Enhancement of humoral immune responses against viral vaccines by a non-pyrogenic 6-O-acylmuramyldipeptide and synthetic low toxicity analogues of lipid A.

6-O-Acyl derivatives of N-acetylmuramyl-L-alanyl-D-isoglutamine (MDP) and synthetic, low toxicity lipid-A analogues were examined for their ability to enhance the potency of current viral vaccines. 6-O-(2-Tetradecylhexadecanoyl)-MDP (B30-MDP) in non-irritative vehicles such as physiological saline, phosphate-buffered saline (PBS), squalene-PBS emulsion, Intralipid or liposomes, significantly stimulated the primary and secondary antibody production of guinea-pigs against influenza split or subunit vaccine and inactivated the hepatitis B virus surface (HBs) antigen. Mice seemed less responsive to the adjuvanticity of B30-MDP than guinea-pigs. Two low toxicity lipid A analogues, acylated beta(1-6)-D-glucosamine disaccharide bisphosphates (which do not have amide-bound or ester-bound 3-acyloxyacyl groups unlike fully toxic Escherichia coli-type lipid A), caused significantly enhanced antibody responses, primary or secondary, when administered to mice by incorporation into liposomes with inactivated HBs antigen.