Obstacles facing the development of a efficacious global HIV vaccine/s fall into several categories. Firstly, the absence of HIV/SIV/SHIV vaccine formulations that elicit long term protection against either infection or disease and secondly, the high cost and complex delivery systems that will preclude the use of even successful vaccines in developing countries. Robust cellular CD8+ mediated immune responses which, until recently, appeared to protect vaccinated macaques from AIDS, have recently been shown to be compromised by single mutations in viral CTL escape mutants and illustrate the requirment for broader immune responses and the importance of neutralizing antibody as a second layer of a defense in acute and chronic infections. This "proof of concept" proposal aims to address several of these limitations by utilizing an inexpensive and well characterized plant expression system in order 1) to produce and test the immunogenicity of plant-derived SHIV/HIVproteins both as potential injectable vaccine candidates and for use in basic research to elucidate the induction of neutralizing antibody and 2) long term, to adapt the immunogenic potential of plant-derived proteins as a first step towards the development of a cheap and easily administered edible vaccine. Specifically, (i) plant-derived SIV 239 p55 Gag protein will be assessed for its ability to induce strong virus specific T cell responses following boosting of gag-primed macaques (ii) variant forms of the HIV 89.6 gp120 glycoprotein, will be assessed in guinea pigs and macaques for their ability to elicit/block neutralizing antibodies, gp120 molecules with different glycosylation profiles will be produced by using signal sequences which target proteins to different compartments in the plant cells and (iii) macaques will be boosted with both Gag plus the optimal form/s of gp120 emulsified in adjuvant to measure cellular and humoral immunity in gag/env plsmid DNA-primed macaques. If successful these macaques will be challenge with SHIV in Phase II. Throughout each aspect of the study, plant-expressed proteins will be compared with proteins produced in other expression systems as well as their ability to bind to well characterized neutralizing antibodies.