ERVW-1 and myeloid sarcoma: Because Syncytin-1 has been thought to be the only HERV-W env locus capable of producing a HERV-W Env protein, and because 6A2B2 may crossreact with Syncytin-1 [16,43], the antigen detected by 6A2B2 in MS brain lesions was considered to be Syncytin-1.