ERVW-1 and myeloid sarcoma: Although 6A2B2 may crossreact with Syncytin-1 [11,28,29], these findings open up the possibility that the protein detected by 6A2B2 in MS lesions may in fact be derived from Xq22.3 HERV-W env. Nonetheless, it was unknown whether a protein encoded by Xq22.3 HERV-W env can be expressed in human cells.