Immunodeficiency in Rhesus Monkeys Associated With the Original Mason-Pfizer Monkey Virus

The Mason-Pfizer monkey virus (MPMV) was reisolated from a cryopreserved sample of the original MPMV-contain-ing rhesus breast carcinoma, and complete integrated MPMV pro-virus was detected in chromosomal DNA of this tumor. Reanalysis of the in vivo pathogenicity and molecular character of MPMV reisolated from the rhesus breast tumor and analysis of the original MPMV after long-term in vitro propagation in human and rhesus cells show that 1) the original MPMV produces an acquired immunodeficiency similar to that caused by the recently described simian acquired immune deficiency syndrome type D retroviruses, and 2) the MPMV genome and its immunosuppressive effect in vivo have remained stable despite prolonged in vitro passage in human and rhesus cells.