(Project 1 ? Robust functional cures with AAV-expressed eCD4-Ig) eCD4-Ig is a potent and exceptionally broad fusion of the first two domains of CD4 to an antibody Fc domain and a short tyrosine-sulfated coreceptor-mimetic peptide. In rhesus macaques, adeno-associated virus (AAV)-expressed eCD4-Ig mediates consistent and very effective protection against SHIV-AD8 and SIVmac239. eCD4-Ig also has properties that make it especially useful for establishing a functional cure in rhesus macaques and perhaps in humans. These include its potency, breadth, difficulty-of-escape, low immunogenicity when expressed by AAV, consistent expression by AAV, potent intrinsic ADCC activity, and collaboration with serum antibodies to mediate ADCC. These properties allow eCD4-Ig to circumvent two major problems associated with using AAV-expressed antibodies to establish functional cures, namely immune clearance and viral escape. In preliminary data we show that AAV-expressed eCD4-Ig can suppress replication of SHIV-AD8 for more than a year in 5 of 6 macaques. However we also show that, when compared to the ?Monkey monkey? described in Project 2, this suppression was less robust, meaning that consistent ?blipping? of virus was observed in most eCD4-Ig-suppressed animals. Because the Miami monkey expresses roughly 10 times the amount of total antibody observed in these eCD4-Ig-expressing macaques, we hypothesize that greater expression of eCD4-Ig will result in more robust functional cures. The goals of this project are thus to increase AAV-mediated expression of eCD4-Ig, to establish robust functional cures in SHIV-AD8 and SIVmac239-infected macaques, to amplify the ADCC activities in these macaques by stimulating host antibody responses to epitopes unmasked by eCD4-Ig, to establish a consistent platform that will allow for evaluation of latency reversing agents, and to ask whether long-term expression of eCD4-Ig by itself can impact the viral reservoir. These studies will improve and help understand a viable approach to establishing similar functional cures in humans.