By Dr. Matt Irwin, MD:
Retroviruses of murine (mouse), avian (bird), feline (cat), and human origin are immunosuppressive as well as oncogenic in their hosts.
The evidence of depressed cellular and humoral immune responses... is independent of the transforming function of the virus...
There is no interspecies restriction, i.e. both murine and feline retroviruses can suppress mouse and human lymphocyte proliferation in vitro.