In addition to being identified in PC samples, evidence for XMRV was also found in a study of subjects with Chronic Fatigue Syndrome (CFS) that revealed the presence of XMRV in activated human B and T cells as well as detectable levels of anti-XMRV Env antibodies in nine out of 18 CFS human plasma samples [8]. This evidence concerns the gene ERVW-1 and myalgic encephalomeyelitis/chronic fatigue syndrome.