The acyclic purine nucleoside analogue 9-(2-phosphonomethoxyethyl)adenine [PMEA; formerly referred to as 9-(2-phosphonylmethoxyethyl)adenineJ is a potent and selective inhibitor of human immunodeficiency virus replication in vitro and of Moloney murine sarcoma virus-induced tumor formation in mice. In the latter system PMEA has stronger antiretroviral potency and selectivity than 3'-azido-3'-thymidine (AZT). We have now investigated the effect of the drug in cats infected with the feline immunodefciency virus (FlY). In vitro, PMEA was found to efficiently block FIV replication in feline thymocytes (50% effective dose, 0.6 ,uM).When administered to cats at doses of 20, 5, or 2 mg/kg per day, PMEA caused a dose-dependent suppression of FIV replication and virus-specific antibody production. Seropositive field cats with signs of opportunistic infection (gingivitis, stomatitis, and diarrhea) showed clinical improvement during PMEA therapy (5 mg/kg per day) and recurrence of the disease after treatment was discontinued. Thus, FIV infection in cats is an exceflent model to test the efficacy of selective anti-human immunodeficiency virus agents in vivo.

The coronavirus spike protein S is responsible for important biological activities including virus neutralization by antibody, cell attachment, and cell fusion. Recently, we have elucidated the amino acid sequence of an S determinant common in murine coronaviruses (W.