ERVW-1 and AIDS: But certain striking features make it a promising vaccine candidate for targeting both HIV-1 & 2 such as its cross reactivity to HIV-1, spontaneous control of HIV-1 in African monkeys (believed to be ancestors of HIV-2), existence of certain extremely conserved domains in it against which neutralizing antibody response has been observed i.e. envelope proteins as well as gag. Thus detailed considerations of HIV-2 can guide us towards a profound understanding of both viruses which can prove a landmark for design of a competent vaccine for AIDS