Studies on the immuno-modulating properties of the cholera toxin A1-based fusion protein CTA1-DD

Sammanfattning: The present work was aimed at exploring the immuno-modulating properties of the novel cholera toxin (CT)-based vaccine adjuvant CTA1-DD, which combines the full enzymatic activity of the A1 subunit of CT with B cell targeting. We have studied the efficacy of the CTA1-DD adjuvant to enhance immune responses in mice after nasal administration. Most studies on adjuvants rely on antibody responses as a measure of immunity. Here we have also used adoptive transfer of DO.11.10 OVA-specific transgenic (tg) T cells into naïve mice as a model system to study the effects of the CTA1-DD adjuvant. In addition, we have analyzed whether CTA1-DD has immuno-modulating effects on human peripheral blood lymphocytes.CTA1-DD was shown to bind directly to human peripheral blood B lymphocytes of all Ig-classes and greatly augmented human B cell functions in vitro. These effects were reflected in strongly enhanced costimulation, resulting in augmented T cell responses to polyclonal as well as antigen-specific activation in vitro. In mice, the CTA1-DD adjuvant was shown to be an equally strong mucosal adjuvant as CT, but it did not induce inflammatory changes in the nasal mucosa or accumulate in the nervous tissues, when given intranasally. Neither was the efficacy of CTA1-DD due to endotoxin-contamination of the adjuvant preparation. Intranasal immunization with antigen inserted into the CTA1-DD adjuvant induced clonal expansion and activation of T cell receptor transgenic CD4+ T cells in the nasal associated lymphoid tissue and the draining lymph nodes. These effects were associated with germinal center formations. Furthermore, CTA1-DD promoted a balanced Th1/Th2 response after intranasal administration, with little effect on IgE antibody production. Our data suggests that CTA1-DD can act on B cells as well as on non-B cells to augment APC-function and that the enzymatic activity complements a much weaker inherent adjuvant function of the fusion protein, perhaps residing in the DD-element.We believe that the non-toxic CTA1-DD adjuvant is an attractive solution to the current dilemma between efficacy and toxicity, encountered in CT-holotoxin adjuvant strategies. Taken this together with our finding that CTA1-DD had immuno-enhancing effects also in a human system, the newly developed CTA1-DD adjuvant provides a safe and promising candidate to be included in future mucosal vaccines for human use.