The present invention provides a polynucleotide comprising portions of thegenomes of caprine arthritis-encephalitis virus and HIV-1, resulting in achimeric retrovirus referred to as a "CHIV". The invention also provides avaccine comprising a CHIV immunogen and a pharmaceutically acceptable carrier.A method of stimulating an immune response in an individual against humanimmunodeficiency virus-1 infection by administering a therapeuticallyeffective amount of a CHIV immunogen is also provided. The invention furtherprovides a method of stimulating an immune response in vitro by contacting alymphocyte with a therapeutically effective amount of a CHIV immunogen.