An HIV vaccine poses a unique problem: We don't know what a
protective immune response against HIV is. If you don't know what are
the most important immune parameters, it is difficult to rationally
devise a vaccine. With that said, a vaccine against HIV would
probably need to induce neutralizing antibodies against the spike
proteins gp120, and perhaps gp41. In addition, it would probably be
desireable to induce an effective cell mediated immune response. This
usually requires an attenuated vaccine, rather than a killed or a
subunit vaccine.
Jay Mone'
