An Unusual Virus in Cultures From a Human Nasopharyngeal Carcinoma<xref ref-type="fn" rid="FN2">2</xref>

A new human virus, unassignable to any known morphological group, was observed in cultures of a nasopharyngeal carcinoma from a Kenyan African. The virus was found only in suspension cultures of lymphoblastoid cells released from the original monolayer after 105 days in vitro. The virus is morphologically indistinguishable from 2 recently described viruses from animal tumors. Although having some features of the mouse mammary tumor agent, it differs in several respects. Unlike the mouse mammary tumor agent, the new virus matures by the entry of a preformed immature particle into a bud at a cellular membrane, rather than by the de novo accumulation of crescentic dense material. It is also smaller, has radiating spines on its mature form, and, once released, does not undergo further stages of maturation. Because human nasopharyngeal carcinoma has been linked to Epstein-Barr virus, the finding of a new viral agent associated with it makes it important to intensify the search for a possible viral cause.