The full-length envelope of an HERV-H human endogenous retrovirus has immunosuppressive properties.

We have demonstrated previously that the envelope proteins of a murine retrovirus (Moloney murine leukaemia virus) and a simian retrovirus (Mason-Pfizer monkey virus) have immunosuppressive properties in vivo. This property was manifested by the ability of the proteins, when expressed by tumour cells normally rejected by engrafted mice, to allow the envelope-expressing cells to escape immune rejection and to proliferate. Here, it is shown that this property is not restricted to the envelope of infectious retroviruses, but is also shared by the envelope protein encoded by an endogenous retrovirus of humans belonging to the HERV-H family. These results emphasize the close relationship between endogenous and infectious retroviruses and might be important in relation to the process of tumour progression in humans.