A vaccine adjuvant containing CpG 7909, monophosphoryl lipid, and QS-21 with potential antineoplastic and immunostimulatory activities. CpG 7909 is a synthetic 24-mer oligonucleotide containing 3 CpG motifs that selectively targets Toll-like receptor 9 (TLR9), thereby activating dendritic and B cells and stimulating cytotoxic T cell and antibody responses against tumor cells bearing tumor antigens. Monophosphoryl lipid is a detoxified derivative of lipid A, a component of Salmonella minnesota lipopolysaccharide (LPS); this agent may enhance humoral and cellular responses to various antigens. QS-21 is a purified, naturally occurring saponin derived from the South American tree Quillaja saponaria Molina and exhibits various immunostimulatory activities. Combinations of monophosphoryl lipid and QS-21 may be synergistic in inducing humoral and cellular immune responses.