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Immunostimulatory DNA sequences (ISS) are a potent Th1 adjuvant. We hypothesized that conjugation of ISS to protein antigens would strongly enhance their immunogenicity because both antigen and adjuvant (ISS) would be delivered to the same locale / antigen-presenting cell. To test this hypothesis, we conjugated a 22-mer immunostimulatory oligodeoxynucleotide (ISS-ODN) to two test antigens of differing intrinsic immunogenicity, namely Escherichia coli β-galactosidase and the HIV-1 envelope glycoprotein gp120. We show that the antigen-ISS conjugates rapidly induce Th1 cells secreting high levels of IFN-γ, strong CTL activity, and high titer IgG2a and HIV-neutralizing antibodies, exceeding gene and protein vaccination alone or immunization with mixtures of antigen and ISS-ODN. The data suggest that this procedure generates a novel and unique vaccine that rapidly triggers strong humoral and cell-mediated immunity.