The test immunogen (C4-V3 peptides) is constructed from 4 sequences of the HIV-1 V3 gp120 loop shared by approximately 80% of North American HIV-1 strains. Because of the critical role that this region plays in generating anti-HIV sequences, it is hypothesized that the test immunogen (C4-V3 peptides) will be capable of inducing a broad range of cross-reactive neutralizing antibodies in the majority of recipients.