Induction of protection level of anti-pre-S2 antibodies in humans immunized with a novel hepatitis B vaccine consisting of M (pre-S2 + S) protein particles (a third generation vaccine).

An enzyme-linked immunosorbent assay (ELISA) for anti-pre-S2 antibodies was developed by the use of both recombinant yeast-derived S and M (pre-S2 + S) protein particles as antigens. By this ELISA was determined the amount of both human and chimpanzee anti-pre-S2 antibodies produced by a new type of yeast-derived hepatitis B (HB) vaccine (TGP-943, subtype adr), which consists of modified M protein particles. In seven randomly selected human individuals who were vaccinated intramuscularly with 10 micrograms (as a protein) TGP-943 three times (0, 4th and 24th week), a detectable level of anti-pre-S2 antibodies was found to be rapidly elicited at 4th or 8th week after the first vaccination. The protective level of anti-pre-S2 antibodies in humans was tentatively assessed by comparing the anti-pre-S2 antibody titres in the vaccinated human individuals with that in chimpanzees which produced only anti-pre-S2 antibodies to tolerate well against the challenge by 1000 chimpanzee infectious units of HBV (subtype ayw). From this assessment, it was speculated that all human individuals tested had already acquired the protective level of anti-pre-S2 antibodies at 4th or 8th week after the first vaccination with TGP-943.