AC-0025

Mouse‐human chimeric monoclonal antibodies that could neutralize botulinum neurotoxins were developed and an attempt was made to establish mouse hybridoma cell clones that produced monoclonal antibodies that neutralized botulinum neurotoxin serotype A (BoNT/A). Four clones (2–4, 2–5, 9–4 and B1) were selected for chimerization on the basis of their neutralizing activity against BoNT/A and the cDNA of the variable regions of their heavy (VH) and light chains (VL) were fused with the upstream regions of the constant counterparts of human kappa light and gamma 1 heavy chain genes, respectively. CHO‐DG44 cells were transfected with these plasmids and mouse‐human chimeric antibodies (AC24, AC25, AC94 and ACB1) purified to examine their binding and neutralizing activities. Each chimeric antibody exhibited almost the same capability as each parent mouse mAb to bind and neutralize activities against BoNT/A. From the chimeric antibodies against BoNT/A, shuffling chimeric antibodies designed with replacement of their VH or VL domains were constructed. A shuffling antibody (AC2494) that derived its VH and VL domains from chimeric antibodies AC24 and AC94, respectively, showed much higher neutralizing activity than did other shuffling antibodies and parent counterparts. This result indicates that it is possible to build high‐potency neutralizing chimeric antibodies by selecting and shuffling VH and VL domains from a variety of repertoires. A shuffling chimeric antibody might be the best candidate for replacing horse antitoxin for inducing passive immunotherapy against botulism.

In a randomized double-blind trial 55 children of 15-24 months and 56 children of 4-6 years of age previously immunized with whole-cell DTP (WC-DTP) received acellular pertussis DTP vaccines containing 12.5 micrograms (AC-12.5) or 25 micrograms (AC-25) each of pertussis toxoid (PT) and filamentous haemagglutinin (FHA) per dose of WC-DTP. No differences in antibody responses or adverse events were noted for children who received AC-25 as compared with AC-12.5. All three groups had significant increases in pertussis agglutinins, but the geometric mean titre (GMT) for 4-6-year-old children who received WC-DTP was higher than the GMT for children who received acellular vaccine. No significant differences were noted in the GMT of antibodies to FHA or PT between children who received WC-DTP and recipients of acellular vaccine. The rates of several adverse reactions were significantly (p less than or equal to 0.05) higher for recipients of WC-DTP, and children given WC-DTP were significantly (p less than or equal to 0.00001) more likely to have received acetaminophen. These acellular vaccines are safe and as immunogenic for FHA and PT as WC-DTP when administered as the fourth or fifth dose to children who received three doses of WC-DTP in infancy. The lower (12.5 micrograms) dose of acellular vaccine was as effective as the higher (25 micrograms) dose in inducing antibodies to FHA and PT in children 15-24 months and 4-6 years of age.