The application relates to the human endogenous retroviral protein. This human endogenous retroviral protein is herein generally referred to as HEMO. The application relates more particularly to shed forms of the HEMO protein, more particularly to those shed forms, which are released in the circulating blood. The application also relates to products deriving from the shed forms of HEMO, such as antibodies, nucleic acid vectors and engineered cells, as well as to the medical or biotechnological applications of these shed forms or derived products, notably in the fields of placental development, fetus protection, cancer treatment and stem cell production.