MOLECULAR-IDENTIFICATION OF A NOVEL RETROVIRUS REPEATEDLY ISOLATED FROM PATIENTS WITH MULTIPLE-SCLEROSIS

The partial molecular characterization of multiple sclerosis (MS)-asso ciated retrovirus (MSRV), a novel retrovirus previously called LM7, is reported. MSRV has been isolated repeatedly from leptomeningeal, chor oid plexus and from Epstein-Barr virus-immortalized B cells of MS pati ents. A strategy based on reverse transcriptase PCR with RNA-purified extracellular virions yielded an initial pol fragment from which other regions of the retroviral genome were subsequently obtained by sequen ce extension. MSRV-specific PCR primers amplified a pol region from RN A present at the peak of reverse transcriptase activity, coinciding wi th extracellular viral particles in sucrose density gradients. The sam e sequence was detected in noncellular RNA from MS patient plasma and in cerebrospinal fluid from untreated MS patients. MSRV is related to, but distinct from, the endogenous retroviral sequence ERV9. Whether M SRV represents an exogenous retrovirus with closely related endogenous elements or a replication-competent, virion-producing, endogenous pro virus is as yet unknown. Further molecular epidemiological studies are required to determine precisely the apparent association of virions c ontaining MSRV RNA with MS.