Prior immunity to a carrier enhances antibody responses to hCG in recipients of an hCG-carrier conjugate vaccine

Pre-sensitization with carrier often leads to epitopic suppression of subse quent anti-hapten antibody responses. To ascertain whether epitopic suppres sion occurs in humans, we examined the effect of pre-existing anti-carrier immunity on antibody responses to hCG in volunteers of a clinical trial of an hCG-based conjugate birth-control vaccine. When we studied the correlati on between pre-vaccination anti-carrier immunity and post-vaccination anti- hCG responses, we found that prior immunity to the carriers did not lead to epitopic suppression of anti-hCG responses. On the contrary, it was found that prior immunity to TT, one of the two carriers used in this vaccine, le d to enhancement of anti-hCG responses. Our data indicates that prior immun ity to the carriers may not be detrimental to the performance of conjugate vaccines, and may actually be beneficial in some cases. (C) 1999 Elsevier S cience Ltd. All rights reserved.