Thus, this adjuvant-peptide combination could be an important vaccine component that would generate a protective antibody titer in both the human intestine and breast milk. biotype, Inaba serotype) (17). Multiple doses of TRi-1 the killed-whole-cell vaccine afforded 50% protection in field trials. The most important target population for a cholera vaccine, young children, was even less well protected by this vaccine (less than 25%) (6). A single dose of the live-attenuated vaccine used in clinical trials of North American adults provided 90% protection against the virulent homologous strain and 65 to 80% protection against virulent El Tor biotype, Inaba serotype strains (18, 37, 38). Administration of the CVD 103-HgR vaccine in a large-scale field trial in an area of endemicity of Indonesia did not show any correlation between vaccination and increased protection (12). Another new oral vaccine strain CVD 111, which is a live-attenuated El Tor biotype, Ogawa serotype strain, provided 80% protection in adult volunteers (36). This vaccine is being evaluated together with CVD 103-HgR to determine if the combination can provide further protection against both biotypes in a single dose (40). Despite the potential of live vaccine strains, two problems are related to their use. First, the live-attenuated strains cause side effects such as mild diarrhea, abdominal cramps, and low fever. Second, because these live strains are attenuated by deleting the genes that are carried on a bacteriophage, there is concern that infection of vaccine strains by TRi-1 pathogenesis. Prominent among these is the identification and characterization of the major colonization factor, toxin-coregulated pilus (TCP) TRi-1 (13, 16, 28, 31, 33, 34, 39, 41). TCP and its antigens are obvious targets for testing for inclusion in a subunit cholera vaccine. Of note, there is very little TCP detectable in the commercially available killed-whole-cell cholera vaccines (31), perhaps due to certain culture conditions that need to be optimized for TCP expression. TCP is composed of a homopolymer of TcpA pilin, which is a 20.5-kDa pilin subunit (41). Rabbit polyclonal antibodies directed against TCP provide 100% protection against a challenge with 100 times the 50% lethal dose (100 LD50) in the infant mouse cholera model (31). Various levels of protection in the infant mouse cholera model were achieved by passive administration of monoclonal antibodies (MAbs) raised against TCP. All the MAbs recognized TcpA, but the most protective MAbs mapped to the Sirt4 C-terminal region of the pilin (32, 33). Synthetic peptides TcpA4, TcpA5, and TcpA6 represent contiguous overlapping peptides corresponding to the carboxyl disulfide bond region of the TcpA pilin. Peptides 5 and 6 were recognized by protective MAbs. In other studies, rabbit antibodies raised against TcpA peptides 4 and 6 were found to be the most protective while antibodies to peptide 5 afforded some protection (34). One of the problems of utilizing a peptide-based antigen is that, because of their small size, peptides are not likely to elicit a robust stimulation of the immune system. The inclusion of the appropriate adjuvant in vaccine formulations can overcome this problem TRi-1 (9). Polydi(carboxylatophenoxy) phosphazene (PCPP) (Avant Immunotherapeutics, Inc., Needham, Mass.) is a water-based ionically cross-linkable polymer adjuvant that has been used in human clinical trials. PCPP promotes sustained antigen release while retaining antigenic integrity (25, 26). Another promising adjuvant for human use is the nonionic block copolymer mixture of polyoxyethylene (POE) and polyoxypropylene (POP) (Vaxcel, Inc., Norcross, Ga.). By varying both the molecular weight and the proportions of hydrophilic and hydrophobic components of the POP and POE molecules, the formulations can be designed to achieve differential levels and specificities of adjuvant activity (21, 44). One of these copolymer mixtures, termed CRL-1005, has been used to augment the immune response of mice and rhesus monkeys to a commercially available human influenza vaccine (42, 43). To date none of these adjuvants have been tested for their efficacy in enhancing immune responses directed against small.