Designing Immunogens to Elicit Broadly Neutralizing Antibodies to the HIV-1 Envelope Glycoprotein

To date HIV-1 vaccines have not been able to elicit potent, long lasting, and broadly neutralizing antibodies to the virus. Our knowledge of HIV envelope glycoprotein (Env) structure/function and the existence of a handful of broadly neutralizing antibodies is guiding rational immunogen design. We review here the potential targets on the HIV Env (the glycan shield, the CD4 binding site, the coreceptor binding site, Env fusion intermediates, and the membrane proximal region) and their associated rational immunogen design strategies. Moreover, we discuss immune dampening and immune refocusing strategies designed to counter immunodominant, decoy responses generated by the virus. In this regard, an immunogen design strategy of "in vitro de-evolution" is presented, which begins to distill the HIV Env to its most critical, core functional domains. While we are beginning to have some understanding as to where we would like out immune system to go, we find that our immune repertoire may actually have limits that preclude successful completion of the task at hand. The repertoire limits appear to be a byproduct of autoantibody tolerance mechanisms and the complex structural requirements for effective, potent broadly neutralizing antibodies. Nevertheless, the hope is that through novel insights and creative solutions that we will be able to design immunogens capable of eliciting broadly neutralizing antibodies to the HIV envelope glycoprotein.