, which acquired their outer membrane from the mem-brane of the vesicle, measured about 85-100 m,u in diameter and were morphologically similar to C-type viruses in various animal neoplasms. Although particles did not bud from the plasma membrane, mature virions wereseen extracellularly. There wereno particles found inthin sectionsof the original liposarcoma and infectivit of the particles could not be demon-strated.-J Nat Cancer Inst 44: 507-513, 1970. RECENT EFFORTS to demonstrate a vira