Therapeutic
vaccines for
nicotine addiction show pre-clinical efficacy. Yet, clinical evaluation of the first-generation
nicotine vaccines did not meet expectations because only a subset of immunized subjects achieved effective serum antibody levels. Recent studies suggest that
vaccine design affects B cell activation, and that the frequency of the
hapten-specific B cell subsets contributes to
vaccine efficacy against drugs of abuse. To extend this hypothesis to
nicotine immunogens, we synthesized a novel
hapten containing a carboxymethylureido group at the 2-position of the
nicotine structure (2CMUNic) and compared its efficacy to the previously characterized 6CMUNic
hapten.
Haptens were conjugated to the
keyhole limpet hemocyanin (KLH)
carrier protein, and evaluated for efficacy against
nicotine in mice using the clinically approved
alum adjuvant. Using a novel fluorescent
antigen-based magnetic enrichment strategy paired with multicolor flow cytometry analysis, polyclonal
hapten-specific B cell subsets were measured in mice immunized with either 6CMUNic-KLH or 2CMUNic-KLH. The 6CMUNic-KLH showed significantly greater efficacy than 2CMUNic-KLH on
nicotine distribution to serum and to the brain. The 6CMUNic-KLH elicited higher anti-
nicotine serum antibody titers, and greater expansion of
hapten-specific B cells than 2CMUNic-KLH. Within the splenic polyclonal B cell population, a higher number of
hapten-specific
IgM(high) and germinal centre B cells predicted greater
vaccine efficacy against
nicotine distribution. These early pre-clinical findings suggest that
hapten structure affects activation of B cells, and that variations in the frequency of early-activated
hapten-specific B cell subsets underlie individual differences in
vaccine efficacy.