Infection with HIV-1 worldwide occurs mostly through mucosal exposure. Therefore first line defense against HIV- 1 must include mechanisms that act at the mucosal surface. In addition it is desirable that cytotoxic T Lymphocytes against the virus are induced in order to combat cells that become infected by virus that escaped from this first line of defense. An ideal HIV-1 vaccine would therefore induce both mucosal antibodies and CTL. Cholera Toxin (CT) and E. cold heat-labile enterotoxin (LT) have the capacity to do both. It is unlikely that immune responses to a single HIV-1 gene product will provide full protection from infection. It has been demonstrated that vaccine strategies for SIV that incorporate responses to multiple SIV gene products provide better and broader protection from subsequent challenges. A vaccine formulation that could be flexibly adapted to induce immune responses to multiple gene products is therefore preferable over one that is inherently limited. Such Flexibility would also provide the opportunity to incorporate multiple antigenic variants which seems necessary in the face of the extreme variability of HIV-1. 1. Chemical cross linking of CT or LT to antigenic peptides of HIV-1 in theory would provide the following possibilities: - oral, rectal, or nasal administration of the immunogen - induction of cytotoxic T Lymphocytes to the peptides - induction of mucosal and systemic antibodies to the peptides and to the HIV-1 proteins - combination of multiple peptides from different HIV genes and from different variants in one immunogen. We have established a successful procedure to crosslink peptides to CT. We will use this procedure to pursue the following aims using mice as experimental animals: AIM 1 Determine whether HIV-1 peptides crosslinked to the CT holotoxin confer enhanced immunogenicity when compared to CT mixed with either free peptides or HIV-1 gp120 proteins both systemically and at the mucosal surfaces when administered intrarectally AIM 2 Determine whether different routes of administration (including intragastrically, intranasally and intrarecatally) of HIV- 1 peptides crosslinked to or mixed with LT mutants induce anti HIV- 1 antibodies and cytotoxic T Imphocytes AIM 3 Determine whether the system of crosslinking HIV - 1 peptides to CT or LT mutants allows for simultaneous immunization with multiple epitopes by using multiple antigenic peptides from both allelic variants of the same gene and of different HIV-1 genes.